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2024 Volume 4
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Interacting effects of water and compound fertilizer on the resource use efficiencies and fruit yield of drip-fertigated Chinese wolfberry (Lycium barbarum L.)

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  • Chinese wolfberry (Lycium barbarum L.) is an important cash crop in the Ningxia region of China, but water scarcity, low water use efficiency (WUE) and fertilizer use efficiency (FUE) have limited the growth of its production. Field experiments were conducted in central Ningxia (China) during 2018−2019 to investigate the interaction effects of irrigation and fertilizer levels on agronomic performances (AP), WUE, partial fertilizer productivity (PFP), and economic benefits (EB). The optimal range of irrigation and fertilizer inputs was determined using multiple regression, the entropy weight method, and the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) coupling comprehensive evaluation method. Three drip irrigation levels were designated as a percentage of reference crop evapotranspiration (ETo); low (65% ET0: W1), medium (85% ET0: W2) and high (105% ET0: W3). Three N-P2O5-K2O compound fertilization levels (kg·ha−1) were selected as low (135-45-90: F1), medium (180-60-120: F2) and high (225-75-150: F3). Results showed that AP, WUE, PFP, and EB increased initially and then decreased with increasing levels of irrigation under the same fertilization levels. The PFP decreased with increasing fertilization levels and the lowest PFP was observed at high fertilizer (F3) application level. The above parameters reached the maximum value under medium irrigation. By establishing the multi-objective optimization model, it was found that 252−262 mm of irrigation and 185-62-123~200-67-133 kg·ha−1 of N-P2O5-K2O fertilization level offers more than 90% of yield, WUE, PFP, and EB simultaneously. The present results provide scientific insights into the resource optimization under drip-fertigation for Chinese wolfberry.
  • Jiangsu Province, situated in the eastern part of China, spans 30°45' to 35°08' north latitude and 116°21' to 121°56' east longitude, is strategically positioned in the lower reaches of the Yangtze River and Huaihe River. Bordered by the Yellow Sea to the east, it neighbors Shanghai and Zhejiang to the southeast, Anhui to the west, and Shandong to the north[1]. The province experiences a diverse climate, marked by regional variations, encompassing a transition zone from China's subtropical to warm climate. Jiangsu boasts a rich array of deciduous and evergreen fruit tree species and varieties, capitalizing on its climatic diversity. Furthermore, the Fruit Tree Industry in Jiangsu Province benefits from advantageous conditions such as convenient transportation, robust financial support, a high-end consumer market, and a solid foundation in agricultural policies and scientific technology[2]. As China undergoes economic and social development, coupled with rising living standards, consumers exhibit a growing preference for high-quality, safe, and environmentally friendly fruits, meeting this demand aligns with the strategy of advancing efficient agriculture in Jiangsu[3]. Actively developing the fruit tree industry not only contributes to this agricultural strategy but also effectively enhances the economic well-being of farmers, emerging as a pivotal choice for the evolution of efficient agriculture.

    The evolving landscape of the fruit market, coupled with intensified competition, poses numerous challenges for the development of the fruit tree industry in Jiangsu Province. A comprehensive analysis of the current state of the industry reveals significant gaps in specialized production, modern facilities, the application of new technologies, and fruit safety production when compared to industry standards[4]. These limitations present notable constraints and pressing issues that require immediate attention and resolution. Moreover, the industry faces strong competition originating from neighboring provinces such as Anhui and Shandong. The year 2021 witnessed the introduction of the 'Regulations on the Implementation of the Land Administration Law of the People's Republic of China' which is the most stringent to date. The arable land protection system emphasizing 'non-agriculturalization and non-grainization', along with the concept of 'fruit trees on the hill or slope' proposed at the 2023 Central Rural Work Conference, signifies a substantial challenge for Jiangsu's fruit industry[5]. These regulations impose a considerable squeeze on the fruit industry, demanding a strategic response to navigate the stringent landscape. The overarching concept of 'fruit trees on the hill or slope' as outlined in the 2023 Central Rural Work Conference, indicates a paradigm shift for the fruit tree industry[6]. These transformative changes mean that Jiangsu's fruit trees industry are confronted with the pivotal question of how to navigate and sustain development.

    To gain a profound insight into the current state of the fruit industry in Jiangsu Province, the Jiangsu Provincial Academy of Agricultural Sciences, under the leadership of the fruit tree sector, collaborated with scientific research units and municipal extension units across the province. A systematic research initiative was undertaken to assess the current status and technology demands within the fruit tree industry. The primary objective of this research is to offer valuable insights that can serve as a reference for steering the high-quality development of the fruit tree industry.

    To comprehensively assess the current status and challenges in the development of the fruit tree industry in Jiangsu Province, and to provide informed decision-making support for the scientific advancement of the industry, the Jiangsu Academy of Agricultural Sciences led research activities on the current state and technical requirements of the fruit tree industry. The study focused on the primary fruit tree production areas in Jiangsu Province, including seven cities (Xuzhou City, Lianyungang City, Suqian City, Wuxi City, Suzhou City, Zhenjiang City, Nanjing City). Simultaneously, sporadic fruit tree planting in six additional cities (Yancheng City, Huai'an City, Yangzhou City, Nantong City, Taizhou City, Changzhou City) were also covered. The main emphasis of the research was on the existing issues, technological needs, and product sales in the key fruit tree production areas in Jiangsu Province.

    The primary targets of this research encompass provincial agricultural authorities, local government departments, grassroots agricultural extension workers, emerging agricultural enterprises, large-scale planting households, and experts specializing in relevant fruit tree species.

    The research employs a multifaceted approach, combining field research, seminars, and exchanges, questionnaires, collection of industry reports, expert forums, and other methodologies.

    The main contents of the research include fruit tree main promoted varieties, main promoted technology, planting mode, etc.; outstanding demand for varieties and technology; key technical problems in production; orchard production scale, marketing mode, sales mode, labor input, the use of agricultural machinery, economic benefits, etc.

    The research findings indicate that the fruit cultivation area in the province covers 197,456.2 hm2, the total production is 3.8 million tons, contributing to a primary production output value of approximately CNY¥38 billion. The predominant cultivated fruit trees and their corresponding areas are as follows: peach: 48,492.5 hm2, pear: 32,022.1 hm2, grape: 31,163.3 hm2, apple: 22,335.1 hm2, strawberry: 16,244.6 hm2 (Table 1). Furthermore, there are other fruit trees, including loquat (Eriobotrya japonica), waxberry (Morella rubra), blueberry (Vaccinium spp), citrus (Citrus reticulate), persimmon (Diospyros kaki), kiwi (Actinidia chinensis), etc., with significant planting areas. Notably, loquat and waxberry have larger cultivation areas, measuring 4,036.2 hm2 and 3,464.5 hm2, respectively. Fruits such as blackberry (Rubus fruticosus), green plum (Vatica mangachapoi), cherry (Prunus pseudocerasus), and pomegranate (Punica granatum) exhibit modest development, with areas falling below 1,100 hm2. Dry fruits like chestnut (Castanea mollissima), ginkgo (Ginkgo biloba), and thinshelled walnut (Carya illinoinensis) have also gained traction, with respective development areas of 8,884.5, 7,168.2 and 6,266.7 hm2[7].

    Table 1.  Primary cultivation areas and production centers of key fruit trees.
    Tree species Area (hm2) Yield (ton) Main production area
    Peach 48,492.5 973,660.7 Xuzhou, Suqian, Wuxi,
    Zhenjiang, Yancheng, Nanjing
    Pear 32,022.1 775,309.2 Xuzhou, Yancheng,
    Lianyungang, Nantong,
    Nanjing, Suqian
    Grape 31,163.3 653,021.9 Xuzhou, Zhenjiang,
    Changzhou, Lianyungang,
    Yancheng
    Apple 22,335.1 571,645.8 Xuzhou, Suqian,
    Lianyungang
    Strawberry 16,244.6 529,754.2 Nantong, Xuzhou,
    Nanjing, Suqian,
    Yancheng, Zhenjiang
    Other 47,198.7 299,187.1 Nanjing, Yangzhou, Suzhou, Changzhou, Wuxi, Nantong
    Total 197,456.2 3,802,578.9
     | Show Table
    DownLoad: CSV

    The planting layout of fruit trees in Jiangsu Province is characterized by regionalization, with distinctive features evident across various zones, the total distribution of fruit trees and major fruit trees in each city can be seen in Fig. 1. Presently, the province boasts several strategically advantageous fruit tree production areas, each contributing unique characteristics. These key regions are delineated as follows. (1) Yellow River Road Fruit Tree Production Area (Xuzhou, Suqian, Lianyungang): This area claims the largest fruit tree production region, covering approximately 10,000 hm2. Cultivation includes staple Jiangsu fruit trees such as apples, pears, and peaches. Prominent examples like Fengxian Dashahe apples and Siyang fresh peaches underscore the region's robust brand advantage. (2) Ning Zhen Yang Hilly and Mountainous Fruit Tree Production Area (Zhenjiang, Nanjing, Yangzhou): Similar to the previous zone but encompassing a broader range of tree species, including peaches, pears, grapes, and strawberries. This has resulted in the establishment of characteristic brands such as White Rabbit strawberryies and Dingzhuang grapes, contributing to the region's distinct identity. (3) Evergreen Fruit Tree Production Area Around Taihu Lake (Suzhou, Wuxi): Primarily concentrated in Suzhou and Wuxi, this region focuses on evergreen fruit trees like citrus, loquat, and waxberry. Notable brands such as Xishan Waxberry and Dongshan Loquat have emerged, reinforcing the region's characteristic identity. (4) Suzhong Sporadic Fruit Tree Planting Area: Encompassing various locations, including Yandu, Hai'an, and Rugao, this region is characterized by diverse and unique fruit varieties. Examples include Yandu's pears, Hai'an's small square persimmons, and Rugao's purple peaches adding distinctive features to the area[8].

    Figure 1.  Distribution of major fruit trees in Jiangsu.

    Moreover, cities such as Nanjing, Yangzhou, Suzhou, and Wuxi boast expansive consumer markets. These urban centers have cultivated a local planting circle focusing on distinctive fruit trees such as strawberries, blueberries, kiwis, and cherry peaches. Although the scale of cultivation in these inter-city planting circles may not be extensive, but the economic returns are substantial, showcasing significant growth potential.

    Jiangsu Province has a long history of fruit tree cultivation, with a large area already cultivated in the 1920s. In the 1960s and 1990s, it entered a period of rapid development, and stable development began in the 2020s, with an area of about 200,000 hm2. In recent years, the fruit tree industry in Jiangsu Province has witnessed rapid growth, marked by an increasing diversity of fruit tree types, optimization of variety structures, and expansion of cultivation areas. Consequently, the province has established distinct regional characteristics within the fruit industry[9]. However, the cultivated area of fruit trees in Jiangsu is approximately 197,456.2 hm2, yielding around 3.8 million tonnes of output. Despite these figures, the province ranks only 25th in the nation in terms of fruit production. Considering that Jiangsu is the fourth most populous province in the country, its reliance on fruits from other provinces remains notably high. The topography of Jiangsu is predominantly plain (86.89%), covering an area of 8,970,600 hm2, with mountains occupying 160,700 hm2 (1.50%) and hills spanning 1,191,613 hm2 (11.11%)[10]. In accordance with the latest policy directives, development potential is limited to hilly and mountainous areas, as well as the Yellow River course. However, challenges persist in these areas, such as sticky and acidified soils in hilly and mountainous regions and saline, sandy soils in old road beach locations. Consequently, the prevalence of low-yield and low-efficiency orchards in these areas diminish the enthusiasm for fruit tree development to a certain extent.

    In the realm of fruit tree production, the advancement of three-dimensional planting, integrated management of fertilization and irrigation, meticulous flower and fruit management, adoption of cutting-edge pest and disease control methodologies, and the implementation of eco-friendly prevention measures collectively serve to significantly elevate fruit quality. This strategic approach not only enhances market competitiveness but also contributes to the overall improvement of fruit quality and planting profitability[11,12].

    Peaches, pears, and apples are predominantly cultivated in open fields, with some utilizing facility cultivation[13]. In newly established peach orchards, a V-type structure is predominantly employed, emphasizing a main branch with a jubilant configuration. In pear tree orchards, the newer cultivation practices often involve trunk-oriented and Y-type structures, while apples lean towards a more trunk-centric shape. Notably, strawberry cultivation primarily occurs in greenhouses, characterized by their light, straightforward, and efficient attributes. Rain-sheltered cultivation techniques for grapes have successfully overcome the natural constraints that hinder open-field grape cultivation south of the Yangtze River. This advancement has significantly propelled grape cultivation in the province, now constituting over 85% of the total grape cultivation.

    Kiwi is primarily cultivated in open fields, with a limited number of instances employing rain-sheltered or shade cultivation. Blueberry, waxberry, cherry, and peach, on the other hand, exhibit improved fruiting characteristics when cultivated in facility settings. Notably, rain-sheltered cultivation for waxberry has been successfully tested and promoted to counter the adverse effects of rainy weather. For citrus and dragon fruit, thermal insulation facilities are essential for cultivation. Plant spacing is adjusted based on facility conditions, generally ranging from 2 m by 3−4 m. In the Suzhou region, waxberry and loquat cultivation often involve intercropping with tea, and orchards feature multi-species mixed planting. This approach is designed to increase orchard output per unit area and mitigate the impact of annual variations in the orchard yield, thereby stabilizing annual income.

    Adhering to the 'prevention first, comprehensive control' principle, orchard pest management primarily relies on agricultural, physical, and chemical control methods[14]. Notably, certain green prevention and control products, including insecticide lamps, yellow boards, and fruit bags, have demonstrated relatively high application rates, which play a great role in promoting the control of diseases and pests and improving the safety of fruits. The adoption of biological control measures, such as the use of predatory mites to combat pear small heartworm and psyllids, is steadily increasing. While agricultural and physical controls play significant roles, chemical control remains a primary approach for pest prevention, with an application rate ranging between 65% and 90%[15]. Research and development efforts in the realm of efficient and low-toxicity pesticides, as well as biological control pharmaceuticals, continue to advance, contributing to the evolution of green pest management practices.

    Most orchards utilize natural grass or ground cloth cover as part of their management strategy, while some opt for artificial grass, typically selecting varieties such as hairy leaf camas, ryegrass, and alfalfa[16]. In orchard management, a common practice involves the application of commercial organic fertilizers in conjunction with chemical fertilizers. Some orchards in central Jiangsu adopt a combined planting and breeding model, using biogas slurry as fertilizer in pear orchards, such as the Taixing pear-pig manure-biogas cycle and the Suzhou Xishan loquat-lake-sheep planting and raising cycle. However, it is noteworthy that many fruit growers have yet to adopt the concept of balanced fertilization. The understanding of soil nutrient status and tree fertilizer requirements remains unclear, leading to the excessive use of chemical fertilizers without due attention to soil improvement. Consequently, this has resulted in low organic matter content, poor physicochemical properties of the soil, and adverse effects on the growth, development, and fruit quality of the fruit trees. In addition, some orchards do not pay enough attention to water management. Irrigation and drainage facilities still need to be further enhanced.

    The cultivation system has undergone improvements, with labor-saving and machine-friendly friendly training systems gradually replacing traditional approaches[17]. For instance, cultivation techniques like the open-center shape with two main branches for peaches, the main stem shape for pears, and elevated cultivation for strawberries have been successfully utilized for advancing orchard mechanization. Agricultural equipment, including air-fed orchard spraying machines and furrowing machines have been introduced, leading to a substantial increase in production efficiency. The covered area of various orchard machinery ranges from 600 to 7,500 hm2, indicating how large an orchard can be met by a single type of machinery. Currently, orchards have achieved mechanization in operations such as plant protection, fertilization, and weeding; the application of mechanization in orchards can be seen in Table 2. However, in older orchards, factors such as narrow-row spacing impedes the entry of medium and large agricultural machinery, limiting operations to small machinery and consequently reducing operational efficiency. Presently, the degree of orchard mechanization in the province remains relatively low, at approximately 35%, indicating a gap in both the application ratio and research and development strength compared to developed countries such as European countries and the United States[18].

    Table 2.  Application of orchard mechanization.
    Type of machinery Price (CNY¥) Area covered (hm2) Application ratio Note
    Ditching and fertilizing machine 6,000−40,000 3,750 68.6% Small fertilizer tanks, frequent loading, not suitable for mountainous areas
    Plant protection sprayer 1,600−15,000 1,500 86.9% Wide variation across orchards
    Grass cutter 3,000−50,000 2,250 90.8% Mainframe suitable for orchard with large row spacing and low application probability
    Rotary tiller 4,000−20,000 3,450 69.4% Only suitable for larger spacing, destroys shallow roots
    Trenching machine 3,000−7,000 3,450 72.4% Higher use of new parks and fertilizers
    Unmanned spraying machine 3,000−10,000 2,250 87.5% Most tree forms are unsuitable
    Tractor 25,000−50,000 1,500 15.3% Most models are too large
    Tracked transporter 10,000−35,000 600 90.6% Higher garden requirements
    Ditching and fertilizing machine 50,000−9,000 750 90.2% Most models are too large
    Ridge maker 1,500−4,000 7,500 20.3% Mostly used for gardening, mostly not procured
    Branch and twig grinder 1,000−4,000 4,500 6.2% More applications in peach, pear
    Water and fertilizer integrated system 20,000−50,000 5,250 30.8% Most orchard are not equipped
     | Show Table
    DownLoad: CSV

    Due to neighboring the high-end markets in Zhejiang, and Shanghai, the efficiency of fruit tree cultivation in Jiangsu ranks among the top in the nation. Notably, fruits such as strawberries, loquats, and sweet cherries command higher sales prices (Table 3). The ex-farm prices often exceed CNY¥10 per kilogram or more. However, it is crucial to recognize that the apparent high profitability is counterbalanced by equally high production costs.

    Table 3.  Production and price of major fruit trees.
    Type Yield per kg/hm2 Price out of the garden (CNY¥/kg)
    Peach 22,500−67,500 5−24
    Pear 45,000−112,500 3−24
    Strawberry 37,500−82,500 12−70
    Apple 33,000−52,500 3−8
    Grape 33,000−52,500 8−24
    Loquat 9,000−12,000 24−48
    Waxberry 6,000−13,500 16−28
    Sweet cherry 18,000−28,500 28−44
    Blueberry 15,000−22,500 14−30
    Kiwi 12,000−27,000 12−24
     | Show Table
    DownLoad: CSV

    In the cultivation of peaches, pears, and apples, the associated costs range from CNY¥45,000 to CNY¥80,000 per hm2. Within this expenditure, labor costs constitute approximately 49%−60%, orchard materials account for 27%−38%, and land rent falls within the range of 7%−9% ( Fig. 2). For grapes and strawberrys, the overall cost ranges from approximately CNY¥150,000 to CNY¥230,000 per hm2. Labor costs contribute to about 27%−34%, while material and service costs comprise 51%−62%. Park management costs and material inputs in southern Jiangsu surpass those in the northern part of the region, leading to higher economic benefits in southern Jiangsu compared to its northern counterpart.

    Figure 2.  Orchard production cost structure (per hectare).

    The overarching expenses in orchard cultivation primarily revolve around labor management, agricultural expenditures, and land rent (Table 4). Labor costs represent approximately 45% of the total expenses, notably increasing each year due to substantial labor inputs in activities such as pollination, bagging, shaping, pruning, harvesting, and other essential tasks. Conversely, land rent remains relatively consistent across every year.

    Table 4.  Orchard cost expenditures.
    Managerial labour (person/hm2) Average wage of employees (¥/day) Agricultural expenditure (¥/hm2)
    Fertilization 30 Pruning 45 Permanent workers 80−200 Pesticides 15,000−30,000
    Pesticide application 30 Weeding 30 Temporary/seasonal workers Men: 100−200; women: 80−120 Fertilizers 37,500−90,000
    Thinning fruit 45 Harvesting 45−75 Other 120−300 Irrigation facilities 1,500−3,000
    Bagging 45 Other 45 Other 18,000−45,000
     | Show Table
    DownLoad: CSV

    Following harvest, fruits in Jiangsu Province, especially peaches, pears, and apples undergo wholesale and retail sales. In the northern part of Jiangsu, where fruit production is higher, a greater proportion is directed towards acquisition or wholesale markets, with relatively less emphasis on tourism and leisure farmers' picking activities. Conversely, in the southern region of Jiangsu, where fruit quality tends to be higher, the predominant marketing channels involve wholesale transactions, picking, or sales in the form of gift boxes. For instance, in the Nantong area, approximately 30% of fruit sales occur through picking or retail, around 20% enter local fruit shops, approximately 35% are wholesaled to major cities such as Beijing, Shanghai, and Nanjing, with about 5% involving large truck wholesale at the doorstep. Additionally, approximately 10% of the fruit is sold through e-commerce platforms. Based on statistical data, the sales distribution between online and offline channels stand at an approximate ratio of 1:3.

    In the context of Jiangsu's extensive agricultural landscape, facility agriculture, and agro-tourism, the cultivation of fruit trees has emerged as a preferred initiative for advancing efficient agriculture in numerous regions. The fruit tree industry has been a catalyst for the rapid growth of rural tourism. Various activities, such as peach flower festivals, pear flower festivals, strawberry festivals, and farmers' harvest festivals, have been organized to integrate culture and tourism, facilitating the swift development of tertiary industries and significantly boosting local tourism[19]. For instance, Dafeng Hengbei Village in Yancheng City strategically leverages the advantages of the fruit tree planting industry. Focused on the theme of 'pear orchard scenery, ecological livability, and rural tourism', the village harnesses the cultural appeal of pear orchards, actively promotes rural tourism, and exemplifies an integrated development model across primary, secondary, and tertiary industries. Similarly, Tianlai Village Ecological Theme Manor in Haimen District, Nantong City, received the prestigious title of 'the oldest local garden in China' from the Guinness Book of World Records in 2015. This establishment serves as a diversified and ecological agricultural integrating activities such as fruit picking, sales, lodging, and hot springs. It stands as a noteworthy exemplar of the integrated development of the local industry in the Nantong area.

    The planting area of fruit trees in Jiangsu approximately 197,456.2 hm2, yielding a production of around 3.8 million tonnes. However, Jiangsu's population ranks 4th in the country, indicating that Jiangsu exhibits a high reliance on imported fruits[20]. The majority of business entities in Jiangsu maintain orchard sizes ranging from 300 to 1,500 hm2, predominantly adhering to individual or family-based planting models. This prevailing pattern lacks the formation of industrial clusters characterized by substantial scale and influence. Despite the presence of numerous high-quality brand fruits, the overall output remains insufficient to meet the province's internal demand. Consequently, the competitiveness of Jiangsu's fruit production in the national market is currently below the desired level.

    The fruit tree industry in Jiangsu Province suffers from a lack of a well-structured regional development layout, leading to uncoordinated and repetitive development at a lower level. Numerous fruit tree planting and management entities have pursued geographical and individual differentiation without adequately considering the characteristics of tree species[21]. This has resulted in the improper selection of varieties, leading to increased risks. For instance, in northern Jiangsu, blueberries are cultivated in salinized areas, and Loquat is grown in facilities, while in southern Jiangsu, efforts are ongoing to cultivate sweet cherries. Moreover, the prevalence of regional and seasonal surpluses has become a recurring issue. For instance, during the period from June to August, there is a concentration of mature peaches, pears, and apples in the Xuzhou region, resulting in a stagnation of fruit and a subsequent decline in prices. Simultaneously, the southern region faces a shortage of these fruits during the same period.

    The selection of fruit tree cultivars should ideally align with regional soil and climate conditions, among other factors[8]. Variety selection necessitates a consideration of the region's climate, production conditions, and various other comprehensive factors. Presently, the majority of fruit tree cultivation lacks a well-structured variety planning strategy. Production tends to heavily favor late-maturing varieties, leading to a concentrated maturity period, increased sales pressure, and subsequently lower selling prices. Furthermore, there is a tendency to blindly follow trends in planting, resulting in a prevalence of single-variety cultivation. For instance, the grape variety 'Shine Muscat', known for its distinctive color and aroma, experienced rapid development in Jiangsu Province, leading to its widespread adoption in major markets and subsequently causing a significant decline in its market price. Therefore, it is imperative to adopt a more diversified approach in selecting varieties for cultivation, fostering a richer variety structure that aligns with the diverse consumer demand for fruits.

    The synergy between agricultural machinery and agronomic practices is lacking, and there is a disconnect between orchard management and machinery utilization[22]. In the construction of orchards, most fruit trees are not designed with due consideration for mechanical equipment and facilities. Consequently, orchard construction standards are lower, and row spacing in the fields is narrower, constraining the implementation of mechanical operations in orchards. This is particularly evident in critical tasks such as fruit thinning, bagging, harvesting, and pruning, where the labor-intensive nature and time constraints pose challenges to the overall mechanization of the fruit industry. Additionally, factors such as mechanical operation limitations, maintenance issues, and product prices contribute to the current sub-optimal level of mechanization in fruit tree production in Jiangsu Province.

    The issue of an aging workforce in fruit tree production is progressively worsening, with a majority of orchard laborers falling within the age range of 53 to 75 years. Due to age-related constraints, the adoption of new varieties, technologies, and cultivation methods are limited. This deficiency results in consistently high orchard production costs, thereby impeding the advancement of fruit production in the region. The escalating orchard production costs, exemplified by pear cultivation, underscore the challenges faced. For instance, the fertilizer costs for 1 hm2 of land amount to CNY¥22,500, while labor and machine operation expenses can soar as high as CNY¥30,000. Notably, orchard material and service costs account for a substantial 57% of the overall production costs. In the case of one hm2 of peach cultivation under traditional methods, an average of 520 workers is employed throughout the year. The costs of labor for managing 1 hm2 range from CNY¥45,000 to CNY¥75,000, and agricultural materials contribute an additional CNY¥52,000 to CNY¥80,000. The shortage of labor further exacerbates the situation, resulting in labor and material costs comprising over 60% of the input ratio.

    The predominant cultivation mode in orchard production in Jiangsu Province adheres to traditional practices, lacking standardized construction. Non-standardized planting row spacing is a prevalent issue, resulting in narrow spacing and inter-row depression as the trees grow. This condition adversely impacts ventilation and light transmission, leading to an increased incidence of pests and diseases and a decrease in fruit quality. Moreover, there is a pressing need for upgrading orchard facilities in terms of coverage and quality. Numerous orchards suffer from sub-optimal conditions in terms of old roads, ditches, supporting rooms, and other infrastructure. Furthermore, a significant portion of orchards lack the capacity to invest in essential equipment such as cold storage for fruit preservation. An illustrative example is the promotion of the early cultivation of peach trees in the northern region, where the greenhouse film, often aged and with poor light transmission, not only fails to achieve the intended purpose of promoting early maturity but also significantly compromises the quality of peach fruit.

    The adoption of green and safe production concepts in orchard production still requires significant enhancement[23]. Notably, there are challenges in the standardized use of medications and proper application of fertilizers, leading to environmental concerns. (1) The ecological condition of orchards is sub-optimal. Survey findings indicate that peaches and pears are subjected to medication approximately 7−10 times throughout the year, with some late-maturing varieties receiving up to 12 treatments. In certain production areas, the use of herbicides exceeds the annual usage of chemical pesticides, reaching up to 1/3 of the total. (2) Soil background conditions are less favorable, especially in regions near the Yellow River and hilly hillock slopes, where the soil's organic matter content hovers around 1%. This necessitates the extensive use of chemical fertilizers, contributing to soil acidification and slatting phenomena due to improper fertilizer application. (3) There is a lack of precision in chemical control practices. In some orchards, the quantity and frequency of pesticide use surpass 30% of the recommended standards. Instances of pesticide application just before fruit harvesting are not uncommon, posing challenges in ensuring the safety of fruit products. (4) Orchard inputs vary in quality, and highly toxic pesticides remain accessible through 'special channels', indicating a need for stricter regulation and control measures.

    Jiangsu Province faces a notable gap in the establishment of well-equipped plantlet breeding bases, resulting in challenges related to the quality and quantity of nursery plantlets. This inadequacy necessitates the annual procurement of a substantial number of peach, pear, and strawberry plantlets from other provinces, hampering the autonomous development of the modern fruit industry. Given that most fruit tree plantlets can be acquired through asexual reproduction, safeguarding the rights to fruit tree varieties has emerged as a complex issue. The fruit tree plantlet market has been in an unregulated state for a long time, with plantlets lacking conformity certificates, production licenses, and business licenses entering the market without restraint. The market is inundated with counterfeit and uncertified plantlets, often leading to confusion regarding varieties and instances where the same product is sold under different names. Driven by profit motives, some plantlet dealers engage in speculative practices, promoting varieties unsuitable for cultivation, this has resulted in significant financial losses for growers.

    In Jiangsu Province, the post-harvest scenario predominantly involves fresh fruit, with a significant portion lacking processing into value-added products. The existing cold storage infrastructure is insufficient to meet the market demand for extensive fruit storage[24]. Outdated storage and processing equipment, coupled with inadequate storage technology, contribute to the prevalence of storage-related issues, leading to serious late-stage diseases in some fruits, such as rot disease in peaches and tiger skin disease in pears. According to available statistics, the province's fruit storage capacity is 432,000 tonnes, with cold storage accounting for only 172,000 tonnes and gas-conditioned storage at 13,000 tonnes. This represents a mere 10% of the total fruit production in the province. Furthermore, the fruit processing capacity is 216,000 tonnes, reflecting a processing industry that is not sizable, often equipped with aging machinery, resulting in sub-optimal processing quality and low utilization rates. In terms of commercialization, the packaging is often simplistic, and there is a lack of strict fruit grading, leading to a low level of commercialization and reduced economic efficiency in the sector[25].

    There is a critical need to intensify the exploration of fruit tree germplasm resources, with a particular emphasis on precisely identifying and leveraging specific traits within local variety resources and wild resources[26]. It is recommended to establish a resource protection nursery and promptly initiate the collection, preservation, and evaluation of these resources. Simultaneously, efforts should be directed toward the assessment and utilization of valuable resource traits and genes, aiming to cultivate more new varieties that are well-suited to the local climatic conditions.

    Excellent varieties form the foundation for the sustainable development of the fruit industry[27]. Currently, the primary focus of variety selection and breeding in Jiangsu Province's fruit tree industry revolves around attributes such as high quality, early maturity, disease resistance, and resilience during storage and transportation. Additionally, there is a prominent emphasis on developing labor-saving varieties, characterized by traits like low flower density and medium tree potential, marking a significant direction in innovative variety development. Simultaneously, it is crucial to consider the diverse requirements of different consumer groups, including factors such as quality, nutrition, functionality, and appearance[28]. As the standard of living continues to rise, the demand for fruit products among the populace reflects increasingly diversified, multi-level, and multi-faceted characteristics.

    Jiangsu boasts a robust agricultural scientific research force, and its independent cultivation of high-quality fruit tree varieties, which makes Jiangsu leading in the domestic market. To capitalize on this strength, it is imperative to continue enhancing the layout of fine varieties with independent intellectual property rights in Jiangsu, promoting their breeding and dissemination[29]. Simultaneously, there should be an active initiative to introduce high-quality varieties from both domestic and international sources to meet the diverse demands[30]. Recognizing that the Fruit Tree Industry in Jiangsu Province should not adopt a singular large-scale planting approach akin to the 'apple mode', the following recommendations are proposed: (1) Leveraging the distinctive characteristics of the transitional zone between the northern and southern production areas in Jiangsu, precise positioning of different maturity varieties should be undertaken in various planting areas. This approach aims to achieve staggered harvests, effectively regulating market supply. (2) Implementing precise positioning of different maturity varieties in each production area layout to ensure a uniform distribution of varieties at varying stages of maturity, thereby alleviating the pressure associated with concentrated fruit maturation.

    Currently, there is a growing demand for mechanization in fruit tree production, with an increasing emphasis on simplification. Agricultural mechanization stands as a pivotal trend for future development[31]. Given that the majority of orchards in Jiangsu have an area between 300−1,500 hm2, it is imperative to align with regional agricultural characteristics and production needs. Therefore, there should be accelerated research and development efforts aimed at creating efficient and practical agricultural machinery. This involves the creation of practical, labor-saving small-scale machinery capable of seamlessly integrating into the entire production chain. Promoting orchard mechanized production models through various means is essential. This approach aims to garner recognition among technicians and fruit tree production practitioners regarding the labor-saving, quality-enhancing effects of mechanized production. Accelerating the widespread adoption of mechanization in production is a crucial step forward for the modern fruit tree industry.

    The progress of the fruit tree industry necessitates a robust focus on the research and development as well as the widespread promotion of new varieties, technologies, and facilities[32]. This effort is crucial for enhancing the scientific and technological content of the fruit tree sector, providing a solid foundation for industrial development. Tailoring strategies for different regions and varieties, emphasis should be placed on the research and development of labor-saving cultivation techniques, particularly in flower and fruit management, disease prevention and control, soil, fertilizer, and water management, as well as shaping and pruning[33]. These techniques aim to simplify management processes, reduce labor input, and enhance overall efficiency. To maximize the impact of technological advancements in Jiangsu Province, concerted efforts should be directed toward creating synergy in technology demonstration, promotion, and training. This approach aims to fortify the concept of standardized cultivation, accelerating the industry's transition towards simplification and intelligent development.

    The ecological and safety aspects of orchards in Jiangsu must undergo gradual improvement, adopting a multi-dimensional and systematic perspective[34]. Addressing the primary needs for pest and disease prevention and control in fruit trees entails the integrated application of agricultural control, physical control, and biological control, among other green prevention and measures[35,36]. (1) From the perspective of producers, fostering a green and safe production consciousness is imperative, only when the operational entity prioritizes fruit safety from a profound level of consciousness can a comprehensive adoption of green and safe production technologies be achieved. (2) From a technical perspective, there is a need to optimize the green and safe production technology system. This involves the development of simple, effective, and standardized technical procedures, coupled with intensified efforts in the promotion and implementation of these standards. (3) From the perspective of agricultural production management, regulatory bodies must rigorously control the production, operation, and traceability of agricultural inputs. Strengthening supervision and imposing penalties for fruit-related activities will further enhance overall safety measures.

    The plantlet constitutes the fundamental cornerstone of the fruit tree industry's development. Collaboration between scientific research institutions and enterprises is essential, utilizing joint research and development and cooperative strategies to establish a plantlet breeding technology system characterized by 'excellent rootstock + excellent new varieties + advanced technology'[37]. To fortify plantlet production management, industry standards should be developed for plantlet production, grading, and management, ensuring that the quality and purity of plantlets align with the requirements of modern fruit industry practices. Furthermore, it is crucial to intensify intellectual property rights protection. Plantlet breeding businesses ought to secure breeder's licenses, and there should be encouragement for these enterprises to allocate a portion of sales revenue back to the breeder, fostering a fair and supportive intellectual property rights framework.

    The adoption of a brand strategy, anchored by leading enterprises, should be leveraged to elevate the regional prominence of the fruit tree industry. This involves establishing several moderately scaled, distinctive, and influential fruit brands with the capacity to propel fruit products[38]. Simultaneously, the development of regional characteristics for fruit brands should be cultivated. Recognizing that traditional avenues for consumption growth are constrained, there is a need for a deeper exploration of the cultural significance of fruit trees. This involves steering the fruit tree industry towards leisure and tourism, thereby enhancing the value and comprehensive benefits associated with fruit. Actively championing the diversified development of the fruit tree industry, a developmental approach centered on 'traditional fruit trees + distinctive fruit trees' should be pursued. This can be achieved by integrating leisure and tourism, farming experiences, and rural tourism development, ultimately crafting regional fruit tree brands that provide individuals with opportunities to connect with nature and savor the fruits of the land.

    In summary, the fruit tree industry is a specialized and technically advanced sector, requiring substantial investments in aspects such as variety introduction, breeding, facilities and equipment, and technology promotion, resulting in a relatively long return period. Considering the current stringent policies prohibiting the 'non-agriculturalization' of arable land, future expansion of orchards in Jiangsu will be challenging. Therefore, the focus should be on stabilizing the existing fruit tree planting area while increasing efforts to renew old orchard varieties and facilitate their adaptation to mechanized transformations. Support measures should prioritize orchards with positive driving effects and distinctive regional characteristics, ensuring appropriate retention and limited development, all while elevating the overall level and quality of cultivation. While emphasizing the ecological benefits of greening, equal attention should be given to the economic advantages brought about by fruit tree development, fostering the sustainable growth of the fruit tree industry in Jiangsu Province.

    The authors confirm contribution to the paper as follows: conception and experiment design: Shen Z, Kan J, Yu M; survey research and data collection: Kan J, Li X, Zhao M, Wang X; analysis and interpretation of results: Qiao Y, Han J, Yang Y, Wei M; draft manuscript preparation: Kan J, Shen Z. In addition, fruit tree related counterparts in various urban areas of Jiangsu also participated in this investigation. All authors reviewed the results and approved the final version of the manuscript.

    The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.

    This work was supported by the Jiangsu Agricultural Science and Technology Innovation Fund (CX[23]2001) , Jiangsu Agricultural Industry Technology System (JATS[2023]386, JATS[2023]387, JATS[2023]395) and Seed industry project of Jiangsu Province (JBGS[2021]084).

  • The authors declare that they have no conflict of interest.

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  • Cite this article

    Deng Z, Yin J, Eeswaran R, Gunaratnam A, Wu J, et al. 2024. Interacting effects of water and compound fertilizer on the resource use efficiencies and fruit yield of drip-fertigated Chinese wolfberry (Lycium barbarum L.). Technology in Horticulture 4: e019 doi: 10.48130/tihort-0024-0016
    Deng Z, Yin J, Eeswaran R, Gunaratnam A, Wu J, et al. 2024. Interacting effects of water and compound fertilizer on the resource use efficiencies and fruit yield of drip-fertigated Chinese wolfberry (Lycium barbarum L.). Technology in Horticulture 4: e019 doi: 10.48130/tihort-0024-0016

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ARTICLE   Open Access    

Interacting effects of water and compound fertilizer on the resource use efficiencies and fruit yield of drip-fertigated Chinese wolfberry (Lycium barbarum L.)

Technology in Horticulture  4 Article number: e019  (2024)  |  Cite this article

Abstract: Chinese wolfberry (Lycium barbarum L.) is an important cash crop in the Ningxia region of China, but water scarcity, low water use efficiency (WUE) and fertilizer use efficiency (FUE) have limited the growth of its production. Field experiments were conducted in central Ningxia (China) during 2018−2019 to investigate the interaction effects of irrigation and fertilizer levels on agronomic performances (AP), WUE, partial fertilizer productivity (PFP), and economic benefits (EB). The optimal range of irrigation and fertilizer inputs was determined using multiple regression, the entropy weight method, and the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) coupling comprehensive evaluation method. Three drip irrigation levels were designated as a percentage of reference crop evapotranspiration (ETo); low (65% ET0: W1), medium (85% ET0: W2) and high (105% ET0: W3). Three N-P2O5-K2O compound fertilization levels (kg·ha−1) were selected as low (135-45-90: F1), medium (180-60-120: F2) and high (225-75-150: F3). Results showed that AP, WUE, PFP, and EB increased initially and then decreased with increasing levels of irrigation under the same fertilization levels. The PFP decreased with increasing fertilization levels and the lowest PFP was observed at high fertilizer (F3) application level. The above parameters reached the maximum value under medium irrigation. By establishing the multi-objective optimization model, it was found that 252−262 mm of irrigation and 185-62-123~200-67-133 kg·ha−1 of N-P2O5-K2O fertilization level offers more than 90% of yield, WUE, PFP, and EB simultaneously. The present results provide scientific insights into the resource optimization under drip-fertigation for Chinese wolfberry.

    • Chinese wolfberry (Lycium barbarum L.) has been cultivated in China for more than 500 years. Fruit, root bark, and young leaves of this plant have both medicinal and nutritional values[1,2]. As of 2020, more than half of the commercial production of Chinese wolfberry in China comes from the Ningxia region. Furthermore, Chinese wolfberry is an important cash crop in the Ningxia region and generates substantial amounts of household income. Irrigation and fertilizer are two key factors that determine the quantity and quality of the yield of Chinese wolfberry[3]. The average irrigation water utilization efficiency in Ningxia region is only 0.47 which is lower than the country average[4]. The central region of Ningxia in the northwestern China is a typical arid region with an average annual evaporation of 7−8 times the annual precipitation. Therefore, water shortage for agriculture is a huge challenge for developing agricultural production in this region.

      With the expansion of Chinese wolfberry cultivation in Ningxia and a decreasing amount of water from the Yellow River, optimization of irrigation, and fertilizer management schemes for Chinese wolfberry production became decisive. Further, improving the irrigation and fertilizer use efficiency is a key issue that needs to be urgently addressed to sustain Chinese wolfberry production. To this end, drip irrigation along with plastic mulching is beneficial to conserving soil moisture, reducing evapotranspiration, and effectively saving water in the arid regions such as central Ningxia[5]. Several studies showed that drip irrigation coupled with plastic mulching increased the yield and water use efficiency of Chinese wolfberry compared to drip irrigation without mulching[6,7].

      Water is an essential input for Chinese wolfberry production and many studies showed that sustainable irrigation methods could increase the production and water use efficiency[8,9]. Moreover, Du et al.[10] reported that drip irrigation combined with mulching saved 42% to 60% of the water consumption of Chinese wolfberry compared to traditional border irrigation. When the irrigation quota was 277.5 mm during the growing season of Chinese wolfberry, water use efficiency and dry fruit yield could reach an optimal value. The irrigation quota above 229 mm has decreased the yield of Chinese wolfberry which expresses that excessive irrigation is not conducive to the growth and development of Chinese wolfberry[11]. Ma & Tian[5] reported that the plant height, crown width, chlorophyll, and photosynthetic rate were the highest, and the yield per hectare was 11.6% higher for treatment with film mulching than without mulching for a Chinese wolfberry variety. Sun et al.[12] concluded that drip irrigation under mulch decreased the water and fertilizer consumption by 35%~42% and 20%, respectively, while increasing the yield of Chinese wolfberry by 11.5% compared to border irrigation. Zhang et al.[13] further reported that saving direct labor economy reached CNY¥900 ha−1, and the comprehensive benefit increased by CNY¥3,000 ha−1. In addition, reducing the irrigation quota could minimize the soil salinization which is an important issue in arid regions.

      Fertilizer is another key factor which determines the growth and yield of Chinese wolfberry[14]. Chinese wolfberry is a fertilizer-responsive crop and its yield increases with the application of synthetic fertilizers. Dry fruit yield of Chinese wolfberry was within the range of 1,847 to 2,575 kg·ha−1 when the N, P, and K fertilization ratio was 6.6:1.8:3.5[15]. Wu & Zhang[16] reported that under three different soil fertility conditions, fertilizer formulations increased leaf dry weight, leaf area, and chlorophyll content, as well as improved the yield and quality of Chinese wolfberry. Among them, fertilizer formulation with high nitrogen, medium phosphorus, and low potassium had the highest yield and 100-grain weight of Chinese wolfberry. Similarly, Zhang et al.[17] also found that formula mixed chemical fertilizers (N : P2O5 : K2O = 1:0.75:0.5) could improve the yield and quality of Chinese wolfberry, and soil quality compared to conventional chemical fertilizers. Similar findings were reported for similar crops such as tomato, brinjal, black pepper, and strawberry[1822].

      The interaction of irrigation and fertilizer could have better effects on agronomic performances of Chinese wolfberry and resource use efficiencies than the individual effect[23,24]. A combination of irrigation and fertilization could effectively improve the water and fertilizer utilization rates in crops[17,25]. Similar interaction effect of irrigation and fertilizer applications were reported for other horticultural crops namely, apple[26], cherry tomato[27], and mango[8]. Liu & Li[28] established a water and fertilizer production function to predict the yield of Chinese wolfberry using a binary quadratic polynomial regression model and found that medium irrigation (5,010 m3·ha−1) and medium fertilizer (607.50 kg·ha−1) is the optimal application level of irrigation and fertilizer, respectively. This study showed that the influence of irrigation amount on the yield of Chinese wolfberry was greater than the amount of fertilizer, but an excessive amount of fertilizer and irrigation was not conducive to the increase of the yield of Chinese wolfberry. All these studies showed that only the correct combination of irrigation and fertilization could ensure the yield and quality of Chinese wolfberry.

      The effect of a single factor such as irrigation, fertilization, and mulching method on agronomic performances of Chinese wolfberry and resource use efficiency was investigated in previous studies. Nonetheless, studies on the interaction effect of water and fertilizer on the growth, yield, and resource use efficiency of Chinese wolfberry are very limited. However, the optimum level of water and fertilizer would enhance productivity and resource use efficiency in Chinese wolfberry, especially in the resource-poor arid regions, and the optimum level could only be quantified by evaluating the interaction effects. Hence, the objective of this study was to determine the optimum level of water and compound fertilizer (i.e., N-P-K inclusive) by evaluating the interaction effects of water and fertilizers on the resource use efficiencies and fruit yield of drip-fertigated Chinese wolfberry. Further, this study aims to provide a reference for optimal resource allocation for effective water and nutrient management of Chinese wolfberry in arid regions.

    • Field experiments were conducted during the Chinese wolfberry growing seasons (April−September) in 2018 and 2019. The experiments were located at the RunDe Chinese wolfberry plantation in Hexi town, Tongxin County, WuZhong City, Ningxia Province, China (36°58'48" N, 105°54'24" E, altitude 1,240 m amsl). This region belongs to an arid zone with a typical continental monsoon climate. The average annual precipitation is around 145−280 mm which is received mostly in July through September. The average annual temperature is recorded at 8.8 °C, while the mean annual sunshine duration amounts to 2,983 h. The frost-free period spans approximately 150 d, with an effective accumulated temperature (calculated by summing the daily temperatures when the daily mean temperature exceeds 10 °C) reaching around 3,397 °C. The drought index is measured at 8.4, and the groundwater depth is determined to be more than 30 m. A decagon micro meteorological monitoring station was installed in an open place 10 m away from the experimental location to monitor meteorological variables. The effective rainfall (≥ 5 mm) during the experimental period was 149 and 155 mm in 2018 and 2019, respectively. The changes in weather variables of daily mean air temperature, rainfall, and reference crop evapotranspiration during the growth period of Chinese wolfberry from 2018 to 2019 are shown in Fig. 1. During the whole growth period of the crop, the temperature and precipitation reached a peak in June to July, and the precipitation was mainly confined to June–September (Fig. 1a). In addition, the variation of reference crop evapotranspiration was similar to that of the temperature (Fig. 1b). In the same period, the reference crop evapotranspiration in 2019 exceeded that of 2018, and the inter-annual variation was inconsistent or irregular.

      Figure 1. 

      (a) Daily rainfall and daily mean temperature, and (b) reference crop evapotranspiration (ET0) during the study period in 2018 and 2019.

      The physicochemical properties of soil in the experimental field are shown in Table 1. The soil in this region is generally silt loam in texture and most of them are saline-alkaline soils. There were no substantial variations in the measured soil chemical properties across the experimental years. The soil was low in terms of soil carbon and other nutrients, representing most of the marginal soils in the arid regions.

      Table 1.  Soil physicochemical properties of the experimental site during the study period.

      Year pH Organic
      matter
      (g·kg−1)
      Total
      N
      (g·kg−1)
      Available
      N
      (mg·kg−1)
      Available
      P
      (mg·kg−1)
      Available
      K
      (mg·kg−1)
      Total
      salt
      (g·kg−1)
      2018 8.27 9.77 0.41 13.7 4.87 112 2.22
      2019 8.25 9.95 0.47 14.2 5.64 91 2.09
    • A popular variety 'Ningqi No.7' of Chinese wolfberry crop at the 4-year maturity stage was selected for this study and the crops were already established in a 75 and 300 cm spacing (Fig. 2). A 60 cm wide plastic film strip was laid on the cropping line to mulch the soil. Nearly 240 cm of intercrop space was uncovered and exposed to the environment (Fig. 2). A drip irrigation pipe with 16 mm inner diameter was used for irrigation and it was kept 5 cm away from the Chinese wolfberry tree (Fig. 2). The average discharge rate of the pipe was 3.0 L·h−1 and the amount of irrigation is controlled by an electronic water meter mounted on a drip irrigation pipe. Spring irrigation and winter irrigations were 300 and 450 m3·ha−1, respectively.

      Figure 2. 

      The layout of the plants, spacing, and drip irrigation used in the field experiments.

      Three levels of drip irrigation and three levels of fertilization were arranged in a randomized complete two-factor factorial block design and each treatment was replicated three times. The irrigation levels were selected considering the historical precipitation and evapotranspiration of the study area. Three levels of drip irrigation were applied based on reference crop evapotranspiration (ET0), which were low irrigation (65% ET0, W1), medium irrigation (85% ET0, W2), and high irrigation (105% ET0, W3) as presented in Table 2. In this study, the application of fertilizer treatments involved the application of a compound fertilizer which consisted of a combination of all three N-P-K fertilizers. Three levels of N-P2O5-K2O fertilizer treatments were 135-45-90 (F1), 180-60-120 (F2), and 225-75-150 (F3) kg·ha−1. Each treatment plot had a row of ten Chinese wolfberry trees.

      Table 2.  Irrigation scheduling of Chinese wolfberry during the two years of experiments.

      Year Growth stage Irrigation
      date (m/d)
      Number of irrigation Irrigation (mm)
      Low (W1) Medium (W2) High (W3)
      2018 Spring slightly growing stage 5/4 1 17.8 23.3 28.8
      Flowering stage 5/17 2 22.6 29.6 36.5
      6/2 3 26.3 34.5 42.6
      Fruit ripening stage 6/19 4 39.3 51.4 63.5
      7/5 5 30.6 40.0 49.5
      7/21 6 26.7 34.9 43.1
      Deciduous stage 8/4 7 24.3 31.7 39.2
      Total 187.6 245.4 303.2
      2019 Spring slightly growing stage 5/5 1 18.3 24.0 29.6
      Flowering stage 5/19 2 24.5 32.1 39.2
      6/4 3 38.7 50.7 62.6
      Fruit ripening stage 6/20 4 35.2 46.1 56.9
      7/3 5 30.3 39.6 48.9
      7/13 6 27.4 35.8 44.2
      Deciduous stage 8/5 7 25.7 33.6 41.5
      Total 200.1 261.9 322.9

      Fertilizers namely urea (N 46%), superphosphate (P2O5 44%), and potassium chloride (K2O 60%) were applied a total of seven times to the fields at different growth stages of the crop. The fertilizer was fertigated with drip irrigation at the middle stage in each irrigation event. The supply of fertilizer for different growth stages were; 20% at the spring slightly growing stage (one time), 20% at the flowering stage (two times equal application), 50% at the fruit ripening stage (three times equal application), and 10% at the deciduous stage (one time). Separate differential pressure tanks with 13 L capacity were used to set up fertigation of each treatment plot.

    • The plant height and leaf area of Chinese wolfberry were measured for three trees from each plot which were randomly selected in each measurement. The plant height was measured using a meter stick for three replicates and the average value of each growth stage was calculated. A portable leaf area meter (CI-202, CID Bioscience, Camas, WA, USA) was used to measure the leaf area. Three sample plants were calibrated in each plot, and the maximum leaf area of the sample plants at each growth stage was taken as the leaf area value of the plot.

    • Chinese wolfberry crops bear fruit for two seasons namely summer and autumn. Generally, the quality and yield of autumn fruits are relatively low and therefore, the yield of summer fruits was only considered in this study. The yield can be categorized into dry fruit yield and fresh fruit yield, with dry fruit being more convenient for preservation and transportation compared to fresh fruit. Hence, this study adopts dry fruit yield as the standard for evaluation. Summer fruits were harvested in late June (first pick), early July (second pick), mid-July (third pick), late July (fourth pick), and early August (fifth pick). A total of 10 Chinese wolfberry trees were harvested from each treatment plot in both years. The harvested fruits were subjected to gradient drying under the following combinations of temperature and time; 40 °C - 2 h, 45 °C - 15 h, 55 °C - 15 h and 65 °C - 6 h. The dried weight of 100 grains for a plot was repeated and the maximum value of the mean was taken as the weight of 100-grain Chinese wolfberry.

    • Water consumption was calculated based on the water balance equation (Eqn 1)[29].

      ET=I+P+URDΔW (1)

      where, ET is evapotranspiration (mm), I is irrigation amount (mm), P is rainfall (mm), U is groundwater recharge (mm), R is runoff (mm), D is deep percolation (mm), and ΔW is the change in soil moisture between the onset and end of the study (mm). The groundwater recharge, runoff, and deep percolation were negligible due to the prevailing conditions of the experimental site during the experiment period. Therefore, the Eqn (1) could thus be simplified as,

      ET=I+PΔW (2)

      The irrigation amount was calculated based on the reference crop evapotranspiration (ET0) using the Penman-Monteith equation[30].

      Water use efficiency (WUE) was calculated based on Badr et al.[25] as follows,

      WUE=Y/ET (3)

      where, WUE is water use efficiency (kg·m−3), Y is dry fruit yield (kg·ha−1) and ET is evapotranspiration (mm).

    • The partial factor productivity of fertilizer was calculated as proposed by Ierna et al.[31] using the following formula,

      PFP=Y/FT (4)

      where, PFP is partial factor productivity of fertilizer (kg·kg−1), Y is yield (kg·ha−1) and FT is the total amount of N-P2O5-K2O fertilizer (kg·ha−1).

    • The economic benefit was calculated using a simple benefit-cost analysis as shown in Eqn 5.

      E=GwWwFwHwOw (5)

      where, E is Economic benefits (CNY¥·ha−1), Gw is the gross profit, Ww is the water fee, Fw is the fertilizer cost, Hw is the harvesting cost, and Ow is other costs (pesticides, weeding, etc.).

    • The data were analyzed using the analysis of variance (ANOVA) procedure for the factorial experiments and mean separation was performed using least significance differences (LSD) at the 5% level. The SPSS 19.0 software (Chicago, IL, USA) was used in statistical analysis and the Matlab (Version 2016b, Natick, MA, USA) was used to calculate the evaluation values. The Origin (Version 2018, Irvine, CA, USA) was used for graphical visualization.

    • In both years, plant height was significantly (p < 0.05) affected by irrigation, but not significantly influenced by fertilization. Although the interaction of irrigation and fertilizer was not significant on plant height in 2018, it was significant (p < 0.05) in 2019 (Table 3). The plant height showed an unclear relationship with fertilization rate under the same level of irrigation in both years (Fig 3). Similarly, the relationship between plant height and irrigation level was random at the same fertilizer application level for both years (Fig 3). It is because of the synergistic effect of water and fertilization on plant height from the measured data, as shown in Table 3. Under the same irrigation and fertilization level, the average plant height in 2018 was 2%−12% higher than that in 2019.

      Table 3.  Level of significance of growth parameters and yield under different irrigation and fertilizer treatments in 2018 and 2019.

      Treatment Plant height Leaf area Yield
      2018 2019 2018 2019 2018 2019
      Level of significance
      Irrigation * * * ** * *
      Fertilization ns ns ns * * ns
      Irrigation × fertilization ns * ns ns ** **
      * means significant at the 0.05 probability level, ** means significant at the 0.01 probability level, and ns means non-significant.

      Figure 3. 

      Effects of different irrigation and fertilizer treatments on plant height, leaf area, and yield in 2018 and 2019. Error bars show the standard error (n = 3). Different letters on top of the bar indicate a significant difference for the means at p < 0.05 according to the LSD test.

      The interaction effect of irrigation and fertilization was not significant on the leaf area in both years. Irrigation exhibited a significant effect (p < 0.05) on the leaf area in 2018 and it was strongly significant (p < 0.01) in 2019. Fertilization did not significantly influence leaf area in 2018 but it was significant in 2019 (Table 3). Generally, the leaf area was smaller in 2019 than the previous year (Fig. 3). This could be due to dryer weather in 2019 compared to the year 2018, which appears to decrease the leaf area.

      In both years, irrigation and fertilization had a strong significant interaction effect on yield (p < 0.01) (Table 3). At low-level irrigation (65% ET0, W1), the yield of Chinese wolfberry significantly (p < 0.05) increased with the increasing fertilization rate in 2018. The lowest yield (1,506 kg·ha−1) in 2018 was recorded for W1F1 treatment whereas the highest yield (2,056 kg·ha−1) was observed for W2F2 treatment. At the irrigation level of W2, the yield increased first and then decreased with increasing fertilizer application, and the highest yield (2,356 kg·ha−1) was received for W2F2 treatment in 2018 (Fig. 3). At the W1 irrigation level, the yield was not significantly different between different fertilizer treatments for 2019. The W3F3 treatment provided the lowest yield (1,325 kg·ha−1) while the highest was observed in the W2F3 treatment (1,954 kg·ha−1) in 2019. Under the high irrigation regime (105% ET0, W3), increasing fertilizer levels decreased the yield significantly (p < 0.05) (Fig. 3). For F1 and F2 fertilization levels, the yield significantly increased (p < 0.05) initially and declined thereafter with increasing irrigation levels in 2018 (Fig. 3). Nevertheless, this trend was not seen in the F3 treatment. For F2 and F3 fertilizer application levels, increasing irrigation levels significantly (p < 0.05) increased the yield initially and then significantly (p < 0.05) decreased during the year 2019 (Fig. 3). For the same year, yield significantly (p < 0.05) increased with increasing irrigation levels for F1 fertilizer treatment.

      In general, the W3F1 treatment showed the highest plant height in both years and the leaf area was highest for W1F2, W1F3, W2F1, W2F2, and W2F3 treatment combinations over the two years. However, the highest yield was obtained with W2F2 and W2F3 treatments in 2018 and 1019, respectively (Fig. 3).

      Overall, under the same irrigation and fertilization regime, the changes in leaf area and yield were similar. However, the changes in plant height of Chinese wolfberry were not uniform. In 2018, the yield of Chinese wolfberry reached the highest under the medium irrigation-fertilizer regime (W2F2), while in 2019, the highest yield was obtained under the medium irrigation and high fertilization (W2F3). Accordingly, the medium irrigation level could be the key to obtaining high yield in Chinese wolfberry. Furthermore, the interaction effect of irrigation and fertilization was highly significant on yield than plant height and leaf area (Table 3).

    • Water use efficiency (WUE) was significantly (p < 0.05) influenced by irrigation in 2019 and it was strongly significant (p < 0.01) in 2018 (Table 4). Fertilization had no significant effect on WUE in 2019, and conversely, it showed a significant effect in 2018 (p < 0.05). The interaction of irrigation and fertilization had a significant effect on WUE in both years. The highest WUE (0.55 kg·m−3) was attained for W2F2 treatment, and it was 40%−41% higher than the lowest values (W3F1 and W3F3) in 2018. The highest WUE value in 2019 was recorded for the W2F3 treatment (0.39 kg·m−3) and it was 41 % greater than the lowest value obtained for the W3F3 treatment (Table 4).

      Table 4.  Treatment effects on water use efficiency (kg·m−3) and partial factor productivity of fertilizer (kg·kg−1).

      Treatment Water use efficiency
      (kg·m−3)
      Partial factor
      productivity of
      fertilizer (kg·kg−1)
      2018 2019 2018 2019
      W1F1 0.42d 0.34b 5.58b 4.89b
      W1F2 0.43c 0.31cd 4.40cd 3.36cd
      W1F3 0.47b 0.33bc 4.34d 3.24d
      W2F1 0.42d 0.32c 6.59a 5.2a
      W2F2 0.55a 0.31cd 6.55a 3.82c
      W2F3 0.44c 0.39a 4.78c 4.5b
      W3F1 0.37ef 0.32c 6.52a 5.76a
      W3F2 0.42d 0.27d 5.55b 3.63c
      W3F3 0.39e 0.23e 4.75c 2.89e
      Level of significance
      Irrigation ** * * *
      Fertilization * ns ** **
      Irrigation × fertilization * * * *
      Means with different letters are significantly different (p < 0.05) based on the LSD test. * Means significant at the 0.05 probability level, ** means significant at the 0.01 probability level, and ns means non-significant.

      The interaction effect of irrigation and fertilization was significant (p < 0.05) in PFP during both years (Table 4). The maximum values for PFP were recorded with W2F1, W2F2, and W3F1 treatments in 2018 and the corresponding PFP values were 6.59, 6.55, and 6.52 kg·kg−1, respectively. The lowest values in 2018 were observed for W1F2, and W1F3 treatments which were 4.40 and 4.34 kg·kg−1, respectively. At a higher level of irrigation (W3), PFP decreased with increasing fertilizer application rate in 2018 (Table 4).

      In 2019, the maximum values for PFP were 5.2 and 5.76 kg·kg−1 for W2F1 and W3F1 treatments, respectively. The W1F3 treatment exhibited the lowest PFP value (3.24 kg·kg−1) in 2019. In the same year, the irrigation levels W1 and W3 showed a similar trend on PFP to that of 2018 with increasing fertilization levels (Table 4).

      In general, under W1 and W2 irrigation levels, PFP decreased with increasing fertilizer application rates. Furthermore, under the low fertilization level (F1), PFP increased with increasing level of irrigation. The PFP reached the minimum value at W3F3 for the year 2019, which could be an indication that the yield of Chinese wolfberry can be retarded under the high level of irrigation and fertilization.

    • At present, Chinese wolfberry cultivation provides an annual comprehensive output value of 13 billion RMB and an average annual income of CNY¥13,500 to 195,000 ha−1[32]. The effect of different irrigation and fertilization treatments on economic benefits in 2018 and 2019 were estimated and presented in Table 5. The economic benefits in 2018 and 2019 were between CNY¥155,596 ha−1 (W1F1) to CNY¥218,001 ha−1 (W2F2), and CNY¥132,423 ha−1 (W3F3) to CNY¥205,199 ha−1 (W2F3), respectively. In 2018 and 2019, the highest economic benefits were higher by 28.5% and 35.5% compared to the lowest economic benefits, respectively. This result indicates that a higher level of irrigation and fertilization do not always maximize the economic benefits, thus emphasizing the requirement for an optimum level of irrigation and fertilizer management for Chinese wolfberry production.

      Table 5.  Effects of different irrigation and fertilization treatments on economic benefits.

      Treatment Water fee
      (CNY¥ ha−1)
      Fertilizer cost
      (CNY¥ ha−1)
      Harvesting cost
      (CNY¥ ha−1)
      Other costs
      (CNY¥ ha−1)
      Gross profit
      (CNY¥ ha−1)
      Economic benefits
      (CNY¥ ha−1)
      2018 2019 2018 2019 2018 2019 2018 2019 2018 2019 2018 2019
      W1F1 500 534 2,878 6,778 6,847 15,000 180,752 182,584 155,596 157,325
      W1F2 500 534 3,838 7,027 6,344 15,000 187,375 169,178 161,010 143,462
      W1F3 500 534 4,797 7,706 6,606 15,000 205,499 176,150 177,496 149,213
      W2F1 654 698 2,878 8,010 7,218 15,000 213,607 192,474 187,065 166,680
      W2F2 654 698 3838 9,253 7,536 15,000 246,746 200,947 218,001 173,875
      W2F3 654 698 4,797 8,397 8,793 15,000 223,925 234,487 195,077 205,199
      W3F1 808 862 2,878 7,917 7,900 15,000 211,108 210,656 184,505 184,016
      W3F2 808 862 3,838 8,958 6,785 15,000 238,883 180,940 210,279 154,455
      W3F3 808 862 4,797 8,330 5,964 15,000 222,120 159,046 193,185 132,423

      The water fee is the smallest proportion of the total expenditure and the cost difference of the water fee between treatments is also small. The low cost of water fees and considerable economic losses in cutting down irrigation levels are the major reasons for the lack of interest by farmers in water saving. Suboptimal or super-optimal application of water and fertilizer not only affect the economic return but also waste a very competitive resource like water.

    • Farmers cultivating Chinese wolfberry aim at high economic return and it is usually considered that a high water and fertilizer input would increase the economic return. However, the results of this study showed that higher irrigation and fertilization levels increased the yield of Chinese wolfberry only up to a certain extent, usually referred to as an optimum level of input. Application beyond this level has led to economic loss, and reduction of water use efficiency and PFP. Moreover, excessive use of chemical fertilizer deteriorates the soil health, increases fertilizer loss to the environment, causing soil and water pollution, and eventually affecting the sustainability of agriculture[14]. Water use efficiency, economic benefits and ecologically sound crop production are the keys to sustainable agricultural development in arid regions. Therefore, the Chinese wolfberry yield, WUE, PFP, and economic benefits were selected as targeting variables for the optimization process of relevant inputs.

      Based on the least square method, four binary quadratic regression equations were established, considering irrigation and fertilizer levels as the independent variables and Chinese wolfberry yield, WUE, PFP, and economic benefits as the dependent variables (Table 6). In addition, the amount of irrigation and fertilization were calculated when the above dependent variables were maximized (Table 7).

      Table 6.  Regression equations between irrigation and fertilization inputs and yield, WUE, PFP and economic benefits.

      Dependent variable/Y Regression equation R2 P
      Yield/Y1

      Y1 = −4120.2737 + 37.5905I + 5.7081Y − 0.0628I2 − 0.0031F2 − 0.0129IF

      0.67 * (0.037)
      WUE/Y2

      Y2 = −0.7415 + 0.007I + 0.0018F − 0.000013I2 − 0.00000144F2 − 0.000003IF

      0.63 * (0.043)
      PFP/Y3

      Y3 = −3.233 + 0.122I − 0.0325F − 0.0002I2 + 0.000047F2 − 0.000043IF

      0.74 * (0.029)
      Economic benefits/Y4

      Y4 = −490877.3168 + 4339.0072I + 648.5543F − 7.2545I2 − 0.3537F2 − 1.4897IF

      0.67 * (0.038)
      I and F represent the amounts of irrigation and fertilization, respectively. * Means significant at the 0.05 probability level.

      Table 7.  The optimum level of irrigation and fertilization for maximum yield, WUE, PFP, and economic benefits.

      Dependent variable/Y Maximum value of dependent variable Irrigation
      amount
      (mm)
      Fertilization
      (N-P2O5-K2O)
      (kg·ha−1)
      Yield/Y1 1859.74 259.7 192-64-128
      WUE/Y2 0.42 225.5 204-68-136
      PFP/Y3 6.31 269.5 135-45-90
      Economic benefits/Y4 195,101.33 261.5 183-61-122

      It is difficult to obtain the maximum yield, WUE, PFP, and economic benefits simultaneously. When the amount of irrigation and fertilization (N-P2O5-K2O) were 259.7 mm and 192-64-128 kg·ha−1, respectively, the Chinese wolfberry yield reached the maximum of 1,859.74 kg·ha−1. The WUE reached the maximum of 0.42 kg·m−3 at the amount of irrigation and fertilization (N-P2O5-K2O) of 225.5 mm and 204-68-136 kg·ha−1, respectively. The greatest PFP (6.3 kg·kg−1) was achieved at 269.5 mm and 135-45-90 kg·ha−1 irrigation and fertilization (N-P2O5-K2O) levels, respectively. The maximum economic benefit of CNY¥195,101 ha−1 was achieved with the irrigation and fertilization application of 261.5 mm and 183-61-122 kg·ha−1 of (N-P2O5-K2O), respectively. The irrigation amount at the time of the highest economic benefit was 0.67% higher than that at the time of the highest yield, and the corresponding fertilizer application amount was 4.86% lower than that at the time of the highest yield.

      The WUE reached the maximum at a 13.8% lower irrigation amount and 10 % higher fertilization rate than the maximum economic benefit point. The amount of irrigation and fertilization rate was higher than 3% and 26.3%, respectively, for the highest PFP compared to the highest economic benefits.

      The interaction effect of irrigation and fertilization inputs on yield, WUE, and economic benefits showed a downward convex shape, while the PFP decreased with increasing fertilization application (Fig. 4). The maxima of yield, WUE, and economic benefits were reached at similar levels of irrigation and fertilization, however, input values to maximize the PFP differs greatly from the other three indicators. Ecological sustainability, water and fertilizer savings are the goals of our multi-objective optimization problem to achieve high yield and high economic benefits. A comprehensive evaluation method by combining the entropy weight method and the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) was established to evaluate each irrigation and fertilization treatment in 2018 and 2019, as shown in Fig. 5.

      Figure 4. 

      Relationship of (a) yield, (b) water use efficiency (WUE), (c) partial factor productivity (PFP) and (d) economic benefits with the amount of irrigation and fertilization (N-P2O5-K2O) during the two years. The red dots in the figure represent the measured experimental data during 2018 to 2019.

      Figure 5. 

      Effects of irrigation and fertilization on comprehensive evaluation index for (a) 2018, and (b) 2019.

      It can be found that the maximum index value appeared in the medium level of irrigation and fertilization region in 2018 and a medium level of irrigation and high level of fertilization region in 2019. This observation is consistent with the irrigation and fertilization level reflected by the measured data in these two years. To have an overlapping area in the maximum value of comprehensive evaluation indicators in both years, 90% of the maximum value of comprehensive evaluation indicators was determined as acceptable regions. According to this, when the irrigation range was 252 to 262 mm and the fertilization range was 185-62-123 to 200-67-133 kg·ha−1, the Chinese wolfberry yield, WUE, PFP, and economic benefits reached above 90% of their maxima concurrently.

    • Plant height and leaf area are commonly used as growth parameters of Chinese wolfberry[33]. Yin et al.[34] reported that plant height was significantly affected by irrigation, thus increasing irrigation level was beneficial for the growth of Chinese wolfberry. However, the effect of fertilizer on plant height was not significant as it also accumulated with tree age, and therefore, fertilizer amount in two years may not change the plant height significantly[35]. The results of this study are consistent with previous findings where irrigation had a significant effect on plant height, while fertilizer application had no significant effect on the plant height of Chinese wolfberry.

      Leaf plays an important role in photosynthesis and transpiration, thus the leaf size has a great influence on the growth and the yield formation[4]. It was reported that the leaf area increased first and then decreased with the increasing irrigation and fertilizer levels[36,37] which is similar to the findings of this study. The interaction effect of irrigation and fertilization did not significantly influence the leaf area. Irrigation levels significantly influenced the leaf area which was also noticed in other studies[3,38,39].

      It was found that the interaction effect of water and fertilizer considerably influences the Chinese wolfberry yield. In both years, suboptimal and excess application of irrigation reduced the yield whereas a high level of fertilization did not result in the highest yield. This could be because Chinese wolfberry is a perennial plant that used up a larger portion of the absorbed nutrients for vegetative growth rather than for the conversion of reproductive growth[40]. Under high irrigation levels, nutrient leaching beyond the root zone may have decreased plant available nutrients and eventually results in a lower yield[5]. However, insufficient irrigation retards the plant growth decreases the leaf area and lowers the photosynthetic efficiency which is not conducive to high yield. Dai et al.[41] also confirmed that water shortage reduced the production of the crop. The results showed that Chinese wolfberry yield was lower in 2019 (1,954 kg·ha−1) than in 2018 (2,056 kg·ha−1). The possible reason for this is that the evapotranspiration in 2019 was higher than that in 2018 while the precipitation remains almost the same, which could have decreased the soil moisture availability to the plants and ultimately reduced the yield[42]. Therefore, the optimum level of irrigation and fertilization could increase the agronomic performances and provide the highest yield[43].

    • The interaction of irrigation and fertilizer was significant in WUE which showed a good agreement with previous studies[44,45]. In general, the WUE showed a parabolic relationship with increasing irrigation and fertilization wherein irrigation had a stronger relationship than fertilization. The maximum WUE was achieved with medium level of irrigation and medium fertilizer treatment in 2018 whereas under medium level irrigation and high fertilizer level in 2019. At a high level of irrigation, the WUE decreased with increasing fertilization. High irrigation level often induces the leaching losses of nutrients, especially N, possibly the reason for this observation. At the same level of irrigation, the WUE of high fertilization level was generally higher than that of a low fertilization level[46]. Likewise, Eissa et al.[47] reported that 28%−42% increase in WUE with higher levels of N (240 kg·ha−1) as compared to the lower level (120 kg·ha−1) in wheat. This is because fertilizer improves growth and yield in some crops and improving WUE, while excessive fertilization will affect the absorption of nutrients by Chinese wolfberry, resulting in excessive soil nutrients and reduced WUE. Improved WUE could be achieved through the proper application of N and P fertilizer was documented in several studies such as Li et al.[48] and Wei et al.[49].

      Meanwhile, previous studies showed that PFP decreases with the increase of fertilization, and increases initially and then decreases with the increase of irrigation[35,50] which is in agreement with the results of this study as well. In this experiment, the PFP values corresponding to the highest yield treatments (i.e., W2F2 in 2018, W2F3 in 2019) were 0.61% lower than the highest PFP values in 2018, and 21.88% lower than in 2019. These results showed that a low level of fertilization yielded higher PFP, but didn't meet the production requirements. However, excessive nitrogen fertilization promotes vegetative growth and impedes the supply of nutrients to reproductive components of the crop, leading to yield reduction[51]. Several studies showed that higher levels of nutrient application failed to support high yield. For example, Okebalama et a.l[52] pointed out that P fertilizer had a greater effect on corn grain yield than N fertilizer and P fertilizer should be supplied not exceeding the critical level of 60 kg·ha−1 (in Plinthic Acrisol) and 90 kg·ha−1 (in Gleyic Plinthic Acrisol) for optimum maize yield. Trujillo Marín et al.[27] reported that a 30% N application rate increased the yield of fresh fruit by 32.9%, and increased nitrogen accumulation by 9.0% compared to a 70% N application rate in tomato. Moradi et al.[53] found that 60 kg·ha−1 gave the highest yield of rice than the other two levels of N application rates; 40 and 60 kg·ha−1. All these findings support the results of this study that either low or high nutrient application is not conducive for high yield.

      The ultimate aim of the farmers is to gain high economic return which influences the viability of the farming. The economic benefits of medium level irrigation (W2) 17.7% (2018), 17.6% (2019), and 2% (2018), 13.7% (2019) times higher than low and high irrigation levels, respectively. At the same level of irrigation, economic benefits increased initially and then decreased with increasing fertilization. Therefore, this study emphasizes that increasing either irrigation or fertilization beyond the optimal level decreased the economic benefits[41,42,54,55]. Considering the cost of inputs, cutting down the fertilizer cost is more beneficial than reducing the expenditure on water. However, saving water is also equally important on the basis of environmental protection. Therefore, it is necessary to seek an irrigation and fertilization management scheme that can ensure not only the efficient management of irrigation and fertilizer but also take into account economic benefits in both water-deficient and non-water-deficient areas.

    • The interaction effect of irrigation and fertilizer was significant on WUE and PFP and was strongly significant on the yield. Obviously, the interaction of water and fertilizer is the effective method to improve the comprehensive benefits of Chinese wolfberry[5]. This study developed appropriate relationship models between inputs (irrigation and fertilization) and yield, WUE, PFP, and economic benefits by combining the quadratic polynomial stepwise regression, and spatial analysis method. The solution of the models showed that no irrigation and fertilizer management scheme maximized all indicators. Similar observations were reported in other studies[56,57]. In addition, the entropy weight method was combined with TOPSIS to comprehensively evaluate all the treatments for the two years of experiment. Few studies have shown that appropriate adjustment of the confidence interval can solve the problem of comprehensive benefits[56,58].

      Therefore, a 90% confidence interval was set as an acceptable range in this study to maximize the yield, WUE, PFP, and economic benefits. More than 90% of the maximum values were achieved at the irrigation range of 252−262 mm and the N-P2O5-K2O fertilization range of 185-62-123 to 200-67-133 kg·ha−1 without spring and winter irrigation. The irrigation and N-P-K fertilizer application amount of local Chinese wolfberry park are 300 mm and 396-166-225 kg·ha−1 respectively, and the annual income is CNY¥13,000 ha−1. If the irrigation and fertilizer management scheme proposed in this study is adopted, it could save water by 13%−16%, N-P2O5-K2O fertilizer by 50%-60%-41% to 53%-63%-45% and increase economic benefits by about 8%.

    • Lack of appropriate irrigation and fertilizer management is one of the deeply rooted issues in Chinese Wolfberry cultivation in northwest China. This study attempts to find the optimal irrigation and fertilization level based on yield, WUE, PFP, and economic benefits for Chinese Wolfberry over a two-year field experiment. None of the treatment combinations provided the maximum values for yield, WUE, PFP, and economic benefits. The WUE decreased with increasing irrigation level. The WUE with low irrigation level (65% ET0) and medium irrigation level (85% ET0) were all higher than that of high irrigation levels (105% ET0) in both years. With increasing fertilization, PFP showed a decreasing trend. Both low (65% ET0), and high (105% ET0) irrigation levels were not conducive to the effective utilization of fertilizer. The irrigation and fertilizer schemes corresponding to the maximum yield and economic benefits in 2018 and 2019 were medium irrigation levels (85% ET0) with medium and high fertilizer treatments, respectively.

      The least square method, multiple regression, and comprehensive evaluation of a multi-objective optimization problem revealed that the yield and economic benefits do not decrease, when the irrigation range was 252−262 mm and the N-P2O5-K2O fertilization range was 185-62-123~200-67-133 kg·ha−1. At this application level, yield, WUE, PFP, and economic benefits of Chinese wolfberry reached 90% of the maximum value, which would maximize the comprehensive benefit. The finding of this study is of importance in providing the baseline of irrigation and fertilization levels for farmers cultivating Chinese wolfberry in the northwest China and other regions with similar soil and climate characteristics. Nevertheless, further studies may be required to validate the findings of this research across different geographical regions.

    • The authors confirm contribution to the paper as follows: study conception and design: Deng Z, Yin J; data collection: Deng Z, Wu J, Zhang H; data curation: Deng Z, Yin J, Eeswaran R, Abhiram G; analysis and interpretation of results: Deng Z, Yin J, Eeswaran R, Abhiram G; draft manuscript preparation: Deng Z; writing – review & editing: Yin J, Eeswaran R, Abhiram G; fund acquisition & supervision: Yin J. All authors reviewed the results and approved the final version of the manuscript.

    • All data generated or analyzed during this study are included in this published article.

      • This work was financially supported by the First-class Subject Project at Ningxia University (Grant No. NXYLXK2017A03), and the talent plan of Ningxia youth 'support project' in 2017.

      • The authors declare that they have no conflict of interest.

      • Copyright: © 2024 by the author(s). Published by Maximum Academic Press, Fayetteville, GA. This article is an open access article distributed under Creative Commons Attribution License (CC BY 4.0), visit https://creativecommons.org/licenses/by/4.0/.
    Figure (5)  Table (7) References (58)
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    Deng Z, Yin J, Eeswaran R, Gunaratnam A, Wu J, et al. 2024. Interacting effects of water and compound fertilizer on the resource use efficiencies and fruit yield of drip-fertigated Chinese wolfberry (Lycium barbarum L.). Technology in Horticulture 4: e019 doi: 10.48130/tihort-0024-0016
    Deng Z, Yin J, Eeswaran R, Gunaratnam A, Wu J, et al. 2024. Interacting effects of water and compound fertilizer on the resource use efficiencies and fruit yield of drip-fertigated Chinese wolfberry (Lycium barbarum L.). Technology in Horticulture 4: e019 doi: 10.48130/tihort-0024-0016

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