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Soils serve as a critical surface layer on Earth, acting as reservoirs for water, nutrients, air, and heat necessary for plant growth. Soils therefore can support human and animal well-being by facilitating element biogeochemical cycles, and food webs[18, 19]. Plastic-greenhouse soils differ from open-field soils due to intensive anthropogenic activities, such as multiple cropping, semi-closed plastic covers, excessive use of chemicals, and frequent irrigation[1, 5, 20]. Hence, plants grown in plastic-greenhouse soils are often subjected to greater water and nutrient loss, low atmospheric carbon dioxide concentration, low soil temperature, high atmospheric humidity, soil compaction, and soil degradation compared to open-field crops (Table 1).
Table 1. The constraints for plastic-greenhouse horticulture production, corresponding reasons and remediation measures from soil perspective.
Constraints Reasons for the constraints Remediation from soil perspective Ref. Low atmospheric [CO2] Partly sealed environment by plastic covers limits CO2 diffusion from atmosphere to greenhouses Application of organic or inorganic amendments to soils, accelerating their quick decomposition [47,48] High atmospheric humidity Plastics limit the diffusion of evaporated water, strengthened by frequent irrigation Organic or plastic mulch, and drip irrigation to allow low evaporation [37,49] Low soil temperature Off-season horticulture production, frequently in winter period Decreased soil-specific heat capacity, and heat production and preservation [22,50] Nutrient loss Heavy chemical and organic fertilizer input and frequent irrigation, facilitating leaching of $ {\text{NO}^-_3} $, and production of NOX and NH3 Limiting leaching or gaseous N loss by water conservation soil interlayer or less irrigation [5,51] Soil compaction Extensive mobility of machine and human Increasing organic fertilizer input, and frequent ploughing [52,53] Soil pollution, acidification, and salinization Heavy chemical input and residue leftover Addition of organic fertilizer, and decreasing the origin of residual toxins [26,54] As a result, plastic-greenhouse soils should fulfill certain requirements. They should provide sufficient water and nutrients for crop growth and oxygen for root and soil respiration as the open-field soils. In addition, different from open-field soils, they should store and buffer water and nutrients with minimal loss, considering the high input of fertilizers and frequent irrigation; they should supply extra carbon dioxide for enhanced plant photosynthesis in the partly sealed environment[21] and extra heat for root growth concerning low temperature in winter[22]; they should minimize soil evaporation to avoid high atmospheric humidity, achieving high transpiration for nutrient uptake, and reducing the risk of pathogen infection[23, 24].
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Based on the requirements of plastic-greenhouse soils, the soil profile can be designed and consist of four soil layers: a mulch layer, a root-carbon layer, a soil-carbon mix layer, and a water conservation layer (Figs 1a & 2, Table 2). More specifically, the mulch layer isolates soils from the atmosphere, preventing soil evaporation for water conservation and humidity alleviation. Additionally, the mulch layer absorbs heat from solar radiation, warming the soil, and preventing soil salts from moving into the root-carbon layer from the buffer layer due to high porosity, thus reducing soil salinization[25]. The root-carbon layer is a thinner layer designed to receive carbon-containing compounds to produce nutrients and CO2 for plant production, to generate heat from microbial decomposition, and to remediate soil toxins resulting from high microbial enzyme activities[26], which facilitates root proliferation and nutrient uptake.
Figure 1.
Profile of plastic-greenhouse soils as (a) conceptual framework and two examples for horticulture production as sand mulching profile charactered by sand mulch in (b) Almería, Spain modified based a previous study[25], and as sunken profile charactered by digging to obtain subsoils of clay in (c) Shouguang county, China.
Figure 2.
Plastic-greenhouse soil profile that motivates carbon and nutrient cycling, and heat production, and saves nutrient and water for that can counteract the environmental constraints of high atmospheric humidity, high water and nutrient loss, low atmospheric CO2, low soil temperature, soil compaction, and soil degradation. Some of the symbols were adopted from IAN/UMCES Symbol and Image Libraries.
Table 2. The profiles of plastic-greenhouse soil, their primary function and the practices to establish the cost-effective soil layer.
Soil profile Primary function Practices Soil mulch layer Evaporation inhibition Rice husk mulching Root-carbon layer Root and microbe activation Manure or compost application Soil-carbon mix layer Increase soil resilience Biochar or peat input Water conservation layer Water and nutrient preservation Deep placement of
clay soilsThe soil-carbon mix layer combines original soil with carbon-containing compounds through tillage. This layer serves as a buffer layer to store extra nutrients and water for root growth, and to buffer or decompose toxic metabolites resulting from soil-plant interaction, such as microbial metabolites, root exudates or plant residues[27]. The bottom water conservation layer using easily-compacted materials is necessary to preserve water and nutrient within the above layers for root growth and plant production, and thus minimize water and nutrient leaching out to underground water body. The depth of these four layers depends on the specific requirements of a local soil and climate.
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The solar greenhouse with a north wall inside to support its roof was developed in the 1950's and has since been continuously upgraded. Its use has reached 810 thousand ha in Northern China[12]. However, the soil profiles have yet been fully understood to our knowledge. Based on the authors' survey in Shouguang county and the concept of plastic-greenhouse soil profile, we have proposed one soil profile called 'Sunken soil profile', as shown in Fig. 1c. More specifically, local farmers remove the topsoil of approximately 50 cm from the original farmland used for wheat or corn production. This practice provides materials for the construction of north walls supporting the entire solar greenhouse, and the wall is thought to preserve heat within the plastic greenhouses[20]. Unexpectedly, this practice builds a water conservation layer as the local subsoils contain greater clay content, decreasing the loss of water and nutrients from the rooting zone[40]. The root-carbon layer is a mix of the original subsoil and manure, such as poultry litter or cow manure. This layer is readily formed by broadcasting manure on the top of subsoil layer and then rotary tillage. The surface layer is then covered by organic mulch, frequently rice husk, which alleviates plant diseases from soil pathogens due to decreased atmospheric humidity, according to the survey from local farmers.
Similar to Almería's sand mulching profile, the plastic-greenhouse soil cultivation is more profitable and suitable for smallholders than modern soilless cultures (Table 3). In addition, this sunken profile substantially decreases the ratios of leaching to total application of the nutrients (including nitrate) in the topsoil of approximately 20 cm compared to open-field soils[1, 41, 42].
Table 3. The comparison of the costs of tomato production in plastic greenhouses between sunken profile and soilless culture (CNY ha−1) in the Shouguang county, Northern China in 2022.
Items Sunken profile Soilless culture Total costs 379,500 657,000 Seedlings 45,000 48,000 Water and fertilizers 108,000 165,000 Workforce 180,000 285,000 Substrate 0 90,000 Others 46,500 117,000 Income 634,500 877,500 Tomato yield (t·ha−1) 211.5 292.5 Net profits 255,000 220,500 The price of tomato was CNY3,000 t−1. The others include machine and land rent, fertigation energy consumption, and pesticide. The data were based on a survey of the local smallholder farmers. In addition, current soil profile has been modified by the use of plastic film rather than organic mulch when organic material being not available or expensive, or without the removal of topsoil using topsoil to mix with manure as root-carbon layer directly. The modifications were frequently observed in Southern China where the winter season was relatively warm compared to Northern China.
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The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.
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About this article
Cite this article
Dong J, Gruda N, Tang C, Yang S, Cai Z, et al. 2024. How to design cost-effective soil profiles in plastic greenhouses? Vegetable Research 4: e011 doi: 10.48130/vegres-0024-0010
How to design cost-effective soil profiles in plastic greenhouses?
- Received: 11 October 2023
- Accepted: 08 March 2024
- Published online: 02 April 2024
Abstract: Plastic-greenhouse soils, spanning approximately 4.8 million hectares worldwide, are predominantly cultivated by smallholder farmers for horticultural production. These soils contribute greatly to the production of vegetables, herbs, and fruits, and thus to a healthy diet and high farmers' income. Nevertheless, the current challenge is a comprehensive understanding and design of cost-effective profiles for plastic-greenhouse soils of low to medium technology. Here, we devised a novel conceptual framework of a plastic-greenhouse soil profile, considering the environmental limitations imposed by the plastic covering. The profile comprises four distinct layers: a mulch layer to reduce evaporation, a root-carbon layer to facilitate nutrient, CO2 and heat generation, a soil-carbon mix layer for effective soil buffering, and a water conservation layer to store water and nutrients. Two typical examples of this concept were summarized, the sand mulching profile in Almería, Spain and the sunken profile in Shouguang, China. This soil profile design is affordable and cost-effective for smallholder farmers to produce horticulture product sustainably, therefore, it is worth being applied worldwide. Future studies should adopt the current concept but modify it based on the local soil profile and available resources. More importantly, controlling organic input and thus microbial functions are required to facilitate either plant or soil health.
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Key words:
- High tunnel soil /
- Microbial community /
- Plastic shed /
- Soil layers /
- Soil profile /
- Organic amendments