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Crop growth and yield depends on the fixed carbon content (CC) and their distribution to plant parts (e.g. roots and shoots). Understanding and calculating the total CC (TCC) accumulated in field crops is very important due to the current issues of food security and global warming. However, there is a lack of research that shows how much CC is partitioned into the roots and shoots. Our previous research work confirmed that the increase in CC in plant tissues (roots and shoots) depends on total dry matter accumulation and partitioning[1−4 ], because plant growth and yield correlates with net carbon gain on a whole plant basis[5, 6 ].
The IPCC report[7] revealed that about 1.2 billion tonnes of carbon at annual rate of 4‰ could be stocked every year for the sustainability of agricultural systems. As the crop growth and yield depends on the total CC (TCC) of plants, therefore, any agronomic practices that help the plants to sequester more atmospheric CO2 (photosynthesis) increases the TCC accumulation in plants in its distribution to below ground CC to roots (BCC) and above ground CC to shoots (ACC). Therefore, crop production may be defined as: maximizing photosynthetic efficiency of crops to store more carbon above (ACC) and below (BCC) ground parts. The increase in CC above ground part (ACC) depends on: number and size of leaves, number of tillers, reproductive tillers, stems, seed size and number, grain yield and harvest index etc., increase partitioning of CC for better roots development depends on: roots number and length, root proliferation and total root biomass. The increase in CC of roots (BCC) will help the plants to uptake more water and nutrients from the soil and transfers it for better shoot development (ACC) e.g. increase in grain yield, yield components and harvest index.
The TCC accumulation and its partitioning in plant bodies depends on three major factors: (1) plant genotypes e.g. plant species, varieties, hybrids, exhaustive (grasses) and restorative (legumes) crops, growth habit, growth stages, photosynthesis, C4 crops (e.g. maize, sorghum, millets, etc.) and C3 crops (e.g. wheat, rice, and barley etc.); (2) agronomic practices (chemical fertilizers, organic fertilizers, biofertilizers, plant nutrition, irrigation, tillage practices, soil types, SOC, plant density, seed rates, sowing time, etc. ); and (3) environmental condition viz. biotic stresses (plant competition, weeds, diseases, insects, pests, etc.) and abiotic stresses (low and high temperature stress, low and high water stress, light quality and duration, wind, chemicals, gases, soil pollution, water pollution, etc.).
In recent years, many international organizations[8−18] and researchers[19−43] reported about the importance of carbon footprints in plants, animals, soil, water, environment, ecosystems etc. There is still a lack of comprehensive research and reports on the precise amount of carbon sequestered or stored by individual plants. Because carbon estimation in field crops, especially in roots, is very difficult, costly and time consuming.
The primary objective of this paper is to create a simplified model for estimating the allocation of above-ground carbon content (ACC) and below-ground carbon content (BCC) in field crops, specifically cereals. The purpose of developing a simplified model is to facilitate the estimation of carbon content partitioning in field crops, such as winter crops (e.g., wheat and barley) and summer crops (e.g., maize and rice), specifically targeting students and researchers. This model aims to simplify the process and make it more accessible for those interested in studying carbon content allocation in field crops.
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For the estimation of the total carbon content (TCC) accumulated by plants and its distribution (partitioning) into above ground (shoots) and below ground (roots) parts, efforts were made to calculate the two important factors for above ground parts (ACC) and below ground parts (BCC), 0.42 (% CC in shoot biomass) and 0.38 (% CC in root biomass), respectively. Then three simple equations (1, 2 and 3) were developed to easily estimate the CC in above ground biomass (AGB), below ground biomass (BGB) and total biomass (TBM):
$ ACC = AGB \times 0.42 $ (1) $ BCC = BGB \times 0.38 $ (2) $ TCC = ACC + BCC $ (3) The total CC (TCC) per plant or per unit area can be easily calculated in field crops by just adding ACC with BCC as shown in Eqn (3).
Based on the model developed in this study: Out of the 100% total carbon content (TCC) fixed/accumulated by field crops, 82% is partitioned into shoots or above ground carbon content (ACC) and 18% into roots or below ground carbon content (BCC). On the other hand, out of the 100% total biomass (shoots biomass + roots biomass on dry basis) (TBM) accumulation by field crops, 80% is partitioned into above ground biomass (AGB) and 20% into below ground biomass (BGB).
Note: Multiplying the amount of CO2 by 12/44 or 0.27 is equal to the amount of carbon, means that 1 kg of CO2 is equal to 0.27 kg of carbon. On other hand, multiplying the amount of carbon by 44/12 or 3.67 (44/12) is equal to the amount of CO2, means that 1 kg of carbon is equal to 3.67 kg of CO2 (where 12 is the molecular weight of carbon, and 44 is the molecular weight of CO2 (C + O2 = 12 + 16 × 2 = 44).
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In 2018, wheat produced in metric tonnes (MT) and the total carbon content (TCC) accumulated and partitioned into roots or below ground CC (BCC) and shoots, or above ground CC (ACC) for the world leading countries was calculated through this model (Table 1). For example, in 2018, the total wheat produced in Pakistan was 25.4 MT[2, 44].
Table 1. Approximate estimation of carbon content (CC) fixed by wheat crop in metric tons (MT) for the leading countries in the world during 2018−2019.
Countries Metric tons (MT) GY AGB ACC BGB BCC TBM TCC European Union 147.0 420.0 176.4 105.0 39.9 525.0 216.3 China (mainland) 126.7 362.0 152.0 90.5 34.4 452.5 186.4 India 98.6 281.7 118.3 70.4 26.8 352.1 145.1 Russian Federation 72.0 205.7 86.4 51.4 19.5 257.1 105.9 United States of America 49.7 142.0 59.6 35.5 13.5 177.5 73.1 Canada 31.3 89.4 37.6 22.4 8.5 111.8 46.1 Pakistan 25.4 72.6 30.5 18.1 6.9 90.7 37.4 Ukraine 23.4 66.9 28.1 16.7 6.4 83.6 34.4 Australia 21.9 62.6 26.3 15.6 5.9 78.2 32.2 Turkey 21.0 60.0 25.2 15.0 5.7 75.0 30.9 Argentina 20.0 57.1 24.0 14.3 5.4 71.4 29.4 Kazakhstan 14.0 40.0 16.8 10.0 3.8 50.0 20.6 Iran Islamic Rep. 13.4 38.3 16.1 9.6 3.6 47.9 19.7 Other countries 71.7 204.9 86.0 51.2 19.5 256.1 105.5 World 736.1 2103.1 883.3 525.8 199.8 2628.9 1083.1 Source: FAO outlook[11] and Amanullah et al.[64]. Where: CC = Carbon content, MT = Metric tons, GY = Grain yield, AGB = Above ground biomass, ACC = Above ground CC, BGB = Below ground biomass, BCC = Below ground CC, TBM = Total biomass (AGB + BGB), TCC = Total CC (ACC + BCC). The above ground biomass (AGB) or shoot dry weight (shoot biomass) was calculated using Eqn 4:
$ \begin{split}{\boldsymbol{AGB}} =\;&{\boldsymbol{ Grain}}\; {\boldsymbol{Production}}\; {\bf\div}{\bf{ 0.35}} ({\boldsymbol{Factor}}) \\=\;& 25.4 \div 0.35 \\=\;& 72.6 \;(MT)\end{split} $ (4) The carbon content of the AGB or shoot CC (ACC) was calculated using the following equation:
$\begin{split} {\boldsymbol{ACC}} =\;&{\boldsymbol{ AGB}} \times {\boldsymbol{factor}}\; ({\bf{0.42}})\\ =\;& 72.6 \times 0.42 \\=\;& 30.5 MT \;({\bf{82}}{ {\%}})\end{split}\tag{1} $ The total biomass (TBM) (shoots + roots) was calculated using Eqn 5:
$\begin{split} {\boldsymbol{TBM}} =\;&{\boldsymbol{ AGB}} \times {\bf{1.25}} \;({\boldsymbol{Factor}})\\ =\;& {\bf{72.6}} {\bf\times}{\bf{ 1.25}}\\ =\;&{\bf{ 90.7}}{\boldsymbol{ MT}}\end{split} $ (5) The below ground biomass (BGB) or root biomass was calculated using Eqn 6:
$\begin{split}{\boldsymbol{ BGB}} =\;&{\boldsymbol{ TBM}}{\bf \times} {\bf{0.20}}\; ({\boldsymbol{Factor}})\\ =\;& 90.7 \times 0.20 \\=\;& 18.1 MT \end{split}$ (6) The CC of the BGB or root biomass (BCC) was calculated using Eqn 2:
$ \begin{split}{\boldsymbol{BCC}} =\;&{\boldsymbol{ BGB}} {\bf\times} {\boldsymbol{factor}}\; ({\bf{0.38}}) \\=\;& 18.1 \times 0.38\\ =\;& 6.9 MT\; ({\bf{18}}{ {\%}})\end{split} \tag{2}$ The total CC (TCC) fixed by wheat in Pakistan during 2018 was calculated using Eqn 3:
$\begin{split}{\boldsymbol{ TCC}} = \;&{\boldsymbol{ACC}} + {\boldsymbol{BCC}}\\ =\;&\bf 30.5 \;(82{ {\%}}) + 6.9 \;(18{ {\%}}) \\=\;&{\bf{ 37.4}}{\boldsymbol{ MT}}\; (\bf100{ {\%}})\end{split}\tag{3} $ Example 2 (rice)
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In 2018, rice produced in metric tonnes (MT) and the total carbon content (CC) fixed in rice below (BCC) and above (ACC) ground parts for the world leading countries was calculated (Table 2). For example, in 2018 the total rice produced in China was 141.3 MT[2, 44].
Table 2. Approximate estimation of carbon content (CC) fixed by rice crop in metric tons (MT) for the leading countries in the world during 2018.
Countries Metric tons (MT) GY AGB ACC BGB BCC TBM TCC China (mainland) 141.3 314.0 131.9 78.5 29.8 392.5 161.7 India 113.5 252.2 105.9 63.1 24.0 315.3 129.9 Indonesia 46.7 103.8 43.6 25.9 9.9 129.7 53.4 Bangladesh 35.3 78.4 32.9 19.6 7.5 98.1 40.4 Viet Nam 28.7 63.8 26.8 15.9 6.1 79.7 32.8 Thailand 22.8 50.7 21.3 12.7 4.8 63.3 26.1 Myanmar 18.2 40.4 17.0 10.1 3.8 50.6 20.8 Philippines 12.9 28.7 12.0 7.2 2.7 35.8 14.8 Brazil 8 17.8 7.5 4.4 1.7 22.2 9.2 Japan 7.5 16.7 7.0 4.2 1.6 20.8 8.6 Pakistan 7.6 16.9 7.1 4.2 1.6 21.1 8.7 United States of America 6.5 14.4 6.1 3.6 1.4 18.1 7.4 Cambodia 6.4 14.2 6.0 3.6 1.4 17.8 7.3 Egypt 4.2 9.3 3.9 2.3 0.9 11.7 4.8 Nigeria 4.3 9.6 4.0 2.4 0.9 11.9 4.9 World 511.4 1136.4 477.3 284.1 108.0 1420.6 585.3 Source: FAO outlook [11] and Amanullah et al.[64]. Where: CC = Carbon content, MT = Metric tons, GY = Grain yield, AGB = Above ground biomass, ACC = Above ground CC, BGB = Below ground biomass, BCC = Below ground CC, TBM = Total biomass (AGB + BGB), TCC = Total CC (ACC + BCC). The above ground biomass (AGB) or shoots dry weight (shoot biomass) was calculated using Eqn 4:
$\begin{split}{\boldsymbol{ AGB}} =\;&{\boldsymbol{ Grain}}\; {\boldsymbol{Production}} \bf\div 0.45\; ({\boldsymbol{Factor}}) \\=\;& 141.3 \div 0.45\\ =\;& 314.0\; (MT)\end{split}\tag{4} $ The carbon content of the AGB or shoots (ACC) was calculated using the following Eqn 1:
$\begin{split}{\boldsymbol{ ACC}} =\;&{\boldsymbol{ AGB}} {\bf\times} {\boldsymbol{factor}}\; ({\bf{0.42}}) \\=\;& 314.0 \times 0.42 \\=\;& 131.9 MT\; (82{\text{%}})\end{split}\tag{1} $ The total biomass (TBM) (shoots + roots) was calculated using Eqn 5:
$\begin{split}{\boldsymbol{ TBM}} = \;&{\boldsymbol{AGB}} {\bf\times}{\bf{ 1.25}} \\=\;&\bf 314 \times 1.25\\ =\;&{\bf {392.5}} {\boldsymbol{MT}}\end{split}\tag{5} $ The below ground biomass (BGB) or root biomass was calculated using Eqn 6:
$ \begin{split}{\boldsymbol{BGB}} =\;&{\boldsymbol{ TBM}} {\bf\times} {\bf{0.20}}\; ({\boldsymbol{Factor}})\\ =\;& 392.5 \times 0.20 \\=\;& 78.5\; MT\end{split}\tag{6} $ The CC of the BGB or root biomass (BCC) was calculated using Eqn 2:
$\begin{split}{\boldsymbol{ BCC}} =\;&{\boldsymbol{ BGB}} {\bf\times} {\boldsymbol{factor}}\; ({\bf{0.38}})\\ =\;& 78.5 \times 0.38 \\=\;& 29.8\; MT\; ({\bf{18}}{ {\%}})\end{split}\tag{2} $ The total CC (TCC) fixed by rice crop in china during 2018 was calculated using Eqn 3:
$\begin{split}{\boldsymbol{ TCC}} =\;&{\boldsymbol{ ACC}} + {\boldsymbol{BCC}}\\ =\;&{\bf{ 131.9}}\; ({\bf{82}}{ {\%}}) + {\bf{29.8}}\; ({\bf{18}}{ {\%}})\\ =\;&{\bf {161.7}}\;{\boldsymbol{ MT}}\; ({\bf{100}}{ {\%}})\end{split}\tag{3} $ Example 3 (maize)
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In 2018, maize produced in metric tonnes (MT) and the TCC, BCC and ACC for maize in world leading countries was calculated (Table 3). For example, in 2018 the total maize produced in USA was 392.5 MT[2, 44].
Table 3. Approximate estimation of carbon content (CC) fixed by maize crop in metric tons (MT) for the leading countries in the world during 2018.
Countries Metric tons (MT) GY AGB ACC BGB BCC TBM TCC United States of America 392.5 981.1 412.1 245.3 93.2 1226.4 505.3 China (mainland) 257.2 642.9 270.0 160.7 61.1 803.7 331.1 Brazil 82.3 205.7 86.4 51.4 19.5 257.2 105.9 Argentina 43.5 108.7 45.6 27.2 10.3 135.8 56.0 Ukraine 35.8 89.5 37.6 22.4 8.5 111.9 46.1 Indonesia 30.3 75.6 31.8 18.9 7.2 94.5 39.0 India 27.8 69.6 29.2 17.4 6.6 86.9 35.8 Mexico 27.2 67.9 28.5 17.0 6.5 84.9 35.0 Romania 18.7 46.7 19.6 11.7 4.4 58.3 24.0 Canada 13.9 34.7 14.6 8.7 3.3 43.4 17.9 France 12.7 31.7 13.3 7.9 3.0 39.6 16.3 South Africa 12.5 31.3 13.1 7.8 3.0 39.1 16.1 Russian Federation 11.4 28.5 12.0 7.1 2.7 35.7 14.7 Nigeria 10.2 25.4 10.7 6.3 2.4 31.7 13.1 Hungary 8.0 19.9 8.4 5.0 1.9 24.9 10.3 Philippines 7.8 19.4 8.2 4.9 1.8 24.3 10.0 Ethiopia 7.4 18.4 7.7 4.6 1.7 23.0 9.5 Egypt 7.3 18.3 7.7 4.6 1.7 22.8 9.4 Serbia 7.0 17.4 7.3 4.4 1.7 21.8 9.0 Pakistan 6.3 15.8 6.6 3.9 1.5 19.7 8.1 World − − − − − − Source: FAO outlook [11] (Accessed on 5-5-2020). Where: CC = Carbon content, MT = Metric tons, GY = Grain yield, AGB = Above ground biomass, ACC = Above ground CC, BGB = Below ground biomass, BCC = Below ground CC, TBM = Total biomass (AGB + BGB), TCC = Total CC (ACC + BCC). The above ground biomass (AGB) or shoot biomass was calculated using Eqn 4:
$ \begin{split}{\boldsymbol{AGB}} =\;&{\boldsymbol{ Grain}}\; {\boldsymbol{Production}} {\bf\div} {\bf{0.40}}\; ({\boldsymbol{Factor}}) \\=\;& 392.5 \div 0.40\\ =\;& 981.1\; (MT)\end{split}\tag{4} $ The carbon content of the AGB or shoot CC (ACC) was calculated using the following Eqn 1:
$\begin{split}{\boldsymbol{ ACC}} =\;&{\boldsymbol{ AGB}} {\bf\times} {\boldsymbol{factor}}\; ({\bf{0.42}}) \\=\;& 981.1 \times 0.42 \\=\;& 412.1 \;MT\; ({\bf{82}}{ {\%}})\end{split} \tag{1}$ The total biomass (TBM) (shoots + roots dry weights) was calculated using Eqn 5:
$\begin{split}{\boldsymbol{ TBM}} =\;& {\boldsymbol{AGB}} {\bf\times} {\bf{1.25}}\\ =\;&{\bf{ 981.1}} {\bf\times} {\bf{1.25}} \\=\;&{\bf{ 1226.4}}\;{\boldsymbol{ MT}}\end{split}\tag{5} $ The below ground biomass (BGB) or root dry weight (root biomass) was calculated using equation-6:
$\begin{split}{\boldsymbol{ BGB}} =\;&{\boldsymbol{ TBM}} {\bf\times} {\bf{0.20}}\; ({\boldsymbol{Factor}})\\ =\;& 1226.4 \times 0.20 \\=\;& 245.3\; MT\end{split}\tag{6} $ The CC of the BGB or root biomass (BCC) was calculated using Eqn 2:
$\begin{split} {\boldsymbol{BCC}} =\;&{\boldsymbol{ BGB}} {\bf\times} {\boldsymbol{factor}}\; ({\bf{0.38}}) \\=\;& 245.3 \times 0.38 \\=\;& 93.2 \;MT\; ({\bf{18}}{ {\%}})\end{split}\tag{2} $ The total CC (TCC) accumulated by maize crop in the United States of America (USA) during 2018 was calculated using Eqn 3:
$\begin{split}{\boldsymbol{ TCC}} =\;&{\boldsymbol{ ACC}} + {\boldsymbol{BCC}}\\ =\;&{\bf{ 412.1}}\; ({\bf{82}}{ {\%}}) + {\bf{93.2}}\; ({\bf{18}}{ {\%}})\\ =\;&{\bf{ 505.3}}\;{\boldsymbol{ MT}}\; ({\bf{100}}{ {\%}})\end{split}\tag{3} $ Example 4 (barley)
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In 2018, barley produced in MT and the TCC fixed in the barley growing area in the world leading countries was estimated (Table 4). For example, in 2018 the total barley produced in the Russian Federation was 17.0 MT[2, 44].
Table 4. Approximate estimation of carbon content (CC) fixed by barley crop in metric tons (MT) for the leading countries in the world during 2018−2019.
Countries Metric tons (MT) GY AGB ACC BGB BCC TBM TCC Russian Federation 17.0 56.6 23.8 14.2 5.4 70.8 29.2 France 11.2 37.3 15.7 9.3 3.5 46.6 19.2 Germany 9.6 31.9 13.4 8.0 3.0 39.9 16.5 Australia 9.3 30.8 13.0 7.7 2.9 38.6 15.9 Spain 9.1 30.4 12.8 7.6 2.9 38.0 15.7 Canada 8.4 27.9 11.7 7.0 2.7 34.9 14.4 Ukraine 7.3 24.5 10.3 6.1 2.3 30.6 12.6 Turkey 7.0 23.3 9.8 5.8 2.2 29.2 12.0 United Kingdom 6.5 21.7 9.1 5.4 2.1 27.1 11.2 Argentina 5.1 16.9 7.1 4.2 1.6 21.1 8.7 Kazakhstan 4.0 13.2 5.6 3.3 1.3 16.5 6.8 Denmark 3.5 11.6 4.9 2.9 1.1 14.5 6.0 United States of America 3.3 11.1 4.7 2.8 1.1 13.9 5.7 Poland 3.0 10.2 4.3 2.5 1.0 12.7 5.2 Morocco 2.9 9.5 4.0 2.4 0.9 11.9 4.9 Iran 2.8 9.3 3.9 2.3 0.9 11.7 4.8 Ethiopia 2.1 7.0 2.9 1.8 0.7 8.8 3.6 Algeria 2.0 6.5 2.7 1.6 0.6 8.2 3.4 Romania 1.9 6.2 2.6 1.6 0.6 7.8 3.2 India 1.8 5.9 2.5 1.5 0.6 7.4 3.1 World − − − − − − − Source: FAO outlook[11] (Accessed on 5-5-2020). Where: CC = Carbon content, MT = Metric tons, GY = Grain yield, AGB = Above ground biomass, ACC = Above ground CC, BGB = Below ground biomass, BCC = Below ground CC, TBM = Total biomass (AGB + BGB), TCC = Total CC (ACC + BCC). The above ground biomass (AGB) or shoot biomass was calculated using Eqn 4:
$\begin{split} {\boldsymbol{AGB}} =\;&{\boldsymbol{ Grain}} \;{\boldsymbol{Production}} {\bf\div} {\bf{0.30}}\; ({\boldsymbol{Factor}}) \\=\;& 17.0 \div 0.30 \\=\;& 56.6\; (MT)\end{split} \tag{4}$ The carbon content of the AGB or shoot CC (ACC) was calculated using the following Eqn 1:
$\begin{split}{\boldsymbol{ ACC}} =\;&{\boldsymbol{ AGB}} {\bf\times} {\boldsymbol{factor}}\; ({\bf{0.42}})\\ =\;& 56.6 \times 0.42 \\=\;& 23.8\; MT\; ({\bf{82}}{ {\%}})\end{split}\tag{1} $ The total biomass (TBM) (shoots + roots dry weights) was calculated using Eqn 5:
$\begin{split} {\boldsymbol{TBM}} =\;&{\boldsymbol{ AGB}} {\bf\times} {\bf{1.25}}\\ =\;&{\bf{ 56.6}} {\bf\times} {\bf{1.25}}\\ =\;&{\bf{ 70.8}}\;{\boldsymbol{ MT}}\end{split}\tag{5} $ The below ground biomass (BGB) or root dry weight (root biomass) was calculated using Eqn 6:
$\begin{split}{\boldsymbol{ BGB}} =\;&{\boldsymbol{ TBM}} {\bf\times} {\bf{0.20}}\; ({\boldsymbol{Factor}})\\ =\;& 70.8 \times 0.20 \\=\;& 14.2\; MT\end{split}\tag{6} $ The CC of the BGB or root biomass (BCC) was calculated using Eqn 2:
$ \begin{split}{\boldsymbol{BCC}} =\;&{\boldsymbol{ BGB}} {\bf\times} {\boldsymbol{factor}}\; ({\bf{0.38}})\\ =\;& 14.2 \times 0.38\\ =\;& 5.4\; MT\; ({\bf{18}}{ {\%}})\end{split}\tag{2} $ The total CC (TCC) fixed by wheat in Pakistan during 2018 was calculated using Eqn 3:
$\begin{split}{\boldsymbol{ TCC}} =\;&{\boldsymbol{ ACC}} +{\boldsymbol{ BCC}}\\ =\;&{\bf{ 23.8}}\; ({\bf{82}}{ {\%}}) + {\bf{5.4}} \;({\bf{18}}{ {\%}})\\ =\;& {\bf{29.2}}\;{\boldsymbol{ MT}}\; ({\bf{100}}{ {\%}})\end{split}\tag{3} $ The TCC (shoots + roots), ACC (shoots) and BCC (roots) for cereal crops can be easily calculated:
Parameter Equal to Parameter Symbol Factor Equation ACC = AGB × 0.42 1 BCC = BGB × 0.38 2 TCC = ACC + BCC 3 AGB = GY ÷ 0.35* 4 TBM = AGB × 1.25 5 BGB = TBM × 0.20 6 TBM = AGB + BGB 7 Where: W, R, M and B stands for wheat, rice, maize and barley, respectively. Factor: * 0.35 for wheat, 0.45 for rice, 0.40 for maize, and 0.30 for barley.
GY = Grain yield; AGB = Above ground biomass; ACC = Above ground CC; BGB = Below ground biomass; BCC = Below ground CC; TBM = Total biomass (AGB + BGB); TCC = Total CC (ACC + BCC). -
This model was used to calculate the TCC (kg·ha−1) accumulated by the four major cereal crops (wheat, rice, maize and barley) and its distribution into ACC (kg·ha−1) and BCC (kg·ha−1) for the 40 leading countries during 2019 (USDA). The grain yield data (t ha−1) was accessed on the USDA website on 8th May 2020 and converted into kg·ha1 (t·ha−1 × 1,000 = kg·ha−1). The results revealed that remarkable variations were observed in TCC, ACC and BCC among the 40 countries for each crop. For example, the TCC for wheat crop ranged from 4,414 for Pakistan to 13,243 kg·ha−1 for New Zealand (Table 5). For the rice crop, the TCC ranged from 4578 (Philippines) to 11,444 kg·ha−1 (Australia) as shown in Table 6. The lowest TCC (5,150 kg·ha−1) in the case of maize crop was calculated for Korea Democratic and the highest (15,450 kg·ha−1) for Chile (Table 7). In the case of barley, the TCC ranged from 3,443 (Algeria) to 13,733 kg·ha−1 (Chile), respectively (Table 8). These results revealed that out of the TCC (100%) accumulated by the crops (wheat, rice, maize and barley), 82% was partitioned into ACC (shoots) and 18% to BCC (roots). The higher TCC partitioning into shoots (ACC) than roots (BCC) in different crop species was the possible cause of higher shoot dry matter (shoot biomass) than total root dry matter (roots biomass) production[45−47]. The differences in the ACC and BCC among the four crop species was attributed to the genetic differences among the crops species[4, 46,47]. Variation in C content among plant organs are also reported in previous research[48,49].
Table 5. Carbon content (kg·ha−1) calculation for wheat crop in 40 leading countries in the world during 2019−2020.
Countries Kilograms per hectare (kg·ha−1) GY ACC BCC TCC New Zealand 9000 10800 2443 13243 Namibia 6000 7200 1629 8829 Saudi Arabia 6000 7200 1629 8829 Switzerland 6000 7200 1629 8829 Chile 6000 7200 1629 8829 China 6000 7200 1629 8829 EU-27 6000 7200 1629 8829 Egypt 6000 7200 1629 8829 Zambia 6000 7200 1629 8829 Uzbekistan 5000 6000 1357 7357 Japan 5000 6000 1357 7357 Mexico 5000 6000 1357 7357 Norway 5000 6000 1357 7357 Macedonia 4000 4800 1086 5886 Mali 4000 4800 1086 5886 Serbia 4000 4800 1086 5886 Ukraine 4000 4800 1086 5886 Korea, Republic 4000 4800 1086 5886 Belarus 4000 4800 1086 5886 Albania 4000 4800 1086 5886 Bosnia-Herzegovina 4000 4800 1086 5886 Bangladesh 4000 4800 1086 5886 Zimbabwe 4000 4800 1086 5886 South Africa 3000 3600 814 4414 Azerbaijan 3000 3600 814 4414 Armenia 3000 3600 814 4414 Argentina 3000 3600 814 4414 Canada 3000 3600 814 4414 Brazil 3000 3600 814 4414 Iran 3000 3600 814 4414 India 3000 3600 814 4414 United States of America 3000 3600 814 4414 Uruguay 3000 3600 814 4414 Tajikistan 3000 3600 814 4414 Turkey 3000 3600 814 4414 Russian Federation 3000 3600 814 4414 Pakistan 3000 3600 814 4414 Sudan 3000 3600 814 4414 Syrian Arab Rep. 3000 3600 814 4414 Lebanon 3000 3600 814 4414 Grain yield data of 2019 taken from USDA website accessed on 8 May 2020. *GY (grain yield), CC (carbon content), ACC (above ground CC), BCC (below ground CC) and TCC (total below and above ground CC). Table 6. Carbon content (kg·ha−1) calculation for rice crop in 40 leading countries in the world during 2019.
Countries Kilograms per hectare (kg ha−1) GY ACC BCC TCC Australia 10000 9333 2111 11444 Turkey 9000 8400 1900 10300 Peru 8000 7467 1689 9156 Morocco 8000 7467 1689 9156 Egypt 8000 7467 1689 9156 United States of America 8000 7467 1689 9156 Uruguay 8000 7467 1689 9156 EU-27 7000 6533 1478 8011 Japan 7000 6533 1478 8011 Argentina 7000 6533 1478 8011 Chile 7000 6533 1478 8011 China 7000 6533 1478 8011 Korea 7000 6533 1478 8011 Mexico 6000 5600 1267 6867 Paraguay 6000 5600 1267 6867 Russian Federation 6000 5600 1267 6867 El Salvador 6000 5600 1267 6867 Taiwan 6000 5600 1267 6867 Brazil 6000 5600 1267 6867 Guyana 6000 5600 1267 6867 Viet Nam 6000 5600 1267 6867 Ukraine 5000 4667 1056 5722 Indonesia 5000 4667 1056 5722 Iraq 5000 4667 1056 5722 Iran 5000 4667 1056 5722 Dominican Republic 5000 4667 1056 5722 Bangladesh 5000 4667 1056 5722 Colombia 5000 4667 1056 5722 Suriname 5000 4667 1056 5722 Mauritania 5000 4667 1056 5722 Niger 5000 4667 1056 5722 Kazakhstan 5000 4667 1056 5722 Sri Lanka 4000 3733 844 4578 Nicaragua 4000 3733 844 4578 Nepal 4000 3733 844 4578 Panama 4000 3733 844 4578 Korea, Democratic 4000 3733 844 4578 Malaysia 4000 3733 844 4578 Senegal 4000 3733 844 4578 Philippines 4000 3733 844 4578 Grain yield data of 2019 taken from USDA website accessed on 8 May 2020. * GY (grain yield), CC (carbon content), ACC (above ground CC), BCC (below ground CC) and TCC (total below and above ground CC). Table 7. Carbon content (kg·ha−1) calculation for maize crop in 40 leading countries in the world during 2019.
Countries Kilograms per hectare (kg·ha−1) GY ACC BCC TCC Chile 12000 12600 2850 15450 Turkey 12000 12600 2850 15450 United States 11000 11550 2613 14163 New Zealand 11000 11550 2613 14163 Uzbekistan 10000 10500 2375 12875 Jordan 10000 10500 2375 12875 Switzerland 9000 9450 2138 11588 Canada 9000 9450 2138 11588 Argentina 8000 8400 1900 10300 Bangladesh 8000 8400 1900 10300 Egypt 8000 8400 1900 10300 EU-27 7000 7350 1663 9013 Albania 7000 7350 1663 9013 Australia 7000 7350 1663 9013 Iran 7000 7350 1663 9013 Kyrgyzstan 7000 7350 1663 9013 Uruguay 7000 7350 1663 9013 Ukraine 7000 7350 1663 9013 Serbia 7000 7350 1663 9013 Russian Federation 6000 6300 1425 7725 Saudi Arabia 6000 6300 1425 7725 Paraguay 6000 6300 1425 7725 Taiwan 6000 6300 1425 7725 Tajikistan 6000 6300 1425 7725 Iraq 6000 6300 1425 7725 Kazakhstan 6000 6300 1425 7725 Lao 6000 6300 1425 7725 Malaysia 6000 6300 1425 7725 Azerbaijan 6000 6300 1425 7725 Bosnia-Herzegovina 6000 6300 1425 7725 Brazil 6000 6300 1425 7725 Belarus 6000 6300 1425 7725 China 6000 6300 1425 7725 Korea, Republic 5000 5250 1188 6438 Cambodia 5000 5250 1188 6438 Viet Nam 5000 5250 1188 6438 South Africa 5000 5250 1188 6438 Pakistan 5000 5250 1188 6438 Thailand 4000 4200 950 5150 Korea, Democratic 4000 4200 950 5150 Grain yield data of 2019 taken from USDA website accessed on 8 May 2020. * GY (grain yield), CC (carbon content), ACC (above ground CC), BCC (below ground CC) and TCC (total below and above ground CC). Table 8. Carbon content (kg·ha−1) calculation for barley crop in 40 leading countries in the world during 2019−2020.
Countries Kilograms per hectare (kg·ha−1) GY ACC BCC TCC Chile 8000 11200 2533 13733 New Zealand 7000 9800 2217 12017 Zimbabwe 6000 8400 1900 10300 Switzerland 6000 8400 1900 10300 EU-27 5000 7000 1583 8583 Saudi Arabia 5000 7000 1583 8583 Ukraine 4000 5600 1267 6867 United States 4000 5600 1267 6867 Uruguay 4000 5600 1267 6867 Serbia 4000 5600 1267 6867 Norway 4000 5600 1267 6867 Korea, Republic 4000 5600 1267 6867 Brazil 4000 5600 1267 6867 Belarus 4000 5600 1267 6867 Canada 4000 5600 1267 6867 Argentina 4000 5600 1267 6867 Azerbaijan 3000 4200 950 5150 Bosnia- Herzegovina 3000 4200 950 5150 China 3000 4200 950 5150 Japan 3000 4200 950 5150 Kenya 3000 4200 950 5150 India 3000 4200 950 5150 Mexico 3000 4200 950 5150 South Africa 3000 4200 950 5150 Tunisia 2000 2800 633 3433 Turkey 2000 2800 633 3433 Ethiopia 2000 2800 633 3433 Russian Federation 2000 2800 633 3433 Peru 2000 2800 633 3433 Uzbekistan 2000 2800 633 3433 Tajikistan 2000 2800 633 3433 Iran 2000 2800 633 3433 Georgia 2000 2800 633 3433 Kyrgyzstan 2000 2800 633 3433 Lebanon 2000 2800 633 3433 Moldova 2000 2800 633 3433 Macedonia 2000 2800 633 3433 Colombia 2000 2800 633 3433 Algeria 2000 2800 633 3433 Grain yield data of 2019 taken from USDA website accessed on 8 May 2020. * GY (grain yield), CC (carbon content), ACC (above ground CC), BCC (below ground CC) and TCC (total below and above ground CC). The TCC accumulation in crop plants and its partitioning into above ground parts (ACC) and below ground parts (BCC) depends on these three major factors: (1) plant genotypes (species, varieties, hybrids, growth habit, growth stages); (2) agronomic practices (chemical fertilizers, organic fertilizers, biofertilizers, plant nutrition, irrigation, tillage practices, soil types, SOC, plant density, seed rates, sowing time, etc. ); and (3) environmental condition viz. biotic stresses (plant competition, weeds, diseases, insects, pests, etc.) and abiotic stresses (low and high temperature stress, low and high water stress, light quality and duration, wind, chemicals, gases, soil pollution, water pollution etc.). Total dry matter accumulation and its partitioning into roots and shoots depends on plant nutrition[46, 49], light availability[50], soil types[45], plant competitions[51], organic sources[52], beneficial microbes[52,53], plant species[4, 45,54], plants genotypes[2, 55], plant tissues[48, 56−58], and plant growth stages[46, 59,60], etc.
The differences in the TCC accumulation and its partitioning into ACC and BCC in different crop species under study may be attributed to the differences in genetic makeup and differences in plant heights, leaf area, leaf area index and crop growth rate, water and nutrients use efficiency[45,46, 61]. Bagrintseva & Nosov[62] and Mut et al.[63] reported changes in the total biomass accumulation in different crops. Therefore, crops which could sequester more carbon above (shoots) and below ground (roots) indicating more carbon dioxide sequestration from the atmosphere and therefore the cultivation of these crops could help reduce global warming. Therefore, plant breeder's efforts to produce crop species and ideotypes with higher TCC accumulation could be useful. As the cereals and grasses are executive crops[64], so the use of sustainable soil management practices[8, 11, 65], could also increase the TCC accumulation and reduce CO2 in the atmosphere.
In our previous experiments[45, 66], the NPK source which was associated with higher total biomass (TCC) also increases both root biomass (BCC) and shoot biomass (ACC). The increase and decrease in the CC accumulation in both roots (BCC) and shoots (ACC) in this study showed positive relationship with increase in biomass production and partitioning[1] and better growth[45,46]. Bagrintseva & Nosov[62] reported more DM partitioning in wheat and barley with combined application of N + P + K than N + P. Amanullah & Stewart[67 ] reported that N toxicity had reduced total biomass formation and partitioning into shoots (ACC) and roots (BCC).
In other studies[59] where both organic and inorganic soils were compared. The results revealed that the higher BCC under three organic soils (S3, S4 and S5) at different growth stages was attributed to the longer root lengths and formation of a greater number of roots per plant[59], that increased water use efficiency that allocated more total biomass (TCC) into below ground biomass (BCC)[45,46]. In contrast, the lesser BCC obtained under inorganic soils (S1 and S2) was attributed the shorter root lengths and less number of roots per plant produced[59], and low WUE with lesser allocation of dry matter into roots[45]. Likewise, the higher ACC under three organic soils (S3, S4 and S5) at different growth stages was attributed to formation of taller plants with more number of leaves and larger leaf area, and formation of a greater number of tillers per plant[59] and high WUE with greater allocation of dry matter into shoots[45]. In contrast, the lesser ACC obtained under inorganic soils (S1 and S2) was attributed to development of shorter plants with less number of leaves and less leaf area and formation of a less number of tillers per plant[59] and low WUE with and so lesser allocation of DM into shoots[45].
Integrated nutrients management in field crop production, especially plant residue incorporation improve soil fertility that improves crop growth and total biomass[2−4, 68] and reduces the problem of food security. Amanullah,[69] in a FAO global conference (Rome, Italy) reported that integrated use of organic carbon source (animal manures and plant residues), plant nutrients (macro and micro nutrients) and bio-fertilizers (beneficial microbes) is key to improve soil organic carbon and field crops productivity. The best management practices that increase SOC could reduce soil pollution and improve the health of all on the earth[70]. According to Lal,[71] field crop production in Africa, Asia and South America could be increased by millions every year, by increasing soil organic matter by one ton per hectare.
The variations in the TCC estimated for different countries and it's partitioning into roots (BCC) and shoots (ACC) may be attributed to the differences in the genetic make of the crop varieties used in different countries, the variation in the environmental conditions among the countries, and different agronomic practices used in different countries. The review of global data[72] showed that TCC transfer was highest in maize, which yielded the greatest soil C sequestration potential (1.0 Mg C ha−1 yr−1 or 19% total assimilation), followed by sorghum (1.0 Mg C ha−1, 17%) and wheat (0.8 Mg C ha−1 yr−1, 23%). Variation in TCC among cereals such as maize, sorghum, wheat and rice has been earlier reported by McKendry[73]. According to Zengeni et al.[72] higher TCC transfer to soils occurred under clayey soils and warmer climates provided that exudation is high enough to offset respiration C losses. According to Ma et al.[21], plant organ C content is 45.0% in reproductive organs, 47.9% in stems, 46.9% in leaves and 45.6% in roots.
For increasing TCC accumulation in plants and it's partitioning into ACC and BCC it is important to (1) select high yielding plants genotypes, (2) use best agronomic (management) practices and (3) planting of crops in suitable environmental conditions. The best agronomic practices that improve crop growth and development, increase grain and total biomass thus increase TCC in different crop species (Tables 5−8). Any biotic or abiotic stress that could reduce the productivity (yield or biomass) of field crops could reduce the TCC and its partitioning into ACC and BCC under different environments. The agronomists study various crop production problems and work for better soil and crop management practices to obtain higher yield[74].
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The increase in carbon sequestration (1 kg of carbon is equal to 3.67 kg of CO2) through the process of photosynthesis in field crops is essential to combat the issue of food security and global warming. However, the lack of simplified and easy way of carbon estimation restricts researchers to estimate data on total carbon content (TCC) sequestered or captures by the field crops and it's partitioning into roots and shoots. In this study, highly simplified calculations have been developed to provide easy estimation of carbon content in below-ground parts (BCC) and above-ground parts (ACC) of various field crops, including wheat, rice, maize, barley, and more. Best agronomic practices that improve or increase the rate of photosynthesis under field conditions significantly increase the capture or sequestration carbon. Crops with higher TCC took more CO2 (higher photosynthetic efficiency) from the atmosphere therefore increase the yield per unit area and decrease the negative impacts of global warming and food security. The simplified approach for carbon content (CC) estimation utilized in this study can be highly beneficial for researchers and students. It allows for easy estimation of the carbon content fixed in the roots and shoots of diverse field crops, including wheat, rice, maize, and barley. The total carbon content (TCC) in plants exhibited a positive correlation with total biomass. Furthermore, both below-ground carbon content (BCC) and above-ground carbon content (ACC) demonstrated a positive association with TCC. It was confirmed from the model, that out of the total 100% TCC accumulation by field crops, 82% is partitioned into ACC (shoots) and 18% into BCC (roots). The practices that increase grain yield, harvest index, and total biomass increased carbon content in roots and shoots of different crop species. The best agronomic practices that increase grain yield in field crops per unit area will also increase the TCC accumulation and it's portioning into ACC and BCC. Selecting carbon superior genotypes of crop species along with best management practices including sustainable soil management practices will significantly reduce CO2 emission and increase soil health, productivity and sustainability with more carbon sequestration into the soils.
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The author declares that there is no conflict of interest.
- Copyright: © 2023 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/.
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Amanullah. 2023. A simple model for estimation of above and below ground carbon in cereal crops. Technology in Agronomy 3:8 doi: 10.48130/TIA-2023-0008 
A simple model for estimation of above and below ground carbon in cereal crops
- Received: 07 April 2023
- Accepted: 29 May 2023
- Published online: 19 July 2023
Abstract: Carbon (C) is an essential part of healthy soil. Healthy soils play an important role in improving the life of all living organisms on earth (plants, humans, animals, birds, insects, microbes etc.). Best agronomic practices for field crop production sequester more carbon (due to higher photosynthesis) below and above the ground that makes the soils healthy and sustainable. Healthy soils increase yield per unit area and so reduce the problem of food insecurity. Higher photosynthetic efficiency (higher CO2 uptake by the plants) reduces the problem of global warming and climate change. According to an estimate, plants capture about 860 gigatons of CO2 each year from the atmosphere, storing it in their shoots, and roots (1 kg of carbon is equal to 3.67 kg of CO2). The aim of this study was to develop a simple calculation (model) for researchers to easily estimate the carbon content (CC) capture by plants in below (roots) and above ground (shoots) parts. Considerable variation in total CC (TCC) accumulation and its partitioning into above ground parts (ACC) and below ground parts (BCC) exists which depends on crop species and genotypes, crop nutrition, crop competitions and intercropping, fertilizers application, irrigation, tillage, biotic and abiotic stresses, soil types and environment etc. The CC estimation is explained in detail with four examples on major cereal crops (wheat, rice, maize and barley) for the world leading countries in 2018−2019. In the first example using wheat, the TCC estimated for wheat crop in Pakistan was 37.4 metric tons (MT) of which 30.5 MT was allocated into ACC (shoots) and 6.9 MT into BCC (roots). The highest value of TCC accumulation for wheat crop was estimated for the European Union which was 216.3 MT (176.4 ACC + 39.9 BCC). In the second example using rice crop, TCC for the world leading countries was estimated and the leading country was China with TCC of 161.7 MT (131.9 ACC + 29.8 BCC). Example three is about the CC estimation for maize crop, and the leading country was USA having the highest TCC value of 505.3 MT (ACC = 412.1 MT, BCC = 93.2 MT). The Russian Federation ranked first for barley crop and the highest TCC value of 29.2 MT was recorded (23.8 MT ACC + 5.4 MT BCC). It was confirmed while using this model that out of the 100% (TCC) fixed, about 82% CC is partitioned into above ground parts (ACC) and the remaining 18% CC is allocated into below ground parts (BCC). Due to this model, we can easily calculate the TCC accumulation and its partitioning into ACC and BCC per unit area (kg·ha−1). For example, the TCC was easily calculated for the 40 world leading countries for wheat, rice, maize and barley during 2019. The results revealed that the TCC ranged from 4,414 to 13,243 kg·ha−1 for wheat, 4,578 to 11,444 kg·ha−1 for rice, 5,150 to 15,450 kg·ha−1 for maize, and 3,443 to 13,733 kg·ha−1 for barley among the top 40 countries. This is the most simplified approach for estimating carbon content in the below-ground (roots) and above-ground (shoots) parts of field crops.
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Key words:
- Carbon content (CC) /
- Roots or below ground CC (BCC) /
- Shoots or above ground CC (ACC) /
- Total CC (TCC) /
- Cereals /
- Wheat /
- Barley /
- Maize /
- Rice