Biomass allocation and carbon storage in the major cereal crops: A meta-analysis

Crop biomass is the reservoir of carbon (C), a valuable input to the soil, thus supporting the soil fauna and enhancing soil health. There are limited studies that compared the major cereal crops for C storage for regenerative agriculture and to optimize C sequestration strategies. The objective of this study was to quantify the extent of variation in biomass allocation and C storage between maize (Zea mays L.), sorghum (Sorghum bicolor [L.] Moench), and wheat (Triticum aestivum L.) for crop production, and C sequestration potential. The study used metadata from 40 global studies that reported on the allocation of plant biomass and C between roots and shoots of the major cereal crops. Key statistics were computed to determine the variability between genotypes for total plant biomass (Pb), shoot biomass (Sb), root biomass (Rb), root-to-shoot biomass ratio (Rb/Sb), total plant carbon content, shoot carbon content, root carbon content, total plant carbon stock (PCs), shoot carbon stock, root carbon stock, and root-to-shoot carbon stock ratio (RCs/SCs). Maize exhibited the highest variability for Pb (with a coefficient of variation [CV] of 31.2% and a mean of 4.2 +/- 1.3 Mg ha-1 year-1), followed by wheat (CV of 24.2% and a mean of 1.5 +/- 0.4 Mg ha-1 year-1) and sorghum (CV of 16.8% and a mean of 2.0 +/- 0.8 Mg ha-1 year-1), respectively. A similar trend was observed for PCs, with maize (CV of 40.1% and mean of 1.6 +/- 0.7 Mg ha-1 year-1) showing the highest total plant C stock variability, followed by wheat (24.4% and 0.2 +/- 0.1 Mg ha-1 year-1) and sorghum (16.3% and 0.9 +/- 0.3 Mg ha-1 year-1), respectively. Maize (with a CV of 24.4% and mean of 0.1 +/- 0.03 Mg ha-1 year-1) exhibited the highest variability for Rb/Sb, while wheat (30.92% and 0.2 +/- 0.05 Mg ha-1 year-1) exhibited the highest variability for RCs/SCs. Correlation analysis revealed the following significant associations: Pb and mean annual temperature (MAT) (r = -0.47), and Sb and MAT (r = -0.43), and Pb and mean annual precipitation (MAP) (r = -0.34), and Sb and MAP (r = -0.30). Rb had a strong, significant positive correlation with MAT (r = 0.72) and MAP (r = 0.85). The meta-analysis revealed that maize and sorghum have the highest variability for Pb and plant carbon stocks, while wheat exhibited the highest variability for the below-ground biomass and carbon stocks. The data aided in crop selection and suggested that the best cultivars could be developed and identified for production and C sequestration potential for cultivation by farmers, land rehabilitation, and climate change mitigation. There is sufficient genetic variation in maize, sorghum, and wheat cultivars for manipulation of biomass and carbon allocation. Root carbon is a major contributor to soil organic carbon. Above-ground biomass is important for atmospheric carbon sequestration.