The Characteristics of Stoichiometric Ratios of Carbon, Nitrogen and Phosphorus in Farmland Soils Under Different Land Use Patterns in Typical Red Soil Regions of Hunan Province

Soil nutrient stoichiometric ratios are key indicators for characterizing nutrient cycling and element balance in farmland ecosystems. Taking typical red soil regions in Hunan Province as the research subject, this study explores the effects of different land use patterns on soil C, N and P stoichiometric characteristics, further reveals the variation rules of soil nutrients in red soil areas, and clarifies the types and degrees of regional soil nutrient limitation.

This study selected plow layer soils from 15 pairs of adjacent paddy, paddy-upland rotation, and upland across five counties from north to south in Hunan Province, China, to explore the stoichiometric ratios of C, N, and P.

Compared with upland soils, paddy and paddy-upland rotation had higher soil organic carbon (SOC) and total nitrogen (TN) content, and enzyme activity C:N ratio (E_C:N), as well as lower C:N and microbial biomass C:N ratio (MBC:MBN), indicating relatively higher N supply capacity and organic C mineralization potential. Meanwhile, paddy exhibited lower total phosphorus (TP) and available phosphorus (AP) content, enzyme activity C:P ratio (E_C:P) and enzyme activity N:P ratio (E_N:P), but higher C:P, N:P, AN:AP, microbial biomass C:P ratio (MBC:MBP) and microbial biomass N:P ratio (MBN:MBP), suggesting relatively insufficient P supply. However, paddy-upland rotation did not significantly alter soil TP content or E_C:P and E_N:P ratio. Nevertheless, the relatively low content of AP suggests that paddy-upland rotation could, to a certain extent, promote the accumulation of total soil phosphorus, while the availability of such phosphorus remained low. The analysis of correlation and redundancy showed that soil organic carbon, total nitrogen, and total phosphorus were key influencing factors for the stoichiometric ratios of C, N, and P in cultivated soil, microbial biomass, and extracellular enzymes in red soil regions.

In summary, in typical red soil regions of Hunan Province, paddy and paddy-upland rotation had relatively sufficient N supply, with high potential for organic carbon mineralization (which is easily mineralized). The flooded environment might be the main reason for maintaining their relatively high organic carbon content. The total phosphorus content in paddy-upland rotation fields was relatively high, yet its availability needed to be improved.