Soil C:N:P ratio in subtropical paddy fields: variation and correlation with environmental controls

Purpose Paddy soils may play an essential role in global greenhouse gas mitigation and food security; however, ecological indices of soil organic carbon (C), total nitrogen (N), and total phosphorus (P), and their environmental controls in paddy soils at regional scale, are not fully understood. The aim is to quantify the stoichiometry ratio of C, N, and P, and its correlation with environmental factors in subtropical paddy soils. Materials and methods A first-hand regional-scale field survey of subtropical paddy soil profiles was conducted in the Hunan Province of central China. The survey included 110 paddy sites and 587 soil horizons. Pearson correlation analysis was employed to investigate the correlation of soil C:N:P ratio with altitude, parent material, soil horizon, soil group, and soil physiochemical properties. Results and discussion The depth-weighted average value of C:N, C:P, N:P, and C:N:P ratios in subtropical paddy soil profiles was 12.6, 49, 3.9, and 38:3:1, respectively. Soil organic C content was positively related with total N content, and the average C:N ratio did not vary distinctly with parent materials or soil groups. In contrast, there was no relationship neither between soil organic C and total P nor between total N and total P, and the mean values of both C:P and N:P ratios varied significantly with parent materials, soil groups, and soil horizons. Correlation analysis showed that C:N ratio was only correlated with altitude and soil bulk density, whereas C:P and N:P ratios were correlated not only with altitude and soil bulk density but also with soil texture (sand, clay, silt), and total iron and its dithionite-citrate-bicarbonate (DCB)–extractable fraction. Conclusions Our study suggests a strong coupling effect between element C and N, but noncoupling effect between C and P and between N and P in subtropical paddy soils. The ratios of C:P and N:P are inconstant and more sensitive to environmental factors than C:N ratio.