Spatial variation in stoichiometric characteristics of carbon, nitrogen, phosphorous and sulfur in benchmark soils across different cropping systems

Dynamic elements including carbon (C), nitrogen (N), phosphorus (P), and sulfur (S), in soil are distinguished by significant geographical heterogeneity. Despite the decisive role that soil nutrients have in regulating the processes in a terrestrial ecosystem, their spatial distribution and stoichiometric relationships remain poorly understood across different geographical regions. This lack of detailed knowledge limits our ability to accurately assess ecosystem productivity and nutrient dynamics. The present study addresses this critical gap by examining the spatial variability and stoichiometry of soil organic carbon (SOC) and key soil nutrients (N, P, S), including their elemental ratios (C:N, C:P, C:S). This research aims to investigate the spatial distribution and stoichiometric ratios of these essential elements. By understanding these patterns, this study will provide insights for enhancing health of soil, boosting fertility, and guiding better agricultural interventions in the studied regions. In the present study, an overall of 1440 samples of 16 benchmark soils were collected from rice–wheat, cotton–wheat, maize–wheat, and fallow–wheat cropping areas of the Punjab province, Pakistan. The collected samples were fractionated and studied for total SOC, N, S, and P quantification. The degree of spatial dependence and geographical patterns of C, P, N, S contents and their ratios in the studied cropping systems were then assessed. The average amount of SOC, total N, P and S varied from 224.7–355.7, 20.3–29.4, 5.1–6.6 and 4.1–5.5 mmol/kg under the studied cropping systems of Punjab. Semi-variogram modeling depicted the strong spatial dependency for C, S, N, and P, while a moderate fluctuation was seen for C:N, C:P and C:S ratios in the order of fallow–wheat (FW) > rice–wheat (RW) > cotton–wheat (CW) > maize–wheat (MW) cropping systems. High spatial variability was found in FW compared to CW, MW and RW cropping systems. Moreover, a consistent stoichiometric C:N:P:S ratio of 62.2:5.4:1.2:1, was explored across the studied benchmark soil series under various cropping systems of the Punjab. SOC revealed a strong correlation with N, P, S concentration and C:P, C: N, and C:S ratios in soil. A better understanding of the spatial variability for C, N, P, S concentrations and C:N, C:P, C:S ratios is useful for increasing carbon storage by managing C:N:P:S stoichiometry and refining agricultural management practices which ultimately improves soil health.