The stratification of soil organic carbon and total nitrogen affected by parent material and cropping system

Abstract

The stratification ratio (SR) is a good indicator of the quantitative evaluation of the soil nutrient variation with depth, which is inter-related with nutrient cycles and agricultural productivity. However, the effects of the parent material and cropping system on the SR of soil organic carbon (SOC) and total nitrogen (TN) have received little attention. The current study collected 444, 437, and 363 soil samples at the depths of 0–20, 20–40, and 40–60 cm, respectively, in subtropical southwest China, where the predominant parent materials are alluvial deposits, purple shales, and limestone and the cropping systems are rice–upland crop rotation, upland crop rotation, and rice monoculture. A two-way analysis of variance (two-way ANOVA) and a redundancy analysis (RDA) were applied to investigate the effects of the parent material, cropping system, topography, and climate on SOC and TN contents, and the corresponding SR (SR1, 0–20 cm:20–40 cm; SR2, 0–20 cm:40–60 cm). Results indicated that the parent material and cropping system were the main factors linked to the SR of the SOC and TN, whereas topography and climate seemed to have weaker effects on the SR in the agricultural landscape. Generally, alluvial deposit- and purple shale-derived soils presented higher SR than limestone-derived soils. Rice–upland crop rotation systems increased the SR compared to rice monoculture and upland crop rotation systems. Exceptions were observed in rice–upland crop rotation and rice monoculture systems under limestone. The study highlighted the efficient SR indicator in examining the SOC and TN depth distribution corresponding to the parent material and cropping system and is expected to provide valuable information regarding the optimization of the cropping pattern in different lithological regions, thereby enhancing agricultural productivity.