Assessment of the arable soil structure status on the Northern Slope of Tianshan Mountain

Abstract

The Northern Slope of the Tianshan Mountains is an important grain-producing region in arid northwestern China, where soil quality is increasingly threatened by intensive agricultural use. However, a spatially explicit understanding of soil structural degradation and its driving mechanisms is still constrained. Here, we quantify the soil structural status and identify the key influencing factors in this region. A total of 80 sampling sites were selected across the study area, and soil samples were collected from two depths: topsoil (0–20 cm) and subsoil (20–40 cm) at each site. Key soil physical, hydraulic, and chemical properties were measured and the Compaction Verification Tool (CVT) was used to evaluate soil structural status utilizing saturated soil hydraulic conductivity (Ksat) and air capacity (AC). Random Forest regression and grouped correlation analyses were employed to disentangle the drivers of soil structure variation. Soil organic matter, available phosphorus, total nitrogen, and Ksat were significantly higher in the topsoil, whereas soil bulk density and hydraulic characteristics showed no significant stratification along the vertical soil profile. The CVT classification identified substantial soil structural degradation, with 14% of topsoil and 16% of subsoil sites classified as severely compacted. Severe structural degradation was associated with lower nitrogen but higher concentrations of available phosphorus and potassium, indicating that soil structural deterioration may alter nutrient distribution and availability. Soil texture and organic matter were identified as the factors controlling soil compaction status in the region.