Assessment of soil aggregate pore structure after 8 years of cultivation from the parent material of a Mollisol

Abstract

Soil erosion exposes the underlying parent material (PM) to the surface and an appropriate soil restoration approach is required to maintain soil quality. However, the current knowledge on soil restoration (e.g., improvement of soil aggregate structure) is mainly obtained from studies on well-developed soils. It remains unclear how aggregate pore structure of soils can be improved following different agricultural practices during the early stage of pedogenesis. The present study quantified the effects of 8 years of different agricultural practices (land use types, mineral fertilizers, and different amounts of organic inputs) on the aggregate stability, aggregate pore morphology, and surface properties of a topsoil (0–20 cm) and compared the findings with those of a prior PM and a long-cultivated Mollisol (MO). The results showed that clay content and the specific surface area of soil aggregates decreased, while soil organic carbon, aggregate stability, and surface fragment structure increased for all treatments as compared to those for the PM. Mineral fertilization alone did not increase aggregate stability; however, the combination of mineral and organic fertilization increased aggregate stability by 117%. Compared to the PM, the treated soils showed an increase in porosity as determined by synchrotron radiation X-ray micro-computed tomography (SR-µCT). Compared to naturally restored grasslands, the soil under crop rotation with tillage showed a decrease in pore roundness by 15%; however, supplementation with a large amount of organic input during cultivation increased pore roundness. The principal component analysis using all the indicators showed that the soil structure after 8-year cultivation was not comparable to that of the well-developed MO. Our results revealed the development of PM structure under various agricultural practices and highlighted the co-interaction effects of mineral fertilizers and organic inputs on the properties of soil aggregates during the early stage of pedogenesis.