Effects of Compost Use on Soil Physical Quality of Vertosols

Compost is widely used to improve soil fertility and structure, yet its effects on soil physical properties in Vertosols remain insufficiently documented. This study evaluated the effects of repeat compost application on soil carbon and nitrogen contents and selected soil physical properties in Vertosols from three farms in Queensland, Australia (Roma, Dalby, and Goovigen). Compost had been applied at rates between 5 and 22 Mg ha−1 yr−1 for periods ranging from 3 to 11 years, depending on the site. Intact and disturbed soil samples from the top 0–8 cm were analyzed for bulk density, water retention, hydraulic properties, aggregate stability, and water repellence. Aggregate stability was assessed using laser diffraction before and after ultrasonic dispersion. Compost application significantly increased total carbon and nitrogen contents at all sites (p ≤ 0.01), although effects on soil physical properties varied by site. In Dalby, compost improved water retention and aggregate stability; in Goovigen, it resulted in lower Disaggregation Ratios. Compost did not induce soil water repellence at any site. The results indicate that compost amendments improve soil carbon and nitrogen concentrations and can modify soil physical properties in Vertosols, although responses depend on site conditions and management history.