Subsoil manuring improves the soil physical properties and crop rooting behaviour in soil profiles in dryland cropping systems over three seasons

The deep-banding of nutrient-rich organic amendments has been shown to improve crop yields and to ameliorate soil physicochemical constraints present in dense clay subsoils. However, the management practice needs further validation on a range of these constrained cropping soils, with different crops grown in different climates. This study involved a series of soil measurements undertaken at a high (Tatyoon) and medium (Kiata) rainfall site in Victoria, Australia from 2018 to 2020, where these respective soils were classified as Sodosol and Vertosol. The impacts of four amendment treatments involving a control, surface manuring, subsoil manuring and deep-banded gypsum applied at a soil depth of 25 −35 cm on the condition of the subsoil were assessed through measurements of saturated hydraulic conductivity (Kc), rainfall accumulation in the soil profile, and crop root growth. Subsoil manuring had increased the Kc at 25 cm depth by 25 −110 % 3 −4 years after placement, at both sites. Water accumulation and extraction from the soil profile (0 −130 cm) were respectively 30 and 50 mm greater in response to the manure amendments at the high-rainfall site in 2019, but produced no significant effect at the medium rainfall site. Increased root lengths were observed in the subsoil layers with all three amendments, but only in barley (Hordeum vulgare) grown at the high-rainfall site in 2019. We attribute the relatively small changes in the condition of the subsoils at these sites to limited rainfall that occurred during the study, which stranded the deep-banded amendments in dry subsoil.