Dr Katherine Dunsford1, Prof. Roger Armstrong1, Dr Garry O'Leary1
1Agriculture Victoria, Horsham, Australia
Biography:
Katherine is a Research Scientist with Agriculture Victoria based at Horsham. She completed her PhD in understanding the causes of poor grain yield responses to N and P fertilisers in 2019. Her areas of research include crop nutrition, particularly N and P, as well as soil water interactions in cropping systems using APSIM and more recently amelioration of subsoil constraints using organic amendments.
Abstract:
Subsoil manuring has been shown to markedly increase grain yields on poorly structured clay soils in the high rainfall zone, but its effectiveness has been more limited at medium rainfall zone (MRZ) sites. A lack of crop response typically corresponded to minimal decomposition of organic ameliorants applied to clay subsoils, which was attributed to prolong periods of dry soil conditions in the amelioration zone. Data from two subsoil manuring experiments, located in the Victorian MRZ over three years (2018 to 2020), was used to parameterise and initiate crop simulations using APSIM. Simulated soil water was converted into a soil water index (SWI) and results were used to examine the proportion of time where adequate water was present within the amended layer. Simulated SWI values from Kiata (negative/no response) confirmed a very limited period of time where the soil water in the amended layer was potentially adequate to enable decomposition of the organic ameliorant. By contrast, results from Horsham (neutral to positive response) confirmed much greater periods of time where adequate soil water was present within the amended layer. These results support the theory that poor crop responses to subsoil organic amelioration on clay soils in the MRZ result from inadequate soil water to facilitate decomposition of organic matter.