The intensive vegetable cropping regime in Werribee South, which can see up to four cropping cycles annually, has extensively modified the soils by regular cultivation, application of fertiliser and irrigation. The topsoil has been thoroughly mixed and the differentiation into topsoil and subsoil is more determined by the depth of cultivation. Immediately below the cultivation depth is generally a hardpan.
Poor plant health caused by salinity issues (particularly after low rainfall) and issues with soil structure (e.g. crusting) and drainage caused by sodicity have been problematic for over 15 years in the region.
Managing saline-sodic soils is a significant issue in Werribee South. The soils receive the majority of the salts from irrigation water, fertilisers and soil additives such as gypsum and lime, with a very minor contribution from sea spray. The soil loading varies significantly between farms and even across fields.
Strongly sodic soils are prone to surface sealing, reduced aeration and reduced permeability, and are difficult to cultivate. All Werribee South soils are sodic, but the degree of sodicity varies from field to field and even possibly within fields. Salinity impacts on crop health are an additional challenge, particularly during dry periods when irrigation water (sourced recycled water from Western Treatment Plant and river water from the Werribee River) has high EC.
Gypsum has been widely used in recent years to address soil structure and the fertiliser calcium thiosulfate is used to improve plant health in saline growing environments. We've teamed-up with Fresh Select and Stuart Grigg Ag-Hort Consulting to explore the impacts of variable application rates of gypsum in combination with calcium thiosulfate (and considering EM field mapping and a host of test results) on crop health over the course of several crop rotations. Opportunities to enhance nutrition with compost is a relatively new concept that will also be explored during the trial.