Corinne Celestina1, Jon Midwood2, Ashley Franks1, James Hunt3
1 Department of Physiology, Anatomy and Microbiology, La Trobe University, Bundoora VIC 3086, firstname.lastname@example.org
2 Southern Farming Systems, Inverleigh VIC 3321
3Department of Animal, Plant and Soil Sciences, La Trobe University, Bundoora VIC 3086
Subsoil manuring – the incorporation of organic amendments into dense clay subsoil by deep ripping – can improve crop yields on hostile subsoils. Adoption of the technique is limited in part due to a lack of understanding regarding what is driving the yield response and which amendment type and incorporation method are most effective for improving plant growth. In order to address these research gaps, two long-term experiments were established at Westmere in the high rainfall zone of south-western Victoria in 2012 and 2014. Both experiments were set up as two-way factorial designs testing type of amendment (nil, poultry litter, synthetic fertiliser) and method of incorporation (no till, deep rip, mouldboard plough). The 2012 experiment also included an additional incorporation treatment of surface application plus deep ripping. The nutrient content of the synthetic fertiliser treatment was balanced so that it matched that of the poultry litter. Fertiliser was applied each year so that nitrogen was non-limiting. Over eight (site)x(year) combinations, crop yields were not improved by application of amendments and there was never a significant positive interaction between amendment and incorporation treatments. Additionally, poultry litter and synthetic fertiliser performed similarly. This indicates that (1) deep placement of amendment had no advantage over surface application of the same amendment; (2) there was no benefit of using an organic amendment over an synthetic source of equivalent nutrition; and (3) subsoil manuring did not increase yields via amelioration of subsoil constraints. Nitrogen was the key driver of crop yield and grain quality after subsoil manuring.