Dr Corinne Celestina1, Dr James Hunt1, Dr Peter Sale1, Dr Ashley Franks2
1Department of Animal, Plant and Soil Sciences, AgriBio the Centre for AgriBiosciences, La Trobe University, Bundoora, Australia, 2Department of Physiology, Anatomy and Microbiology, La Trobe University, Bundoora, Australia
Organic amendments such as manures, composts and plant residues are often used in crop production systems as alternatives to inorganic fertilisers, to restore degraded soils or to ameliorate soil physicochemical constraints. These organic amendments can indirectly affect crop yields by increasing soil organic matter content and thereby improving soil biological activity, cation exchange capacity, structural integrity and so on. However, organic amendments can also provide large amounts of nutrients to the plant which can directly affect crop yields via fertilisation. Therefore, crop yield responses to the application of organic amendments could be due to an ‘organic matter’ effect, to the plant nutrients contained in the amendment, or some combination of both factors. Because of the way in which many of these experiments are conducted these factors can be confounded, leading to difficulties in accurately ascribing yield responses to nutrient and non-nutrient effects. Using subsoil manuring on poorly-structured clay soils in south-eastern Australia as a case study, we demonstrate how to use properly designed and assessed field experiments to separate the effects of fertilisation from other non-nutrient effects of the organic amendment on crop yield. We discuss: how to identify genuine soil constraints to plant growth; the selection of proper control treatments; the use of appropriate sampling protocols to assess treatment differences; and, additional measurements that can be used to elucidate the drivers of crop yield responses.
Dr Celestina is a Research Officer in the Crop Agronomy Group at La Trobe University, where she works on the GRDC-funded National Phenology Initiative. In 2018 she completed her PhD at La Trobe University on understanding the drivers of the crop yield response to subsoil placement of organic amendments.