Mr Tony Swan1, Mr Mathew Dunn2, Mr John Francis3, Mr John Stevenson4, Dr Xiaoxi Li1, Dr Jeremy Whish5, Prof. James Hunt1,6, Mrs Laura Goward1, Dr John Kirkegaard1
1CSIRO Agriculture & Food, PO Box 1600 Canberra, Acton, Australia, 2NSW Department of Primary Industry, Wagga Wagga Agricultural Institutee, Wagga Wagga 2650, Australia, 3Agista, Wagga Wagga 2650, Australia, 4Warikirri Cropping, Level 17, 140 William Street, Melbourne, Australia, 5CSIRO Agriculture & Food, St Lucia Brisbane, Australia, 6School of Agriculture, Food and Ecosystem Science, The University of Melbourne, Melbourne, Australia
Biography:
Tony Swan is a Senior Experimental Scientist with CSIRO in Canberra who has worked in the agricultural industry for 40 years across many areas including soil acidity, sodicity, salinity, perennial pastures and nitrogen fixation. He has focussed on stubble management in cropping systems using disc and tine openers and impacts of herbicide resistant annual ryegrass. More recently, he has integrated this knowledge into farming systems research, collaborating widely with progressive growers and advisers, scaling up research outcomes to the whole farm level. In 2020 he was awarded the GRDC Research Excellence Award for outstanding contribution to the agricultural grains industry.
Abstract:
Diversifying a crop sequence to include a legume can be profitable and increase the resilience and sustainability of modern farming systems. Benefits can include increased soil nitrogen (N) availability and improved rotational and environmental outcomes. Large-seeded legumes sown into retained cereal residues in modern no-till crop sequences can emerge easily, facilitating stubble retention, reducing N tie-up and improving the conversion of carbon-rich cereal stubbles into stable soil organic matter. Yet despite compelling evidence of economic and environmental benefits of diverse systems, adoption on commercial farms in SE NSW remains low. We explored the reasons for this by scaling up the results from the small-plot experiments to commercial farm scale.
Three fully phased replicated field experiments (2014-2023) confirmed that including a legume into a 3- or 4-year cropping sequence, can be as profitable as the Baseline sequence of canola-wheat-wheat currently favoured by growers. The systems incorporating a legume were less risky (higher profit:cost ratio) and required significantly less inorganic N fertiliser (35 to 66% kg/ha/year) compared to Baseline sequences. The 6-year average (2018-23) increase in soil mineral N prior to sowing non-legumes across the system was 29 kg N/ha/year when a legume crop was included.
At farm scale, when the business is managed at a high level of efficiency, changing management strategies to include legumes was effective and profitable for growers by reducing the (i) amount of synthetic N required, (ii) ryegrass weed seedbank, and (iii) economic fluctuations at the whole-farm level. Our work suggests outcomes of experimental research on the value of diverse crops into cereal-based systems should be combined with a clear understanding of farm- and industry level constraints.