Prof. James Hunt1, Tony Swan2, Paul Breust3, Laura Goward2, Brad Rheinheimer2, Tony Pratt3, Mark Peoples2, Dr John Kirkegaard2
1The University of Melbourne, 2CSIRO Agriculture and Food, 3FarmLink Research,
Biography:
Professor James Hunt holds the William Farrer Lectureship in Agronomy at the University of Melbourne. He is an agronomist and crop physiologist specialising in water limited productivity of dry-land cropping and mixed farming systems. His research focuses on using combinations of management and genetics to increase productivity and profitability of grain-based farming systems. Prior to joining the University of Melbourne, he worked for La Trobe University for six years, CSIRO for seven years and the Birchip Cropping Group for five years.
Abstract:
Sheep commonly graze crop stubble following harvest, yet there are few published studies on the impact of stubble grazing on subsequent crop yield. To address this, we established an 8-year experiment (2010-2017) near Temora NSW to quantify the impact of stubble grazing on crops in a canola-wheat-wheat rotation with two offset phases. Stubble grazing (nil or grazed following harvest) and burning (nil or burnt before sowing) were applied in factorial combination. Grazing stubble increased grain yield by 0.1 t/ha when averaged across all phase years, but interacted with phase year and burning and the increase was significant in only 5 of 15 individual phase years. In 3 of the 5 phase years the yield increase was associated with higher soil mineral N measured before sowing (mean = 21 kg/ha). In one phase years the yield increase was associated with a reduction in frost-induced sterility (mean = 19%) due to both grazing and burning. We conclude that yield increases following stubble grazing are due to the combined effects of increased soil mineral N supply and reduced frost damage. We hypothesize that grazing stubble increased soil mineral N by cycling N contained in stubble through excreta and reducing carbon input to soil at the start of the summer fallow which reduced N immobilization. It is possible that this agronomic benefit is associated with reduced soil organic matter and increased CO2 emissions from soil.