The effect of stubble on nitrogen tie-up and supply – The Mallee experience

Authors: Vadakattu Gupta¹, John Kirkegaard², Therese McBeath¹, Rick Llewellyn¹, Stasia Kroker¹, Steve Szarvas, Bill Davoren¹, Willie Shoobridge¹, Alan Richardson²

¹CSIRO Agriculture & Food Waite campus, ² CSIRO Agriculture & Food Canberra

Project Title: Productive, Profitable and Sustainable Paddock Rotations

Key Words: stubble, nitrogen tie-up, nitrogen supply, n cycle

Key Messages

• Cereal stubble should be thought of as a source of C for microbes, not as a source of N for crops. In the Mallee under no-till systems, only 1-2% of the N requirement of wheat crops is derived from the previous wheat stubble.
• N tie-up in cropping soils is only a temporary constraint as the immobilised N will be released through microbial turnover, generally later in the crop season in spring.
• N tie-up by cereal residue is not just a problem following incorporation – it also occurs in surface-retained and standing-stubble systems.
• Management of tie-up is reasonably straightforward – supply more N (5 kg N for each t/ha of cereal residue) and supply it early to avoid impacts of N tie-up on crop yield and protein.
• Deep-banding N can improve the N uptake, yield and protein of crops, especially in stubble-retained systems.