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
- 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.