Vadakattu Gupta1, Therese McBeath1, Rick Llewellyn1, John Kirkegaard2, Alan Richardson2 and Enli Wang2
Research Team: Bill Davoren1, Stasia Kroker1, Steve Szarvas1, Willie Shoobridge1
1CSIRO Agriculture & Food Waite campus, 2CSIRO Agriculture & Food Canberra
Funding: CSP00186, MSF00003, CSP00138
Peer Review: Dr. Margaret Roper, CSIRO, Floreat Park, WA
Key Words: nitrogen cycling, nitrogen, N, stubble, nitrogen tie-up
- During the 2016 season, stubble retention practices had no significant effect on wheat grain yield and protein.
- 15N stubble labelling studies have shown that at Karoonda approximately 5% of the 2015 wheat crop N was sourced from the 2014 wheat crop stubble.
- The management of cereal stubble influences the microbial activities related to cycling of C and N and its supply to the growing crop. Stubble removal resulted in lower microbial biomass C and N, lower N mineralization and reduced N supply in the surface soil.
- Stubble management practices had no significant effect on soilborne pathogen levels and disease incidence.
Why was the trial done?
In many Australian agricultural soils, carbon availability is the most limiting constraint of microbial functions, hence management of C inputs is the key to improving biological functions including those involved in N mineralization. Crop residues are one of the major sources of C for soil biota. Therefore, stubble retention can provide benefits through changes in soil physical, chemical and biological properties which influence carbon turnover, nutrient generation and subsequent availability of nutrients to crops. Although stubble retention benefits are expected to be realised in all soil types, the magnitude and nature of change in biological functions can vary depending on stubble type and timing of its management and is influenced by soil type and environmental factors (e.g. rainfall). As part of the GRDC project (CSP00186) replicated field experiments were conducted at Karoonda (South Australia), Temora (New South Wales) and Horsham (Victoria), to strengthen our knowledge on seasonal changes in the (1) the biological value of stubble (2) mineralisation: immobilisation balance and (3) the direct supply of N from stubble to crops as influenced by stubble management.
How was the trial done?
At the Karoonda experimental site, following the harvest of 2015 wheat, replicated stubble retention treatment plots were established and represented No-stubble (stubble cut low and removed), Surface (stubble cut low and retained), Standing (stubble cut at standard height of harvest and retained) and Incorporated (cultivation to 10cm depth following harvest). The trial was sown with knife points on the 1st of June 2016 following a late May break of over 25mm rainfall. Wheat cv. Scepter wheat was sown at 70 kg/ha together with 50 Kg/ha DAP and 24 kg/ha Urea placed below the seed (N20, P10).
Surface soil samples were collected at sowing and were analysed for microbial biomass (MB) and activity, mineral N and N supply potential (the amount of N that could potentially be supplied through N mineralization). N mineralization in-crop was also measured using PRSTM probes (www.westernag.ca) which were incubated (ave. 14 days) in the Surface at 10 cm depth inside open PVC cores in field experimental plots. Plant biomass, grain yield and N uptake were also measured.
We thank the Loller family, Karoonda, for allowing to conduct the stubble trials on their farm during 2015 and 2016 seasons; funding for this work was provided through GRDC projects CSP00186, MSF00003 and CSP00138.