Effect of stubble burning and seasonality on microbial processes and nutrient cycling

by Frances Hoyle School of Earth and Environment M087, The University of Western Australia, 35 Stirling Highway, Crawley WA 6009.
Phone: (08) 6488 1884
Email: fhoyle@agric.uwa.edu.au

Management practices involving plant residues, such as reduced cultivation and stubble burning, can have a major impact on biological soil N release to subsequent crops by changing the activity of microorganisms in soil (as this is their food source). The amount, type and management of the plant residues can affect both the timing and the amount of nutrients supplied (N, S, P) to the crop.

The effect of long term stubble management is currently under investigation to identify factors influencing microbial activity, soil organic matter-C turnover and related nutrient cycling.

The experimental site (established 1987, G. Reithmuller, W.A. Department of Agriculture) is located on a red-brown earth (heavy clay loam) at Merredin (eastern wheatbelt of WA) and has been used to determine the effect of stubble management on microbial processes. The site has been continuously cropped, since establishment, in a wheat:legume rotation and stubble has been either retained or burnt.

In our investigation, the main aims of the trial were to assess the effect of long term stubble management and temperature (to reflect seasonal differences) on the activity and associated amount of N supply from microorganisms.

Trial details

In 2003, wheat (Triticum aestivum L.) cultivar `Wyalkatchem' was sown at 110 kg/ha after adjustment for seed size and assuming a field emergence of 70%, to achieve a target density of 200 plants per m 2. The trial was sown on 7 th June in a randomised block design, with various row spacing treatments and replicated six times.

For the purpose of this investigation, three replicate plots were sampled from both the stubble retained or burnt treatments sown on 180 mm row spacings. All treatments were sown with a basal fertiliser of 150 kg/ha Agras (17.5% N) on narrow points with press wheels.

Initial screening of a range of parameters was conducted prior to sowing to characterise the background soil fertility and biological activity of the site. Physical soil and stubble parameters included bulk density, soil moisture and water holding capacity.