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Effect of Rice Stubble Burning on Soil Health
by C A Kirkby and Alison Fattore February 2006 RIRDC Publication No W05/195 RIRDC Project No CSL-13A
Each of the soils from the sites retaining stubble had significantly more C, N, P and S than the corresponding property that burnt stubble despite differences in other management strategies. The biological properties of the stubble retained soils suggest that they would be considered healthier than the corresponding stubble burnt soils and two measurements used to indicate soil stress, the microbial quotient and a stress indicator derived from FAME analysis, suggest that the stubble retained soils were less stressed than the stubble burnt soils. The findings also support the view that for rice, or other summer crop stubble, to decompose at the fastest rate in the field it should be incorporated as soon as possible after harvest, before winter, and not during the sowing of the following summer crop, before summer.
The similarity of the C:N:P:S ratios at all the sites, regardless of stubble treatment, suggest that the soil organic matter at all the sites could be similar in composition regardless of the type of organic matter inputs, further work is needed to clarify this. Further, the similarity of the ratios to the published ratios for soil humic material suggest that the majority of the organic matter at these sites is humic type material with little fresh organic matter remaining. Although it is well known that adding nitrogen fertilizer can overcome nitrogen tie-up and enhance stubble decomposition the precise values of these ratios suggest that phosphorus and sulphur tie-up could also be potential problems and that adding phosphorus and sulphur could, under certain circumstances, also enhance stubble decomposition. It is suggested that there needs to be a balance of available nutrients to optimise nutrient availability and potential carbon sequestration in stubble retained systems, especially in the early years after switching from a stubble burning regime.
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