Abstract
Rice straw increasingly remains on the fields for nutrient supply to the next generation of crop plants. It can be applied either fresh or after burning to black carbon or ash. A central concern during rice cultivation is accumulation of carcinogenic arsenic and the question arises how much rice straw application contributes to nutrient versus arsenic supply in paddy fields. Laboratory incubation experiments were performed to assess the effect of rice straw, black carbon and ash on element mobilization. Our experiments showed initially higher silicon and phosphorus release from black carbon compared to fresh straw amendments. However, more re-sorption to soil lead to finally slightly lower pore water concentrations for black carbon versus fresh straw amendments. Highest arsenic, iron, manganese and dissolved organic carbon concentrations were observed after fresh rice straw application. Black carbon and ash application lead to only minor increases of arsenic compared to controls without amendments. Overall, for silicon and phosphorus the soil acts as sink while for iron and arsenic it was the main source. In summary, burning of rice straw to black carbon prior to application seems to yield a high increase in desired nutrient and a decrease in undesired arsenic mobilization in paddy soils.
Highlights
Rice is the major staple food worldwide
Despite knowledge about the effect of straw application and application of straw burned to a mixture of ash and charred material on element availabilities in paddy soils[9,10], little is known about the different effects of black carbon and ash
Rice straw not ploughed into the soil will be decomposed under aquatic conditions once the field is flooded for the generation of rice plant cultivation
Summary
Rice is the major staple food worldwide. High yield production requires sufficient nutrient supply. The most common way is to just leave the fresh rice straw in the field after harvesting and threshing for natural decomposition of the organic carbon and release of nutrients until the crop cycle starts[2]. Rice straw is more prone to microbial decomposition compared to black carbon or ash, and induces a lower redox potential in the paddy soil pore water which promotes mobilization of Fe and P11. Despite knowledge about the effect of straw application and application of straw burned to a mixture of ash and charred material on element availabilities in paddy soils[9,10], little is known about the different effects of black carbon and ash. We compared nutrient versus arsenic release from different forms of rice straw (fresh straw, black carbon, ash) over time in incubations with and without paddy soil. We discuss in which form (fresh, black carbon, ash) rice straw is used best to maximize nutrient and minimize arsenic release
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