Biogeochemical impacts of silicon-rich rice residue incorporation into flooded soils: Implications for rice nutrition and cycling of arsenic
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Soil incorporation of Si-rich rice residues may aid smallholder rice farmers in improving crop yields and may affect As uptake. Here, the biogeochemical impacts of rice residue incorporation into flooded soil without plants were evaluated.
Various particle sizes of fresh rice straw (FS), fresh rice husk (FH), rice straw ash (RSA) and rice husk ash (RHA) residues were incorporated into soil (1 % w/w) in a flooded pot experiment. Pore-water chemistry was monitored weekly and dissolved CH4 concentrations and genes specific for methanotrophy and methanogenesis in DNA extracts of soil were evaluated.
FH-amended soil had the highest level of dissolved Si, followed by FS and then ash (RHA or RSA). Particle size had little effect on the dissolved Si concentration for any residue tested. No amendments had any substantial effect on pore-water pH. FS-amended soil had much higher As, Fe, and CH4 concentrations in pore-water compared to ash and FH, and its extracted DNA also had higher amplifications of genes indicative of methanogenesis.
FH, RHA, or RSA are attractive amendments for smallholder rice farmers to increase plant-available Si without exacerbating CH4 emissions, which may improve rice nutrition through the beneficial impacts of Si on combating biotic and abiotic stress including decreased arsenic uptake.
KeywordsSustainable farming Methane emissions Methanogenesis Biocycling Abiotic and biotic stress
Rice husk ash
Rice straw ash
We thank Laura Lapham for assistance with gas chromatography, Sarah McCurdy and Michael Schaefer for assistance with rice residue collection, the Soil Testing Laboratory at the University of Delaware for assistance with soil and rice residue characterization, Guangchao Li and Douglas Turner for assistance with X-ray fluorescence analysis, and Taylor Dieffenbach for assistance with soil DNA extraction. This project was funded by the 2014 University of Delaware Research Foundation grant No. 14A00765 and National Science Foundation grant No. 1338389 and No. 1330580 awarded to ALS. Funding for ESP was provided in part by a USDA-ISE grant number 2011-51160-30530.
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