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Changes during winter in water-stable aggregation due to crop residue quality

Le Guillou, C., Angers, D.A., Leterme, P., Menasseri-Aubry, S. (2012). Changes during winter in water-stable aggregation due to crop residue quality, 28(4), 590-595.


There is a need to develop practices that contribute to increased water-stable aggregation (WSA) during winter in a humid temperate climate when soil is particularly prone to water erosion. Our objectives were to determine the effects of crop residue quality on WSA during winter and to relate these effects to biochemical indicators of fungal and bacterial biomass. Three graminae crop residues were selected for their different C/N ratios and biochemical characteristics (green oat residues, C/N=18.8; wheat straw, C/N=125.6; and mature miscanthus residues, C/N=311.3). In October 2009, crop residues were added with an equivalent amount of C in the 0-10cm layer to a Luvisol in north-west France. WSA, expressed as mean weight diameter (MWD), amino sugar, soil mineral N and water contents were measured at regular intervals during 5months. Aggregate MWD of the control soil decreased rapidly and remained low until the last sampling date in March which illustrates the structural vulnerability of bare soils in winter in this pedo-climatic area. The incorporation of all three crop residues had significant positive impacts on aggregate MWD. Despite widely different C/N ratios, the maximum MWD under each treatment was similar (three times greater than the control soil). Maximum MWD occurred at times that clearly depended on residue quality. Maximum values occurred early for green oat (29day), but were delayed to 50day for wheat straw and to 154day for miscanthus. Results from correlation analysis suggest that variations in WSA were partly mediated by microbial agents with a dominant effect of bacteria for green oat and a combined role of fungal and bacterial biomass for wheat straw. We suggest that the maximum MWD associated with the miscanthus late in the experiment is related to changes in the composition of the fungal community. Overall, our study shows that autumn application of crop residues increases WSA during winter with its effect being microbially mediated and determined by residue quality. © 2012 British Society of Soil Science.

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