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Title: CARBON AND NITROGEN MINERALIZATION AS AFFECTED BY WETTING AND DRYING CYCLES

Author
item Mikha, Maysoon
item RICE, CHARLES - KANSAS STATE UNIVERSITY
item MILLIKEN, GEORGE - KANSAS STATE UNIVERSITY

Submitted to: Journal of Soil Biology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/14/2004
Publication Date: 2/1/2005
Citation: Mikha, M.M., Rice, C.W., Milliken, G.A. 2005. Carbon and nitrogen mineralization as affected by wetting and drying cycles. Journal of Soil Biology and Biochemistry. v. 37:339-347.

Interpretive Summary: Drying and rewetting of soil effects soil structure and can increase soil erosion and nutrient release. We investigated the source of carbon (C) and nitrogen (N) losses that occur upon rewetting of dry soil, and whether it is from microbial death and/or destruction of soil structure (specifically soil aggregates). A moderately well drained Kennebec silt loam was sampled to a 10 cm depth. Soil under constant water content was compared with soil subjected to a series of four wet-dry cycles during the experimental period (96 days) and incubated at 25 degrees centigrade. Mineralized C and N were measured during the drying and rewetting periods. Aggregate size distributions were studied by separating the soil into four aggregate size classes (> 2000, 250-2000, 53-250, and 20-5 micron) by wet sieving. In general, our results suggested that wet-dry cycles caused a significant C flush, especially within the first 8 hours after rewetting; but, the extent of the C flush was significantly reduced with repeated wet-dry cycles. The flush of C was mainly related to microbial activity and microbial turnover (microbial origin), rather than to destruction of soil aggregates. Overall, repeated wet-dry cycles reduced microbial activity; upon rewetting they regained activity, but were not sufficient to match the constant water content treatment. Further studies using soils of different C and texture are needed to further determine the effect of wet-dry cycles on soil aggregation and nutrient release.

Technical Abstract: Drying and rewetting of soil is an important process in soil aggregation, soil organic matter (SOM) decomposition, and nutrient cycling. We investigated the source of the C and N flush that occurs upon rewetting of dry soil, and whether it is from microbial death and/or aggregate destruction. A moderately well drained Kennebec silt loam (Fine-silty, mixed, superactive, mesic Cumulic Hapludoll) was sampled to a 10 cm depth. Soil under constant water content (CWC) was compared with soil subjected to a series of four wet-dry (WD) cycles during the experimental period (96 d) and incubated at 25 degrees centigrade. Mineralized C and N were measured during the drying and rewetting periods. Aggregate size distributions were studied by separating the soil into four aggregate size classes (> 2000, 250-2000, 53-250, and 20-53 micron) by wet sieving. Repeated WD cycles significantly reduced cumulative N mineralization compared with CWC. The reduction in cumulative mineralized C resulting from WD compared with CWC increased as the WD treatments were subjected to additional cycles. The flush of mineralized C significantly decreased with repeated WD cycles. There was no significant effect on aggregate size distributions or on aggregate-associated C and N resulting from to the WD cycles compared with CWC treatment. Therefore, the flush of mineralized C and N seemed to be mostly microbial in origin in as much as aggregate distribution was unaffected by WD cycles.