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United States Department of Agriculture

Agricultural Research Service

Title: Potential C and N Mineralization and Microbial Biomass from Intact and Increasingly Disturbed Soils of Varying Texture

Author
item Franzluebbers, Alan

Submitted to: Soil Biology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 31, 1998
Publication Date: N/A

Interpretive Summary: Methodology for determining the effect of land management systems on nutrient cycling and storage in soil organic fractions is often sensitive to variations in soil texture and handling of samples. This makes evaluation of biological soil quality uncertain in landscape evaluations of management in the Southern Piedmont USA because of various degrees of soil erosion that have exposed subsoil clay to the surface. In the kaolinitic soils of the Piedmont, I found no interaction of clay content with soil sample pretreatment on microbial biomass or potential activity. Drying and coarsely sieving soil compared favorably to keeping soil moist and intact in the determination of microbial biomass and activity. The practical outcome from this study is that ecological evaluation of soil quality can be greatly simplified compared with conventional protocols. Numerous soil samples from complex landscape evaluations can be collected, stored, sieved, and later analyzed for microbial biomass and activity, rather than immediately analyzed from field-moist and intact soil cores. This approach can increase soil ecological understanding from complex landscapes while at the same time reducing analytical resource inputs.

Technical Abstract: Potential C and N mineralization and soil microbial biomass C were determined following drying and sieving pretreatments in five soils varying in soil texture (3-35% clay) from the southern Piedmont USA. Compared with field-moist-intact soil cores, rewetting following drying of intact soil cores resulted in a flush of C mineralization (CMIN) during 0-3 d of incubation, but was not significantly different during 3-10 and 10-24 d periods. Soil disturbance by sieving resulted in greater CMIN earlier than later in the incubation and led to significant immobilization of N of surface soil where respiration was highest. Increasing soil disturbance through smaller sieve openings resulted in a 10 to 60% greater flush of CMIN that may have been due to disruption of macroaggregates that protected soil organic C. With a pre-incubation period of 10 d following rewetting of dried soil, soil microbial biomass C was unaffected by drying or extent of sieving. Clay content had no significant impact on disturbance effects. Carbon mineralization during 0-3 d was highly related to CMIN during 0-24 d, basal soil respiration, and soil microbial biomass C, although increasing soil disturbance altered these relationships in a predictable manner.

Last Modified: 9/1/2014
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