SOIL TEXTURAL CONTROL ON DECOMPOSITION AND SOIL ORGANIC-MATTER DYNAMICS

Soil texture affects litter decomposition by altering soil water avail ability, pore size distribution, nutrient availability, and surface ar ea. We examined the direct and indirect effects of soil texture on lit ter decomposition and soil organic matter mineralization during 91-d l aboratory incubations. Treatments included texture (73, 55, and 40% sa nd), soil water pressure (- 0.012, - 0.033, and - 0.30 MPa), and nutri ent availability (with or without additional N and P). Wheat litter (T riticum aestivum L.) was placed on the surface or incorporated into th e soil. Soil texture had no effect on litter decomposition (P greater than or equal to 0.23). Litter decomposition was fastest for the - 0.0 12 MPa treatment across all soil types (P < 0.01), and the difference between water pressure treatments was greatest in the loam (40% sand) soil. The effects of texture and soil water pressure could be combined into one variable (percentage water-filled pore space), which account ed for more of the variability in litter decomposition and native soil C mineralization than either texture or soil water pressure alone. Su rface-applied litter decomposed significantly faster than incorporated litter, but the effect was not consistent across different soils (P = 0.04). Litter addition stimulated the mineralization of native soil C , the greatest effect occurring when litter was incorporated into the fine-textured soil.