An aerobic incubation procedure was used to evaluate the susceptibility to mineralization of N and S in five Gleysolic soils and their particle-size fractions (2-50 p.m, l-2 pm, 0.2-l pm and <0.2 pm). During an 8-wk incubation, the release of mineral N and S increased with decreasing particle size. The N:S ratio of the mineralization products was generally narrower than that of the starting materials.Total N mineralized from size fractions after 8 wk accounted for 4.5-25.4Vo of fraction N. For S the corresponding range was 23433%o of fraction S. The proportions of N and S released after 8 weeks showed no consistent relationship to particle size, although, in a number of cases, the proportions of N and S released were greater for the finer size fractions. It was concluded that complexing of organic fractions with clays did not, in itself, confer increased resistence to mineralization of N and S.
Levels of C, N, Sl and organic P (P") were detetmined in fine, medium and coarse clayand silt-size sepirrates obtained from five Gleysolic soils by an ultrasonic disperston method. Contents of C, N, S and Po increased with decreasing particle size, with average C values, increasing from3.7o/c in the silt to lO.lVa in fine clay fractions. The corresponding increases for N, S and Pu were 0.26-I.l1c/a,0.037-0.1'787o and 0.043-0. l72Vo, respectively. C/N and C/S ratios decreased with decreasing particle size, indicating :r relative enrichment of N and S in the finer particle-size fractions. N/S showed litth variation with particle size, while C/Pu ratios were erratic. The three clay fractions accounted on average for 31.3a/" of the soit material, and for 39.l%a of soil carbon. In contrast, the ctay fractions togethel accounted on average for 52-59o/a of soil N, S and P". For personal use only.the coarse, medium and fine clay fractions were enriched in C relative to the whole soil.
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