CARBON MINERALIZATION IN SOILS OF DIFFERENT TEXTURES AS AFFECTED WATER-SOLUBLE ORGANIC-CARBON EXTRACTED FROM COMPOSTED DAIRY MANURE

The water-soluble organic C in composted manure contains a portion of labile C which can stimulate soil microbial activity, The objective of this experiment was to evaluate the effects of water-soluble organic C extracted from composted dairy manure on C mineralization in soil wi th different textures. Three soils with textures varying from 3 to 54% clay were amended with 0 to 80 mg water-soluble organic C kg(-1) soil extracted from a composted dairy manure and incubated for 16 weeks at 23 degrees C. The total amount of C mineralized was greater than the amount of C added in the three soils. Differences in mineralizable C w ith and without added water-soluble organic C were approximately 13 - 16 times, 4.8 - 8 times, and 7.5 - 8 times greater than the amount of C added to clay, loam, and sand soils, respectively. The results of th is experiment suggest that immediately following composted manure appl ications, C mineralization rates increase, and that most of the C mine ralized comes mainly from the indigenous soil organic C pool.