SOIL ORGANIC-MATTER MINERALIZATION AFTER COMPOST AMENDMENT

The addition of composts and manures to soils has often resulted in in creased plant yields that are not obviously related to the nutrients i n the added organic material. A study was conducted to determine if co mpost additions to soil resulted in increased mineralization of soil o rganic matter (SOM). The organic matter of a Sassafras sandy loam soil (fine-loamy, siliceous, mesic Typic Hapludult) was labeled with C-14 by incubating uniformly labeled wheat (Triticum aestivum L.) straw wit h the soil through a minimum of 60 wetting-drying cycles during 2 yr. A municipal solid waste-biosolids compost (MSWC) or a biosolids compos t (BC) was added to the labeled soil or to acid-washed sand and incuba ted for 1440 h. Decomposition of MSWC was low with 95% of the compost- C remaining in sand or soil after 1440 h. Ninety-two percent of BC-C r emained in sand and 86% remained in soil after 1440 h. Total and (CO2) -C-14 data indicated that neither compost stimulated SOM decomposition . Municipal solid waste-biosolids compost reduced slightly SOM decompo sition at 545 and 715 h, The soil, however, stimulated BC decompositio n. Nitrogen mineralization of the BC + soil mixture was greater than s oil alone, and the N apparently came from the compost. The benefits fr om addition of BC to Sassafras soil was not attributed to increased mi neralization of SOM.