Utilization of compost increases organic carbon and its humin, humic and fulvic acid fractions in calcareous soil

Organic carbon sustainability in a gravelly calcareous soil is a great chal lenge under the humid conditions of south Florida. The beneficial effects o f compost utilization on soil fertility prompted an investigation on (i) ac cumulation of total organic carbon and (ii) the soil organic carbon (SOC) i n humin, humic acid (HA) and fulvic acid (FA) fractions in a gravelly calca reous soil amended with composts or inorganic fertilizer. In 1996 and 1998, compost from municipal solid waste (MSW) (100% MSW), Bedminster cocompost (75% MSW and 25% biosolids) and biosolids compost (100% biosolids) at 72, 8 2.7 and 15.5 Mg ha(-1), respectively, were each incorporated in soil beds a nd inorganic fertilizer (6-2.6-10) NPK at 2.8 Mg ha(-1). A control (no amen dment) treatment was also included. Total organic carbon and various fracti ons of soil organic carbon were determined in two depths (0-10 and 10-22 cm ) for both soil particles (< 2mm) and pebbles (> 2mm). Inorganic and organi c soil amendments had decreased soil pH and increased soil electrical condu ctivity (EC) 19 months from initial application. Total organic carbon conte nts in soil particle were 4-, 3-, and 2-fold higher in MSW compost, Bedmins ter cocompost and biosolids compost treatments, respectively, than those in fertilizer treated or non-treated soils. MSW compost increased total organ ic carbon in pebbles by 4- and 3-fold in the 0-10 and 10-22 cm deep layers, respectively, more than other treatments. The soil organic carbon accumula tion decreased with depth in all treatments in soil particles, but did not in pebbles. Amending soils with MSW compost significantly increased the org anic carbon in humin, HA and FA fractions more than those treated with inor ganic fertilizer or non-amended. MSW compost has a potential to be used as a soil amendment to increase and sustain the organic carbon in calcareous s oils of south Florida.