Compost impacts on dissolved organic carbon and available nitrogen and phosphorus in turfgrass soil.

Compost application to turfgrass soils may increase dissolved organic C (DOC) levels which affects nutrient dynamics in soil. The objectives of this study were to investigate the influence of compost source and application rate on soil organic C (SOC), DOC, NO(3), and available P during 29 months after a one-time application to St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] turf. Compost sources had variable composition, yet resulted in few differences in SOC, DOC, and NO(3) after applied to soil. Available NO(3) rapidly decreased after compost application and was unaffected by compost source and application rate. Available P increased after compost application and exhibited cyclical seasonal patterns related to DOC. Compost application decreased soil pH relative to unamended soil, but pH increased during the course of the study due to irrigation with sodic water. Increasing the compost application rate increased SOC by 3 months, and levels remained fairly stable to 29 months. In contrast, DOC continued to increase from 3 to 29 months after application, suggesting that compost mineralization and growth of St. Augustinegrass contributed to seasonal dynamics. Dissolved organic C was 75%, 78%, and 101% greater 29 months after application of 0, 80, and 160 Mg compostha(-1), respectively, than before application. Impacts of composts on soil properties indicated that most significant effects occurred within a few months of application. Seasonal variability of SOC, DOC, and available P was likely related to St. Augustinegrass growth stages as well as precipitation, as declines occurred after precipitation events.