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Compost Source and Rate Effects on Soil Macronutrient Availability Under Saint Augustine Grass and Bermuda Grass Turf

Compost application to turf grasses can increase availability of nutrients in soil and improve growth, but can potentially lead to accumulation of macronutrients in soil and contribute to leaching and runoff losses. The objectives of this study were to investigate the influence of compost source and application rate on concentrations of plant-available macronutrients in soil over 29 months after a one-time application to saint augustine grass [Stenotaphrum secundatum (Walt.) Kuntze] and Bermuda grass [Cynodon dactylon (L.) Pers.] turf. Compost application increased soil organic C, P, Ca, and S concentrations by 3 months after addition, but further increases from 3 to 29 months were seldom observed. In contrast, NO3-N and K levels declined while Mg levels increased slightly from 3 to 29 months. Seasonal or cyclical patterns of soil macronutrient levels were apparent, as lower concentrations were observed during dormant stages of Bermuda grass growth in winter. Initial macronutrient concentrations of compost sources strongly influenced macronutrient dynamics in surface soil, while higher application rates resulted in higher levels of P, K, Ca, Mg, but not NO3-N and S. Higher levels of macronutrients in Bermuda grass than saint augustine grass turf suggested plant-mediated uptake and assimilation differed between turf grass species. Utilization of turf grass systems for compost application should take into account plant species composition and the related impacts of plant uptake. Macronutrient concentrations were significantly correlated with both total organic C and dissolved organic C (DOC). Formation of organic matter-cation complexes appeared to influence macronutrient dynamics in soil, and may contribute to leaching and runoff losses.