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Alan L. Wright, Tony L. Provin, Frank M. Hons, David A. Zuberer and Richard H. White

Compost application to turfgrasses may contribute to accumulation of macronutrients in soil and eventually pose leaching and runoff hazards. The objectives of this study were to determine the influence of compost on soil-dissolved organic C (DOC) and accumulation of NH4OAc-EDTA-extractable and water-soluble nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S) in St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] turf. Dissolved organic C increased from 3 to 29 months after application for unamended and compost-amended soils, indicating contribution from decomposition of both compost and St. Augustinegrass residues. Dissolved organic C was 75%, 78%, and 101% greater 29 months after application of 0, 80, and 160 mg·ha−1 of compost, respectively, than before application. Dissolved organic C and macronutrients exhibited considerable seasonal variation, because DOC and EDTA-extractable P, Ca, Mg, and S increased after compost application, whereas NO3 declined. Water-soluble K, Ca, and Mg declined, whereas P and S increased from 0 to 29 months. Similar seasonal changes in macronutrient concentrations occurred for unamended and compost-amended soil, indicating that composts, in addition to turfgrass residues, influenced DOC and macronutrient dynamics. Long-term nutrient accumulation occurred in compost-amended turfgrass, but seasonal dynamics were more related to the growth stage of turfgrass than compost. Formation of DOC-cation complexes appeared to contribute to macronutrient mobility, because decreases in DOC and nutrient concentrations occurred during turfgrass dormancy in winter and after high precipitation levels, indicating the potential for leaching of DOC-associated nutrients from soil.

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Alan L. Wright, Tony L. Provin, Frank M. Hons, David A. Zuberer and Richard H. White

Application of organic amendments can increase dissolved organic C (DOC) concentrations, which may influence movement of nutrients and heavy metals in soils. The objectives of this study were to investigate the influence of compost sources and application rates on concentrations of soil DOC, NO3-N, and extractable P over 29 months after a one-time application of compost to bermudagrass [Cynodon dactylon (L.) Pers.] turf. Few differences were evident between compost sources for soil total organic C (TOC), DOC, and NO3-N. However, the initial P content of compost sources significantly influenced soil extractable P. Increasing the rate of compost application increased soil TOC initially, but levels remained fairly stable over time. In contrast, DOC continued to increase from 3 to 29 months after application, suggesting that compost mineralization and growth of bermudagrass contributed to DOC dynamics in soil. Dissolved organic C was 98%, 128%, 145%, 175%, and 179% greater 29 months after application of 0, 40, 80, 120, and 160 Mg compost/ha, respectively, than before application. Rate of compost application had less effect on DOC than TOC, as DOC concentrations appeared controlled in part by bermudagrass growth patterns. Soil NO3-N was generally unaffected by compost application rate, as NO3-N decreased similarly for unamended soil and all compost treatments. Soil extractable P initially increased after compost application, but increasing the application rate generally did not increase P from 3 to 29 months. Seasonal or cyclical patterns of TOC, DOC, and extractable P were observed, as significantly lower levels of these parameters were observed in dormant stages of bermudagrass growth during cooler months.

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Xiaoyan Dai, Donald M. Vietor, Frank M. Hons, Tony L. Provin, Richard H. White, Thomas W. Boutton and Clyde L. Munster

Large, volume-based applications of composted municipal biosolids (CMB) can enhance turfgrass growth and quality and soil physical and chemical properties. In addition, CMB additions could affect short-term dynamics of soil organic carbon (SOC) and enhance C sequestration and environmental quality compared with turfgrass fertilized with inorganic nutrients in mineral soil. The objective was to compare changes in SOC among contrasting sources of Tifway bermudagrass sod (Cynodon dactylon L. Pers. × C. transvaalensis Burtt-Davey) after transplanting. Three sod sources from fields grown with two commercial sources of CMB or inorganic phosphorus fertilizer were transplanted on silica sand in replicated box lysimeters. Storage of SOC within 0 to 5-cm and 5 to 50-cm depths was greater in CMB than fertilizer-grown sod during 10 months of establishment and maintenance. Leaching losses of dissolved organic C (DOC) were two times greater for CMB than for fertilizer-grown sod over seven simulated rain events, but the ratio of DOC in leachate to total SOC mass was 0.3% or less for CMB-grown sod. An increase in δ13C values of SOC over sampling dates indicated the proportion of SOC derived from turfgrass increased, whereas that from CMB decreased. The benefit of greater rates of SOC storage during establishment and maintenance of CMB compared with fertilizer-grown sod was achieved without substantive loss of DOC in leachate.