Groundwater phosphorus and trace element concentrations from organically amended sandy and calcareous soils of Florida
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The effects of organic amendments on vegetable crop production, phosphorus (P), and trace element (Zn, Cu, Mn, B, Cd, Pb, Ni) concentrations in groundwater were investigated on calcareous and sandy soils in south Florida. Treatments consisted of applying yard trash and food compost, biosolids compost, a cocompost of municipal solid waste and biosolids, and inorganic fertilizer. A randomized complete block design with four replications was used at both study sites. Total Kjeldahl phosphorus (TKP) and soluble reactive phosphorus (SRP) were periodically measured in grab samples collected for two years for both soils from wells above and below the spodic horizon at Ft. Pierce and from one depth at Homestead. Treatments were similar (P > 0.05) except on two sampling dates from the deep wells in the sandy soil at Ft. Pierce, one for SRP and one for TKP. Phosphorus concentrations for all treatments averaged < 1.2 mg SRP L1 at Ft. Pierce and 0.04 mg SRP L1 for the calcareous soil at Homestead. From solely a P consideration, organic P sources could be used to offset all or a portion of P required to satisfy vegetable crop nutrient requirements. This statement is consistent with crop yields at Ft. Pierce where yields from the three organic sources were equal to or exceeded inorganic fertilization yields. Micronutrient and trace element concentration responses to organic treatments were more pronounced at Ft. Pierce, perhaps due to soil chemical conditions including lower soil pH. The cocompost should be used cautiously to avoid contamination problems, especially when application rates are based on N fertilization as in this study. Due to the calcareous soil at Homestead, trace element concentrations in the groundwater were considerably lower than Ft. Pierce concentrations. However, the cocompost source was elevated for lead (Pb) (P < 0.05) compared with all other treatments, although higher concentrations were observed only on one sampling date. Results from this study indicated that, combined with the environmental benefits of recycling waste, the use of these organic amendments is a viable alternative to inorganic P fertilizers in the sandy and calcareous soils of peninsular Florida. The compost treatments were comparable to inorganic fertilizer with regard to P concentrations in the groundwater while producing similar or higher vegetable crop yields. 2006 by The JG Press, Inc. All rights reserved.