Plant and soil responses to biosolids-phosphorus in two Florida soils with high phosphorus content
2004
Sarkar, D. | O'Connor, G.A.
Greenhouse studies were conducted to evaluate the effects of biosolids amendments on phosphorus (P) availability in two Florida pasture soils with medium to very high native P content. Three granular, anaerobically digested, heat-treated, exceptional quality biosolids (from Baltimore, MD, Tampa, FL, and Largo, FL), and a commercial fertilizer, concentrated super phosphate (CSP) were applied to A horizons of the two soils: the Millhopper sand [very high native P and oxalate extractable iron + aluminum (Fe + Al)] and the Candler sand (medium to high native P and oxalate extractable Fe + Al). After a four-month cropping season, bahiagrass (Paspalum notatum Flugge) yields did not vary with P-sources and application rates primarily because of the natively high soil-P. The effect of added P on P uptake by bahiagrass was minimal in the Millhopper soil, but significant in the Candler soil. The excessive native P and high P retention capacity of Millhopper soil masked the effect of P addition by the amendments. In the Candler soil, P uptake was much larger in treatments involving CSP and Largo biosolids, which have greater KCl-extractable (hence, readily available) P contents than Tampa and Baltimore materials. Biosolids-P availability varied in the order: Largo >> Tampa > Baltimore. The Mehlich I-P was better correlated with P uptake by bahiagrass in Candler soil than the Millhopper soil. Two factors appeared to control the availability of P in treated soils: the chemical forms of P in P-sources, and the chemical properties of soils. Native P contents and P fixing capacities of soils need to be considered while interpreting soil test results. This study demonstrated the presence of a soil P threshold beyond which there is virtually no effect of P addition on plant P uptake.
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