Effect of sludge treatment, heavy metals, phosphate rate, and ph on soil phosphorus

Abstract

A greenhouse study was conducted to evaluate the effect of sludge treatment, heavy metals, phosphate rate, and pH on soil phosphorus (P) with soybean [Glycine max (L) ‘Lee 741'] as a test crop. Hartsell fine sandy loam soil (previously sludge amended and unamended) was treated with 100 Mg/ha sewage sludge and/or inorganic sulfate salts of cadmiun (Cd), copper (Cu), nickel (Ni), and zinc (Zn) equivalent to the concentration of these metals in the sludge. The soils were adjusted to three different pH levels (5.8, 6.4, and 7.0) and four rates of P were applied. Water‐soluble P, aluminum (AI)‐P, calcium (Ca)‐P, iron (Fe)‐P, and total P were measured for all soil treatments. Decreased Al‐P and Fe‐P were found when inorganic metals of Cd, Cu, Ni, and Zn were added to previously amended and unamended soils. Most of the sludge P shifted into Ca‐P and Fe‐P fractions while that of the inorganic P went into soluble and Al‐P fractions. Higher soluble P was observed at soil pH 7.0, Al‐P and Fe‐P at pH 5.8, and Ca‐P at pH 6.4 and 7.0. Lower Al‐P and Fe‐P were observed at pH 7.0. Aluminum‐P was better correlated with P uptake by plants than were soluble P, Ca‐P, and Fe‐P, while Mehlich 1‐extractable P was better correlated with seed P than Bray Pl‐extractable P.