Extractability and Plant Availability of Molybdenum from Inorganic and Sewage Sludge Sources

Abstract

AbstractA greenhouse experiment was conducted to evaluate the influence of soil pH on the plant uptake and extractability of Mo applied to a soil as an inorganic salt and as a Mo‐enriched sewage sludge. Molybdenum additions of 30, 60, and 120 mg/kg soil from Na2MoO4·2H2O and 20, 44, and 94 mg/kg soil from an anaerobically digested sewage sludge significantly increased Mo concentrations in corn (Zea mays L.), soybeans [Glycine max (L.) Merr.], and alfalfa (Medicago sativa L.) grown on a sandy loam soil. Increases in soil pH significantly increased Mo accumulation in the three crops from both Mo sources. Molybdenum extracted with Tamm's acid ammonium oxalate was not significantly influenced by soil pH, while Mo extracted from sludge treated soils with the ammonium bicarbonate‐DTPA (AB‐DTPA) extractant was significantly increased with increasing soil pH. Multiple regressions between Mo concentrations in the crops and extractable Mo and soil pH indicated that soil pH was a significant variable in 17 of 24 prediction equations. The AB‐DTPA extractant was more effective in predicting Mo concentrations in plant tissue than Tamm's acid ammonium oxalate with sludge Mo additions and is more effective with sludge source Mo as compared to inorganic source Mo. Whether AB‐DTPA will predict Mo uptake by plants grown on soils receiving Mo additions needs to be tested by field evaluation with a large number of soil types.