Bioavailability of biosolids molybdenum to corn

This study was part of a larger effort to generate field data appropriate t o the assessment of biosolids molybdenum (Mo) risk to ruminants. Corn (Zea mays L.) is an important component of cattle diet, and is a logical crop fo r biosolids amendment owing to its high N requirement. Paired soil and corn stover samples archived from two unique field experiments were analyzed to quantify the relationship (uptake coefficient, UC) between stover Mo and s oil Mo load. Both studies used biosolids with total Mo concentrations typic al of modern materials. Data from long-term (continuous corn) plots in Fult on County, IL confirm expected low Mo accumulation by corn stover, even at very high biosolids loads and soil Mo loads estimated to be near 18 kg Mo h a(-1). Uptake slopes were actually negative, but USEPA protocol would assig n UC values of 0.001. Data from plots in Minnesota also suggested essential ly no correlations between stover Mo and soil Mo loads for continuous corn, However, greater Mo accumulation in corn grown following soybean [Glycine mar (L.) Merr.] suggests the possibility of enhanced Mo bioavailability to corn in corn-soybean rotations. Nevertheless, molybdenosis risk to cattle c onsuming corn stover produced on biosolids-amended land is small as stover Mo concentrations were always low and stover Cu to Mo ratios exceeded 2:1, which avoids molybdenosis problems.