BIOSOLIDS EFFECT ON PHOSPHORUS, COPPER, ZINC, NICKEL, AND MOLYBDENUM CONCENTRATIONS IN DRYLAND WHEAT

When biosolids that are low in trace elements are applied on cropland, the tissue concentrations of trace elements may approach a concentration plateau as cumulative quantity of the element added increases. If the plateau concentration is less than that of safe threshold, the application may continue indefinitely. We found that wheat (Triticum aestivum L. 'Vona' or 'TAM107') grain concentrations of P, Cu, Zn, and Ni from an 11-yr field study of biosolids land application follow a plateau model. The grain concentrations of P, Cu, and Zn approach the calculated plateau maximum after 11 applications (in fallow rotation, we completed six applications to one set of plots plus five applications to a second set). Grain Ni levels show a linear response to cumulative inputs of biosolids Ni. possibly, the biosolids are providing a labile source of Ni. The Mo concentrations did not change significantly as cumulative inputs of biosolids Mo increased. Our results indicate that plateau modeling can describe the changes in wheat grain concentrations associated with biosolids application.