Combinations of water treatment residuals and biosolids affect two range grasses

Abstract

The beneficial reuse of water treatment plant residuals (WTR) and biosolids via land co-application is of concern since the WTR is postulated to greatly reduce plant phosphorus (P) availability and, along with biosolids, possibly provide an additional source of trace metals to soil. Potential plant Al toxicity with increasing WTR rates, because of the Al content of WTR [Al2(SO4)3·14H2O], has also been speculated. In a greenhouse study we investigated the efficacy of co-application of WTR and biosolids to the native shortgrass prairie species blue grama (Bouteloua gracilis H.B.K. Lag) and western wheatgrass [Agropyron smithii (Rydb.) A. Love]. Co-application rates were a factorial combination of 0, 2.5, 5, 7.5, and 10 g kg− 1 of WTR and 0, 2.5, 5, 7.5, and 10 g kg− 1 of biosolids. Increasing WTR rate, averaged over biosolids rate, resulted in a decrease (p<0.10) in blue grama P concentration and an increase in Al concentration. Increasing biosolids rate, averaged over WTR rates, significantly affected most constituents. With only WTR addition (no biosolids) to blue grama, we observed an increase in plant Al concentration and uptake, and a decrease in plant Mo concentration. Increasing WTR rate, averaged over biosolids rate, produced a significant decrease in western wheatgrass P and molybdenum (Mo) concentrations. Increasing biosolids rate, averaged over WTR rates, again affected most constituents studied. With only WTR addition (no biosolids) to western wheatgrass, this study observed a decrease in plant Mo concentration and uptake. In both studies no significant WTR-biosolids interactions were observed. These results indicate WTR could reduce P availability even when co-applied with biosolids. Co-application can aid municipalities dealing with excessive biosolids-borne P and Mo application associated with an agronomic (nitrogen) biosolids application rate. However, high application rates of WTR should be avoided due to its adverse effect on P availability to plants, unless a supplemental P source is supplied.