Use of Drinking Water Treatment Residuals as a Potential Best Management Practice to Reduce Phosphorus Risk Index Scores

The P risk index system has been developed to identify agricultural fields vulnerable to P loss as a step toward protecting surface water. Because of their high Langmuir phosphorus adsorption maxima (P max ), use of drinking water treatment residuals (WTRs) should be considered as a best management practice (BMP) to lower P risk index scores. This work discusses three WTR application methods that can be used to reduce P risk scores: (i) enhanced buffer strip, (ii) incorporation into a high soil test phosphorus (STP) soil, and (iii) co‐blending with manure or biosolids. The relationship between WTR P max and reduction in P extractability and runoff P was investigated. In a simulated rainfall experiment, using a buffer strip enhanced with 20 Mg WTR ha −1 , runoff P was reduced by from 66.8 to 86.2% and reductions were related to the WTR P max When 25 g kg −1 WTR was incorporated into a high STP soil of 315 mg kg −1 determined using Mehlich‐3 extraction, 0.01 M calcium chloride–extractable phosphorus (CaCl 2 –P) reductions ranged from 60.9 to 96.0% and were strongly ( P < 0.01) related to WTR P max At a 100 g kg −1 WTR addition, Mehlich 3–extractable P reductions ranged from 41.1 to 86.7% and were strongly ( P < 0.01) related to WTR P max Co‐blending WTR at 250 g kg −1 to manure or biosolids reduced CaCl 2 –P by >75%. The WTR P max normalized across WTR application rates (P max × WTR application) was significantly related to reductions in CaCl 2 –P or STP. Using WTR as a P risk index modifying factor will promote effective use of WTR as a BMP to reduce P loss from agricultural land.