Phosphorus Leaching in Sandy Outwash Soils following Potato‐Processing Wastewater Application

Land application of wastewater presents potential for ground water pollution if not properly managed. In situ breakthrough tests were conducted using potato ( Solanum tuberosum L.)–processing wastewater and a Br tracer to characterize P leaching in seasonally frozen sandy outwash soils. In the first test, P and Br breakthrough were measured in a 7‐m deep well following wastewater [2.94 mg L −1 total P (TP); 280 mg L −1 Br] application at the site that had 13.1 mg water‐extractable P (WEP) kg −1 and 94.4 mg Bray‐1 P kg −1 Bromide was detected in the well after ∼0.4 pore volumes, but there was no P break‐through after 7 pore volumes. In the second breakthrough test, wastewater containing 3.6 mg L −1 TP and 259 mg L −1 Br was applied on 1.5‐m deep lysimeters at low (0.8 mg WEP kg −1 ; 12.1 mg Bray‐1 P kg −1 ) and high soil test P sites (104 mg WEP kg −1 ; 585 mg Bray‐1 P kg −1 ). Leachate TP concentration during the test remained constant (0.04 mg L −1 ) at the low P sites but increased from ∼3.5 to 5.6 mg L −1 at the high P sites. These results indicate no P leaching in low P soils, but leaching in high P soils, thus suggesting that most of the P leached at the high P sites was mainly due to desorption and dissolution of weakly adsorbed P from prior P applications. This was consistent with P transport simulations using the convective–dispersive equation. We conclude that P concentration in land‐applied wastewater should be regulated based on soil test‐P level plus wastewater P loading.