Irrigation and Polymer Effects on Herbicide Transport through the Unsaturated Zone of a Sparta Sand

Abstract

AbstractState‐sponsored monitoring programs show that the Sparta sand (sandy, mixed, mesic Entic Hapludoll) of the Lower Wisconsin River Valley (LWRV) is susceptible to herbicide movement through the vadose zone, especially atrazine [2‐chloro‐(4‐ethylamino)‐6‐(isopropylamino)‐s‐triazine]. Experiments were initiated to examine the effect of irrigation scheduling and pesticide formulation on transport through the vadose zone. Intact Sparta sand (SP) columns were extracted from the LWRV and instrumented to simulate temperature, irrigation and drainage conditions encountered in the field. Labeled 14C‐atrazine, alachlor [2‐chloro‐N‐(2,6‐diethylphenyl)‐N‐(methoxymethyl) acetamide], and metolachlor [2‐chloro‐N‐(2‐ethyl‐6‐methylphenyl)‐N‐(2‐methoxy‐1‐methylethyl) acetamide] were monitored in the leachate. Treatments included irrigation schedules to match no‐irrigation or rainfed (RF), evapotranspiration (ET) and ET plus an additional 25% (ET +). Formulation treatments consisted of standard pesticide tank‐mix mixtures with and without the addition of a polymer (2% by volume). Increased water input significantly increased metolachlor transport through the SP profile. Due to variability in the leachate data, no significant differences in the total amount of atrazine leached through the columns were shown to exist between the ET and ET + treatments; however, after initial irrigation, atrazine concentration in leachate from ET + treatment was 10 to 15 times greater than leachate of the ET treatment. When compared to the standard herbicide formulation, the use of the polymer significantly reduced and delayed the peak concentrations of metolachlor in the leachate. A significant difference also was observed in the amount of metolachlor retained in the surface soil (0–10 cm) of those columns receiving the polymer treatment compared to those receiving the standard application of the herbicide.