Pesticide and Nutrient Movement into Subsurface Tile Drains on a Silt Loam Soil in Indiana

Abstract The objectives of this study were to determine field‐scale pesticide and nutrient losses to subsurface tile drains over a 3‐yr period on a low organic matter and poorly structured silt loam soil under typical agricultural management practices. A subsurface drain spacing study was instrumented to measure drain discharge rates and to collect drainflow samples continuously on a flow‐proportional basis. Two replicates of three drain spacings (5, 10, and 20 m) were included in the study. Water samples were analyzed for all applied pesticides (atrazine, cyanazine, alachlor, carbofuran, terbufos, and chlorpyrifos) 1 as well as major nutrients (N, P, K) and sediment. Small amounts of carbofuran, atrazine, cyanazine, and alachlor were detected in subsurface drainflow within 3 wk of pesticide application and after less than 2 cm net subsurface drainflow from the soil. This early arrival of pesticides at the drain is consistent with preferential flow concepts. Annual carbofuran losses in subsurface drainflow ranged from 0.8 to 14.1 g ha −1 , or 0.05 to 0.94% of the amount applied to the soil. Losses of all other pesticides were ≤0.06% of the amount applied. The rank‐order of pesticide mass losses corresponded with the rank‐order of sorption coefficients of the pesticides. Total mass of pesticides, nutrients, sediment, and water removed by subsurface drains on a per‐area basis was greatest for the 5 m spacing and least for the 20‐m spacing. Annual nitrate‐N losses to subsurface drainflow ranged from 18 to 70 kg ha −1 and averaged 41.7 kg ha −1 . Annual average ammonium‐N, soluble P, and K losses were 0.5, 0.04, and 2.6 kg ha −1 , respectively.