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.

Relative contributions of diverse, managed ecosystems to greenhouse gases are not completely documented. This study was conducted to estimate soil surface fluxes of carbon dioxide (CO(2)), methane (CH(4)), and nitrous oxide (N(2)O) as affected by management practices and weather. Gas fluxes were measured by vented, static chambers in Drummer and Raub soil series during two growing seasons. Treatments evaluated were corn cropped continuously (CC) or in rotation with soybean (CS) and fertilized with in-season urea-ammonium nitrate (UAN) or liquid swine manure applied in the spring (SM) or fall (FM). Soybean (SC) rotated with CS and restored prairie grass (PG) were also included. The CO(2) fluxes correlated (P 8 kg ha(-1) yr(-1) in CCSM; differences were driven by pulse emissions after N fertilization in concurrence with major rainfall events. These results suggest fall manure application, corn-soybean rotation, and restoration of prairies may diminish N(2)O emissions and hence contribute to global warming mitigation.

Leaching of agrichemicals into subsurface tile drainage water is a concern for water quality. The objective of this 3‐yr study was to determine field‐scale pesticide and nitrate (NO3) losses to instrumented subsurface drains as affected by drain spacing (5, 10, and 20 m). Small amounts of carbofuran [2,3‐dihydro‐2,2‐dimethyl‐7‐benzofuranyl‐methylcarbamate]; atrazine [2‐chloro‐4‐(ethylamino)‐6‐(isopropylamino)‐s‐triazine]; cyanazine [2‐chloro‐4‐(1‐cyano‐1‐methyl‐ethyl‐amino)‐6‐ethylamino‐s‐triazine]; and alachlor [2‐chloro‐2′,6′‐diethyl‐N‐(methoxymethyl) acetanilide] were detected in subsurface drainflow in the first large rainstorm after chemical application, which occurred between 3 to 14 d after applications and produced 0.2 to 1.0 cm net drainflow. Annual carbofuran losses in subsurface drainflow ranged from 0.6 to 28.1 g ha−1, or 0.04 to 1.9% of the amount applied to the soil, depending on year and drain spacing. Losses of all other pesticides were ≤0.1% of the amount applied. Total mass of pesticides, NO3‐N, 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 NO3‐N losses to drainflow ranged from 14 to 105 kg ha−1 during the 1988 to 1991 period. The data indicate that preferential flow may be the primary mechanism of pesticide leaching to shallow ground water in silt loam soils, but that total amounts leached are often quite small. Conversely, NO3‐N leaching is most significant during the off‐season, when most of the drainflow occurs.

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