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.
Subsurface drainage is a beneficial water management practice in poorly drained soils but may also contribute substantial nitrate N loads to surface waters. This paper summarizes results from a 15-yr drainage study in Indiana that includes three drain spacings (5, 10, and 20 m) managed for 10 yr with chisel tillage in monoculture corn (Zea mays L.) and currently managed under a no-till corn-soybean [Glycine max (L.) Merr.] rotation. In general, drainflow and nitrate N losses per unit area were greater for narrower drain spacings. Drainflow removed between 8 and 26% of annual rainfall, depending on year and drain spacing. Nitrate N concentrations in drainflow did not vary with spacing, but concentrations have significantly decreased from the beginning to the end of the experiment. Flow-weighted mean concentrations decreased from 28 mg L(-1) in the 1986-1988 period to 8 mg L(-1) in the 1997-1999 period. The reduction in concentration was due to both a reduction in fertilizer N rates over the study period and to the addition of a winter cover crop as a "trap crop" after corn in the corn-soybean rotation. Annual nitrate N loads decreased from 38 kg ha(-1) in the 1986-1988 period to 15 kg ha(-1) in the 1997-1999 period. Most of the nitrate N losses occurred during the fallow season, when most of the drainage occurred. Results of this study underscore the necessity of long-term research on different soil types and in different climatic zones, to develop appropriate management strategies for both economic crop production and protection of environmental quality.
Little information is available that evaluates long-term use of a range of tillage systems and different cropping sequences on poorly drained soils. This study relates corn (Zea mays L.) growth and yield to several reduced tillage systems used with continuous cropping and a corn-soybean (Glycine max L.) rotation. Experiments were conducted on Chalmers silty clay loam (fine-silty, mixed, mesic Typic Haplaquoll) with 40 g kg-• organic matter for 12 yr, and Clermont silt loam (fine-silty, mixed, mesic Typic Ochraqualf) with 10 g kg-• organic matter for 7 yr. Both soils are nearly level and poorly drained. Tillage systems compared included moldboard plowing, chisel plowing, ridge planting, and no-till planting. Shallow disking (10 em) was also included at the Clermont site. On the high organic matter Chalmers soil, continuous no-till corn was 25 em shorter at 8 wk, 2% wetter at harvest, and 9.2% lower in yield compared to plowing. Data for chisel and ridge systems were intermediate between plowing and no-till. No-till yields were consistently lower than those for plowing after the first 4 yr. When following soybean, no-till corn was 7 em shorter at 8 wk, 1% wetter at harvest, and 2.6% lower in yield than corn under moldboard plowing. Corn growth and yield from chisel and ridge treatments were equal to those with plowing when in rotation. On the low organic matter soil in continuous notill corn, plant growth and yields were reduced for the first 3 yr, but were equal or better, compared to plowed corn, for the final4 yr. In rotation, no-till corn was equal to plowed corn the first 3 yr and significantly better in 3 of the last 4 yr. Yields with intermediate tillage were similar to plowed yields for continuous and rotational cropping. The relative advantage for no-till planting with time on the low organic matter soil is attributed to improved soil physical properties.
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