ABSTRACT
Strict guidelines were established in the Delaware River Basin in Kansas regarding atrazine usage in an effort to reduce the amount entering rivers and lakes. Incorporation was stressed heavily because atrazine moves primarily in the solution phase in runoff No-till is required under conservation compliance for many acres in com production. The surface-applied herbicides are more susceptible to movement with runoff water. Each best management practice addresses an important concern but may conflict with others. This study evaluated runoff and contaminants in tillage systems that varied in residue management and chemical placement. Three tillage treatments were used on three terraces, which were between 3/4 and 11/2 hectares. The disk tillage treatment was disked in the fall and spring and a field cultivator pass followed chemical application. The Mulch Master treatment was a single tillage operation after chemical application. The no-till treatment had surface-applied chemicals and only planting disturbed surface residue. Atrazine ( 2 kg ha'1) was applied in liquid fertilizer (112 kg N and 50 kg P ha'1). Runoff was measured, sampled, and analyzed for contaminants. The percent of soil surface covered by residue increased over time and was substantially higher for the no-till and Mulch Master treatments, whereas the amount from the disk tillage treatment remained constant. Following planting in 1996, residue cover for each treatment was 79% for no-till, 65% for Mulch Master, and 21% for disk tillage. Less runoff was measured from the no-till treatment because the soil surface was protected by the crop residue and soil structure was improved. Runoff from the Mulch Master treatment was higher than that of the no-till treatment but less than the disk tillage treatment. Plenty of residue remained on the soil surface, but the Mulch Master tillage disrupted the continuous pores that developed. Sediment losses were negligible for the no-till and Mulch Master treatments throughout the 1995 and 1996 growing seasons. However, intense rainfall events produced substantial soil loss in the disk tillage system caused by the combination of low infiltration, high runoff, and an unprotected soil surface. In contrast to the low sediment amounts in runoff water from the no-till treatment, very high atrazine concentrations were measured in the first runoff event. Herbicide concentrations declined with each successive runoff event for all tillage treatments, and by the fourth runoff event, atrazine concentrations were not different among treatments. Incorporation reduced atrazine concentration and loss by two-thirds when it was done after application early in the growing season. When chemical application
occurred late in the growing season, much higher concentrations of atrazine were observed in runoff water for all treatments. Total atrazine loss was greater from the tillage treatments because substantially higher runoff amounts resulted from tillage done during June when intense rainfall events can occur. Best management practices that keep water from leaving the field improve crop production and reduce surface water contamination. When tillage is necessary, preserving as much residue on the surface as possible reduces soil loss and water contamination. New tillage technology that can maintain substantial residue amounts on the soil surface and incorporate herbicides and fertilizers through that residue can reduce the amounts of both sediment and chemical contaminants that leave a field with runoff water.
