Impacts of preplant tillage and tracer application method on preferential flow to groundwater

Eight, one-meter cubic soil monoliths were collected from research plots with 15 years of tillage and crop rotation history. Tillage practices, arranged in a randomized complete block with three replications, were chisel plow, moldboard plow, and ridge tillage. The plots were part of a soybean-corn crop rotation with corn planted the previous year. A test stand was developed that allowed water application using a hypodermic needle style applicator, and collection of leachate using a grid of fiberglass wick extractors. Three anion tracers were applied to simulate nitrogen application by surface broadcast, slot with surface compaction, and with water. Water applications of approximately 100 mm and 430 mm were applied immediately after tracer applications.; Average nitrate-nitrogen (NO₃-N) leaching losses, following approximately 20 mm of drainage, were 19, 6, and 15 kg ha−1, for the chisel plow, moldboard plow, and ridge tillage treatments, respectively. NO₃-N concentrations peaked after 30 to 50 mm of rainfall at 130, 103, and 105 mg L−1 for the chisel plow, moldboard plow and ridge tillage treatments, respectively. For all grid locations, CV values for NO₃-N leaching losses were found to be greater than those calculated for drainage volumes.; Leaching loss affected by nitrogen application method showed that within the slot treatment with surface compaction, more than twice as much NO ₃-N would be leached from the chisel plow, and 10 times more from moldboard plow treatments than from the ridge tillage treatment. NO₃-N loss appeared to closely follow drainage water collection for each water application when the nitrogen was applied as a broadcast type of treatment while the slot with surface compaction treatment had a leaching pattern directly below the application zone. Results for the 530 mm of water application suggest that the greatest amount of NO₃-N would be leached from the slot with surface compaction method-moldboard plow tillage combination. The least amount of NO₃-N loss would be expected from the application with the water method and ridge tillage combination.