Impact of tillage and tracer application method on spatial distribution of leaching losses

The impact of tillage and nitrogen (N) application method on the spatial variation on leaching losses was evaluated using eight, 1-m3 undisturbed soil monoliths. Monoliths were collected in 1992 from research plots with 15 years of continuous tillage and crop rotation history. Tillage practices imposed in the field were moldboard plow, chisel, or ridge tillage. Anion tracers were applied to simulate applying N as a surface broadcast, in a slot with surface compaction, and with water. A rainfall simulator was used to apply 100 mm of water followed 24 h later by an additional application of 430 mm to establish tracer concentrations over a range of drainage. Drainage was collected at the bottom of each monolith using fiberglass wick extractors placed in a 6 × 6 grid of 90 mm × 90 mm cells. Tracer leaching losses and flow-weighted concentrations were calculated from the initial flush of water through 24 h after water application. No significant differences were noted for cumulative drainage distribution curves or for the depth of drainage produced (p 3-N from moldboard plow treatment in comparison with the ridge tillage treatment. Trends in leaching losses for the SLOT (Br) with surface compaction treatment suggested that a tracer leaching pattern existed directly below the application zone. Tracer concentrations peaked above 350 mg L-1 after 100 to 170 mm of drainage for the SLOT (Br) with surface compaction application method and final concentrations remained above 70 mg L-1. Peak concentrations for the surface broadcast (BROAD) and with water application (WATER) methods peaked at less than 110 mg L-1 and were consistent among monoliths. Spatial analysis indicated that leaching losses were randomly distributed. Data supported an assertion that the moldboard plow tillage treatment combined with the slot with surface compaction (SLOT) application of N should be avoided.