IMPACT OF TILLAGE AND TRACER APPLICATION METHOD ON SPATIAL DISTRIBUTION OF LEACHING LOSSES

Abstract

The impact of tillage and nitrogen (N) application method on the spatial variation on leaching losses wasevaluated using eight, 1-m3 undisturbed soil monoliths. Monoliths were collected in 1992 from research plots with 15years 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 surfacecompaction, and with water. A rainfall simulator was used to apply 100 mm of water followed 24 h later by an additionalapplication of 430 mm to establish tracer concentrations over a range of drainage. Drainage was collected at the bottomof each monolith using fiberglass wick extractors placed in a 6 6 grid of 90 mm 90 mm cells. Tracer leaching lossesand flow-weighted concentrations were calculated from the initial flush of water through 24 h after water application. Nosignificant differences were noted for cumulative drainage distribution curves or for the depth of drainage produced (p <0.05). However, in all cases, the cumulative distribution curves were above the 1:1 line, indicating that drainage fromsome cells was greater than others. Spatial analysis indicated that drainage was randomly distributed across themonolith. Tracer leaching losses were not significantly different among tillage treatments or tracer application methodsfor either water application event. However, results for the slot with surface compaction treatment suggest that 10 timesmore NO3-N from moldboard plow treatment in comparison with the ridge tillage treatment. Trends in leaching losses forthe SLOT (Br) with surface compaction treatment suggested that a tracer leaching pattern existed directly below theapplication zone. Tracer concentrations peaked above 350 mg L1 after 100 to 170 mm of drainage for the SLOT (Br)with surface compaction application method and final concentrations remained above 70 mg L1. Peak concentrations forthe surface broadcast (BROAD) and with water application (WATER) methods peaked at less than 110 mg L1 and wereconsistent among monoliths. Spatial analysis indicated that leaching losses were randomly distributed. Data supported anassertion that the moldboard plow tillage treatment combined with the slot with surface compaction (SLOT) applicationof N should be avoided.