Interaction Effects of Tillage and Cover Crop on Soil Nitrate Movement.

The interaction effects of cover crops and tillage systems on nitrate (NO₃-N) leaching are not well documented.  Both tillage systems and cover crops can have significant impacts on water and NO₃-N movement to groundwater under row cropping systems.  This study was conducted to determine the interaction effects of a cover crop and tillage systems on the transport of NO₃-N and bromide (Br) in the soil.  This study took place in a greenhouse with 24 undisturbed soil columns taken from three different tillage system experiment plots, where no nitrogen fertilizer was applied. The soil columns were 43 cm tall and 20 cm in diameter.  The tillage systems used in this study were no-till (NT), chisel plow (CP), and strip till (ST) in a completely randomized design with three replications.  A cereal rye cover crop was planted in each column of the three tillage systems.  NO₃-N and Br were applied as NH₄NO₃ (42 g/m²) and KBr (32 g/m²) to the soil surface of each column in cover crop and non-cover crop treatments.  Each column received 1000 mL of deionized water approximately every 10 days to simulate a rainfall leaching event.  Leachate was then collected and analyzed for bromide and nitrate concentrations.  Preliminary results showed that NO₃-N and Br leachate concentrations were very similar during each leaching event for all tillage systems under cover and non-cover crop treatments. The average of both NO₃-N and Br concentrations leached during the first two leaching events was 13-24% and 15-23% for cover and non-cover treatments, respectively.  After the third leaching event NO₃-N and Br concentrations in the leachate were 0.1-3% and 5-17% for cover and non-cover treatments, respectively. Regardless of the tillage system, the cover crop caused significant reductions in NO₃-N and Br concentrations in the leachate after the third leaching event.