Can a Legume Cover Crop Increase Nitrate Leaching after Termination?.

Increased nutrient leaching due to agricultural practices such as tillage and fertilization is a significant environmental concern. Nitrogen (N) mineralization stimulated by tillage can increase the risk for nitrate leaching before subsequent crops have an opportunity to take up the N released by microbial activity. An alternative measure for reducing potential nutrient loss via leaching and runoff is use of cover crops (CC). A field experiment was conducted at the Southern Illinois University’s farms in Carbondale, IL from 2015 to 2017 to quantify soil solution chemistry and soil nutrient content in corn/soybean rotation as influenced by CC (Hairy vetch or radish/oats or cereal rye) and tillage (conventional till / no–till). The crop rotation for CC treatments was hairy-vetch or radish-oats/corn/cereal rye/soybean. Soil samples collected after corn/soybean harvest and cover crop termination were analyzed for standard soil fertility parameters. Pan lysimeters installed below the ‘A’ horizon with depth varying from 15 to 25 cm were used for measuring soil solution nutrient concentration on weekly or biweekly basis depending on the precipitation amount. Soil solution samples were analyzed for pH, EC, anions (Br^-, Cl^-, F^-, NO₂^- , NO₃^-, and SO₄^2-), dissolved reactive phosphorus, total nitrogen and dissolved organic carbon. Soil nitrate-N in 0-45 cm depth was significantly reduced by CC in conventional tillage plots during spring, 2016. Higher nitrate-N leaching was observed with hairy vetch (Vicia villosa) under both tillage systems in 2015 after corn planting. Hairy vetch and no CC treatments showed increased nitrate-N leaching in conventional tillage plots in 2016 after soybean planting. Long term soil solution monitoring is needed to discover temporal changes in nutrient leaching by leguminous CC and better understand the interaction of CC with tillage that will help producers select an appropriate cropping sequence.

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