Date of Award
8-1-2025
Degree Name
Master of Science
Department
Forestry
First Advisor
Williard, Karl
Abstract
Cover crops can sequester nutrients in the winter and spring fallow seasons, thereby reducing nutrient loss. However, short-term studies cannot adequately capture cover crop benefits because their impacts are expected to accrue over many years. In 2015, a long-term study was initiated to determine cover cropping and tillage practices' effects on nutrient loss at Southern Illinois University’s Research Farms. Six treatments comprising the interaction of three cover crop rotations (hairy vetch (HV), an oats and radish mix (OR), and no cover crop (NC)) and two tillage practices (reduced-tillage (RT) and no-tillage (NT)) were applied to corn and soybean rotations. Treatments with cover crops were planted with cereal rye following corn harvests and hairy vetch or oats and radish following soybean harvests. Soil leachate samples from each treatment were taken within 24-48 hours following each significant rain event (>12.7mm) via gravity-drained lysimeters installed below the undisturbed A horizon. Throughout the five seasons when cereal rye was planted, no cover crop plots leached on average 0.33 kg nitrate-N ha-1 or 15.36% more than cover crop plots (p≤0.080). Treatments had no effect on nitrate-N leaching during hairy vetch/oats and radish seasons (p≥0.164), though there was a weak increase in nitrate-N leaching under the oats and radish rotation compared to the no cover crop rotation (p=0.142). Treatments had no effect on dissolved reactive phosphorus leaching in either cereal rye or hairy vetch/oats and radish seasons (p≥0.299). Soil phosphorus stratification was evident in all treatments, but the greatest differences between 0-5 cm and deeper soil depths occurred in the NCxNT treatment. Treatments had an inconsistent effect on dissolved nutrients in micropore soil water. HV and OR rotations significantly reduced nitrate-N concentrations in all soybean and cereal rye seasons (p<0.001) but not during corn or hairy vetch/oats and radish seasons (p ≥0.2061). Treatments had no effect on ammonium or dissolved reactive phosphorus concentrations in micropore soil water across all seasons (p≥0.140), except across the corn seasons, where the NCxRT treatment saw 62.68% lower ammonium concentrations than the ORxNT treatment (p=0.105).Cereal rye minimized nitrate-N leaching compared to no cover crop rotations by scavenging nitrate-N from the soil water but did so at rates less than other long-term studies. It’s suspected that hairy vetch’s capacity to fix nitrogen and the rapid mineralization of the low C:N biomass supplied the soil water with nitrogen at rates higher than it assimilates, leading to similar nitrate-N losses between hairy vetch and no cover crop plots.
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