Can soil health practices reduce risk of nitrate leaching? Developing an assessment framework
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Nitrogen is an important nutrient for crop yield and quality, but excess nitrogen can leach from fields creating contamination issues in groundwater and surface water supplies. To improve soil nutrient retention, many conservation groups and funding agencies are focused on building soil health in agricultural land. This research seeks to establish a monitoring framework for quantifying the benefits of soil health practices for mitigating groundwater nitrate. Our goal is to provide a cost-effective and environmentally friendly method to promote nutrient use-efficiency and protect water supplies that would benefit many small/rural communities.
Soil samples were collected using a grid-based, composite sampling approach in northeast Kansas in the fall and spring to assess eight large fields with different soil health practices. We measured a large variety of soil health metrics and used a correlation matrix to identify a parsimonious set of metrics to assess potential nutrient leaching. In comparison to more conventionally managed fields, fields with a history of cover crops and no-till agriculture had higher organic matter, soil respiration, microbial biomass, available carbon, and organic nitrogen; all of which are important for soil health. Additionally, fields with more soil health practices also had lower extractable nitrate in the fall and higher extractable nitrate in the spring, suggesting a lower potential for nitrate leaching in the fall and higher nitrate availability for plant uptake in the spring. Early results from these eight fields indicate soil respirable carbon, organic matter, available carbon, water extractable nitrogen forms could be good metrics to predict the potential for nitrate leaching. Future work is needed to connect soil health to surface water and groundwater nitrate levels. This research indicates that use of soil health practices may increase nutrient storage and reduce nutrient leaching throughout the winter, thus providing more nutrients in spring for crop growth.