Ecosystem-based nutrient management is a proposed strategy to maintain the production capacity of agroecosystems while improving degraded soil and water resources by tightening nutrient cycles on farms. Nitrate leaching and nitrous oxide emissions resulting from nitrogen saturation of agricultural soils contribute to widespread eutrophication and global climate change. Current conservation strategies have yet to achieve management goals such as mitigating nutrient and sediment losses to coastal waterways and decreasing soil greenhouse gas emissions. No-till, cover crop interseeding is one approach that could decrease nitrate leaching and nitrous oxide emissions while improving nitrogen provisioning without impacting cash crop yields. Interseeding eliminates the need for late-season tillage and ensures early establishment of winter cover crops, which may maximize plant nitrogen uptake and minimize nitrogen losses. To test this strategy, we established a cover crop-based, rotational no-till cropping systems experiment in central Pennsylvania, USA where we evaluated a legume-grass cover crop mixture no-till interseeded under a standing spelt crop in terms of its impact on soil nitrogen losses. Biogeochemical methods were used to measure above and belowground nitrogen pools and estimate nitrogen fluxes such as nitrogen fixation, nitrate leaching, and nitrous oxide emissions.
We found that reduced tillage in the interseeded systems maintained smaller soil inorganic N pools (<5 mg N/kg soil) than tilled systems (p < 0.001). This was associated with a significant 50% decrease in cumulative nitrous oxide emissions during the fall (p < 0.001). However, there was no significant difference in potentially leachable nitrate over the winter (p = 0.086) despite minimal fall soil nitrate availability in the interseeded systems. Significantly lower spring cover crop biomass N in the interseeded systems (p = 0.022) may indicate increased susceptibility to spring nitrate leaching under a clover-timothy cover crop compared to a vetch-triticale cover crop. Spelt yields were not significantly different among the study systems (p = 0.853). By establishing cover crops prior to spelt harvest, interseeding increased the time under plant cover and minimized substrate availability for nitrous oxide production and decreased nitrous oxide emissions. This suggests that ecosystem-based approaches to nutrient management such as cover crop interseeding could mitigate the climate impact of agroecosystems while maintaining agricultural production capacity.