Plumhoff, M. 2021. Management legacy effects on cover crop productivity and potential to reduce nutrient leaching from farms. Thesis, University of Michigan, Ann Arbor MI.

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Cover cropping is an ecological management practice that provides a variety of ecosystem functions to farms, such as increasing soil organic matter content and improving nutrient retention. Background soil fertility due to unique management legacies is expected to influence the productivity of cover crops and subsequently mediate their effects on ecosystem functions related to nutrient retention. We used a long-term experiment at Michigan State University’s Kellogg Biological Station to test the legacy effects of four distinct management systems (ranging from conventional to certified organic) on the production and function of crimson clover and cereal rye cover crops grown alone and in mixture, with a focus on the potential to reduce nitrate leaching. Cover crops were planted following winter wheat harvest in the summer of 2019 and corn was planted in all treatments the following spring after cover crop termination. We applied bromide as a conservative tracer of water and anion flow in the soil profile to assess management legacy and cover crop treatment effects on potential anion leaching.

We found that via changes to soil fertility, management legacies influenced cover crop productivity and species composition in mixture: in the legacies with lower soil fertility, crimson clover was more competitive than rye and dominated the mixture. Legacies with higher soil fertility—which were those with a history of ecological nutrient management—had higher average cover crop biomass (mean = 3357 kg ha-1) and a higher percent recovery of bromide (mean = 33.28%), an estimate of soil anion retention. Further, percent recovery of bromide was positively correlated with cover crop biomass (r2=.17) and the free particulate organic matter fraction (r2=.29), indicating that the effect of management legacy on cover crop function is mediated by cover crop production and background soil fertility. This experiment reveals complex interactions between soil fertility, cover crop growth, and nutrient leaching potential that depend on soil conditions resulting from specific management regimes.

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