Wilke, B. and S. Snapp
Presented at the All Scientist and GLBRC Sustainability Meeting (2009-05-05 to 2009-05-07 )
The management of grain cropping ecosystems varies in several properties, including fertility maintenance, weed control, tillage, species composition and duration of ground cover. For example, conventional systems are managed with tillage, herbicides and inorganic fertilizers whereas organic systems are primarily managed with intense tillage and organic fertilizers. These management activities feedback to influence patterns in soil properties, particularly in terms of soil nitrogen supply as it relates to this study. Nitrogen availability can in turn influence the rate of biological nitrogen fixation by legume plant species, as is evidenced by multiple previous studies. Two long term agroecology experiments at the W.K. Kellogg Biological Station indicate that organic systems exhibit a slow increase in soil organic matter and soil nitrogen availability over time, whereas conventional systems remain relatively constant over time for these two soil properties. We hypothesize that this slow increase in soil nitrogen availability in the organic systems will feedback to negatively influence biological nitrogen fixation by legume cover crops (red clover), an important source of nitrogen for cash crops in the organic systems. Samples are currently being analyzed, and we hope data will be available by the time of this poster symposium. The implications of this study are two-fold: 1) organic farmers may need fewer legume cover crops over time and 2) improved ecological understanding of how changing resource gradients affect symbiotic relationships in nature.
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