Effects of Agricultural Management with and without Cover Crops On Soil Nitrate In Different Topographical Positions.

The ability to keep nitrate at an optimum level for crop production is an important ecosystem service provided by soil. Nitrate is the primary absorbable source of N for most plants and its concentration should be high enough to support plant growth. On the other hand, the excess amount of nitrate can be leached into underground water or transformed into greenhouse gases. Therefore, synchronizing nitrate supply with crop demand to minimize excess supply is key to minimizing losses to the environment. The objective of this study is to assess the interactive effects of management practices and topography on soil nitrate levels. The study was carried out in ten fields of Long Term Ecological Research site at Kellogg Biological Station, MI. Three agricultural management practices compared were: management with conventional nitrogen inputs, management with cover crops + low nitrogen fertilizer inputs  and certified organic management with cover crops. Three topographical positions of depression, slope and summit were sampled in each studied field. Soil samples were collected bi-weekly/monthly during the growing seasons of 2010 and 2011. The preliminary results from 2010 indicated that topographical effects were equally strong in all three studied managements and exceeded the effects of the management practices on soil nitrate levels. Results from growing seasons with contrasting weather regimes (2010 and 2011) will be presented and discussed.