Wilke, B. J., S. Parr, C. McSwiney, S. S. Snapp, G. P. Robertson
Presented at the All Scientist Poster Reception (2007-05-14 to 2007-05-14 )
Optimizing nutrient efficiency without yield reductions is a primary goal in grain cropping ecosystems. A long-term cropping system trial underway at the W.K. Kellogg Biological Station in Michigan provides insights into the impact of cover crops on soluble nitrogen fertilizer requirements in a corn-soybean-wheat rotation. Monitoring of soil carbon, N, water status and plant productivity over 16 years provided insights into transition years and later years of a long-term test of integrated organic and inorganic N management. The markedly low rate of N fertilizer (0 to 60% of the conventional system) applied to grain crops in the reduced treatments with cover crops was associated with a steady increase in soil inorganic N supply over time. Yields of reduced N input systems increased over time in close association with soil inorganic N status, and were comparable to conventional treatments in later years of the study. Nitrogen efficiency for all systems was calculated by comparing cereal yield to N added as fertilizer and estimated additions from cover crop (red clover) biological N fixation. Marked improvements in N efficiency are observed over time for corn in the low input system, where yield per N input is two-fold higher than conventional and no-till systems. Increased non-crop biomass (over crop and weeds) may enhance recycling of N in reduced input systems, which is evident through greater soil N mineralization. Leaching and gaseous losses provide further insights in this long-term systems trial to help understand the cascading and long-term effects of cover crop amendments on N efficiency.
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