Wilke, B., S. Parr, C. McSwiney, S. Snapp, and G.P. Robertson
Presented at the ASM at Estes Park (2006-09-01 to 2012-09-23 )
Coarse soils require close attention to managing soil carbon and nitrogen (N) mineralization dynamics to optimize nutrient efficiency while maintaining productivity. 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 11 years provided insights into transition years and later years of a long-term test of integrated organic and inorganic N management. A reduced requirement for soluble N application was observed over time in treatments with winter cover crops. The markedly low rate of N fertilizer (0 to 30% of the conventional system rate of 145 kg N per ha) applied to cereals in the reduced treatments with cover crops was associated with a steady increase in soil inorganic N supply over time. Productivity of reduced N input systems increased over time, in close association with soil inorganic N status. Cereal yield in the initial years of the trial (1993-1998) was reduced by an average of 11% in the low input system and 48% in the zero input system, compared to the conventionally managed systems. The later years of the trial (1999-2004) saw cereal yields equalize in the low input system with conventional systems, and a more modest yield reduction of 17% was observed in the zero input system. 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 N efficiency is 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. Soil N accumulation and losses from leaching and gaseous losses require further evaluation in this long-term systems trial to understand the cascading and long-term effects of organic amendments on N management recommendations.
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