Understanding the relationship between nitrogen (N) and crop rotation is very important when making N management decisions. There are several benefits to using crop rotation, including improved nutrient cycling, soil tilth, and soil physical properties; and enhanced weed control. Crop rotation also may influence the rate of N mineralization or the conversion of organic N to mineral N by modifying soil moisture, soil temperature, pH, plant residue, and tillage practices.
The incremental increase in N use over the past five decades, due to emphasis on maximizing yield, has led to a subsequent increase in N in the soil profile of some agricultural fields. Therefore, the influence of agricultural practices on water quality has prompted studies to develop best management practices to optimize the use of fertilizer N and reduce N loss to surface and groundwater. Crop rotation can play a major role in minimizing the potential risk of nitrate leaching to surface and groundwater by enhancing soil N availability, reducing the amount of N fertilizer applied, and minimizing the potential risk of N leaching.
Research on the impact of long-term crop rotation on soil N availability shows that planting alfalfa, corn, oat, and soybean significantly increased the mineralized net N in soil compared with planting continuous corn. Because soil N mineralization can effect yield, crop rotation thus can be used as a management system to enhance the soil nutrient pool, thereby reducing the fertilizer N input and minimizing the risk of leaching of excess N during wet weather.
A combination of conservation tillage practices and crop rotation has been shown to be very effective in improving soil physical properties. Long-term studies in the Midwest indicate that corn-soybean rotation improves yield potential of no-till compared with continuous corn. The reduction in yield of continuous corn in no-till is attributed to low soil temperature during seed germination, which is evident on poorly drained soils under no-till. Studies show that the poor performance of no-till corn following corn is more likely due to the previous crop than to surface residue conditions preventing early-season warming and drying of soils.
The use of a legume cover in crop rotation can provide a substantial amount of N to a succeeding crop. Research has indicated that seeding rates for legumes can be reduced by approximately one-third of that recommended for forage production when used as cover crops without sacrificing biomass or N accumulation. Also, the type of crop grown in the previous year can impact the efficiency of conservation tillage, especially for no-till systems, due to the kind and amount of crop residue from the previous crop.
This article originally appeared on page 49 of the IC-486 (6) -- April 23, 2001 issue.