Improving Nitrogen Utilization with Rotation and Cover Crops

This project provided concrete evidence from 18 paired comparison farms, from detailed trials on a single farm and from experiment station trials that corn, soybean, wheat and cover crop rotations were superior to continuous corn. The return over variable costs was $84 per acre for continuous corn and $103 per acre average for the multi-crop rotations, a 23% increase in farmers fields. The increase was similar for experiment station trials, with most of the advantage coming from increased corn yield and profitability in the rotation. Introducing wheat into the rotation, particularly when clover was used following wheat, gave the greatest increase in corn yield. Farmer corn yields increased from 115 to 134 bushels with rotation. In experiment station trials in the third year of rotation the 1994-95 averages were 174 bu/A with rotation and cover, and 159 bu/A without rotation or cover. Linear program analysis of the farm data using PLANETOR-derived values showed that phosphorus runoff could be held below 8 lbs/A per year and nitrate leaching below 40 lbs/A per year. Without loss of profit using rotations, leaching losses of nitrogen were reduced by 50 to 60% in the experiment station trials. The nitrogen credit for corn was measured at 60-70 lbs/A following wheat with clover, but the 15-18% increase in corn yield following this combination was due apparently to a combination of nitrogen and other yield-influencing effects. Soil quality differences were difficult to measure uniformly across the wide variation in soil types of the farm studies. No decrease in physical, biological or chemical quality was found with high crop diversity in any comparison, and increases were seen in soil carbon, water infiltration and nitrogen mineralization on some farms. Farmer response to these results in field days and in numerous training sessions has been excellent.

Project objectives:

This project was designed to test the degree to which, in the central part of Michigan's field crop region, crop rotations, particularly those including cover crops, would be more profitable, would result in better soil quality and would use nitrogen more efficiently. Rotations were thought to result in reduced loss of nutrients to the environment. These results, in part, would be due to higher levels of soil microbial activity caused by the crop diversity. The specific objectives were:

l. To demonstrate, within Michigan's most common field crop systems, that higher levels of crop diversity significantly increase soil microbial activity.

2. To demonstrate that carefully arranged crop rotation and cover crop sequences can enhance crop-available nitrogen and decease the fall and winter levels of dissolved nitrogen in the soil. These direct effects will be "conditioned by microbial activity" (of Objective 1).

3. To quantify the degree to which a range of
"chemical" and "organic" management options enhance or disrupt these main effects.

4. To develop an economic analysis "framework" for assessing economic and environmental costs and benefits of the above factors.

5. To evaluate multi-year costs and benefits from nutrient management under alternative crop rotations and cover crops by using enterprise budgets and tracking environmental quality parameters.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.