Improving Nitrogen Utilization with Rotation and Cover Crops
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.
1) 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 decrease the fall and winter levels of dissolved nitrogen in the soil.
These direct effects will be “conditioned by microbial activity.”
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
Three studies were conducted as part of this research:
1) Eighteen farms along a transect from southwestern across south-central Michigan, covering
eight counties, were paired for high and low crop diversity.
2) A detailed verification study of clover frost-seeded into wheat was done over two years on a
single farm from this transect.
3) An intensive replicated rotation and cover crop study, the Living Field Laboratory, located
along the defined transect, was monitored in its second and third year for comparative analysis.
Yields from 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 percent increase. 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
bushels/acre with rotation and cover, and 159 bushels/acre without rotation or cover.
Linear program analysis of the farm data showed that phosphorus runoff could be held below 8
lbs/acre/year and nitrate leaching below 40 lbs/acre/year. Without loss of profit using rotations,
leaching losses of nitrogen were reduced by 50 to 60 percent in the experiment station trials. The
nitrogen credit for corn was measured at 60-70 lbs/acre following wheat with clover, but the
15-18 percent 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.
Potential Contributions and Practical Applications:
The economic research demonstrates that under the conditions examined, corn-based crop
systems including rotation with soybean and wheat were more profitable with less nitrate
leaching than continuous corn systems. Moreover, nitrate leaching and phosphorus runoff could
be reduced to “low risk” levels by incorporation of clover interseeding at a cost of as little as two
cents per acre.
Farmer Adoption and Direct Impact:
There is considerable farmer interest and a gradual progression toward more complex rotations
and toward the use of cover crops, particularly following wheat. Farmers are moving rapidly
away from continuous corn. These results will increase that momentum by providing concrete
Corn and soybean producers should seriously consider adding wheat to their rotations,
particularly in fields with problems of soil physical quality. Clover cover should be an option for
every wheat field.