Soybean acreage increased in 1999 due in part to government loan rates. The cash value per bushel of corn and beans is low. The bottom line profit per acre has been squeezed. Ag suppliers have reported less than normal fertilizer applied for crop year 2000 and the soil has less than normal moisture reserves going into the winter. How do we cope and plan for crop year 2000?

One alternative is to refine crop nutrient use based on good soil tests, especially on fields testing optimum or higher for phosphorus and potassium or where manure is applied. Another is to refine nitrogen (N) use based on past experiences and use of the nitrogen contribution from manure and legumes.

Since 1993, Northeast Iowa Demonstration Project (NEIDP) staff have assisted 10 cooperators to evaluate their corn production following the previous soybean crop to determine the most profitable nitrogen fertilizer rates to use. In addition to yield results, the post-maturity cornstalk nitrate nitrogen test has been used to measure the residual nitrogen left in the plant after the crop has been harvested. Joe Wingert, Arlington, was the 1999 cooperator in the Maquoketa watershed.

Cooperators in previous years were mostly from the Postville area. However, Jule Brown, Strawberry Point, was one of three cooperators in 1998.

The results of these demonstrations are consistent with Iowa State University (ISU) recommendations that N use for corn following soybeans can be reduced by at
least one pound for every bushel of soybeans produced the previous year. In most of the demonstrations, a 90-pound per acre N application has proven adequate. Results for 1999 and for all 10 demonstrations conducted since 1993 are shown in table 1.

The single variable in the demonstration has been the rate of nitrogen applied. The profit in dollars per acre includes the cost of nitrogen at 20 cents per unit and the yield response in corn at $2.40 per bushel.

The cornstalk nitrate test measures the amount of nitrate nitrogen (NO3) in the corn plant after it matures. Low stalk nitrate N levels (less than 250 parts per million, or ppm) indicate that additional N would have been likely to increase yields. The marginal range (250-700 ppm) indicates a level very close to the minimal amount needed by the crop, but grain yield may not be reduced. The optimum rate (700-2,000 ppm) indicates that N availability was close to the rate needed by the plant, while levels in excess of 2,000 ppm indicate a high probability that there was more N than needed.

Maquoketa Project. The same corn-following-soybeans N rates (0 to 150 lbs/A) will be used in three field demonstrations (Gary Soules, Joe Wingert and Jule Brown) in crop year 2000. In addition, one- and two-year crop removal and no phosphorus treatments will be included in replicated plots within all three field demonstrations. Two of the sites have soils that test very high while one site will be located on a soil that tests low in phosphorus.

Corn following alfalfa demonstrations were conducted on seven cooperating farms by NEIDP staff since 1992. The results from seven years of variable replicated nitrogen rates are reported in table 2.

There was no response to additional N, there was only an increasing loss in profit (N at 20 cents per unit and corn at $2.40 per bushel) as the amount of applied N was increased.

For more information on NEIDP field demonstrations from 1992 to 1999 or demonstrations planned for crop year 2000, contact the ISUE Maquoketa Watershed Project staff, Fayette, phone 319-425-3233.