Project NewsThe Kregels take 100 percent contribution the first year after a manure application, based on 10 years of cooperation with NEIDP in field demonstrations. They are now trying to refine their management to determine the amount of N contribution they should take for the second year.
To help answer their questions, demonstration plots were set up in corn fields which had received manure in the fall two years earlier and where no commercial nitrogen had been applied to the corn crop the year before. Varying rates of nitrogen were applied on the replicated plots to determine how much second-year carryover contribution could be given to the manure application.
The N treatments, corn yields and end-of-season cornstalk nitrate nitrogen test results are reported in the accompanying table.
| 1996 | 1997 | 1998 | ||||
| Treatment lb/A N |
Yield bu/ A |
Cornstalk NO3 ppm |
Yield bu/ A |
Cornstalk NO3 ppm |
Yield bu/ A |
Cornstalk NO3 ppm |
| 0 | 152 | 1,112 | 152 | 485 | 156 | 140 |
| 50 | 156 | 3,572 | 174 | 1,788 | 185 | 101 |
| 100 | 158 | 5,112 | 177 | 1,558 | 188 | 921 |
| 150 | 168 | 6,902 | 177 | 5,168 | 188 | 2,707 |
To evaluate N management at the end of the season, a residual nitrate nitrogen analysis was completed on the lower cornstalk. Nitrate levels less than 700 parts per million (ppm) indicate that applying more N would likely increase yields. Levels between 700 to 2,000 ppm nitrate nitrogen indicate that adequate N was available to maximize yields. Cornstalk nitrate levels over 2,000 ppm nitrate nitrogen indicate a high probability that more N was available than needed to maximize profits.
The results show that there wasn't enough second-year carryover N from the manure to fully support the N needs of the corn crop. In two of the three years, the addition of 50 pounds of nitrogen provided a significant yield increase, while the 100 pound nitrogen application only produced 2-3 bushels more over the 50 pound rate. When cornstalk nitrate N levels are taken into consideration the 150 pound application appears to be in excess of the nitrogen needs of the crop.
The amount of second-year contribution to take after a manure application can be further refined by the use of the late spring N test. Farmers also need to consider the amount and type of manure applied before making any final decisions on the second year contribution from manure. Reducing nitrogen application on fields with manure history, comparing the results to present management, and making use of the fall cornstalk nitrate N test to determine nitrogen sufficiency are methods producers can refine the nitrogen management on their farms. Refined management can mean increased profit and improved water quality.
For more information on these and other 1998 field demonstrations, contact the NEIDP staff in Postville at 319-864-3999.
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