Seven Maquoketa Watershed farmers hosted on-farm manure management demonstrations during crop year 2002, bringing the total to 17 over three years, 2000-02.

Their average corn income when manure was the only nitrogen (N) and phosphorus (P) fertilizer source resulted in increased gross income of $49 per acre, compared to the zero check, when corn was valued at $2.00 a bushel.

When corn is valued at $2.40 a bushel, the improved yield from manure application resulted in $59 per acre gross income. Both results are shown in figure 1.

The average first-year crop-available N credits from manure averaged 129 pounds per acre for all 17 demonstrations. The manure contribution has ranged from 29 to 286 pounds per acre.

All demonstration farms had high or very high P tests on the manure demonstration sites, so there was not a consistent yield response to the average of 179 pounds per acre added in the manure resource, as shown in figure 2.

This result was expected due to the high or very high pre-demonstration soil tests for P. Thus, adding P fertilizer to these fields resulted in a net loss of income.

The manure N contribution was calculated using adjustment factors of field manure history, N loss from surface application versus manure incorporation and first-year nutrient availability based on the type of manure applied.

Replicated treatments of commercial N applied at the first-year crop-available N rate (contribution) from the manure (MN rate) were applied randomly within each manure demonstration site. The equivalent N application resulted in an average corn yield of 176 bushels per acre from the manure N source and 177 bushels from the commercial N application, as shown in figure 3.

The addition of 100 pounds of N to the manure application resulted in the highest average yield of 186 bushels of corn per acre. However, this is not significantly different from 185 bushels of corn per acre achieved when only 50 pounds of N is added to the manured treatments. The higher N contribution from swine finishing manure applied in excess of 3,000 gallons per acre demonstrated no benefit from the additional N.

On average, the return on the N investment was the greatest when 50 pounds of N was added to the manure application, bringing the average crop-year available N to 179 pounds per acre.

The end-of-season cornstalk nitrate N (residual N in the corn plant at maturity) was in the optimum range, 1,501 parts per million (ppm), when 50 pounds N per acre supplemented the manure application, as shown in figure 4.

The optimum range for cornstalk NO3–N is 700 to 2,000 ppm, indicating a high probability that the appropriate N rate was applied to the crop to provide the most profitable return on the N investment.

These demonstrations indicate that manure is a significant N and P resource for crop production.

The type of manure applied, the amount, method and uniformity of application are all factors that need to be considered when determining whether to supplement a manure application with additional N. The demonstrations show that applying more than 50 pounds per acre of N is not justified when using typical manure application rates.

There is a need for adequate additional N from commercial fertilizer when insufficient amounts of manure are applied.

Maquoketa Watershed Project staff express their appreciation to these manure management field demonstration cooperators: Nick Hayes, Tom Hayes, Don Thole, Pauline Antons and Alan Jacobs, Steve Streets, Dennis Eggers and Rich Feddersen.