Ten Maquoketa Watershed farmers have hosted on-farm manure management demonstrations during the last two crop seasons. Their average corn income when manure was the only nitrogen (N) and phosphorus (P)  fertilizer source, compared with the zero check, resulted in  increased gross corn income of $39 per acre when corn was valued at  $2.00 a bushel and N at 20 cents a pound.

At $2.40 per bushel corn, the improved yields from manure application  resulted in $47 per acre increased gross income, as shown in figure 1.

The average first-year crop-available N credits from manure averaged 150 pounds per acre for the 10 demonstrations.

Because all demonstration farms had high or very high P tests on the manure demonstration sites, there was not a consistent yield response to the 214 pounds average per acre of P added in the manure resource, as shown in figure 2.

This result was expected due to the high to 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 and N loss from surface application versus manure incorporation.

Replicated treatments of commercial N applied at the first year crop available N rate (contribution) from the manure (MN rate) was applied  randomly within each manure demonstration site. The equivalent N application resulted in an average corn yield of 157 bushels per acre from the manure N source and 158 bushels per acre from the commercial N application, as shown in figure 3.

The addition of 50 pounds of N to the manure application resulted in the highest average yield of 165 bushels of corn per acre. The response to the additional N was most evident in the demonstrations  where the manure N contribution was less than 100 pounds per acre. 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, when 100 pounds of N was added to the manure application, bringing the average N available to 250 pounds per acre, there was a loss in yield of 3 bushels per acre versus the 50 pounds per acre additional commercial N treatment.

The end-of-season cornstalk nitrate N (residual N in the corn plant at maturity) was higher, 2,479 parts per million (ppm) nitrate N (NO3-N) with the 250 pounds N per acre, as shown in figure 4.

The optimum range for cornstalk NO3 -N is 700 to 2,000 ppm, with analyses over 2,000 ppm indicating a high probability that the N application rate exceeded the N requirement of the crop.

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

The type of manure applied, 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 isn't 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 the following manure management field demonstration cooperators: Darrell Rosburg, David Moorman, David and Richard Venteicher, Marvin Heims, Randy and Rodney Hamlett, Tom Hayes, C&J Farms, Verle Jones, Don Thole, Bill Hayes, Tim and Jim Recker, Ron and Dwight Reid, Keith Bumgartner and Sons, and Bob Recker.