Manure demonstrations include P and N treatments

by Chad Ingels, manure and nutrient management specialist, Maquoketa Watershed Project

Eight on-farm demonstrations hosted by Maquoketa River Watershed Project cooperators show that manure is a valuable resource that can reduce the need for commercial nitrogen (N) and phosphorus (P) applications.

The crop year 2000 demonstrations started soon after the 1999 crop harvest with the rate of manure application on each demonstration site determined with in-field calibration of the cooperating producers’ usual manure application rate. Maquoketa Watershed Project staff secured a sample of manure for nutrient analysis when it was applied to the demonstration site. Soil sampling was completed at all sites to determine P and potassium soil test levels before manure application.

Five of the manure demonstration sites were planted to soybeans in 1999 and three were corn following corn. There were nine replicated treatments at each demonstration site. Fall application of P at the 150 bushel per acre corn crop removal rate (46 pounds of P per acre) was applied to three plots within each demonstration as was P at the manure P application rate (determined by the calibration rate and analysis of the applied manure). Another set of treatments was the crop removal plus manure P rate combined.

As a check, no manure or N was applied to three treatment areas in each demonstration. To compare commercial N to the N available in manure, 100 pounds of N was applied on replicated areas on soybean sites and 150 pounds of N on replicated areas on corn following corn. The replicated manure treatment areas were three treatments each of 0, 50 or 100 pounds of commercial nitrogen added to the manure and commercial N at the first-year crop available N rate applied in the manure resource.

Eight site average manure and N corn yield results are shown in figure 1. The highest yield was 50 pounds of commercial N in addition to the manure application, that averaged 172 pounds of first-year plant available N in the eight manure resources evaluated.

The addition of 100 pounds of N to manure often results in lower yields than the manure plus 50-pounds per acre treatment. Similar  results were obtained from 24 manure N demonstrations conducted from 1994-1998 near Postville by Northeast Iowa Demonstration Project staff.  This year, six of the eight sites had lower yields when 100 pounds of N was added to the manure, compared to the addition of 50 pounds of N.

Figure 2 provides profitability trend lines for manure and manure plus N, based on 20 cents per pound for N and corn valued at $2.40 or $2 per bushel. Compared with the check (no manure or N) the  dollar return to applied manure was $41 for $2.40 per bushel corn and $35 for $2 per bushel corn.

Residual nitrate-N in the eight-inch cornstalk segment six to fourteen inches above the soil following plant maturity is an indication of the adequacy of N available to the corn plant. Figure 3 indicates that the check treatment stalk nitrate level at 239 parts per million (ppm) nitrate-N was below 700 ppm, which is the lower end of the optimum range of 700 to 2,000 ppm.

Excess N was available with the commercial N applied at the manure N rate (172 pounds per acre) and the 50 or 100 pounds of N applied in addition to the manure. These results were predictable in June when the late spring nitrate test was used on the various N and manure treatments (figure 4).

All eight of the manure demonstration sites had P soil test levels in the high or very high range when sampled in October 1999. The yield response was not significantly different to commercial P or to manure P that averaged 250 pounds per acre (figure 5). The loss in profitability due to commercial P application is nearly equal to the cost of the P applied.

Maquoketa Watershed Project staff thanks manure management cooperators David Moorman, Verle Jones, David and Richard Venteicher, Rodney and Randy Hamlett, Darrell Rosburg, North-east Iowa Community College, Marvin Heims and C&J Farms.

For more information on this and other field demonstrations conducted during crop year 2000, contact the Maquoketa Watershed Project staff in Fayette, telephone (319) 425-3233.

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