The crop nutrient value of manure and its management is of interest to farmers and all citizens. With less bedding used in livestock production, the nitrogen and phosphorus concentrations in most manure sources are greater than a few years ago.

Because manure has relatively high concentrations of nitrogen, phosphorus and potassium available for crop production, manure is valued as a crop production resource by producers. For these same reasons proper management of manure has become an environmental concern.

"Manure Happens, Take Credit" is a phrase that summarizes the interest of livestock producers in northeast Iowa where 32 on-farm manure field demonstrations have been conducted since 1994. Eight demonstrations, on the farms of cooperators Mike Knipper, Dennis Mashek, Loras Hoeger, Pat Maloney, Bill Oberbroeckling and Enoch Hanson, were completed this year with the assistance of Northeast Iowa Demonstration Project staff to refine manure management and nutrient use for crop production. The replicated manure and nitrogen (N) treatments were applied in fields that had not received manure in recent years to reduce the carryover effects of previous manure application.

Manure nutrient contributions were determined by calibrating the manure spreading rate and by analyzing manure samples to determine nutrient content for crop production. Recent research indicates all the nitrogen is available the first year from swine liquid manure. However, this has not been documented in other manure sources. The first-year contribution was 131 pounds of N averaged across the eight demonstrations, with a range from 81 to 225 pounds of N per acre.

A new treatment in 1999 was to apply the same amount of commercial N as the first year N contribution from manure to replicated plots within the demonstration area. The corn yields from commercial N treatments averaged 160 bushels per acre compared to 152 bushels per acre for the manure-only treatment. The stalk nitrate analysis at the end of the growing season was 1,471 parts per million (ppm) and 1,340 ppm of nitrate nitrogen, respectively.

Corn yields and residual nitrate nitrogen in the cornstalks from the eight demonstration sites are shown in table 1.

*Manure sources were dairy, swine and beef.
**Optimum residual nitrate nitrogen in the cornstalk at the end of the season is 700 to 2,000 ppm.

Those same manure management demonstrations have been conducted on 24 other cooperating farms from 1994 through 1998, as shown in table 2.

Table 2. Corn yields and residual cornstalk nitrate N from 24 manure management demonstrations, 1994-1998.

These demonstrations confirm that manure is a significant resource for crop production. The source, quantity, method of application and uniformity of field coverage are all factors that need to be evaluated when determining if and how much additional nitrogen should be spread on manured fields. The 32 demonstrations in the past six years show that applying more than 50 pounds per acre of commercial nitrogen is not economically justified when using typical manure application rates.

Maquoketa Project. Ten producers in the Arlington–Strawberry Point area will host similar but more extensive demonstrations next year: David Moorman, Tom Hayes, David and Richard Venteicher, Randy and Rodney Hamlett, Darrell Rosburg, Marvin Heims, Laverne Jones and Ron Carpenter, Larry Hoefer and Kevin Perrinjaquet, Northeast Iowa Community College and Verle Jones.

Replicated phosphorus rates will be included (on adjacent non-manure plots) in the crop year 2000 demonstrations, including commercial phosphorus applied at the rate contributed from manure.

Nine of these cooperators have applied manure on their demonstration areas this fall with first-year nitrogen contributions for the 2000 crop estimated to range from 102 to 286 pounds of nitrogen per acre. The average manure nitrogen contribution is 171 pounds per acre. The phosphorus applied in the manure ranges from 74 to 792 pounds per acre with the average phosphorus contribution of 240 pounds per acre.

Phosphorus management, especially on fields receiving manure, is an important issue as more concern is expressed each year about the hypoxia zone in the Gulf of Mexico. Phosphorus and nitrogen feed the algae plants that eventually die, and the decomposition removes enough oxygen from the water that fish populations cannot survive in those waters.

The good news is that refined manure and commercial nutrient management will result in more net income per acre on manure fields and will protect water quality at the same time.