Demonstration Results -

Manure Application for Corn Fertility

Multi-year, multi-rate demonstrations of manure application for corn fertility in northeast Iowa

Taking a manure sample for nutrient analysis.

The steep hills and trout streams of northeast Iowa are underlain by creviced limestone, resulting in karst topography that makes water resources highly vulnerable to contamination from surface activities. Land use in the area is almost completely agricultural, and livestock are raised on nearly 90% of northeast Iowa farms. Increasing numbers of livestock producers use confinement feeding, which increases manure liquid storage amounts and nutrient content. This has made manure nutrients an increasing threat to groundwater and surface water quality if not properly managed.

The Northeast Iowa Demonstration Project is an interagency project that provides assistance to producers who are adopting new management methods to protect water resources. A major priority for the project has been to provide local information and demonstrations of manure value for meeting crop nutrient needs. Otherwise, excess nitrate and other plant nutrients can end up in streams and groundwater when commercial fertilizers are used without taking enough credit for the manure that has been applied. Refining crop nutrient management and optimizing use of manure, an on-farm nutrient resource, are strategies that also have economic benefits.

Some long-term manure management demonstrations were first established in northeast Iowa by the state-sponsored Big Spring Basin Demonstration project, which began in 1987. Continuing interest of local producers and advisors has caused the Northeast Iowa Demonstration Project to maintain and expand these efforts. Since 1991, the project as conducted 148 field demonstrations (28 multi-year) on 90 different farms - including 23 demonstrations in the nearby Sny Magill Creek water quality project, where extension activities are coordinated by the same staff. Nearly a third of the demonstrations have related to nitrogen and manure management.



The objective of both long and short term manure application demonstrations is to provide information local producers need to improve their management of manure nutrients. They raise questions such as: "How much nitrogen, potassium or phosphorus does my manure contain?" Different livestock and different forms of storage influence the answer. "What is the seasonal availability of manure nutrients in the soil, once it has been applied?" "How can I measure and control the rate at which manure is spread?" "Are there other profitable management strategies to optimize use of my manure resource?"

On-farm demonstrations of manure as a nutrient source for corn production have been conducted throughout the project area, which includes portions of four northeast Iowa counties. Each year new demonstrations are established so farmers in many communities have a chance to observe the results, and all common manure sources are included.

In on-farm demonstrations, cooperators are asked to spread manure at their normal rate and leave a check area with no manure. Project staff help calibrate spreaders and take manure samples for nutrient analysis. They then hand-apply 0, 50 and 100 lb/A. treatments of fertilizer N replicated plots in the manured area. Annual measurements made by project staff on the plots include manure nutrients applied, corn yields, soil and plant nitrate analyses. The end-of-season stalk nitrate (NO3)

Calibrating a solid manure spreader with portable wheel scales.

test is a measure of whether the corn crop received enough or more nitrogen than it needed for economic crop production. Stalk nitrate test results can be used to "fine tune" nitrogen fertilizer inputs in the future.

The demonstrations prove that modest rates of manure application are sufficient for corn production with little or no additional fertilizer. From results like those in Tables 1 and 2, the project advises that 50 lb of N added with the average rate of manure typically yields maximum profits, regardless of the time of year when manure was applied. The 50 lb rate acts as a "safety net" to compensate for any lack of uniformity of spreading patterns that farmers have to deal with when using manure as a nutrient source.

Table 1. Average corn yields and stalk nitrate tests from 18 different on-farm manure management demonstrations, 1994-97. Cooperators used dairy or swine manure from their livestock operations.

Table 2. Effect of season of manure application on average corn yields for 1994-1995. Crop is no-till corn following soybeans; manure is swine finishing, 3,000 gal./A. surface-applied; fertilizer N spring-applied.

One long-term demonstration looked at various rates of swine finishing manure on continuous corn (Table 3). Even at the 3,500 gal/A. rate, end-of-season cornstalk NO3 was in the excess range after 6 years, showing that the plants had more available N than needed. In crop years 1995 and 1996 this demonstration was changed. Plots that previously received high rates of manure every year received none, to examine how much nutrient carry-over was available. Even with no additional nutrients, yields in the plots were not reduced over the fertilized control, indicating there were still enough nutrients present to sustain crop production for two years.

Demonstration results are publicized through Water Watch, the project newsletter, as well as local news releases and crop management conferences. Information from the demonstrations has also been provided to professional crop consultants and agency technical specialists who assist producers with manure management plans. Surveys show that producers cooperating in the demonstrations, and many of their neighbors, have improved their manure management and often reduced commercial nitrogen purchases, once they are convinced of manure's value.

Demonstration results are also used in manure management training provided for project area producers. (see Manure Utilization Planning and Incentive Education) Overall, the combination of workshops and demonstrations has been so successful in northeast Iowa that a new Iowa State University initiative will be using similar methods in a series of manure management workshops that will be available to livestock producers in all of Iowa's 99 counties over the next three years. For further information on this Statewide Manure Management Initiative, contact your local Extension office.

On-farm demonstrations help producers put their nutrient management plans into action. In northeast Iowa, well planned demonstrations show an immediate corn yield response to moderate amounts of manure applied on fields that have not previously received manure for several years. High to excessive rates also provide enough carry-over residual nutrients for at least two additional years of corn production.

However, producers are still skeptical about their ability to rely on manure nutrient availability, especially nitrogen - and continue to need local demonstrations to convince them that manure nutrient management can be a practical part of their crop planning. Even then most will make management changes slowly or beginning on limited acres to build confidence in new practices. In the end, however, many producers cooperating with the manure demonstrations have eventually made large reductions in purchased fertilizer (and potential pollution) as they gained experience in use of their manure resource.

In Iowa, a long-term series of local, on-farm demonstrations such as those conducted by the Northeast Iowa Demonstration, have so far been the most effective method of providing credibility for the economic and environmental benefits of improved manure nutrient management.

"The manure management demonstration has been helpful to us...before we started this project we were wasting our manure (by not taking enough credit). Now, where we spread manure we take 100 % of the credit the first year." John and Steve Kregel

"I need to watch all production costs. The results from the demonstration on my farm will help me refine my use of purchased fertilizer next year." Tom Hayes

Maquoketa Watershed Project, PO Box 487, Fayette, Iowa 52142

Phone: 319-425-3233, Fax 319-425-3114
E-mail: jrodecap@iastate.edu