Multi-year Multi-rate Demonstrations
of Manure Application for Corn

G. Hanson, E. Palas and J. Rodecap
Agronomy Department, Iowa State University
Northeast Iowa Demonstration Project

S. Brown and G. A. Miller
Iowa State University Extension, 2104 Agronomy Hall

Setting

Livestock is raised on nearly 90 percent of the farms in the four northeast counties of Iowa. In a manure initiative started in 1987, Iowa State University Extension staff helped area farmers determine the nutrient content of solid manure from dairy, beef, and swine feedlots, and also from dairy barn gutters. With the results of over 1,000 manure samples in hand, a project manure management extension specialist was assigned to assist farmers to optimize use of their manure nutrients. It was soon apparent that one roadblock preventing many farmers from taking appropriate manure credits was that they did not know how much manure they were applying to their fields. A set of wheel scales was purchased with funding by five local banks to calibrate manure spreaders. A common estimated application rate had been 10 tons of manure per acre. Calibrated rates from over 100 spreaders showed the average application was 22 tons per acre.

Still, farmers were reluctant to take manure credits - especially for nitrogen. In most cases manure was surface applied. Farmers were unsure how many nutrients were being lost due to volatilization or runoff before spring tillage. How much nitrogen would be available for the first crop? What about second year credit? There also was the issue of uniformity of manure application. Without uniformity, manure credits cannot be taken effectively.

Sampling manure for nutrient content so that it can be applied for maximum benefit to crops is difficult. Although a significant amount of manure is handled as a solid in local dairy and cattle feeding operations, increased popularity of confinement feeding has increased liquid manure storage for most swine operations. Liquid handling makes it possible to better manage the time of application, rates and uniformity; but obtaining a representative manure sample from the storage structure can be a problem. The sample is usually taken when the storage structure is being emptied after mixing, the manure has usually been applied before the laboratory results are back.

Considering these management issues and uncertainties about manure crediting, most farmers are not comfortable relying on manure as a consistent nutrient resource.

In the karst topography of Northeast Iowa, both ground and surface water resources are threatened if manure nutrients are not properly managed. The USDA Northeast Iowa Water Quality Demonstration Project has established a network of demonstrations to thoroughly document nutrient content of various manures, first-year and carry-over availability, sufficiency of modest rates for corn production, and the effects of excess application.

On-farm manure demonstrations for corn production compare various manure resources, nitrogen fertilizer (with and without manure) and check plots. Measurements on the replicated plots include manure nutrient contribution (through manure analysis and spreader calibration), plot yields and soil and plant nitrate nitrogen analysis. New demonstrations are developed annually throughout the project area, and long-term demonstrations are also maintained. Both long-term and short-term manure application demonstrations are designed specifically to address producer concerns about the concentration of manure nutrients and their seasonal availability, control of spreading rates, and other management issues related to optimizing the use of this on-farm resource.

The Burrack-Kregel site was a 10 year manure management demonstration initiated in 1987 by the state-sponsored Big Spring Demonstration Project on continuous corn. Demonstrated was the effect of a fall application of low (1,750 gal.), medium (3,500 gal.), and high (7,000 gal.) rates of swine finishing manure compared to 180 lb./A. applications of commercial N (urea) applied in the fall and spring. A check area had no manure or nitrogen applied. The treatments were replicated three times for eight years (1987-1994). Each treatment area was approximately 30x100 feet. Yields and stalk NO3 tests were hand harvested from the center rows.

The "more is not better" observation was borne out by the demonstration. Average continuous corn yields were identical for 5 years (1989-1994) at 153 bushels per acre on plots receiving 3,500 and 7,000 gallons of manure per acre. The five-year average yield from the 1,750 gallons manure treatment was 145 bushels per acre. The impact of excessive manure application was shown at the end of eight years when the end-of-season cornstalk analysis averaged 8,606 ppm NO3-N (4x excessive) in the 7,000 gallons manure treatment, 4,046 ppm (2x excessive) in the 3,500 gallon manure treatment, and 605 ppm (marginal) in the 1,750 gallon treatment. Similar relationships between the manure treatments were present when the soil was analyzed for P and K, however, soil pH test results were lower following increasing rates of manure application (see graphs).

Graphs of 1987-1996 Burrack-Kregel manure management corn yield and phosphorus.

Area producers showed considerable interest in the Burrack-Kregel site demonstration results, which were distributed annually through project newsletters and extension crop meetings. They began to raise additional questions, "How quickly will a field without manure history respond to manure application?", and "How much carryover nutrients are available to the next year's crop?" In fall of 1994 the demonstration design was changed to address their questions. During crop years 1995 and 1996 neither manure nor commercial fertilizer was applied to the areas which had previously received manure. Instead, 3,500 gallons of swine finishing manure was applied to the check areas and to the areas which had previously received 180 lb./A. commercial N in the spring.

The check areas responded immediately to the manure application, producing yields equal to the fall application of 180 pounds of commercial nitrogen. Likewise the manure application on the previous spring urea treatments produced similar yields, indicating that a modest application of manure would provide sufficient N to the crop the first year of application. The areas which had medium and high rates of manure the previous eight years also produced well the first year with no additional N fertilizer, indicating there was carry-over N from the previous manure applications. The late spring soil nitrate and fall cornstalk nitrate tests added information on the environmental impact of various manure application rates.

The cooperators who provided manure for this demonstration site admitted they were skeptical at first about manure nutrient credits, and followed results for three years before starting to make changes in their own crop/manure management practices. Now, however, they have discontinued starter fertilizer and commercial N following manure application on all of their continuous corn fields, and they have asked the Demonstration Project staff to assist with field demonstrations designed to further explore how much commercial fertilizer can be saved on corn the second year following a manure application. They now hire trucks to move manure to more distant farms, and have contracted with another livestock producer to purchase additional manure to apply to a nearby rented farm. They have commented that the work being done by the Northeast Iowa Demonstration Project provides information they cannot get from any other source, and that, without having local manure demonstration data; they would not be treating manure as a resource for their farm.

Over the last four years manure demonstrations were established on seventeen additional farms using a design similar to the long-term demonstration. Time of application varied (fall, winter or spring) as well as the type, rate and nutrient content of the manure, according to what was available from the cooperating farmer. Spreading rates for manure applications were calibrated and manure samples analyzed for each demonstration to determine nitrogen credits.

Average corn yields and end-of-season cornstalk residual nitrate levels from the seventeen sites are shown in table 1. Based on these results, project staff advise local producers that applying 50 lb. N per acre in addition to a typical manure application should provide sufficient nitrogen for their corn crop. Since manure spreading patterns (uniformity) and nutrient concentrations are not always consistent; the 50 lb. N application will compensate for this variability. They can also expect an immediate yield response from moderate manure applications on fields that have not received manure for several years, while high to excessive rates provide carry-over residual nutrients for the next crop year.

All producers who have cooperated with field demonstrations, spreader calibrations, and manure sampling activities have made adjustments in their manure management and reduced purchases of commercial fertilizer. But the impact of these on-farm demonstrations doesn't stop at the farm gate.

Methods used to transfer manure management results from demonstrations to local practice have included intensive information marketing, one-on-one assistance, and an innovative incentive education workshop program. Through these efforts, results have reached a large audience.

• Self-guided tours of selected demonstrations have allowed farmers to observe manure and nitrogen management options throughout the growing season. Signage plus a mailbox containing brochures with previous demonstration details help visitors understand the manure demonstration.
• A manure management poster has been displayed at more than 25 events attended by over 5,000 people, including 12 locations outside the project area. An average of 250 results brochures and 150 bumper stickers ("Manure Happens * Take Credit") are requested each time the display is used.
• Frequent news releases tailored to the style needed by small community news media, and a project newsletter Water Watch with a bimonthly circulation of 1,700 convey demonstration results to interested local producers.
• A survey conducted by the Demonstration Project in 1995 showed 92 percent of farmers surveyed were aware of the project's Water Watch newsletter and results from N and manure field demonstrations were cited most often as the most useful information it carried.

Farm Services Agency (formerly ASCS-FmHA) offices provided referrals to beginning farmers in the project area for a manure utilization/crop fertility planning demonstration. The Iowa Leopold Center for Sustainable Agriculture also provided funding. An extension manure management specialist worked individually with producers to develop a manure nutrient inventory, calibrate spreaders and sample manure. The program had given these young farmers increased management skills and confidence. Of the 17 who completed the program, only three said they were making fertilizer decisions for their own farms when the program began. By the end, this number had increased to 14.

An innovative incentive education workshop program was designed to reach a large number of producers making more efficient use of staff time and resources. Demonstration results are used to reinforce the technical information provided. Participants learn to analyze and sample their soil resource, set realistic yield goals, develop a manure nutrient inventory, determine manure and legume credits, and prepare nutrient and pest management plans for their own farms. A second-year workshop participants' survey indicates that 92 percent have reduced nitrogen use and 82 percent of those did so by taking manure nitrogen credits. Eighty percent of the surveyed producers indicated they were more involved in soil test interpretation, compared to half before the program began.

There are legitimate reasons why farmers hesitate to rely on nutrient credits from their manure resource, including uncertainties about nutrient content, application rate, and uniformity of spread patterns as well as the timing of application and cost of moving manure given historically inexpensive commercial fertilizer sources. For areas where improved manure management is both an environmental and economic priority, the Northeast Iowa Demonstration Project has shown the steps needed to effectively cause change in management practices. First, a local database of manure analytical results and spreader calibrations is generated to quantify the potential nutrient resource. Second, a long-term series of local, on-farm demonstrations provides credibility for the economic and environmental benefits of improved manure utilization. Demonstration results enhance education programs, but farmers want to observe the demonstrations firsthand, and may still make changes slowly or on limited acres to build confidence.

As farmers become more environmentally aware of manure and try to refine its use they will in turn expect their fertilizer suppliers, crop consultants and custom manure applicators to recognize manure as a resource. Demonstration Project staff have provided training on spreader calibration and manure crediting to crop consultants and ag businesses as a result of farmer-initiated questions. One farmer relayed that he had requested his custom applicator calibrate his spreading rate. The custom applicator had never thought of doing this but complied with the farmer's wishes. A year later the custom applicator returned to the farm and stated calibrating was the best thing he had ever done for his business and he now lets his other farmer customers know what is applied per acre so they too can take credit.

Another positive outcome of the manure demonstration effort has been the farmer-to-farmer dialogue that takes place as a result of the educational outreach efforts. When farmers meet, either at incentive program meetings or at the local coffee shop, they do talk about what has happened with the manure demonstrations and how they save money by taking manure credits. One farmer even wrote a guest editorial for an area newspaper on how developing a manure management plan reduced his commercial fertilizer needs. This peer reinforcement is ultimately one of the best ways to get manure best management practices established on the land.

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