Odor and Nutrient Management Newsletter

Spring 2000

Manure application with dry spreaders

by Jeffery Lorimor, Department of Agricultural and Biosystems Engineering

photoVariability is one of the main reasons farmers are reluctant to take full credit for manure nutrients. This problem is generally worse with dry manure than with liquid manure. To fully use manure nutrients, spreaders must meet two application criteria: 1) they must apply the right overall amount, and 2) they must distribute the manure uniformly across the swath.

Research during the past few years has documented the lack of uniformity provided by box spreaders. In 1993, spinner-type spreaders had a coefficient of variation of 50 percent across a 40-foot swath with poultry manure. Reducing the swath width to 30 feet helped significantly. In 1998, research indicated a 30 percent coefficient of variation average for 10 different spreaders and off-center spread patterns for 7 of these 10 spreaders.

Tests of two rear-discharge spreaders with beaters (not spinners) and one side-discharge spreader at Iowa State University in 1999 showed coefficients of variation of 100 and 108 percent for the rear discharge spreaders. Figure 1 shows the distribution for one spreader; the second spreader had a very similar distribution pattern.

figure 1. Spread distribution from a single pass of a rear-discharge dry manure spreader
Figure 1. Spread distribution from a single pass of a rear-discharge dry manure spreader. Notice the 18-foot swath width.

A 6-foot overlap (30 percent of the swath width) does not significantly improve the uniformity (Figure 2).

Figure 2. Spread distribution from rear-discharge dry manure spreader with 12-foot swath width.
Figure 2. Spread distribution from rear-discharge dry manure spreader with 12-foot swath width.

By driving even closer, a more uniform pattern can be achieved (Figure 3). The data in this figure represent a 6-foot swath width (12-foot overlap). Notice that the narrow swath width has increased the overall application rate from approximately 15 tons/acre to approximately 25 tons/acre. Although the uniformity has been improved, many producers would consider a 6-foot swath width to be undesirable.

Figure 3. Spread distribution from a rear-discharge dry manure spreader with 6-ft swath width.
Figure 3. Spread distribution from a rear-discharge dry manure spreader with 6-ft swath width.

The distribution for the side-discharge spreader was significantly better, with a coefficient of variation of 66 percent (Figure 4).

Figure 4. Distribution pattern for side-discharge spreader with 100-foot swath width.
Figure 4. Distribution pattern for side-discharge spreader with 100-foot swath width.

What can you do? If you want to fully use your manure nutrients, you need to check your spreader distribution across the swath, as well as calibrate the total amount of manure it applies. Be willing to take a narrower swath. From Figure 2, it is apparent that small overlap may not be enough to achieve uniform application rates. You may have to experiment to find the swath width that gives an acceptable uniformity; it may mean driving faster to put on less with each pass, while making more passes.

If you achieve uniform application rates and avoid streaks, the payoff is lower fertilizer costs. As always, it is up to you to figure out a way to do a good job and make the system work until better spreaders can be developed.

This article uses some material from another article called Solid manure application: Toward a sophisticated spreader, by Tom Richard and Mark Hanna, ISU Department of Agricultural and Biosystems Engineering.

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Iowa Manure Matters: Odor and Nutrient Management is published by Iowa State University Extension, with funding support from the USDA Natural Resource Conservation Service through Cooperative Agreement No. 74-6114-8-22. To subscribe or change the address of a current subscription, write to Angela Rieck-Hinz, 2104 Agronomy Hall, Iowa State University, Ames, Iowa, 50011-1010 or call 515-294-9590, fax 515-294-9985 or email: amrieck@iastate.edu. Please indicate you are inquiring about the Odor and Nutrient Management Newsletter. The newsletter's coordinators are Angela Rieck-Hinz, extension program specialist, Department of Agronomy, Wendy Powers, environmental extension specialist, Department of Animal Science, and Robert Burns, Department of Agricultural and Biosystems Engineering; the editor is Jean McGuire, the subscription manager is Rachel Klein, the production designer is Beth Kroeschell, and the web page designer is Liisa Jarvinen.

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