Manure application with dry spreaders
by Jeffery Lorimor, Department of Agricultural and Biosystems Engineering
Variability 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.
A 6-foot overlap (30 percent of the swath width) does not significantly improve the uniformity (Figure 2).
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.
The distribution for the side-discharge spreader was significantly better, with a coefficient of variation of 66 percent (Figure 4).
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.
© 1997-2004, Iowa State University. All rights reserved.
Page last updated October 5, 2004
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