Spring 2004
Managing corn and soybean residue with manure application
by Mark Licht and Mahdi Al-Kaisi, Department of Agronomy
Crop residue is important to soil and water quality and helps improve soil structure, infiltration and fertility. Also, crop residue reduces soil erosion and surface water runoff. Therefore, balancing residue cover on the soil surface and applying livestock manure are vital to improve soil productivity and environmental quality.
Complete residue
cover can reduce soil erosion due to surface runoff significantly (up
to 98 percent), compared to an unprotected soil surface. To meet conservation
compliance requirements, a standard of at least 30 percent residue cover
must remain on the soil surface after planting. In some cases, disc-covered
manure application can reduce residue cover to below 20 percent, depending
on how fragile the crop residue is. The type of manure application equipment
used can significantly affect the amount of residue cover remaining on
soil surface.
The results presented were obtained from a manure management study conducted
in seven counties in Iowa. In the study, residue cover was estimated after
the application of liquid manure at four different rates with three different
types of manure applicators. The target application rates were 0, 2000,
3000, and 4000 gallons per acre. As the application rate increased, the
applicator speed was reduced. The manure applicators used consisted of
a disc-covering unit, a shovel incorporator, and a slot-injector manure
applicator. The disc-covered applicator utilized discs to cover the manure
that was applied directly on the soil surface (Figure 1). The shovel incorporator
and the slot injector applicators placed the manure below the soil surface
(Figures 2 and 3). In this study, the disc-covered manure applicator was
used on corn stalks and all three applicators were used on soybean stubble.
 |
 |
 |
The disc-covered applicator under soybean stubble reduced residue cover by an average of 61 percent more than under corn stalks (Figure 4). This significant difference in remaining residue cover can be attributed to the relatively higher amount of corn residue compared to soybean residue. The difference also can be attributed to the nature of each crop residues. Soybean residue is generally more fragile than corn residue; therefore, more soybean residue will be incorporated in the soil with disc covers than corn residue.
The type of application equipment also had a significant impact on the amount of residue remaining after manure application (Figure 5). Disc-covered manure application has shown to reduce soybean surface residue by 73 percent compared to residue reductions resulting from manure applications with the shovel incorporator and slot injector of 66 and 22 percent, respectively. Disc-covered applicators were more aggressive in overturning soil and residue to cover the applied manure. The shovel incorporator had more visible disturbance due to the shovel mixing of the applied manure with the soil. On the other hand, the slot injector was less disruptive to surface residue because it applies the manure below the soil surface.
The rate of manure application had a relatively smaller impact on corn and soybean surface residue cover. However, the rate of manure application can impact residue cover depending on the types of both the manure applicator and crop residue. Under corn residue, disc-covered application at a higher application rate and at a lower application speed significantly increased the amount of residue cover remaining after manure application than the low and optimal application rates (Figure 4). This result can be attributed mainly to the lower application speed, which causes less soil and residue disturbance. Similarly, soybean residue cover after disc-covered application resulted in a significantly lower residue cover for the low application rate compared to the high application rate (Figure 5). However, application rate did not cause a significant reduction in soybean surface residue due to the use of the shovel incorporator nor slot injector applicator because these methods are less disruptive than disc-covered applicators.
Effective manure application and residue management can be combined to improve both soil productivity and environmental quality. The slot injector applicator disturbed the minimum amount of soybean surface residue while applying manure at high rates. Under corn residue, the disc-covered manure applicator left more than 30 percent residue cover, therefore meeting conservation compliance requirements.
