Surface Cover and Biomass in No-tillage Cropping Systems as Affected by Crop Rotation, Winter Cover Crop, and Winter Weeds

Forbes Walker1, Nick Ryan1, Don Tyler1, Jason Wight2, Fred Allen2 and Daniel Yoder1

Biosystems Engineering and Soil Science Department1; Plant Science Department2 University of Tennessee, Knoxville TN

Abstract: The accumulation and maintenance of an adequate layer of surface residue is an essential characteristic of successful no-till systems. The quality and quantity of surface residue varies with cropping and management systems and the time of year. In 2002, a long-term, no-till rotational study was established at the University of Tennessee's Research and Education Center at Milan, Tennessee. The summer crops in this study (maize, Zea mays; cotton, Gossypium sp.; soybean, Glycine max) are rotated with wheat (Triticum aestivum) and hairy vetch (Vica villosa) and compared with a no cover-crop control. In April 2006, surface residue was assessed immediately prior to planting for six common crop rotations: continuous maize, continuous cotton, continuous soybean, 2 year maize-cotton rotation, 2 year maize-soybean rotation, cotton-soybean-maize-cotton rotation. The percentage of residue coverage was assessed visually using a line-transect method and compared with the relative contributions to the residue biomass from previous crops, winter cover crops and winter weeds. Estimates of the organic carbon and organic nitrogen content of the biomass will be made and compared with soil carbon and nitrogen at 0 to 5 and 5 to 15 cm depths. Prior to planting, residue cover (from crop residue and cover crop) was greater than 50 percent for most rotations except for continuous soy and the maize soy rotations that were assessed at 20 and 33 percent cover (respectively) when there were no winter cover-crops. Differences in the quantity and quality of the biomass were observed between treatments. Further samples will be collected after the 2006 harvest and prior to the 2007 planting season.

Background: No-till is the dominant tillage system in Tennessee (Figure 1). Common variations to the recommended 3 year maize-cotton-soybean rotation (Figure 2) include 2 year maize-cotton and 2 year maize-soybean rotations as well as numerous other variations.

Background (continued):

It is hypothesized that in crop rotations will influence the quantity and quality of soil residue cover and thus soil quality. The addition of winter cover crops such as winter wheat and hairy vetch to different rotations could further impact residue quality and quantity.

Research objectives were to determine:

1. The impact of common crop rotations on the quantity and quality of soil residue cover

2. The impact of winter wheat and hairy vetch as winter cover crops on the quantity and quality of soil residue cover

Materials and Methods

Assess pre-plant (April 2006) residue cover and surface biomass from 4 replicates for 6 crop rotations in west TN and 3 different winter cover crops (winter wheat, hairy vetch and no-cover control)

• Estimates of residue cover using line-transect method• From 0.5m2 samples, compare relative contribution of crop

residue, winter cover crop and winter weeds to pre-plant ground cover and residue biomass

• Estimates of percent carbon and nitrogen in different residues from 0.5m2 samples

Preliminary Results - April 2006

• Winter covers significantly increase soil coverage• Significantly more residue coverage in continuous cotton compared

to continuous soy • Significantly lower surface cover of soil in continuous soy (20

percent) and maize-soy (33 percent) rotations compared to other rotations (greater than 50 percent) with winter fallows

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Figure 1. Percentage of Major Crop Areas Planted with No-Till in Tennessee: 1990 to 2004 (Tennessee Dept. of Agriculture)

2004

Soy; 470,000 ha

Maize; 280,000 ha

Cotton; 228,000 ha

Figure 2. Recommended 3 year maize- cotton-soybean rotation

CottonMaize

Soybean

Figure 3. Assessment of residue cover using line transect and biomass sampling methods

Figure 6. View of rotation experiment plots after maize harvest, prior to cotton and soybean harvests, October 2006

Rotation / Year

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Figure 4. Estimates of residue coverage using line-transect method, April 2006

Figure 5. Estimates of residue biomass (dry basis), April 2006

Same letters for same cover crops under different rotations are not significantly different (p = 0.05)

Same letters for same cover crops under different rotations are not significantly different (p = 0.05)

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