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INTRODUCTION

Differences in cotton growth and productivity occur within most cotton fields in the SE USA Coastal Plain. Many of these differences in nonirrigated fields are due to the amount of water available to the crop during the growing season. Different soil types within a field can hold different amounts of water in the rooting zone, and the lower yielding areas tend to have either too much or too little water than other areas of those fields. Soil-management techniques that increase rainfall infiltration and reduce run-off and soil water evaporation may improve growing conditions in areas prone to water-deficit stress. These techniques may also improve productivity in wet areas of fields by reducing the amount of run-on water from other areas. Since residue-management techniques may influence the variability for yield, they may also have an affect on the amount of variability for fiber properties.

OBJECTIVE

I. Determine how cotton yield and quality are affected by residue management systems on different soil types.

APPROACH

A six-year study was initiated in the fall of 1996 at the Pee Dee Research and Education Center near Florence, SC. Three residue management strategies are being examined using conventional (incorporating plant residues with a disk) and conservation-tillage (leaving plant residues on the surface) practices. The three residue management treatments are continuous cotton only, continuous cotton with a rye winter cover crop, and cotton rotated with corn (corn grown in 1997 and 1999). Treatments are arranged as a randomized complete block with three replicates. All plots are deep tilled with a ParaTill prior to planting. The experimental plots are twelve 38" wide rows that are 400 to 700 feet long so that several soil types are present within each plot. This field was soil mapped by USDA-NRCS soil scientists on a 100-ft grid prior to the initiation of this study. Major soil types in the experimental field are Bonneau sand, Eunola sandy loam, and Norfolk loamy sand which are common to the South Carolina Coastal Plain. The plots are harvested with a two-row cotton picker in 50-ft sections so the effects of these management strategies can be determined for each soil type within each plot. In addition, bolls from the bottom, middle, and top of the canopy were hand-harvested from a 20-ft section of each plot in each soil type and fiber properties from each canopy position were determined. The Agroecology split-landscape study was also planted in cotton in 2000. This long-term study was initiated three years ago to evaluate the economic, ecological, and environmental benefits of new or innovative cropping practices, compared to traditional practices. Treatments used in the split landscape study are shown in Table 1.

RESULTS

The yields of cotton grown with conventional versus conservation tillage averaged over all residue management systems are shown in Table 2. Conservation tillage and conventional tillage did not differ for yield in 1997, which was a good year for rainfall at the Pee Dee Research and Education Center. Conditions were drier in each year thereafter and cotton grown with conservation tillage had higher lint yields than cotton grown with conventional tillage.

Figure 1 shows the effect of the residue-management treatments on conservation-tillage cotton yield for the Bonneau sand and Norfolk loamy sand (data from the Eunola loamy sand were not included because a small number of data points compared to the other two soil types) in the experimental field. The data are averaged over 1998 and 2000 (the two years where cotton was grown following corn). The Bonneau sand is more drought-prone than the Norfolk loamy sand, which explains the lower lint yields of the Bonneau sand. For both soil types, continuous cotton without a winter cover crop (the fallow bar on the graph) had the lowest yield of the three treatments. Continuous cotton grown with a rye winter cover crop had the same yield as cotton rotated with corn (a high residue-producing crop).

Source: Bauer, Frederick, 2000 unpublished data.

Cotton grown with conservation tillage had a longer fiber length than cotton grown with conventional tillage when averaged across the three soil types (Fig. 2). The increase in fiber length was similar for all three soil types (surface tillage by soil type interaction not significant). Surface tillage had no effect on micronaire. Averaged over tillage systems, the soil types did not differ in fiber length or micronaire.

Source: Bauer and Frederick, 2000, unpublished data

Similar types of responses as these were found in the Agroecology split-landscape study. Cotton lint yield was 29% higher with the innovative cropping system than with the traditional cropping system (Fig. 3). A significant portion of this yield increase was probably due to the conservation tillage practices, since lint yield was 15% greater with conservation tillage than with disking in the replicated plot study in 2000 (Table 2). The higher lint yield of the innovative cropping system was associated with substantially less water runoff during rainfall events (see Research Results- Water Quality). Differences between the two sides of the split landscape field for lint yield were greatest on the Norfolk loamy sand and Bonneau sand. The innovative and traditional cropping systems did not differ in fiber length or micronaire (data not shown)

Source: Bauer, Frederick, S. Robinson, 2000 unpublished data.

CONCLUSIONS

Two more years of study are planned before conclusions from the experimental field can be made. The preliminary findings indicate:

Residue management had an affect on cotton yield in drier years, with systems that left considerable amounts of residue on the soil surface resulting in higher yield than systems where the ground was left uncovered.

Soil types respond similarly to residue management for cotton yield and fiber properties. This similarity indicates that variability across fields will not be affected when farmers use different residue management systems. This result also suggests that yield maps generated from fields with one residue management system are predictive of the patterns of yield variability that will occur should farmers switch to another residue management system.

For further information about this research, please contact: Dr. Phil Bauer 843-669-5203 ext. 7250 email

For more information about general managment practices for producing cotton in South Carolina, please visit: Pee Dee REC's Cotton News