Increasing Farm Sustainability through the Use of Cover Crops for Weed Suppression in Non-Transgenic Conventional Cotton

View the project final report

• 2004 annual report
• 2005 annual report

Commodities

• Agronomic: cotton, oats

Practices

• Crop Production: conservation tillage
• Education and Training: demonstration, display, extension, farmer to farmer, on-farm/ranch research
• Natural Resources/Environment: biodiversity, soil stabilization
• Pest Management: allelopathy, integrated pest management, mulches - killed
• Production Systems: general crop production
• Soil Management: organic matter, soil quality/health

The project spans a two year growing season in Hawkinsville, Georgia. In both years the cooperating farmers were asked to plant Black Oats as a cover crop in a conservation tillage system for the purposes of controlling weeds. Three farms were used in the research with each farm having two treatments each and one farm having three treatments. Two farms had treatments where herbicide was applied at a standard rate and timing to control weeds and one treatment where herbicide was applied at a level that would be determined to be economically detrimental to the farmer. One of these farms also had a control treatment where no herbicide was applied. These farms planted a conventional non-transgenic variety cotton. The third farm planted a genetically modified cotton seed and had the same herbicide treatments as the other two farms. During the growing season, weed populations were monitored in each plot. At harvest samples from each plot was collected and analyzed for typical cotton parameters. Analysis of the weed populations across the two years indicated there were treatments that had significant increases or decreases in weed populations that was independent of the treatment. In all treatments except one, the average wed population was less than 3500 weeds per acre. The plots where conservation tillage had been used for 10 plus years had average weed populations of less than 1000 per acre except one treatment where the grass covered the entire plot from planting. The plots where genetically modified cotton was planted had the least number of weeds per acre, but were not significantly different from that of the ten plus year conservation tillage plots with conventional cotton planted. Lint yield from the conventional cotton on ten plus year conservation tillage land verses modified cotton on conservation tillage land showed no significant difference across the two years. However, there was a difference between treatments when the two year average was compared. A complete economic analysis was not conducted, but based on the yield of each plot and the input cost, the use of conventional cotton seed would be more economical than the use of genetically modified seed. However, prior to planting the test plots for a third year, the conventional seed provider stated that the supply of seed was very limited thereby leading to only one test plot being planted.

Tables, figures or graphs mentioned in this report are on file in the Southern SARE office.
Contact Sue Blum at 770-229-3350 or
sueblum@uga.edu for a hard copy.

Introduction

Increasing sustainability of farm operations will require that natural means of weed suppression be incorporated into the farming operation. One alternative is the proper use of cover crops. Cover crops not only supply nutrients (e.g. legumes fix nitrogen and cereal crops recycle nutrients), but also break pest cycles, provide needed soil organic matter, increase available water, and help suppress weeds. Proper use of cover crops may not totally eliminate the use of chemicals, but any reductions will lower the overhead and maintenance cost incurred by the farmer. Prior to transgenic varieties, the difficulty of handling high residue restricted farmers from using cover crops to control weeds and build soil ecosystems. However, improvements in planting equipment now allows the farmer to successfully incorporate high residue cover crops into their farming operation. Additionally, many farmers believe that conventional cotton produces better quality lint over than that of transgenic varieties. Data shows that since the inception of RR cotton, most characteristics used to measure the quality of cotton have been in a range that reduces the price that a farmer can receive for a bale of cotton (Steve Brown, 2003). Drought conditions since the introduction of transgenic varieties may have stressed the cotton thereby lowering the quality of transgenic varieties. This point further increases the need to use a conventional variety of cotton with high residue producing cover crops. If the quality of conventional and transgenic cotton varieties are similar in non-drought years, the use of conventional cotton with cover crops as the means of weed suppression would allow the farmer to be a better environmental steward and potentially be more profitable.

Transgenic cotton including the Round-Up (RR) varieties first appeared in 1997 and now occupies approximately 90% of the cotton planted in Georgia and the other southern states. Within Georgia alone reduced tillage systems are used on approximately 600,000 acres. There is concern that continued reliance on RR cotton will create weed species with resistance to glyphosate (actual Round-Up chemical). Resistant weed species may require potentially more toxic herbicides to be used or growers will have to revert back to using plowing methods as a means of weed control. Either method of weed control will be detrimental in making these southern farms sustainable systems. Therefore the farmer needs an alternative method of weed control other than transgenic cotton varieties which relies or encourages over use of glyphosate.

To demonstrate if a Black Oats cover crop can be used and how effective the cover is in suppressing weed pressure in a conservation tillage system. Additionally the research will compare yield and quality differences in non-GMO modified and GMO cotton.