Is That
Really Cotton?

 Sidney Belcher, Michael Patterson, Charles Burmester, and Robert Goodman

Cotton in the southeastern United States has traditionally been grown in conventional rows spaced 36 to 40 inches apart. Recently, cotton growers in Alabama and other southeastern states have tried producing in rows spaced seven to 10 inches apart, termed ultra-narrow row (UNR). Ultra-narrow row cotton acreage nationwide has increased rapidly from 3,500 in 1996 to 200,000 acres estimated in 1999. Alabama farmers planted about 5,000 acres of UNR cotton in 1997 and 25,000 acres in 1998.

Farmers are interested in this system for several reasons. First, equipment and labor cost reductions may be possible. Second, under some conditions yield increases may result from more evenly spaced plants. Third, the UNR system may be well-suited for marginal cropland. Transgenic cotton varieties, plant growth regulators, and weed control using over-the-top herbicides make this system manageable, and for the first time, a commercial possibility. UNR cotton production in the Southeast was investigated in the past, but was not adopted due to a lack of weed control and plant growth regulation options. Short (less than 32 inches tall), weed-free cotton is necessary in UNR to increase yield and to ensure efficient harvesting with machines that are currently available.

Plant populations for UNR cotton range from 120,000 to160,000 plants per acre, roughly double to triple that for conventional row (CR) cotton (35,000 to 45,000 plants per acre). UNR cotton is usually planted with a grain drill and harvested with a cotton stripper equipped with a broadcast head, while CR cotton is planted with row unit planters and harvested with spindle pickers.

Close row spacing of UNR cotton requires the use of broadcast, over-the-top herbicide sprays. Consequently, post-directed sprays (applied to the soil and base of the plant) and cultivation are not alternatives in UNR cotton. This is important because it limits the types of herbicides that may be used in UNR cotton, and eliminates mechanical cultivation as a weed control alternative.

Field trials were conducted in 1998 and 1999 at the Tennessee Valley Research and Extension Center (TVREC) in Belle Mina and the Wiregrass Research and Extension Center (WREC) in Headland. Two row spacings (CR and UNR), two plant growth regulator programs (high and low level), and two weed control programs (preemergence plus postemergence and postemergence only) were evaluated in all possible combinations (eight treatments) of these factors. Preemergence (PRE) treatments were applied prior to cotton emergence from the soil while postemergence (POST) treatments were applied after plant emergence. All trials were conducted in a no-till system and managed according to current Alabama Cooperative Extension System recommendations.

Weed control at both locations was maintained in the good to excellent range (80 to 100% control) and plant growth regulator application decisions were made by taking current and future environmental factors into account (i.e. soil moisture, plant growth, precipitation chances, etc.). Grower-type management was used to simulate what growers would experience in the field. Paymaster 1220 BGRR cotton (a transgenic variety allowing POST application of Roundup Ultra herbicide) was planted in both years at both locations. (Paymaster 1220 BGRR cotton is a registered trademark of Paymaster Cotton Seed, 144 South St., Spanish Village Suite B, Tupelo, MS 38801.) The plots at TVREC were not irrigated while plots at WREC received small amounts of irrigation to supplement rainfall both years.

Results of the study show that good to excellent weed control can be maintained in CR and UNR cotton using a PRE-plus-POST or a POST-only weed control system. However, at WREC for both years and at TVREC in 1999, the PRE-plus-POST systems resulted in taller plants with more total nodes. Cotton in the PRE-plus-POST system outcompeted weeds more readily than cotton in the POST-only system because of the “growth window” (lack of weed pressure) afforded the cotton with the PRE-plus-POST system.

Yields were not significantly different between CR and UNR systems at TVREC, but UNR had greater yields than CR cotton at WREC (see table). Overall production costs (variable and fixed costs) were slightly higher for UNR cotton than CR cotton at both locations. Profits were greater for UNR cotton at the WREC due to higher yields in the UNR system while each system essentially had the same profit at TVREC (see table). PRE-plus-POST weed management systems provided better economic returns than POST-only systems at TVREC while lower level plant growth regulator treatments also provided better economic returns at TVREC (see table). At WREC, the best economic return for both UNR and CR cotton was provided by a POST-only weed management system using the higher level plant growth regulator treatment.

In these studies, cotton production costs were not lowered by switching to the UNR system, and higher yields with UNR appear necessary to increase profits over CR cotton. Results from these two locations indicate that soil type and length of growing season may be important factors to consider before starting UNR cotton production.