Larry M. Curtis

Subsurface Drip Irrigation Placement and Cotton Irrigation Water Requirement in the Tennessee Valley

Fluctuations in dryland cotton yield in the Tennessee Valley region of northern Alabama are common and are usually related to irregular drought periods during the growing season. Subsurface drip irrigation (SDI) has gained popularity as a water delivery system for small, irregular-shaped cotton fields. A seven-year study was conducted with the objective to determine the response of seed cotton yield to SDI tape orientation relative to crop row direction and different irrigation rates under dryland conditions of the Tennessee Valley. Seven treatments were tested in a randomized incomplete block design which consisted of three irrigation treatments (33%, 66%, and 99% pan evaporation), two SDI tape orientations (parallel and perpendicular), and a dryland control. All SDI treatments produced yields significantly higher than non-irrigated, dryland cotton in four out of seven years. Maximum yield was obtained at a median pan evaporation water replacement value of 74%. No statistical differences were observed between SDI tape orientations on seed cotton yield in all years except in 1999 when parallel out yielded perpendicular at lower irrigation rates. Results confirm the long-term efficacy of supplemental irrigation to increase seed cotton yield irrespective of SDI tape placement during sporadic periods of drought. These results are applicable only for fields with the same soil type or with similar water movement characteristics.

Precision Fertilization Using Sub-Surface Drip Irrigation (SDI) for Site-Specific Management of Cotton

Results are presented for a first year study that investigates different fertigation treatments for cotton produced using precision agriculture in the Tennessee Valley of Alabama. The study evaluates the timing and placement of soluble nitrogen and potassium (K2O) fertilizer on cotton using four different fertigation treatments and a non-fertigated control irrigated with sub-surface drip irrigation (SDI) tape. The pressure-compensating SDI product was installed in 2005 using an auto-guidance system to ensure all tape runs are precisely located parallel and 80 inches apart. The experimental plots consist of four replications of five eight-row treatments that compare four fertigation management scenarios and one conventional side-dress treatment. Each of the resulting twenty treatment plots has eight 360-foot rows of cotton on 40-inch row spacing, with SDI tape buried approximately 15 inches between every other row of cotton. The response to treatments is quantified by measuring yield, quality, and nutrient uptake of the cotton. Results show that fertigated cotton yields were higher than the non-fertigated control, with higher yields observed in the three treatments receiving fertigation within 50 days of square. The two highest yielding treatments also received 20 and 40 pounds, respectively, of pre-plant surface nitrogen and potassium. Fertigated cotton yields averaged 3.0 bales per acre compared with 2.6 bales per acre for the non-fertigated control and 2.2 bales per acre in a nearby sprinkler-irrigated study.

Sub-surface Drip Irrigation-Fertigation for Precision Management of Cotton

Four years of field research are presented for a subsurface drip irrigation study installed at the Tennessee Valley Research and Extension Center in northern Alabama in 2006. Study objectives are to evaluate the effect of four precision fertigation management scenarios and a non-fertigated control on cotton yield, nutrient uptake, and lint quality. Approximately 7,500 feet of SDI tape and four positive displacement liquid fertilizer injectors were used to evaluate four replications of five nutrient timing treatments in a randomized complete block design. Each of the twenty treatment plots was made up of eight, 345-foot rows of cotton on 40-inch row spacing, with drip tape between every other row of cotton. In 2006, fertigated cotton yields were significantly higher than the surface-applied control. In 2007 and 2008, however, yield in surface-applied control was significantly higher than the fertigated treatments. Higher non-fertigated control versus fertigated yields in 2007 and 2008 were possibly due to beneficial downward movement of surface-applied fertilizer as a result of early season rainfall in 2007 and the leaching of fertigated nutrients beyond roots zone in 2008 after heavy seasonal rainfall. In 2009, overall yields in all treatments were lower and there was no significant difference between treatments. Fertigated cotton yields averaged 3.0, 2.9, 3.5, and 2.0 bales per acre and the control yields averaged 2.7, 3.1, 3.9, and 1.7 bales/acre in 2006, 2007, 2008, and 2009, respectively. Generally, surface sidedressing enhanced nutrient uptake over fertigation but none had a direct effect on cotton fiber quality. Results of this study indicate that surface sidedressing and fertigation are not mutually exclusive under rainfed cotton production; and observed response to SDI fertigation appears related to the amount and distribution of rainfall during the growing season.