AGRONOMY AND SOILS Deep Subsurface Drip Irrigation for Cotton in the Southeast

Lo ng-term cotton (Gossypium hirsutum L.) yield with various irrigation rates and crop rotations, irrigated with subsurface drip irrigation (SSDI) is not known for the US Southeast. A SSDI system was installed in Southwest GA (1998) and maintained for 10 years. t he soil is a tifton loamy sand (Fine-loamy, kaolinitic, thermic Plinthic Kandiudults) and treatments consisted of three crop rotations, two drip tube lateral spacings, and three irrigation levels. Crop rotations were alter nate year cotton (cotton-peanut; Arachis hypogeae L), two years (cotton-maize (Zea mays L.) -peanut), and three years between cotton (cotton-maizemaize-peanut). Drip tube laterals were installed underneath each crop row and alternate crop row furrows. Cotton was not grown in 1999 and 2006. Crops were irrigated daily at 100, 75 and 50% of estimated crop water use. No lint yield difference resulted from crop rotation. Lint yield differences were attributed to irrigation treatments in 4 of 8 years. Lint yields were greatest at the 75% irrigation level compared to 50%, and in 3 out of 4 years compared to the 100% irrigation treatment. Higher lint yield with irrigation also coincided with lower seasonal rainfall totals. Drip tube lateral spacing affected lint yield 4 out of 8 years. Across all years, yield data indicates that alternate row furrow lateral spacing is as effective as every-row lateral spacing. Some fiber qualities were affected by ir rigation, lateral, and rotation treatments, but these effects were small and inconsistent. Subsurface drip irrigation in the Southeast is optimal at the 75% irrigation level with tubing in alternate row furrows.