SDI installation for evaluating crop row direction and lateral offset distance
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Maintaining crop rows in subsurface drip irrigated (SDI) fields at precisely the same relative locations to the drip laterals, year after year, is difficult. In 2005, an elaborate SDI system was installed to determine the effects on cotton production of horizontal distance of crop rows from SDI laterals, as well as perpendicular orientation of crop rows to laterals at lateral spacings of 0.75, 1.0, and 1.5-m. Additional factors included maximum irrigation capacities of 5 and 7.5 mm/d and crop row spacings of 0.75-m and 1.0-m. Increasing crop row to SDI lateral offsets caused increased differences in cotton lint yield between pairs of rows irrigated by laterals installed in alternate furrows. Cotton yields from crop rows closest to the lateral largely compensated for reduced yield of rows farthest from the SDI lateral, however, average yields of row pairs declined from 1755 kg/ha to 1616 kg/ha as offsets increased from zero to 380 mm in 0.75-m crop rows. Cotton lint yield from crop rows planted perpendicular to drip laterals were significantly reduced by increasing lateral spacing from 1923 kg/ha at 0.75-m to 1762 kg/ha at 1.5-m when averaged across row spacing and irrigation capacity. There was no difference in average cotton yield between traditional (SDI in alternate furrow, row parallel to lateral, and zero offset) and perpendicular row to SDI lateral plantings with laterals spaced at 1.5 m (1755 kg/ha verses 1721 kg/ha, respectively). Knowledge of crop response to SDI lateral positions and orientations could improve rainfall and irrigation water use effectiveness.
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