FEASIBILITY OF CYCLIC REUSE OF SALINE DRAINAGE IN A TOMATO COTTON ROTATION

Use of saline drainage water for crop irrigation has been proposed as a strategy to reduce drainage volume and conserve good quality water. Over a 6-yr period, two cyclic drainage-water reuse practices were tested in a 3-yr rotation of processing tomato (Lycopersicon esculentum L.) and cotton (Gossypium hirsutum L.). In both practices, drainage water (EC(i) = 7.4 dS m(-1) and 0.74 mmol L(-1) B) was applied to processing tomato after first bloom to take advantage of salt-induced enhancement of fruit quality and increased crop salt tolerance at later developmental stages. In one practice, drainage water was also applied to the following cotton crop after thinning. Nonsaline water was used for irrigation at all other times and throughout for the control. When saline water was applied once every 3 yr, yields of both crops were unaffected. Tomato yields were generally lowest when saline water was applied 2 out of 3 yr, but saline water improved tomato fruit quality by increasing (o)Brix in most years. Changes in soil chemical and physical quality may limit long-term reuse. Both B and salts accumulated in the soil over time, particularly at depth (60-140 cm), whereas Se was more readily leached and showed greater fluctuations in the rootzone with irrigation treatment. Calculations using reclamation formulae estimated that for low B drainage water, the amount of drainage wager used exceeded that of nonsaline water needed to return soil EC(e) to control levels, resulting in significant water savings. For high B drainage water, more than twice the amount of nonsaline water was needed to fully reclaim the profile than was saved by reuse. However, moderately B-tolerant crops could be successfully grown during the reclamation period, making cyclic reuse for at least 6 yr an attractive option for growers facing limited supplies of nonsaline water supplies, or as a means to reduce effluent volumes.