Effect of controlled drainage/subirrigation on tomato yield and water quality

Controlled drainage/subirrigation has been shown to improve yields and reduce nitrate loss in field crops. Controlled drainage/subirrigation used in conjunction with a high value horticultural crop such as processing tomatoes has the potential for significant economic returns. A four hectare field experiment was established on sandy loam soil. The field was modified to allow the implementation of two water table management treatments, controlled drainage/subirrigation (CDS) and free tile drainage (DR). Volume of tile drainage, concentration of nitrate in the tile drainage water and crop yields were measured. The objectives of this study were to determine the economic and environmental benefits of the CDS system and to obtain practical information on the management of this system at the farm scale. Precipitation was 263.7 mm below normal over the entire year from May, 1995 to April, 1996. The CDS treatment reduced tile drainage volume by 45% even though an additional 78.5 mm of subirrigation water was added to the CDS treatment during the growing season. The CDS treatment reduced nitrate concentration in tile drainage water by 6.3% and total nitrate loss by 50% when compared to the DR treatment. The CDS treatment stored 75 mm more water in the top 120 cm soil profile than the DR treatment. The CDS treatment increased marketable tomato yields by 11%. Thus, the CDS treatment effectively reduced total nitrate loss and improved yields for processing tomatoes.