Title: Impact of irrigation water quality, irrigation systems, irrigation rates and soil amendments on tomato production in sandy calcareous soil
Abstract: Low quality water for irrigation can impose a major environmental constraint to crop productivity. Effects of water quality, irrigation system, irrigation rates, and type of amendment on the yield and quality of tomato plants were investigated during the 2 growing seasons of 2005/2006 and 2006/2007. Two water quality treatments (fresh water with electrical conductivity (EC) of 0.86 dS m^{-1}, and saline water with EC of 3.6 dS m^{-1}), 2 drip irrigation systems (surface and subsurface), 3 irrigation rates (2, 4, and 6 L h^{-1}) and 3 amendment types (clay deposit, and organic matter and without amendment) were applied. The results revealed that the water quality significantly affected both the yield and water use efficiency (WUE). The decreases in yields due to using low quality water were 39.2% and 17.6% for the first and second season, respectively. At a high irrigation rate (6 L h^{-1}), tomato yields were higher and decreased significantly at a low irrigation rate (2 L h^{-1}) in both seasons. When fresh water was used, the amendment type affected both the yield and WUE in both seasons. Clay deposit increased the yield by 11.7% and 15% in the control treatments in the first and second season, respectively. Low quality of irrigation water significantly increased fruit pH, and significantly decreased the other 3 traits (average fruit weight, total soluble solid, and fruit thickness). The influence of salinity was more obvious on average fruit weight than the other 2 traits. Application of clay deposits on sandy soils modifies the distribution of soil water content in the root zone area where water could be retained by clay deposits applied in the subsurface layer. Using saline water increased the salt accumulation in the surface to about 15 dS m^{-1} compared with 5 dS m^{-1} for fresh water treatments. The clay deposit amendments for subsurface sandy soils using good irrigation water show quite valuable effects in storing irrigation water and then enhance the root growth and the yield.