Tomato has the utmost economic importance in the world’s food crops. The foremost challenge in the world of agriculture is to sustain the continuously growing global population, and it is becoming more and more difficult due to climatic change, as this imposes further abiotic stress. In irrigated cropland, salinity stress is the leading factor that causes reduction in crop quantity and quality. Nitrogen is one of the most limiting nutrient in crop production systems, especially for the high nitrogen demanding crops like tomato. Evaluation of the effects of irrigation water quality and fertilization on soil salinity and crop yield is necessary to plan, manage and implement the irrigation and fertilization schemes under different soil and climatic conditions. Different analytical and numerical models have been developed to predict water flow and solute transport in the vadose zone. Model predictions can be very helpful in decision making to plan and manage different irrigation and fertilization schemes.

A greenhouse pot experiment was performed to evaluate the interactive effect of irrigation water salinity and nitrogen application rates on tomato growth, yield, and fruit quality. The data collected from this experiment were used to calibrate and validate the HYDRUS-1D model. The model simulates water flow, solute and heat transport in vadose zone soil. The HYDRUS-1D positively simulated drainage flux, soil water storage, root zone salinity, as well as yield reductions due to salinity stress based on root water uptake. After successful calibration and validation of HYDRUS-1D, the model was used to investigate interactive effects of various levels of irrigation salinity and nitrogen application rates on tomato yield, nutrients uptake by tomato plants and nitrate leaching below the root zone. Both irrigation water salinity and nitrogen application rates significantly affected the crop yield. Use of potable water is recommended at least once during a growing season to leach the salts below the root zone at or before the flowering in order to avoid/delay the salinity buildup and minimize yield loss. Nitrogen application at or below the rate of 300 Kg/ha is recommended to avoid both the environmental pollution and human health risks.