Thermography study of moderate electrical conductivity and nutrient solution distribution system effects on grafted tomato soilless culture

In recent decades, salinity in the culture of tomatoes has been one of the most studied parameters. This study aimed to evaluate the effect of a moderate increase in salinity, fertigation distribution, and its control using thermography on a soilless culture of grafted tomato. A tomato crop (cv. Ramyle) grafted onto tomato rootstocks (cv. Emperor) was cultivated in coir crop units at the University of Almeria from Nov. 2012 to May 2013. A plot design subdivided with four blocks was used, with salinity values of 2.0 and 2.5 dS·m^-1 in the main plots and fertigation distribution systems with either one (DD1) or four (DD4) drip manifolds in the subplots. The crop productivity was measured using total crop yield, commercial value, and size. The quality parameters in the fruits were not significantly affected. Thermographies were used to aid the control of differential transpiration exerted by salinity. The difference in salinity did not significantly affect the total or commercial production. However, despite being grafted plants, there was a statistically significant effect (P ≤ 0.05) on the fruit size distribution when the electrical conductivity (EC) of the nutrient solution was increased from 2.0 to 2.5 dS·m^-1, with a lower production (16%) of large fruits and an increased production of smaller fruits. The DD₄ system significantly increased large tomato production (22%) compared with DD₁, and the quality parameters in the fruits were not significantly affected. As a result of the improvement in tomato size, the DD₄ distribution system economically offset the required higher initial expenditure compared with the DD₁ system. Thermography was revealed to be a robust, simple, and quick tool for diagnosing the effect of salinity on transpiration.