Salt and irrigation management of soil-grown Mediterranean greenhouse tomato crops drip-irrigated with moderately saline water

Five integrated experiments, irrigated with water of moderate salinity (about 1.6 dS m−1), were conducted in an Spanish Mediterranean greenhouse to provide a better insight into soil salt accumulation processes in tomato crops and how to leach away these salts by irrigation both during and outside the cropping period. Salts (mostly chloride and sodium coming from the irrigation water) accumulated in the soil wet bulb leading to soil solution electrical conductivities (ECSS) of about 6 dS m−1 or higher during the second half of the crop cycles. During the first phases of these tomato crops it appears to be advisable to apply the crop evapotranspiration (ETc) requirements or slightly higher rates (1.1 ETc). Subsequently, before salts accumulated reach hazardous levels, it is necessary to over-irrigate with a leaching fraction to avoid further salinity increments. Moreover, crop water requirements must be applied with a single daily irrigation, rather than several shorter ones. After the cropping period, the application of 60–70 mm of irrigation water leached away most of the accumulated salts and led to ECSS slightly below 3 dS m−1, considered appropriate for planting a new crop. This amount of water, which has to be adapted to the soil salinity content and characteristics, supplied with daily irrigation rates of about 3–10 mm d−1, led to lower ECSS values, compared with higher irrigation rates. Moreover, the application of crop water requirements with water (11–33% of the irrigation rate) and nutrient solution, instead of nutrient solution over the whole event, substantially reduced the total fertiliser supplied and the concentration of the main nutrients in the wet bulb, but did not negatively affect the biomass, productivity or fruit quality of tomato crop. However, this fertigation strategy requires low-cost, fast monitoring systems of water and nutrients in the soil and/or the plant