UPTAKE CONCENTRATIONS OF A TOMATO CROP IN DIFFERENT SALINITY CONDITIONS

In the near future, it is likely that closed soilless growing systems will be increasingly adopted in Mediterranean countries because they reduce water and fertiliser use, and appreciably reduce nutrient loss to the environment. However, closed systems increase the salinity of the circulating nutrient solution through the progressive accumulation of ions not required by crops and/or applied in excess of crop requirements. Additionally, it is necessary that nutrients be added to the solution according to crop absorption to avoid fluctuations of nutrient concentrations in the circulating solution. To obtain information for the management of circulating nutrient solutions in soil-less systems in a Mediterranean environment, an experiment was conducted with tomato during the 2002-03 growing season. Five different salinity treatments (2.5, 4.0, 5.5, 7.0 and 8.5 dS m^-1 in the drainage solution) were compared. The first treatment was the control, the higher salinity levels were obtained by adding NaCl. Total aerial dry matter production, and the absorption of macronutrients and of Na and Cl were measured for each treatment. Uptake concentrations of the macronutrients, and Na and Cl were determined for each treatment. With increasing salinity, both dry matter production and nutrient uptake tended to decrease, while Na and Cl uptake increased. An antagonistic effect of NaCl on K and N uptake was observed. For the other nutrients, no antagonistic effects were observed with the decreases in uptake being proportional to the decrease in dry matter production. Uptake concentrations for each nutrient were almost constant with increasing salinity except for K, Na and Cl. With an increase of 1 mmol L^-1 of NaCl in the circulating solution, the uptake concentration of Na and Cl increased by 0.06 and 0.068 mmol L^-1, respectively, and that of K decreased by 0.018 mmol L^-1.