Yield and blossom-end rot of tomato as affected by salinity and cation activity ratios in the root zone

Tomato plants were grown in rockwool slabs under glasshouse conditions at different salinities (3-9 mS cm(-1)) and times of the year to assess the possibilities for improving the taste of tomato fruit without reducing fruit quality in other respects. Various salts and combinations of salts (comprising Na, K, Ca, Mg, Cl, NO3-N, P and SO4-S) were applied to increase the salinity in the root zone. Yield was reduced by increased salinity due to reduced fruit size whereas the percentage fruit dry matter increased. Blossom-end rot was affected by the various nutrient elements applied to increase the salinity. The ion activity ratios a(k)/root a(Ca)+a(Mg) and a(Mg)/a(Ca) in the root zone seem to be crucial and more important than the salinity for the development of both internal and external blossom-end rot. The higher the ion activity ratios, the higher is the risk of blossom-end rot. The incidence of internal blossom-end rot exceeded that of external blossom-end rot in spring and autumn.