Growing systems that recirculate the nutrient solution are attractive, because they couple saving of water and fertilizers with decreased leaching. However, the longer irrigation water is collected and re-used, the higher the concentration of salts. Maintaining the EC of the nutrient solution within (conservative) boundaries requires flushing rates of 30 percent or more, in spite of the recirculating facilities. In order to determine the processes responsible for the reduction of fresh yield, that is often the consequence of growth under salinity stress, we investigated the effect on production (that is, yield quantity and quality) of a tomato crop, of high EC in combination with two water uptake rates. Associated results about leaf growth are presented in the first paper of this series. Climate in two identical glasshouses was controlled to maintain a constant ratio (65 percent) of potential evaporation, while preserving equal assimilation levels. Half of the rows in each house were given a 2 dS/m treatment in the root medium whereas the other half were given 10 dS/m. Leaf growth, canopy development and fresh and dry yield were traced during a whole spring growing season. Parameters of yield that were measured were: total fresh and marketable yield, fruit size distribution, fruit elasticity, fruit dry matter and sugar content, acidity and salinity. Fresh yield was affected by both treatments as follows: high EC significantly reduced yield, whereas the low transpiration treatment only mitigated the effect of high EC. In particular, in the high transpiration treatment marketable yield was reduced by 30 percent (due both to 25 percent smaller fruits and to 20 percent blossom-end rot, BER), whereas in the low transpiration treatment high EC reduced both size and yield by 15 percent, and incidence of BER was only 2 percent. Dry matter and sugar content were higher in the high EC treatments, so that total dry matter yield was the same everywhere, except the high EC, high transpiration treatment, where BER reduced marketable dry matter by 25 percent. Fruit elasticity (both at harvest and after one week) was not affected by any treatment, if differences in size were accounted for. It is concluded that an appropriate use of available tools for manipulating indoor climate, makes it possible to offset the effect of a high salinity of irrigation water. In particular, it is shown that a grower could accept a decrease in yield if there were a sufficient increment in quality of the product.
Stanghellini, C., van Meurs, W. T. M., Corver, F. J., van Dullemen, E., & Simonse, L. (1998). Combined effect of climate and concentration of the nutrient solution on a greenhouse tomato crop. II: yield quantity and quality. Acta Horticulturae, 458, 231-237. https://doi.org/10.17660/ActaHortic.1998.458.27