THE INFLUENCE OF K:CA:MG:NA RATIO AND TOTAL CONCENTRATION ON YIELD AND FRUIT QUALITY OF SOILLESS-GROWN TOMATOES: A MODELLING APPROACH

This study describes an application of Systematic Variation method (SV) for optimizing cation proportions (K, Ca, Mg, Na) and the total element concentration of hydroponically-grown tomatoes. A randomized complete-block design with 5 replications (3 plants per experimental unit) was used to compare a factorial combination of 4 proportions of K:Ca:Mg:Na and 2 total concentrations of elements (30 and 60 meq L^-1). Each of the cation proportion treatment was defined by a high proportion of one cation (V=0.64) and an equally low proportion of the others (v=0.12) for a total amount of one (V + 3v = 1). The highest total and marketable yield were obtained in treatment with high proportion of K (avg. 2.94 and 2.72 kg plant^-1, respectively) and Ca (avg. 2.84 and 2.65 kg plant^-1, respectively), while treatments with high proportion of Mg (avg. 2.59 and 2.22 kg plant^-1, respectively) and Na (avg. 2.21 and 2.09 kg plant^-1, respectively) gave the lowest values. The highest incidence of blossom-end rot was observed in treatments with high proportion of Mg and K (avg. 10.8 % and 3.7 % of total yield, respectively). Fruit quality (soluble solids, titratable acidity, EC) improved by increasing the proportion of K and Na and the total concentration. The SV method showed that for maximise the marketable yield it is necessary to include a large amount of K and Ca in the nutrient solution.