Influence of Nutrient Concentration and Composition on the Growth, Uptake Patterns of Nutrient Elements and Fruit Coloring Disorder for Tomatoes Grown in Extremely Low-volume Substrate

In order to modify nutrient solution for tomatoes grown in extremely low-volume substrate (ELVS) combined with low-node-order pinching and high-density planting (LN&HD), the effects of nutrient solution concentration and supplemented K and P were investigated. Plant growth, nutrient uptake, and fruit yellow-shoulder disorder were measured in two experiments. Treatments included three nutrient solution concentration levels (0.6, 0.9, and 1.2 dS·m−1 EC) in Experiment 1 and added K or P (EC 0.9+K, EC 0.9+P) and P+K (EC 0.9+P+K) on the basis of Enshi nutrient solution at EC 0.9 dS·m−1 in Experiment 2. Tomatoes ‘CF Momotaro York’ were grown in a 250 mL pot filled with granular rockwool combined with LN&HD. A high-frequency and small-volume fertigation system was used based on the integrated solar radiation amount. In Experiment 1, mineral elemental uptake rate, plant growth and fruit yield increased with increasing nutrient solution concentration, and fruit yellow-shoulder disorder decreased. In Experiment 2, P supplementation treatments of EC 0.9+P and EC 0.9+P+K largely enhanced fruit yield, shoot weight and all nutrient uptake rates. In contrast, yield improvement was not observed at EC 0.9+K, and only K uptake was promoted in K-supplemented treatment. The fruit yellow-shoulder incidence and index tended to decrease in the following order: EC 0.9 > EC 0.9+P > EC 0.9+K > EC 0.9+P+K. In conclusion, it was effective to increase P and K concentrations of nutrient solution on the basis of Enshi nutrient solution formula (EC 0.9 dS·m−1), to maintain optimal tomato vegetative growth, achieve higher yield comparable to that with EC 1.2 dS·m−1, and produce fewer P- and K-deficiency symptoms in the case of ELVS combined with LN&HD culture by a high-frequency and small-volume application method.