Effects of nitrogen form, nighttime nutrient solution strength, and cultivar on greenhouse tomato production

Higher greenhouse tomato (Lycopersicon esculentum Mill.) yield is obtained by using 25% of NH4-N in solution compared to using NO3-N as the sole nitro gen (N) source. However, blossom-end rot (BER) may occur in tomato fruit wh en NH4-N was present in nutrient solutions. High nutrient solution strength s improve tomato fruit quality, but can also increase BER. Two NH4-N concen trations in solution (0 and 25%), and two nighttime solution strengths (NSS ) (1X and 4X Steiner solution strength applied at 7 p.m.) were used to grow five indeterminate type greenhouse tomato cultivars: Caruso, Jumbo Match, Max,, and Trust. A significant interaction occurred between NH4-N concentra tion and NSS factors: 0% NH4-N and high NSS increased marketable yield and fruit:whole plant ratio, and reduced BER. In contrast, a concentration of 2 5% NH4-N and high NSS reduced marketable yield and the fruit:whole plant ra tio, and increased BER incidence. Max, Match, and Trust tomato cultivars pr oduced high marketable yield and high dry weight of stem and leaves,:but: w ere susceptible to BER. Use of NH4-N in solution reduced vegetative growth, and high NSS increased stem and leaf dry weight of the tomato plants. Frui t firmness was greater for the Max cultivar, and was unaffected by NH4-N an d NSS at the mature green, breaker, and red ripe fruit development stages. However, at the fully ripe stage, fruit firmness was higher with high NSS a nd with 25% NH4-N.