The effects of N-NO3: N-NH4 ratios and calcium concentration of the nutrient solution on the growth parameters and partitioning of nitrogen and calcium in tomato plants (Solanum lycopersicum L.)

Abstract

Calcium (Ca) and nitrogen (N) are essential elements for plant growth; however, the N form ratio in the nutrient solution affects plant growth as well as the uptake and partitioning of other nutrient elements differently. This experiment was conducted to determine the effects of different N-NO3: N-NH4 ratios and calcium levels on calcium movement, partitioning, and N metabolism in tomato (Solanum lycopersicum) plants. Nitrogen was applied at four N-NO3: N-NH4 ratios (NR1 = 100:0, NR2 = 75:25, NR3 = 50:50, NR4 = 25:75) and Ca at three levels (80, 160, and 320 mg/l) using hydroponic culture. A factorial experiment was conducted in a greenhouse at the Isfahan University of Technology Research Center using a completely randomized design with four repetitions, three plants in each replication. The results showed that the Ca application decreased shoot length, but increased shoot diameter. Elevation of Ca concentration in the nutrient solution by 320 mg/l Ca treatment increased total amino acid, protein, yield, and Ca content of the fruit, but suppressed the nitrogen content of the shoot, root, and fruit. The highest nitrate and ammonium contents of tomato plants were in NR1 and NR2 treatments, respectively. With increasing the level of Ca, the concentration of Ca increased in the apoplast and xylem sap, but decreased in the symplast. The results showed that the NO3: NH4 ratio significantly affected the growth and calcium partitioning of tomato plants. The NO3: NH4 ratio of 75:25 corresponding to 320 mg/l of Ca improved yield and Ca movement to the distal of tomato fruit, resulting in preventing blossom-end rot and the best fruit quality.