Population density and nitrogen fertility effects on tomato growth and yield

Greenhouse hydroponics and field experiments were conducted to determine how nitrogen (N) fertilizer treatments affect tomato (Lycopersicon esculentum Mill.) growth, yield, and partitioning of N in an effort to develop more sustainable fertilization strategies. In a hydroponics study, after 4 weeks in nitrate treatments, shoot dry weight was five times greater at 10.0 than at 0.2 mM nitrate. An exponential growth model was strongly correlated with tomato root growth at all but 0.2 mM nitrate and shoot growth in 10 mM nitrate. Root dry weight was only 15% of shoot biomass. In field studies with different population densities and N rates, height in the 4.2 plants/m² was similar, but shoot weight was less than in the 3.2 plants/m². At 12 weeks after planting, shoot fresh weight averaged 3.59 and 2.67 kg/plant in treatments with 3.2 and 4.2 plants/m², respectively. In 1998, final tomato yield did not respond to N rate. In 1999, there was a substantial increase in fruit yield when plants were fertilized with 168 kg·ha^-1 N but little change in yield with additional N. Nitrogen content of the leaves and the portion of N from applied fertilizer decreased as the plants grew, and as N was remobilized for fruit production. Both studies indicate that decreasing N as a way to reduce N loss to the environment would also reduce tomato growth.