Nitrogen nutrition of greenhouse pepper.: II.: Effects of nitrogen concentration and NO3 : NH4 ratio on growth, transpiration, and nutrient uptake

The objective of this research was to study the effects of N concentration and N-NO3 : N-NH4 ratio in the nutrient solution on growth, transpiration, and nutrient uptake of greenhouse-grown pepper in a Mediterranean climate. The experiment included five total N levels (0.25 to 14 mmol.L-1, with a constant N-NO3 : N-NH4 ratio of 4) and five treatments of different N-NO3 : N-NH4 ratios (0.25 to 4, with a constant N concentration of 7 mmol.L-1). Plants were grown in an aero-hydroponic system in a climate-controlled greenhouse. The optimum N concentrations for maximum stem and leaf dry matter (DM) production were in the range of 8.0 to 9.2 mmol.L-1. The optimum N-NO3 : N-NH4 ratio for maximal stem DM production was 3.5. The optimum value of N concentration for total fruit DM production was 9.4 mmol.L-1. Fruit DM production increased linearly with increasing N-NO3 : N-NH4 ratio in the range studied. The N concentration, but not N source, affected leaf chlorophyll content. Shorter plants with more compacted canopies were obtained as the N-NO3 : N-NH4 ratio decreased. The effect of N concentration on transpiration was related to its effect on leaf weight and area, whereas the effect of a decreasing N-NO3 : N-NH4 ratio in reducing transpiration probably resulted from the compacted canopy. Nitrogen uptake increased as the N concentration in the solution increased. Decreasing the N-NO3 : N-NH4 ratio increased the N uptake, but sharply decreased the uptake of cations, especially Ca.