Effects of nitrate‐, ammonium‐, and organic‐nitrogen‐based fertilizers on growth and yield of tomatoes

Mineral and organic fertilizers contain different forms and amounts of nitrogen (N), which can affect yield and product quality. The aim of this study was to determine appropriate amounts of N applied as nitrate (NO₃⁻), ammonium (NH₄⁺), and organic N (a mixture based on chicken manure) for optimal growth and quality of tomatoes. A pot experiment with sand as substrate was established in a greenhouse with six‐week‐old tomato plants (Lycopersicon esculentumMill. cv. “Armada”). Nitrogen was applied in nutrient solutions at different NO₃⁻: NH₄⁺ratios combined with different chloride levels (NO₃⁻‐dominated, NO₃⁻= NH₄⁺at low Cl–, NO₃⁻= NH₄⁺at high Cl–, and NH₄⁺‐dominated, respectively) or as organic N at four N‐application rates (250, 500, 750, 1000 mg N plant–1week–1). No significant differences in shoot biomass and yields of red tomatoes were observed between NO₃⁻‐ or NH₄⁺‐fed plants. Nitrogen rates above 750 mg N plant–1week–1did not significantly increase marketable fruit yield, but enhanced shoot‐biomass production. The NH₄⁺‐N‐dominated treatments (which also had high Cl–concentrations) showed increasing incidence of blossom‐end‐rot (BER)‐infected fruits. In the organic‐N treatments, shoot‐biomass production and yields were lower than in the inorganic‐N treatments, but fruit quality was good with few BER‐infected fruits. The results show that with a total N supply below 750 mg N plant–1week–1, NH₄⁺can be used as equivalent N source to NO₃⁻, resulting in equivalent yields of marketable fruit under the conditions in this experiment.