Nitrogen form affects yield and taste of tomatoes

Different nitrogen forms in organic or mineral fertilizers affect yield, quality and taste of tomatoes. Tomato plants were grown in a greenhouse for 10 weeks and fertilized with two different organic fertilizers (manure or grass and clover mulch) or with three different mineral nutrient solutions (NO3-:NH4+) ratios 4:1 or 1:4). In an attempt to mimic the nutrient supply of the organic production systems, mineral fertilizers with ammonium as the dominating N-source were combined with two chloride levels. Total nitrogen supply was 650 mg N plant(-1) week(-1) in all treatments. There was no difference in the yield of red tomatoes between the treatments (mean 1.95 kg FW plant(-1)). However, the yield of green tomatoes at the final harvest was significantly higher in the mineral nutrient treatments (mean 1.37 kg FW plant(-1)) compared with the organic treatments (mean 0.88 kg FW plant(-1)). Plant biomass was higher for the mineral nutrient treatments (mean 1.05 kg FW plant(-1)) compared with the organic treatments (0.89 kg and 0.72 kg FW plant(-1) in the manure and the grass and clover mulch treatments, respectively). Significantly higher scores were achieved for sweetness, acidity, flavour and acceptance for the tomatoes grown with the organic or the ammonium-dominated treatments compared with the tomatoes grown with the nitrate dominated nutrient solution. It is suggested that ammonium is an equivalent nitrogen source for tomato plants compared with nitrate and that, when tomato plants are supplied with reduced nitrogen forms such as ammonium or organic nitrogen, an improved tomato fruit taste can be observed. (c) 2005 Society of Chemical Industry.