Low ammonium/nitrate ratio for high tomato yields and high fruit quality

The effect of ammonium/nitrate ratio on pH controlled nutrient flow solutions on yield and quality of tomato (Angela variety) was studied. Six nutrient solutions of _NH4-N/ (_NH4+NO3)-N at 6 meq N/l with different ratios: 0, 10, 20, 20, 30, 50 and 100% were tested in an experimental greenhouse in Israel. The pH of all treatments was kept uniform and constant around 6.8 by using surface flow nutrient solutions, the chemical composition of the solutions is described in Table 1. Each of these six tested treatments was replicated four times in randomized blocks. The highest marketable yields (4.06 kg/plant) were obtained from the 0 _NH4-N(100% _NO3) treatment, and no considerable decrease in yield was observed in the 10-30% _NH4-N treatments (Figure 1). Significantly lower yields were measured in the 50% _NH4-N(2.99 kg/plant) and 100% _NH4-N(1.63 kg/plant) treatments, due to a reduction in the number of fruits per plant and reduction in average fruit weight. The high ammonium treatment had a detrimental effect on the vegetative development of the plants: reduced leaf area, thinner stem, smaller inflorescence and reduced number of flowers. Plant chemical composition was affected by high ammonium treatments: more N and less K, Ca and Mg were detected. The application of ammonium-N (_NH4-N) at 10-50% in the nutrient solution increased the percentage of high quality fruit and decreased the percentage of soft fruit after 8 days of storage at 18º C. Low concentrations of _NH4-N at 10-30% had no detrimental effect on tomato yield, but effectively improved tomato quality after storage.

Table 1. Chemical composition of nutrient solutions used in the experiment.