The effects of ammonium and nitrate on hydroponic tomato crop have been studied since hydroponics is used as a means of commercial production. In general, it has been found that small proportions of ammonium improve plant growth and yield. However, these studies were carried out with all the roots exposed to these combinations. We tested the hypothesis that separating the half of the roots and exposing this portion to high concentration of ammonium helps to increase growth, yield and fruit quality, without ammonium toxicity symptoms. For this reason, an experiment was conducted which treatments were: 1) 12 meq·liter-1 of NO3-:water; 2) 9 meq·liter-1 of NO3-:3 meq·liter-1 of NH4+; 3) 6 meq·liter-1 of NO3-:6 meq·liter-1 of NH4+; and 4) water:6 meq·liter-1 of NH4+. We used a completely randomly design with five replications. The experimental unit consisted of a tomato plant with split roots in quantities of 50 %. Each part grew up in a container divided into two parts of the same volume, which was filled with red volcano gravel called “tezontle”. Plant height, diameter, root volume and length, fruit yield per plant, fruit quality (polar and equatorial diameter, total soluble solids and titratable acidity) and shelf life were quantified. The results indicated that NO3-:NH4+ ratios had a significant effect (P ≤ 0.05) on all variables, except for root length and tritable acidity.

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