Effects of NH4 and NO3 Nutrition with and without pH Adjustment on Tomato Growth, Ion Composition, and Water Relations1

Fertilization of tomato ( Lycopersicon esculentum Mill.) in solution culture with NH 4 -N resulted in reduced shoot and root concentration of Ca, Mg, K, P, and NO 3 , increased leaf and root resistances to water flux, and decreased water use efficiency as compared to plants cultured with NO 3 -N. Solution adjustment to pH 6.5 decreased shoot/root fresh weight ratio with both N forms; decreased leaf diffusive resistance and water stress but increased root resistance to water flux and shoot NH 4 concentration under NH 4 -N nutrition. Solution pH had little effect on tissue ion concentration.