EFFECTS OF NITROGEN FERTILIZATION ON GROWTH, LEAF NUTRIENT CONCENTRATION AND PHOTOSYNTHESIS IN THE PEACH CV. REDHAVEN GRAFTED ON THREE ROOTSTOCKS

One year old peach plants of the cv. Redhaven grafted on the rootstocks ID 20, GF 677 and MRS 2/5 were maintained in a greenhouse and irrigated once per day for a period of 82 days with 125 ml of modified Hoagland's nutrient solution containing 1 mM N in the form of potassium nitrate, ammonium nitrate, ammonium sulphate and urea. The rootstock MRS 2/5 reduced significantly fresh weight of scions. Furthermore, shoot/root ratio of Redhaven on MRS 2/5 was smaller than on the ID 20 rootstock. Nitrogen content of basal leaves of Redhaven on MRS 2/5 tended to be lower than on the other two rootstocks. Besides, some differences were recorded among treatments in the concentrations of the rest nutrient elements. Net photosynthesis tended to be lower with the MRS 2/5 rootstock and under potassium nitrate nutrition. Redhaven on MRS 2/5 had higher transpiration rate and lower water use efficiency than on the other two rootstocks. Stomatal conductance was lower at potassium nitrate than at ammonium sulphate or urea treatments.