INCREASING YIELD AND FRUIT QUALITY OF 'SAYER' DATE PALM WITH APPLICATION OF OPTIMUM LEVELS OF NITROGEN, PHOSPHORUS AND POTASSIUM

Date palm (Phoenix dactylifera) is one of the most important horticultural crops in Khuzestan Province. Among the date palm cultivars in this province ‘Sayer’ is one of the most commercial cultivars. The low annual average of yield and fruit quality is a problem for date growers. On the other hand, most of the date growers are not applying chemical fertilizers or applying them in improper amounts. Due to the importance of date palm and so the importance of mineral elements especially nitrogen, phosphorus and potassium in increasing the yield and fruit quality, determination of optimum levels of them for date palm fertilization is a necessity. In order to increasing yield and fruit quality of ‘Sayer’ date palm, this experiment with twelve treatments and four replications was carried out in a randomized complete block design on 48 ‘Sayer’ date palm during four years in Khuzestan Province. Treatments consisted of three levels of nitrogen (N₁=700, N₂=1000 and N₃=1300 grams tree^-1), two levels of phosphorus (P₁=500 and P₂=650 grams tree^-1) and two levels of potassium (K₁=1000 and K₂=1300 grams tree^-1). The sources of nitrogen, phosphorus and potassium were urea, triple super phosphate (TSP) and potassium sulfate, respectively. These treatments along with 20 kg of manure and chemical micronutrient fertilizers based on general recommendation were applied for each tree in winter by localized placement method (Chalkood). The number of 20-25 leaflets from the middle of the leaf in the second row was picked up, and mineral nutrients of them were determined, each year. At harvesting time, plant parameters such as yield, concentration of mineral elements in leaf, average of weight, length, diameter and volume of fruit flesh, weight of stone and weight ratio of fruit pulp to its stone, pH, acidity, brix, reducing sugar, total sugar in fruits were determined. Data were analyzed with the MSTATC statistical program and means of data were compared with Duncan’s Multiple range test. The results showed that application of 700 g N, 500 g P₂O₅ and 1300 g K₂O for each tree caused the highest yield and fruit quality. Therefore, annual application of these is recommended to date growers.