THE EFFECT OF FERTIGATING DIFFERENT LEVELS OF NITROGEN, PHOSPHORUS AND POTASSIUM ON GREENHOUSE CUCUMBER YIELD

High yielding varieties of cucumber grown in greenhouse require high amount of nitrogen (N), phosphorus (P) and potassium (K). Optimum application rates of these nutrients are not available for greenhouse cucumber growers in the Kingdom of Saudi Arabia. Greenhouse studies were thus conducted to determine the effect of different levels of N, P, and K applied through irrigation water on cucumber yield. Three experiments were set up to study each nutrient element separately. In each experiment one nutrient was applied in 4 different levels while the other 2 were held at high levels so that they would not be limiting plant growth and yield. For the N experiment, the rates were 125, 150, 175 and 200 ppm N with basic fertigation of 70 ppm P₂O₅ and 200 ppm K₂O. For the P experiment, the rates were 40, 50, 60 and 70 ppm P₂O₅ with 200 ppm N and 200 ppm K₂O. For the K experiment, the rates were 140, 160, 180 and 200 ppm K₂O with 200 ppm N and 70 ppm P₂O₅. The design for each experiment was a complete randomized design with four replicates. In the N experiment, the highest yield (49.5 t/ha) was obtained at 150 ppm N with 70 ppm P₂O₅ and 200 ppm K₂O. In the P experiment, 60 ppm P₂O₅ with 200 ppm N and 200 ppm K₂O gave the best yield (42.0 t/ha). In the K experiment, the highest yield (33.2 t/ha) was obtained when K₂O was applied at 200 ppm with 200 ppm N and 70 ppm P₂O₅. Potassium levels increased yield linearly indicating higher K levels may still increase yield, whereas N and P showed a typical nutrient response curve and interaction. However, further studies to confirm these results are underway.