Interactive Effects of Potassium and Phosphorus on Phenology and Grain Yield of Sunflower in Northwest Pakistan

Potassium (K) and phosphorus (P) applications improve growth, increase yield and yield components of sunflower (Helianthus annuus L.) on K and P deficient soils in Northwest Pakistan. A field experiment was conducted using sunflower cv. Hysun-33 at the New Developmental Research Farm of KPK Agricultural University, Peshawar, Pakistan, during summer 2006. The experimental design was a randomized complete block in split plot arrangements, with six levels of K (0, 25, 50, 75, 100, and 125 kg K ha−1) as main plots and four levels of P (0, 45, 90, and 135 kg P ha−1) as sub-plots with three replications. Sunflower yield and yield components responded positively to K and P fertilization but the magnitude of response varied with the levels of K and P. Days to flowering and maturity, grains per head, 1000-grain weight, shelling percentage, and grain yield increased tremendously in the K and P-fertilized plots as compared to the control with no K and P applied. The combined application of 100 kg K and 45 kg P ha−1 significantly increased yield components, grain yield, harvest index, and shelling percentage of sunflower, suggesting that 100 kg K ha−1 in combination with 45 kg P ha−1 could maximize productivity of sunflower planted after wheat on the K and P deficient soils in the study area.