Phosphorus Fertigation and Preplant Conventional Soil Application of Drip Irrigated Summer Squash

Abstract

Two field experiments were conducted to evaluate squash response to the following phosphorus (P) fertigation rates and method of application: (1) 0 mg P L-I irrigation water (IW) (Po), (2) 30 mg P L-, IW (P'D)' (3) 60 P L-I IW (P6IJ), (4) 90 P L-I IW (P9,,)and (5) preplant soil P application at a rate equivalent to PJotreatment. Squash seeds were planted for two seasons and were irrigated twice a week to replenish 80% of the class A pan evaporation. Plant and soil samples were collected and analyzed for chemical analysis. Fruit yield was detern1ined from harvesting the middle two rows. With P fertigation, fruit yield, fruit numbers and P uptake were higher than with preplant soil application and the yield was related positively to P uptake. The P fertilizer use efficiency (PFUE) was also higher with fertigation and decreased with increasing P rates. Soil pH in the top soil decreased by the highest P rate due to the acidifying effect of phosphoric acid applied through fertigation. Being slightly soluble, P accumulated more in the top 15 cm soil and was higher with higher rates. With preplant application, P accumulated deeper in the top 30 cm. It can be concluded that the lowest fertigated P rate was adequate to achieve the highest yield and PFUE and was superior to preplant application method.