Effects of combined application of P and K on the yield,quality and nutrient utilization of watermelon in gravel-mulched field

On the base of applying nitrogen 200 kg/ha,a field experiment with three potassium rates( 0,130,260kg/ha) and four phosphorus rates( 0,90,130,170 kg/ha) was conducted to study the effects of combined application of P and K on the yield,quality and nutrient utilization efficiency of watermelon in Gravel-mulched field. A late mature watermelon cultivar,Longkang 9,was used as material. The results show that the yield and quality of watermelon increase with the increase of P and K application rates. With P170treatment,the single fruit weight and yield of watermelon increase by 13. 75% and 43. 79% respectively,and the average sugar,Vc and protein contents by 13. 75%,9. 48% and 11. 90% compared with P0. With the K260treatment,the single fruit weight,yield of watermelon increase by 9. 22% and 7. 54%,and the average sugar,nitrate contents increase by5. 86% and 11. 24% compared with K0. Significant positive interactive effect of P and K exists in the photosynthesis,yield and nutrient utilization efficiencies. Under low potassium rates,all the tested parameters keepincreasing within a certain range of P application rate,while under high potassium levels,with the increase of phosphorus application rate,better effects are obtained with individual P application than individual K application.The highest photosynthetic rate,yield and nutrient utilization efficiency were achieved with K260P170treatment.Therefore,the optimum fertilizer application rates were P2O5170 kg/ha and K2O 260 kg/ha at the base of applying N 200 kg/ha,hence,the most suitable ratio of N ∶ P2O5∶ K2O is 1 ∶ 0. 85 ∶ 1. 3 for good yield and quality of watermelon in this soil condition.