Effect Of Different Kinds Of Potassium Fertilizer On The Yield And Quality Of Watermelon

It has been known that watermelon demands more K than other crops.Suitable application of potassium fertilizer can effectively increase the yield and quality of watermelon.In the present study,field experiment was conducted to investigate the effect of different potassium(K)fertilizer on the yield,quality and K content in the watermelon plant in different growing stage at different soil available K levels.A method for K nutrition diagnosis based on leaf potassium content has been preliminaryly established.Three watermelon special fertilizers were manufactured based on the rule of watermelon growth and the absorption of nitrogen,phorsphorus and K.The effects of the watermelon special fertilizers on yield,quality and soil fertility were investigated.The main results are listed as follows:(1)At low soil K level,the application of K significantly increased the biomass and yield of watermelon.The K content in each part of watermelon plant significantly increased at 50 mg/kg and 70 mg/kg available K level.However,at 85 mg/kg soil available K level,the stem K content was significantly increased at fruiting and expanding stage,as well as in fruit K at maturity.Also at this soil available K level,the fruit soluble sugar content was improved,while the titratable acid content was decreased by K application.(2)The leaf K content could be significantly increased in watermelon at flowering stage.At low soil available K level of 84 mg/kg,the watermelon yield was increased with the K application rate.At moderate soil available K level of 170 mg/kg,the K application rate of 225 kg/hm2 led to the highest yield,which was 58.3%higher than that of no fertilizer treatment.The K application rate of 225 kg/hm2 resulted in the highest soluble solids content at different soil K levels.(3)The diagnosis of K nutrition of watermelon plant and the critical value was studied between the leaf K content and watermelon yield.It was found that there was a significantly negative correlationship between the K content in young leaves and the maturity yield at flowering stage.It was suggested that the content of K in young leaves at this stage could represent the K nutrition status and forcast the yield.It was recommended that the young leave at flowering stage was the diagnosis organ for K nutrition.Critical value was calculated as 32.61 g/kg.(4)Three kinds of watermelon special fertilizer(cow manure watermelon special fertilizer,pig manure watermelon special fertilizer and pigeon manure watermelon special fertilizer)were manufactured.The results showed that the application of three kinds of watermelon led to 44.98%?30.87%and 7.8%higher yield than that of traditional fertilization,respectively.To the fruit quality,compared with the traditional fertilization,watermelon special fertilizers significantly increased the ratio of sugar to acid in fruit,which was 10.51%and 13.89%higher in cow manure watermelon special fertilizer and pig manure watermelon special fertilizer,respectively.According to the results above,cow manure special fertilizer was best on both yield increase and fruit quality improvement.(5)The application of watermelon special fertilizers had a significant effect on the fertility maintainance.The available rhizosphere soil K level could be kept stable during the whole growth period of watermelon,of which cow manure watermelon special fertilizer and pigeon manure watermelon special fertilizer treatments were higher than that of traditional fertilization treatment.The number of fungi in watermelon rhizosphere in special fertilizer treatments was higher than that in traditional fertilization treatment.The soil enzyme activities in watermelon rhizosphere were the highest at the expanding stage,of which the invertase activity in cow manure special fertilizer treatment was the highest during the whole growth period.