Effects of two potassium sources on grape yield


22 May 2017

2016 Annual Interpretive Summary

Most grape growers prefer to use potassium sulfate (K2SO4) rather than potassium chloride (KCl) as a K source because of the apprehension that KCl could be detrimental to grape yield and quality. This perception has lowered the normal use of KCl in fruit and vegetable production. In order to clarify this issue and to demonstrate to growers that these two K sources are typically equally effective and beneficial to grape yield and quality, a two-year field experiment was conducted on grape in Guangxi province, Southern China. The experiment consisted of four treatments including: 100% K2SO4, 50% K2SO4+50% KCl, 100% KCl, and 100% KCl + compound fertilizer (12-40-0-10S-1Zn), all replicated four times. Each treatment also received equal amounts of nitrogen fertilizer as urea (N 46%) and phosphate fertilizer as fused Ca-Mg phosphate (P2O5 18%). The NPK rates for each treatment were 240-135-167 kg N-P2O5-K2O/ha. P and K fertilizers were used in two splits [i.e., applications as basal (50%) and at bud sprouting stage (50%)]. Nitrogen fertilizer was applied in seven splits including two soil applications [i.e., basal (21%) and at bud sprouting stage (43%) and five topdressings (36%) from flowering to fruit swelling stages, fertigated in an interval of about 15 days]. The compound fertilizer was applied as basal and at bud sprouting stage.

Results showed that the treatment of 100% KCl produced the highest grape yield, followed by 50% K2SO4+50% KCl and 100% KCl + compound fertilizer, but the yield differences were not statistically different among them. The treatment of 100% K2SO4 produced significantly lower grape yield (10.4-15.8%) than the other treatments. This indicates that shifting K source to KCl by half or full rate in the grape vineyards, receiving K2SO4 as sole K source for years, can significantly increase grape yield. As far as grape quality is concerned, the analytical data showed that there were no noticeable differences in total sugar, soluble solids, active acids, vitamin C or ratio of sugar/acid between different treatments. This further proves that KCl is an alternative K source that is equally effective and beneficial as K2SO4 in grape production in Southern China. Because of its lower price, the use of KCl may be advantageous over K2SO4 in reducing production costs.