Effects of foliar application and fertigation of potassium on yield and fruit quality of ‘Superior Seedless’ grapevine

Mineral nutrition of temperate fruit trees, such as grapevine (Vitis spp.) is an important tool to achieve maximum yield and fruit quality. Potassium (K) is a key element for grapevine quality contributing to adequate berry maturation, concentration of sugars, synthesis of phenols and the regulation of pH and acidity. In addition, through its mobility in the phloem and xylem, K is important in the transport of solutes, the partition of assimilates, and the synthesis of polyphenols responsible for fruit color and aroma. The aim of this work is to study the effect of different treatments of K mineral nutrition on grapevine ('Superior Seedless') yield and fruit quality. Five combined treatments were applied: (T1) 75% of grapevine requirement by fertigation and 25% by foliar spray using potassium sulfate (K2SO4=SOP); (T2) 75% of the requirement by fertigation and 25% by foliar spray using K Leaf fertilizer; (T3) 75% of the requirement by fertigation and 25% by foliar spray using nitrate of potash (KNO3=NOP) fertilizer; (T4) 100% of the requirement given by fertigation using K Leaf fertilizer; and (T5) Control without K mineral nutrition. Potassium fertilization induced a slight increase in yield compared to the Control. Treatment (T2) was more efficient and showed a better yield. Potassium treatments improved grape and berry diameter and weight. Also, K fertilization increased the total soluble solids (TSS). Potassium applied by treatment (T3) significantly increased the fruit diameter and grape weight compared to the control. The highest total soluble solids were measured on berries from the vines that received 75% of tree requirement by fertigation and 25% by foliar spray using NOP fertilizer (T3) and 75% of the requirement by fertigation and 25% by foliar spray using K Leaf fertilizer (T2). Our results showed that K nutrition improved yield and fruit quality of grapevine. Yield, fruit diameter and total soluble solids enhanced when the K requirements were given by a foliar spray combined with fertigation with K Leaf or NOP fertilizers.