Efficiency of foliar applications of potassium sulphate on walnut production

Besides basal dressing and cropping systems using split applications such as fertigation, foliar sprays can also be considered as an effective way to supply nutrients to plants. They are widely used for micro-elements but less so when it comes to macro elements, particularly potassium. When it comes to nut and fruit trees, foliar applications are a fast and effective way to supply potassium during high demand growth stages. Nuts in general and walnuts in particular have the highest demand for potassium during fruit growth. Thanks to a new grade of soluble potassium sulphate, specially designed for foliar applications, it is now possible to supply potassium at this critical stage. A three-year experiment was carried out in cooperation with the “Station de Creysse”, the French research centre specialized in walnut production. This article presents results on the effect of foliar applications of potassium sulphate on yield and quality as a complement to the basal dressing. Three treatments were compared: T0 as control with 100% of the potassium as basal dressing based on the recommended fertilization; in T1, 80% of the potassium is applied to the soil and 20% as foliar; T2 is equivalent to T0 and an additional 20% of the potassium dose as foliar. The cumulative yield over 3 years shows an improvement of 9.4% for T1 over T0 and 23.7% for T2 over T0. Quality parameters such as kernel colour and size were also improved. Income for the grower increased by 8,500 € ha^‑1 over the 3 years.