Response of olive (Olea europaea L.) trees to foliar spray of nano chelated and chemical potassium fertilizers

Abstract

Global challenges resulting from increased population and increased use of water and soil resources encourage researchers to focus on new compounds, such as nano-fertilizers. Hence, the present study aims to find out and compare the impact of foliar spray of two potassium (K) sources with the different formula, i.e. nano-chelated potassium and potassium nitrate, on olive oil yield and content over two successive years (2017–2018). During the bud-swelling stage, before blooming, the pit hardening stage, and shortly after the harvest of table olive, the fertilizers are used at the concentration of 1.84 (K1) and 2.45 (K2) g potassium nitrate, 3 (nano-K1) and 4 (nano-K2) g potassium nano-chelated, corresponding to 0.81 g (K1 and nano-K1) and 1.08 g (K2 and nano-K2) pure potassium per liter. The results show that fruit yield and characteristics are affected by k2 foliar application. High oil percentage is achieved by k1, which results in a low crop load and the highest leaf carbohydrate content in August. Traits, such as total phenol compound and antioxidant capacity of oil, are strongly enhanced under nano-K1 fertilizer, but quality characteristics of olive oil are relatively affected. Furthermore, nano-K1 treatment can positively affect fatty acid composition through the improvement of leaf mineral content rather than controlling tree. According to the results, fruit yield and traits are better under potassium nitrate (K2) treatment, and the quality of olive oil is more stable after nano-chelate potassium (nano-K1) foliar application.