Foliar application of chitosan nanoparticles and N-ATCA enhances olive yield and oil quality

Olive cultivation in newly reclaimed semi-arid lands is constrained by poor soil fertility and environmental stress, limiting productivity and oil quality. Sustainable biostimulant-based strategies are therefore required to enhance olive performance under such conditions. Here, we evaluated the individual and combined effects of chitosan nanoparticles (CHNPs) and N-acetylthiazolidine-4-carboxylic acid (N-ATCA) on growth, yield, fruit characteristics, and oil quality of Olea europaea L. cv. Arbosana. Using 16 foliar treatments comprising CHNPs (0, 500, 1000 and 1500 ppm), N-ATCA (0, 50, 100 and 150 ppm), and their combinations CHNPs + N-ATCA at concentrations (500 + 50 ppm, 500 + 100 ppm, 500 + 100 ppm, 500 + 150 ppm, 1000 + 50 ppm, 1000 + 100 ppm, 1000 + 150 ppm, 1500 + 50 ppm, 1500 + 100 ppm and 1500 + 150 ppm).Vegetative growth traits, leaf mineral status, fruit yield and quality, and olive oil fatty acid composition and oxidative stability were assessed. The combined application of CHNPs and N-ATCA consistently outperformed single treatments, demonstrating a clear synergistic effect. The highest vegetative growth and leaf nitrogen, phosphorus, and potassium accumulation were recorded with 1500 ppm CHNPs + 150 ppm N-ATCA, while the greatest fruit and oil yields approximately 30% higher than the control were achieved with 1500 ppm CHNPs + 100 ppm N-ATCA. Combined treatments promoted optimal fruit ripening, characterized by enhanced skin coloration without excessive softening. Importantly, all extracted oils met extra virgin olive oil standards, with oleic acid remaining the dominant fatty acid. Moreover, the combined treatments preserved or improved oxidative stability, mitigating the higher oxidation indices observed under individual N-ATCA applications. These findings demonstrate that foliar co-application of chitosan nanoparticles and N-acetylthiazolidine-4-carboxylic acid enhance olive tree performance, yield, and oil quality in newly reclaimed semi-arid environments. This approach offers practical implications for improving olive productivity while maintaining high oil quality under challenging cultivation conditions.