Impact of nitrogen fertilization and rootstock genotype on growth and fruit quality of Nules clementine

This study focuses on understanding the impact of varying nitrogen rates on the growth, fruit production, and quality of clementine Nules variety trees grafted onto Flhorag and Carrizo citrange rootstocks and cultivated at the Sidi Allal Tazi Experimental Station of INRA Morocco, in clay soil, over five seasons. A split-plot design with three blocks of repetitions (two trees per bloc per treatment, n=6) was employed in this experiment. The main plot varied the nitrogen doses, while the subplot involved the genotype of rootstock. Three fertilizer treatments with N rates (T0: control (native nutrient), T1: 270, T2: 540 in g/tree), with 135 P2O5 and 270 K2O g/tree added to citrus trees. The research indicated that both nitrogen rate and rootstock genotype significantly influenced vegetative growth, yield, and fruit quality of Nules clementine. Increased nitrogen levels enhance vegetative growth, especially in Carrizo citrange rootstock, evidenced by greater tree height, canopy diameter, and volume. Significant and positive correlation was found between canopy volume and fruit yield, across both rootstock highlighting the importance of proper nitrogen management in citrus cultivation. Carrizo citrange was proved to be a more efficient rootstock for Nules variety in contrast to tetraploid Flhorag. Higher nitrogen rates with Carrizo citrange result in better yield and fruit quality (size, juice content, and solid soluble content) than with tetraploid Flhorag. Optimal yield and fruit quality in Nules clementine are achieved using 540g of N/tree/year when grafted on Carrizo citrange. The recommended NPK rate for achieving high yield and optimal fruit quality of Nules clementine was 540 N-135 P2O5-270 K2O g/tree/year