Salinity is one of the main stresses that negatively affect plant growth and development. The present research aims to reduce the harmful effects of salinity by Chitosan- Selenium nanoparticles. A factorial experiment was arranged based on a randomized completely design with three replicates, and one-year old grafted C. sinensis (cv. Valencia) seedlings imposed to control, and salinity stress by NaCl (100 mM). Two weeks after starting salinity stress the seedlings treated with distillated water (WT), Chitosan (CS; 0.1% W: V), 20 mg L-1 Selenium nanoparticles (Se NPs), and 10 and 20 mg L-1 Chitosan-Selenium (CS/Se NPs). Salinity stress continued about three month to appeared visual salinity stress symptoms. Then, evaluated the growth and biochemical parameters of seedlings, and concentration of elements in leaves. Our result showed, the salinity stress increased accumulation of Sodium (Na) by 112%, while decreased Potassium (K), Zinc (Zn) and Phosphorus (P) by 15, 12 and 28%, respectively in compared to non-saline conditions in leaves. Due to accumulation of Na intense, occurred an increase in reactive oxygen species (ROS) 39% and Malondialdehyde (MDA) by 118%, damaged cell membrane that appeared as a decrease in membrane stability index (MSI) by 29%. Also, activated the antioxidant system by increase in phenol, flavonoids and anthocyanin, increased osmolyts production such as, soluble carbohydrates (45%) and proline (347%). Furthermore, growth parameters such as leaf number, shoot fresh weight, root and shoot dry weight decreased by 58, 45, 19, and 43%, respectively. On the other hand, foliar spraying with CS/Se NPs (20 mg L-1) under the salinity stress conditions improved the negative effects of salinity stress by decrease in accumulation of Na (19%) and Na/K ratio (21%), due to decrease in the content of ROS (37%) and MDA (20%), and increase in MSI (47%). Finally, improved the growth parameters such as leaf number (268%), fresh weight of roots (32%) and shoots (26%), and dry weight of roots (19%). Our results supported the positive effect of CS/Se NPs application at 20 mgL-1 on managing the negative effects of the salinity stress on the quality of C. sinensis grafted seedlings by reducing Na accumulation and Na/K ratio, protecting against oxidative damage, regulating membrane stability and improving seedling growth.

Commercial agricultural production of orchards is based on water and fertilizer applications. Over-application and orchard spatial variability lead to water and nitrogen (N) losses through leaching and environmental damage. This work introduces a novel advanced method to quantify N and water leaching at the orchard scale by combining soil monitoring, unmanned aerial vehicle (UAV) imagery to estimate tree size, leaf N and canopy content, and water flow and N transport models. Four neighboring commercial orange orchards were selected, and 48 representative trees were instrumented with suction cups and tensiometers at a depth of 90 cm. The physical properties of the soil profiles in the vicinity of each tree were determined. During 2019-2021, UAV structure-from-motion (SfM) photogrammetry was used to classify the tree sizes into small, medium, and big categories. Soil porewater extraction and soil matric potential measurements were conducted every three weeks, while leaf N contents (LNC) were determined through bimonthly leaf tissue sampling. The LNC, N leaching, soil water state, and N use efficiency (NUE) (the ratio between the mass of plant N uptake and the mass of N applied per area) were strongly related to tree size classification. Results of the calibrated hydrological model illustrated that the 'big' trees exhibited minimal N leaching due to higher transpiration compared to the other tree size categories. An NUE map was established using the calibrated model and field measurements, demonstrating that soil spatial variability minimally affected N leaching compared to tree size distribution. The presented holistic approach can be used to identify N-leaching hotspots, improve orchard scale NUE estimates, and promote sustainable agricultural management practices.