The objective of this study was to evaluate the rate of foliar absorption of magnesium (Mg) salts with different deliquescence and efflorescence relative humidity values (DRH and ERH, also known as point of deliquescence (POD) and point of efflorescence (POE), respectively) when supplied to leaves of model plants with different wettability properties. For this purpose, a greenhouse pot experiment was conducted with lettuce (very wettable), broccoli (highly unwettable) and leek (highly unwettable). Foliar sprays contained 0.1% surfactant plus 100 mM Mg supplied as MgCl₂·6H₂O, Mg(NO₃)₂·6H₂O or MgSO₄·7H₂O. Leaf Mg concentrations were determined 1 and 7 days after foliar application. Anion concentrations were also measured in lettuce where a significant foliar Mg absorption was detected. Leaf wettability, leaf surface free energy and fertilizer drop deposit appearance onto the foliage were assessed. It is concluded that despite including a surfactant in the spray formulation, leaf wettability plays a major role in foliar Mg absorption.

Solute fate in soil-plant continuum could either be soil or leaf uptake or leaching beyond the rooting zone. An adsorption coefficient (K_D) is an important chemical property to describe the interaction between the solute and soil, affecting the solute movement in soils from one point to another. Boron (B), manganese (Mn), and zinc (Zn) uptake are evident in the leaves as a constituent of photosynthesis and other plant body-building mechanisms for growth and development. This study investigates the availability of micronutrients (B, Mn, and Zn) to citrus trees through modified application methods and rates. Leaf samples were collected from experimental plots arranged in a randomized complete block design, with 4 micronutrient treatments: control, foliar ×1, foliar ×2, and soil ×1. Boron, Mn, and Zn rates were 1.12, 10.08, and 5.60 kg ha⁻¹, respectively. Composite soil samples were randomly collected at 5 points, and a 1-point adsorption study was conducted in 4 soil depths at an increment of 15 cm from the soil surface. Adsorption coefficient (K_D) for Mn and B was 22 and 3 times higher at 0–15 cm than at soil depth of 15–60 cm. The adsorption coefficient (K_D) for Zn was 2.5 times greater at 0–15 cm than 15–30 cm soil depth, while there was little or no sorption at 30–60 cm. Leaf Mn and Zn concentrations showed that foliar spray was 2 times higher than the soil application method, while B showed that the soil application method was 2 times higher than foliar application method for 2 seasons sampling events. Thus, the behavior of B, Mn, and Zn in the soil via adsorption coefficient (K_D) reflects the availability of B, Mn, and Zn in the citrus leaves.

Climate change as a global issue is increasingly redefining the nutritional constraints in citriculture, thereby increasing the reliance on optimized use of nutrients and irrigation, while rising atmospheric CO ₂ continues to influence the carbon(C)–nutrient balance. Citrus is an evergreen perennial with relatively shallow root system and prolonged fruit development period, the abiotic stresses interact across seasons to alter soil nutrient supply, root nutrient uptake kinetics, whole-tree mineral status, and eventually the fruit nutritional quality. We synthesized current evidences on climate-driven pathways affecting citrus nutrition, impact of high temperature, and water scarcity restricting nutrient mobility and acquisition, nutrient leaching due to heavy rainfall, poor aeration-induced anoxia-related nutrient constraints, and salinization disrupting ionic homeostasis via elevated (sodium/potassium ratio) Na/K and (sodium/calcium ratio) Na/Ca ratios in plant roots. We further collated multi-point facts, that elevated CO ₂ stimulated biomass increase, yet dilutes tissue nutrient concentration, thereby increasing risks for nutrient deficiencies in citrus production system. Across regions, in economic terms, climate change translates into yield instability, fruit grade loss, and adding extra cost investments on irrigation and nutrient management. Finally, we identified priorities for climate-resilient citrus nutrition, as: monitoring-based diagnostics, precision fertigation using 4R (right source, right time, right rate, and right place) strategies, soil organic carbon–centered integrated soil fertility management (ISFM), phytobiome manipulation for microbial consortia development, and nutriomics-mediated climate proofing of rootstock–scion combinations. Together, these approaches provide a conceptual framework to sustain citrus productivity and fruit nutritional quality under current conundrum of climate change.

Nitrogen and micronutrients have a key role in many citrus plant enzyme reactions. Although enough micronutrients may be present in the soil, deficiency can develop due to soil depletion or the formation of insoluble compounds. The objectives of this study were to (1) determine the adsorption, distribution, and availability of Zn in a sandy soil; (2) compare the effectiveness of foliar and soil application methods of Zn on Huanglongbing [HLB] affected trees; (3) compare foliar application rates of Zn for HLB-affected trees; (4) determine the effect of N rates on yield, soil inorganic N distribution patterns, and tree growth parameters. Tree rows were supplied with three N rates of 168, 224 and 280 kg·N·ha⁻¹ and Zn at single and double recommended rates (recommended rate = 5.6 kg·Zn·ha⁻¹) using foliar and soil application methods, in a split-plot experimental design. The results show that Zn concentration in the 0–15 cm soil depth was three times higher than the 30–45 and 45–60 cm soil depths during the study. An adsorption study revealed high Zn (K_D = 6.5) sorption coefficients at 0–15 cm soil depth, while 30–45 and 45–60 cm depths showed little sorption. Leaf Zn concentration for foliar spray was two times higher than the soil application method. A nitrogen level of 224 kg N ha⁻¹ improved canopy volume when compared to other N levels at the expense of reduced fruit weight. Foliar Zn application at 5.6 or 11.2 kg ha⁻¹ and N rate at 224 kg ha⁻¹ appear to be adequate for improving the performance of HLB-affected citrus trees.

This study aimed to investigate the effects of foliar application of different potassium (K) sources on yield and fruit nutrient uptake in 28-year-old Valencia oranges (Citrus sinensis, L.) grafted onto Trifoliata citrange rootstock. In the trial that was conducted with different foliar potassium sources in the region of Köyceğiz (Turkey) in the years 2016, 2017, and 2018 with 5 replications according to the random blocks trial design for this purpose, in addition to the control group where no foliar treatment was applied, the treatment groups received Potassium Nitrate (KNO₃, 46% K₂O; 300 g/100L/da), Potassium Thiosulfate (25% K₂O; 400 ml/100L/da) and Potassium Phosphite (25% K₂O; 500 ml/100 L/da) treatments. For all examined parameters and for all 3 years, the highest results were obtained in the potassium phosphite treatment. This may be due to its higher mobility inside the plant compared to other K sources. The effects of all treatments on yield were found significant, where the yield values for 2016, 2017, and 2018 were found as 139, 143, and 140 kg/tree, respectively. This may be explained with the role of K on promoting the fruit reserves. Regarding the effects of potassium phosphite on all fruit nutrient uptake amounts, the effect of the treatment in all 3 years was found significant except for Fe, Cu, and Mn. In conclusion, among the potassium sources, the most effective fertilizer was determined as potassium phosphite.