Nano-enabled nutrient management: improving pistachio productivity (Ahmad Aghaei) in arid orchards using calcium hydroxide, zinc oxide, cerium oxide nanoparticles

Pistachio (Pistacia vera L.) cultivation in arid regions is severely challenged by physiological disorders such as shell non-splitting, blankness, and nut deformity, which substantially diminish marketable yield. This study represents the first global investigation into the efficacy of arginine-liganded metal hydroxide nanoparticles as a high-precision foliar intervention to alleviate these constraints in the ‘Ahmad Aghaei’ cultivar. A factorial experiment (7 × 2) was conducted using a Randomized Complete Block Design (RCBD) with five biological replicates, where each individual tree served as an experimental unit. Seven treatments were evaluated: arginine-liganded zinc hydroxide nanoparticles (Zn-Arg, 150 mg L-1), arginine-liganded calcium hydroxide nanoparticles (Ca-Arg, 1000 mg L-1), L-arginine (174.2 mg L-1), cerium nitrate (20 mg L-1), cerium oxide nanoparticles (20 mg L-1), cerium hydroxide nanoparticles (20 mg L-1), and a deionized water control. Based on canopy architecture calibration, a spray volume of 1.5 L per tree was applied at 60 and 75 days after full bloom (DAFB) to target critical kernel-filling phases. Arginine-liganded nano-chelates, particularly when applied at 60 DAFB, fundamentally reconfigured crop performance. Ca-Arg at 60 DAFB emerged as the superior treatment for vegetative and quantitative traits, increasing leaf area by $45.2\%$, single-nut dry weight by 31.0% (1.14 g), and branch yield by 31.0% (1140 g/shoot) relative to the control. Zn-Arg at 60 DAFB was most effective in enhancing marketable quality, achieving a 27.3% increase in nut splitting while significantly reducing blankness and deformities by over 60%. Conversely, cerium-based treatments exhibited neutral to detrimental effects; cerium nitrate at 75 DAFB maximized blankness (37.12%) and suppressed yield, while Ce(OH)3 NPs resulted in the lowest nut weights and highest ounce counts (smaller nuts). Principal Component Analysis (PCA) and heatmap clustering confirmed that the synergy between the arginine ligand and the nanoscale mineral core at the 60 DAFB window is the decisive factor in optimizing the sink-source relationship and shell dehiscence. These findings establish arginine-liganded Ca and Zn nanoparticles as a transformative, sustainable strategy for precision nutrient management in pistachio orchards. While arginine-liganded formulations offer a robust physiological blueprint for overcoming arid-induced disorders, the inconsistent performance of cerium underscores the necessity of crop-specific nano-strategies. This study advocates for the integration of ligand-optimized nano-nutrients at the early kernel-filling stage to safeguard yield and quality in global pistachio production. Graphical abstract illustrating the effects of nano-chelated calcium and zinc on leaf area, nut quality, splitting, and yield in pistachio cv. Ahmad Aghaei.