Nano-based soil conditioners eradicate micronutrient deficiency: soil physicochemical properties and plant molecular responses

Abstract

Nano-enabled agriculture is a vibrant research area; nonetheless, reports on effective nanofertilizers are rather scant. Hence, we evolved novel, easy, and scalable synthetic routes for environmentally benign Fe-oxalate capped metal oxide (Fe–Mn and Fe–Cu) nanomaterials (OCIMn_ox and OCICu_ox) for agricultural use (Patent no. 343590). The materials were systematically characterized through PXRD, FT-IR, HR-SEM, HR-TEM, and XPS analyses, which induced the least toxicity to plants, soil microbes, and earthworms. These materials corrected soil acidity by maintaining the soil pH above 6. Their application increased the surface area by ∼1.5–1.7 fold, water holding capacity by ∼1.4–1.5 fold, and organic C by ∼1.3–1.4 fold in soil as compared to non-nanoscale fertilizers (sulphates and EDTAs of Fe/Mn/Cu). The 10 ppm dose of OCICu_ox and OCIMn_ox remarkably enhanced the availability of N (383–385 ppm) and P (75–79 ppm) in soil compared with their non-nanoscale counterparts. Their application in nutrient-fatigued soil could efficiently alleviate Fe, Mn, and Cu deficiency, enhance soil bacterial growth by ∼4–9 fold, and augment siderophore-producing bacteria. Furthermore, oxidative stress factors were minimized in earthworms and plants cultivated in nano-exposed soil. Focused experimentations showed that OCICu_ox and OCIMn_ox stabilized soil pH, probably by adjusting the H⁺ abundance, and optimized nutrient availability by increasing the net-negative charge in soil. Eventually, plant productivity was stimulated through greater N uptake (>6%), 3–10 fold greater up-regulation of expression of vital genes [glutamine synthetase-2 (GS2), glutamate synthase (GOGAT), and nitrate reductase (NR)], and a higher rate of photosynthesis than FeSO₄. In conclusion, the innovatively synthesized OCIMn_ox and OCICu_ox showed great promise as micronutrient nanofertilizers for future applications.