The optimal combination of long-acting nano-iron and fast-acting ionic-iron fertilizers: A synergistic strategy for enhancing fertilizer efficiency and economic feasibility in peanut

Iron-based nanoparticles (Fe-NPs) have attracted attention as potential nano-fertilizers for micronutrient supplementation. However, the sole application of Fe NPs fails to meet the actual requirements of crop production due to their slow biodegradation, delayed fertilizer response, dose-dependent, and high costs. This study proposes a novel foliar spray combining nano-iron (Fe 3 O 4 -NPs) and ionic-iron (FeSO 4 ) fertilizers for iron-deficient peanuts, leveraging the strengths of both forms. Results show that Fe 3 O 4 -NPs had a 39% iron migration rate from fertilized to unfertilized leaves, three times higher than FeSO 4 (12%), indicating their potential for sustained and long-distance nutrient delivery. The optimal combination treatment, 300 mg/L Fe equivalent FeSO 4 + 300 mg/L Fe equivalent Fe 3 O 4 -NPs, enhanced peanut growth biomass, iron nutrition, photosynthesis, and mineral quality. Notably, excessive doses impaired growth and photosynthesis. Compared to other treatments, this combination increased shoot fresh weight by 10–156%, shoot dry weight by 8–175%, and net photosynthetic rate by more than 15%. Cost analysis revealed a 23% reduction compared to single Fe 3 O 4 -NPs in current market. These findings provide valuable insights for optimizing the co-application dosage of nano- and conventional fertilizers, thereby improving nutrient use efficiency and advancing the economic feasibility of nano-fertilizer technologies in sustainable agriculture.