Synthesis and applications of MnO2 -enriched urea nanofertilizer on chili Capsicum annuum L. plant

Abstract

Constant use of several conventional fertilizers on the soil often leads to nutrient losses, soil deterioration, and reduced crop performance. Nanofertilizers are considered one of the most promising alternatives to conventional fertilizers. Plants require both macronutrients NPK (Nitrogen, Phosphorus, and Potassium) and micronutrients (such as manganese, zinc, iron etc.,) for their optimal growth and productivity. Among these, Manganese (Mn) plays a crucial role in several physiological and biochemical processes. Urea is widely used as a fertilizer due to its high nitrogen content (46%), but it can be toxic at higher concentrations. In the present study, we have developed a novel MnO₂-enriched urea nanofertilizer, designed in such a way to provide both nitrogen and manganese in a single conjugate form to overcome Mn deficiency and chlorosis in plants. The nanofertilizer has been synthesized using the hydrothermal method, where KMnO4 is used as a precursor along with urea (CH4N2O) and optimized thoroughly using characterization such as UV–visible absorption, SEM, FTIR, XRD, with varying MnO₂–urea ratios and chosen based on its stable nanoscale features. The effectiveness of the nano fertilizer has been evaluated on Capsicum annuum L. (chili) at concentrations of 0, 10, 20, 30 and 40 ppm with a notable improvement in the physical characteristics of plants like root and shoot length, leaf area, and yield was seen around 30 ppm. Chemical characteristics analyses confirmed higher levels of photosynthetic pigments, strong antioxidant capacity, greater mineral accumulation, and improved nutrient use efficiency at this dose. Overall, the MnO₂-enriched urea nanofertilizer functions both as a corrective for chlorosis and as a controlled nutrient source, making it a promising alternative to conventional fertilizers, contributing synergistic nutrient uptake and environmental sustainability.