Foliar Application of Amino Acids Mitigate High-Temperature Stress and Improve Yield, Quality, and Physiological Responses of Maize

Abstract High temperatures can severely limit maize growth and productivity. This two-year field study evaluated the efficacy of various foliar-applied biostimulants and organic fertilizers in improving grain yield, quality, and physiological traits of maize grown as second crop during 2021 and 2022 under hot climatic conditions. Eight treatments consisting of biostimulants and organic materials, i.e., control (water spray), humic acid (HA), seaweed (SW), organic nitrogen (ON), amino acid (AA), vermicompost (VC), liquid organic fertilizer (LOF), and bat guano (BG) were included in the study. The biostimulant and organic materials (2000 cc ha −1 each) were sprayed at V6 and V12 development stages of maize. Data related to grain yield and related traits (ear length, number of kernels per ear, thousand kernel weight), quality parameters (protein content), and stress-indicative physiological responses (leaf chlorophyll index, proline accumulation, leaf temperature, and stomatal conductance) were recorded. All biostimulant treatments significantly increased grain yield compared to the untreated control. The AA treatment was most effective, producing the highest grain yield and grain protein content. The AA also produced heavier kernels and superior chlorophyll index, while markedly reducing leaf proline levels and leaf temperatures relative to control plants. Treated plants maintained higher stomatal conductance under heat stress, indicating improved gas exchange. These results demonstrate that foliar biostimulants and organic amendments can mitigate high-temperature stress in maize. In particular, amino acid and LOF supplements enhanced the crop’s heat tolerance and productivity. It is concluded that using these biostimulants is a promising strategy to improve maize yield and quality under extreme heat conditions, and it can be recommended to farmers in hot climate regions.