Physiological Effect of Adding Concentrations of Humic Acid on Growth and Protein Percentage of Zea mays L. Plant Genotypes

Background: The global trend at present is to utilise organic fertilisers of various types and sources to minimise the adverse effects of chemical fertilisers as much as possible. Humic acid is an organic fertilizer widely used due to its many benefits in improving the properties of soil and its effect on plant growth and production. The global production of hybrid varieties has been at a steady pace for years, driven by their productivity and the number of genetic combinations introduced, which increases the capacity of their genetic base and thus helps them adapt to environmental conditions or growth factors. Methods: The experiment conducted in Tikrit University, Salah Al-Din, Iraq, to investigated the effect of varying concentrations of organic fertilizer (0, 1, 2 and 3 ml L-1 humic acid) on the three Zea mays plant genotypes (Toro, Vito and Jooly) growth characteristics and protein percentage, in the autumn season of 2025 using an RCBD design repeated three times. Result: Humic acid with 3 ml L-1 superior in plant height, leaves number plant-1, leaf area, dry weight plant-1, leaf chlorophyll content (SPAD) and protein percentage, by percentage increase of 3.96%, 7.89%, 21.43%, 12.25%, respectively and leaf chlorophyll content reached 42.10 SPAD and protein percentage 8.6%. Jooly genotype was superior in the same traits by percentage increase of 15.84%, 2.72%, 8.35% and 9.78%, respectively and leaf Chlorophyll content 46.56 SPAD and protein percentage 8.70%. The interaction between 3 ml L-1 humic acid concentrations and Jooly genotype superior in the same traits by percentage increase of 29.73%, 10%, 30.15% and 3.29%, respectively and leaf chlorophyll content of 48.25 SPAD and protein percentage 8.90 %. It can be concluded from this experiment that adding of humic acid helps in enhancing growth and protein percentage of new Zea mays L. plant genotypes.