effects of humic acid application with irrigation water on yield and yield components of corn (zea mays l.)

agroecology emphasizes the use of organic materials in agriculture. the organic acids are important sources of organic materials. in order to study the effect of different levels of humic acid on yield and yield components of corn (zea mays l.) an experiment was conducted at research station, faculty of agriculture, ferdowsi university of mashhad, iran, during 2009. the experiment was conducted with different levels of humic acid (0, 500, 1500, 2500, 3500 and 4500 g.ha-1) based on randomized complete block design with three replications. results showed that different levels of humic acid imposed a significant effect on the yield parameters such as grain yield, biomass, leaf area index, leaf area duration, height, row number and ear length, but there were no significant effects on harvest index, 1000-grain weight, ear diagonal, and grain number per row did not have significant effect. according to the results, the highest and lowest grain yield belonged to 3500 g.ha-1 humic acid and control treatments respectively. the highest biomass production observed to 4500 g.ha-1 humic acid treatment. while the highest row number and ear length belonged to 3500 gha-1 humic acid treatments. generally, it seems that application of humic acid due to having nutritional ingredients and different physiological effects improves corn performance and reduces environmental pollution and it could be used as a natural material to increase and stabilize field crop production.