the effect of foliar application with humic acid on growth, yield and yield components of wheat (triticum aestivum l.)

wheat crop, considering its high planting area and consumption at national scale, demand a regular yield increase. humic acid, as an organic acid obtained from humus and organic sources without any environmental destructive effects, improves wheat yield particularly in variable environment conditions. in order to evaluate the effects of different levels of humic acid on shoot and wheat yield, an experiment was conducted in 2008 at research greenhouse, faculty of agriculture, ferdowsi university of mashhad. a completely randomized block design with three replications was used with factorial combination of humic acid concentrations (0, 100, 200, 300 mg/l) and four foliar application times (tillering, stem elongation, flag leaf appearance and anthesis). the results showed that the effect of foliar application of humic acid at different times was significant for shoot dry and fresh weights, leaf area, shoot length and chlorophyll content. the highest shoot dry and fresh weights, leaf area and shoot height obtained from foliar application of 300 mg/l humic acid concentration at flag leaf appearance time; and maximum chlorophyll content was obtained at 200 mg/l humic acid at flag leaf. the highest biological and seed weight was obtained at 200 and 300 mg/l humic acid. the most effective time for foliar application to reach maximum spike length and weight, spiklet number, seed number and seed thousand weight was flag leaf emersion time. the lowest percentage of non-prolific spiklet obtained at 300 mg/l humic acid concentration at stem elongation time.