The effects of foliar application of humic acid and garlic extract on nutrients uptake (NPK) and growth of wheat under drought stress conditions

Materials and methods This study was performed during 2018 in a completely randomized design with factorial arrangement in three replications under greenhouse conditions. The studied soil with texture class of loam had pH = 8.11 and EC = 1.28 dS m-1. Experimental factors include drought stress at three levels of 95%, 65% and 45% of field capacity, garlic extract at three levels of foliar application of 0, 2% and 4% and humic acid at two levels of foliar application of 0 and 300 mg l-1. Drought stress were treated by the weight method, 17 days after sowing. Foliar application of humic acid (twice, 13 and 20 days after threating the drought stress) and garlic extract (three times, 18, 24 and 27 days after threating the drought stress) were performed by spraying 150 ml pot-1 of the solutions in each time. The plants were harvested 54 days after sowing and the parameters of shoot dry weight and uptake of nitrogen, phosphorus and potassium in plant were measured. Statistical analysis was done using SAS 9.4 software and the comparison of means was done using Tukey's test at the 5% probability level. Results and discussion The results showed that foliar application of humic acid and garlic extract alone had a positive effect on dry weight and uptake of nitrogen and phosphorus of shoot. In addition, garlic extract also increased the potassium uptake. Drought stress reduced all investigated parameters; however, foliar application of garlic extract under drought stress conditions increased the absorption of nitrogen, phosphorus, and potassium. In 65% of field capacity, nitrogen uptake by using 2% garlic extract and phosphorus and potassium uptake by using 4% garlic extract had a maximum amount compared to others. In general, garlic extract, due to its antioxidant properties and the presence of growth-promoting compounds such as minerals, vitamins, phytohormones, sulfur compounds, enzymes and amino acids, can improve growth parameters and absorption of nutrients in wheat plant. Humic acid improved growth parameters due to its role in increasing cell membrane permeability, respiration and photosynthesis, phosphate absorption, root and cell expansion, and acting as hormone-like substances. Conclusion The foliar application of wheat plant with garlic extract and humic acid as natural stimulants had a favorable effect on the plant growth and nutrients uptake. Garlic extract was more effective than humic acid in reducing the negative effects of drought stress. Finally, the use of natural materials such as garlic extract and some high consumption compounds such as humic acid can be an environment-friendly and safe approach to improve plant growth and to reduce the destructive effects of chemical fertilizers and synthetic growth regulators.