Study on the Effect of Humic Acid and Fulvic Acid on the Wheat Yield and Water Use Efficiency under Drought Stress

Optimum water consumption in agricultural production is of vital importance as one of the most important environmental factors affecting the growth and development of the plants, especially in arid and semi-arid regions such as Iran. On the other hand, drought stress, among other environmental stresses, is one of the most important factors that adversely affect the plant growth and yield. Due to the presence of hormonal compounds, organic acids (at low concentrations) can positively affect the production rate and the quality of agricultural products. Considering the water deficit and the necessity of saving water resources as well as the role of organic acids in reducing the negative effects of stress, in the present study attempts are made to investigate the effect of humic and fulvic acid on wheat yield (Triticum aestivum L.) under drought stress conditions. The present study was carried out at the research farm of the national soil and water research institute located 15 km away from Karaj (with elevation of 1280 m) during the 1394-95 crop year. The experiment was a split-plot experiment based on randomized complete block design with three replications which included two main plots (full irrigation and stress) and 36 sub plots of Sivand cultivar. The treatments consisted of the main factor of irrigation regimes at full irrigation and stress levels (35% lower than water requirement) and a sub-factor including six control treatments (F0H0), no foliar application of fulvic acid, in-soil application of 20kg- ha of humic acid (F0H20), Foliar application of fulvic acid (F5H0), and no application of humic acid (F5H0), (F5H20), (F10H0) and treatment (F10H20). The wheat water requirement in the area was estimated by means of Netwat software and irrigation periods were determined based on weather forecast and soil moisture data. Irrigation was carried out using a system of drip irrigation with a specific pressure and discharge level. The stresses were applied from mid-April through consideration of different irrigation hours as compared to full irrigation time. After completion of the growth period, the plant water requirement was accurately estimated by Cropwat software and the percentage of applied stress was accurately calculated (approx. 35%). The Plant yield and some of its components were measured. Statistical analysis was performed through LSD method at 5% significance level using SAS software The mutual impact between irrigation and fulvic and humic acid applications on total and grain yield was not significant (P <0.05). The highest yield was related to the foliar application of fulvic acid (F10H0) with a total yield of 27331 kg/ha, which had no significant difference with treatment F5H20 (total yield of 25667 kg/ha). Under full irrigation conditions, treatments (F10H0, F5H20) led to 31.81% and 28.44% increase in grain yield (as compared to the treatment yield) respectively. Under low irrigation conditions, treatments (F10H0, F5H20) led to 46.66% and 34.33% increase in grain yield, respectively.The Weight of 1000 Grains The application of humic acid and fulvic acid alone did not significantly increase the weight of 1000 grains. But the combined application of fulvic acid (F5H0) and humic acid (20 kg /ha) significantly increased the weight of 1000 grains (8.5%). Under low irrigation conditions, the combined application of humic acid and fulvic acid (F10H0) increased the weight of 1000 grains (as compared to the control group) by 14.75%. Shoot Height The highest shoot height (126.86 cm) was obtained in foliar application of fulvic acid (F5H0) with the in-soil application of humic acid in full irrigation conditions, which increased the shoot height by 22.68% (as compared to the control group). The lowest average shoot height (99.66 cm) was obtained through no application of fulvic acid and humic acid in stress conditions. Spike Length The application of fulvic acid (F5H0) had no significant effect on spike length. However, the combined application of humic acid (20 kg/ ha-) and fulvic acid (F5H0) increased the mean spike length. Regardless of irrigation conditions, the highest mean spike length was 9.188, 9.105 cm for treatments (F5H20, F10H0) and the lowest mean spike length was 8.258, 8.293 cm, for treatments (F5H0, F0H0). A number of Grains per Spike The combined application of humic acid and fulvic acid (F5H0) and the application of fulvic acid (F10H0) led to 10% increase in the number of grains per spike as compared to the control group. Water Use Efficiency The main effect of irrigation and the use of humic acid and fulvic acid on water efficiency was significant at 1% level. The mean comparison at 5% level showed that tension caused 68% increase in water use efficiency. The use of humic acid and fulvic acid increased water use efficiency significantly. The maximum water use efficiency (3.86 kg / m 3) was in spraying the fulvic acid at a concentration of 10 per thousand. Under full irrigation and low water use, the use of fulvic acid at a concentration of 10 per thousand increased water use efficiency as 43.34% and 62.25% The results of this study showed that the combined application of fulvic acid (F5H0) and humic acid (F5H20) significantly increased all the traits under study. The application of humic acid in drought stress conditions led to 9.09 percent increase in grain yield as compared to the control groups in the full irrigation condition, and the application of humic acid and fulvic acid (F5H0), as well as foliar application of fulvic acid alone (F10H0) under stress conditions led to 23.86% and 24.9% improvement in grain yield respectively ( as compared to control treatments under full irrigation conditions) while foliar application of fulvic acid (F10H0) in drought stress conditions resulted in a 2.65% reduction in grain yield as compared to the same treatment under full irrigation conditions. The results showed that the application of fulvic and humic acid in low irrigation conditions can increase wheat yield and water use efficiency.