Effect of Humic acid on the yield and yield components of Lima Bean (Phaseolus lunatus L.) under drought stress conditions

IntroductionDrought stress is one of the most yield reduction factor of lima bean where effects on the more than 60% of bean world production. In this regard, solutions that help increase productivity with high water efficiency in this region can change the agricultural crop production. One of the solutions is using organic materials (acid humic). Humic acid with linkage of water molecules and folic acid and penetration into plant tissues link to water molecules reduce evaporation and transpiration and finally helps inner plant water.
Materials and MethodsIn order to evaluate the effects of humic acid on yield and yield components of lima bean under water stress conditions, a field experiment was conducted as split plot arrangement in RCBD design with three replications at the Research Station of Shahrekord University in year 1994. Main factors include four treatments of water deficit (irrigation after 50, 70, 90 and 110 mm evaporation from evaporate pan of class A) and sub factor include four levels of humic acid (0, 1, 3, and 6 lit/ha). For this purpose, a semi-deep plowing in the spring then by the two vertical discs were leveling land and finally by furrower created 80 cm row width. Lima bean seeds were prepared by Pars Khomein Company. Seeds were planted in the wet soil. In this way, sterilized seeds were planted in both side of 80 cm width row with 20 cm row plant space in depth of 5 cm at plots area of 3×4 m2. During the plant growth period, the plots were irrigated by furrow irrigation, hand weeding were applied through the experiment. Chemical fertilizers were applied based on the soil test analysis and plant requirements. After achieving the desired density and complete plant establishment, where the plants had two stem nodes, irrigation treatment were applied as cumulative evaporation from class A evaporation pan, and this trend continued until harvest. Humic acid used in the composition of the liquid phase include 12% of humic acid, 3% of folic acid and 3% of potassium oxide. The recommended concentration of humic acid (1, 3, and 6 lit/ha) before flowering was applied two times within two weeks. Plants were harvested when the pods reach 80 to 90% maturity. After harvesting the plants for measurements number of pods per plant, length, width and weight of pods, number of seeds per pod, 100 seeds weight, seed yield and harvest index were transported to the laboratory. Data traits were analyzed by SAS 9, mean comparison of treatments using the least significant difference (LSD) at 5% by MSTAT-C were evaluated. Excel was used to plot the graphs.
Results and DiscussionThe results showed that the humic acid in drought conditions increased yield of pods per plant, 100 seeds weight, grain yield and harvest index was followed. In this experiment, as the width of the seed was not influenced by drought stress and humic acid. Traits of pod weight and seeds number per pod were only affected by drought stress and pod length significantly affected by drought stress and humic acid was used. Drought stress by drying pollen grains, reducing the duration of flowering and young pods loss reduced pod per plant. The current decrease in photosynthesis leads to founder grains shrink and ultimately decreased 100 seeds weight under drought stress. Humic acid appears to increase plant photosynthesis activity as increased enzyme activity of Rubiscoand to improve production of sugar, protein and vitamins in plant and has a positive effect on the various aspects of photosynthesis, seed storage compounds increased. In general, many of the economical yield of a plant, is the result of the growth process that occurs during growth and development. Drought stress can affect performance by influencing these yield processes. The yield was decreased due to stress, so that the performance of the plants in drought stress levels were less than optimum irrigation. Humic acid increased cell membrane permeability, thereby facilitating the entry of potassium, resulting in increased pressure moved into the cell and cell division. On the other hand, increasing energy inside cells leads to the production of chlorophyll and photosynthesis rate. Followed by an important factor in the growth of the nitrogen uptake into cells is developed resonance and finally, the effects of nitrate production decreases, which leads to the increased production. Reduced harvest index in drought stress treatment may be due to reduction of photosynthetic level, reduced photosynthesis remobilization in grain filling stage and more sensitive of vegetative growth compared to vegetative growth to the adverse conditions.
ConclusionA total of 6 liters per hectare application of humic acid under drought stress and moderate stress (irrigation after 70 mm evaporation) is recommended. Because under stress condition, caused the highest yield. Therefore, usage of organic materials in arid and semi-arid areas to fight drought stress and in order to deal with drought stress is recommended for sustainable agriculture.