The Effect of Vermicompost and Mycorrhizal Inoculation on Grain Yield and some Physiological Characteristics of Soybean (Glycine max L.) under Water Stress Condition

Moisture limitation is considered as one of the important limiting factors in soybean growth. Drought stress affects different aspects of soybean growth through making anatomical, physiological and biochemical changes (Tarumingkeng & Coto, 2003). Under dry tension condition, there will be a disturbance in transmitting nutrients, but some useful soil fungi such as mycorrhiza improve production of crops under stress through forming colonies in the root and boosting water and nutrient absorption (Al-Karaki et al., 2004). Using vermicompost in sustainable agriculture strengthens support and activities of beneficial soil microorganisms (such as mycorrhizal fungi and phosphate solubilizing microorganisms) in order to provide nutrients required by plants like nitrogen, phosphorus and soluble potassium as well as improving the growth and performance of the crops (Arancon et al., 2004).
In order to investigate the effects of vermicompost and mycorrhiza fertilizers on grain yield and some physiological characteristics of soybean under water stress condition an experiment was conducted at Agricultural Research Center of Khorramabad during 2013. The field experiment was carried out based on a randomized complete blocks design arranged in split-plot with four replications. The experiment treatments including irrigation in three levels (after 60, 120 and 180 mm evaporation from pan class A pan), nutrient management in six levels (non-use of vermicompost and mycorhiza fertilizer, inoculated with mycorrhiza fertilizer, consumption of 5 and 10 t.ha-1 vermicompost, consumption of 5 and 10 t.ha-1 vermicompost with mycorrhiza) were respectively as the main plots and sub. In current study, RWC, LAI, SPAD were measured during 59 days after planting at the beginning of podding of the control treatment. The temperature of plant leaves were measured by the thermometer (model TM-958 LUTRON infrared Thermometers). To analyze the growth of grains under different treatments totally 7 samples were performed from flowering to harvest through checking the process of grain weight changes and final grain weight were determined during physiological maturation (when dry grain weight is fixed or changes are not significant). Filling rate and the effective grain filling period were measured using relevant formula. The grain yield measured at the time of maturing after harvesting 3 m² per two middle lines in the plot and through eliminating the fringes of the midfield. All statistical analyzes including variance analysis, comparison of means and interactional slicing using SAS software was done. Mean comparisons using LSD test at the probability of error of 5% was done.
The results of this study concluded that by increasing stress intensity, traits of this research with negative effect on economic performance led to irreparable damage to crop plants. So the lowest grain yield with the rate of 3216.7 kg.ha-1 obtained from 180 mm evaporation. So it is expected to take steps to increase performance by avoiding or minimizing the impact of stress. So that the combined use of these fertilizers had a positive effect on reducing plant leaves heat in low and high water stress condition. Most grain yield obtained by combined treatment of 5 and 10 t.ha-1 vermicompost with mycorrhiza that respectively was 23 and 29 percent more than control treatment. In response to levels of fertilizer, the highest amount of LAI, RWC, Final grain weight and effective grain filling period obtained in vermicompost combined with mycorrhiza treatments.
It seems that the use of vermicompost and mycorrhizal fertilizer combination in areas that are subjected to water stress from improvement of plant physiologic condition can be cause improvement of plant growth conditioning and obtaining higher yielding. Accordingly, for saving irrigation water and cost inputs, farming management and achieving the favorite yield under water deficit conditions, it is recommended to use 5 t.h-1 vermicompost with mycorrhiza for growing L17 soybean.