Changes in partitioning and remobilization of assimilate in Maragheh vetch (Vicia sativa) cultivar under the influence of biological fertilizers and supplementary irrigation in the integrated tree, and crop system

Introduction Vetch is one of the legume family that is widely cultivated as a cover crop, reduce erosion, and increase soil fertility. Drought stress that occurs during the reproductive growth period, adversely affects yield and yield components. Supplementary irrigation can be efficient technique to cope with the limited water availability and to stabilize the crop yields. Biological fertilizers such as mycorrhizal fungi, Azotobacter and Thiobacillus spp play an important role in sustainable agriculture. The mycorrhizal symbiosis with plants causes changes in plant water relations and thus improve drought resistance or tolerance in the host plant. Azotobacter has the potentiality to produce different types of amino acids, plant growth hormones, antifungal antibiotics, and siderophore and has a unique ability of atmospheric nitrogen fixation in the soil. The application of sulfur coupled with Thiobacillus spp renders alkali soils fit for cultivation of crops. The formation of sulphuric acid by Thiobacillus spp in soil increases the level of soluble P, K, Ca, Mg, Al and Mn ion. Therefore, this study was conducted to determine the effect of biofertilizers treatment on yield and some quality traits of Vetch (Vicia sativa) under Agroforestry system.   Materials and Methods This factorial experiment was performed as a complete randomized block design with three replications at Urmia University in two years (2016 and 2017). Experimental treatments included once supplemental irrigation and dry farming as the first factor and application of biofertilizers at eight levels {Control (non-application of fertilizer), Mycorrhizal fungus (Rhizophagus intraradices), Azotobacter, Thiobacillus spp, Azotobacter + Mycorrhiza (R. intraradices), Thiobacillus spp + Mycorrhiza (R. intraradices), Azotobacter + Thiobacillus spp, Azotobacter + Thiobacillus spp + Mycorrhizal fungus (R. intraradices)} were the second factor. Supplementary irrigation treatment was applied at the flowering stage (10%) for two years. Vetch plants were harvested on 25-27th of June in two years. At harvest, from each treatment ten plants were taken randomly and plant height, pod per plant, seed per plant, 100 grain weight, were recorded. Whole plot was harvested for determination of seed yield. The analysis of variance for the two-year data was performed using GLM procedure (SAS 9.1.3, SAS Institute Inc., Cary, NC, USA) as combined over years. The effects of irrigation regimes, the application of biofertilizers and interactions of these two factors were analyzed using analysis of variance (ANOVA) and means were compared using Duncan's Multiple Range Test (DMRT) (P≤ 0.05).   Results and Discussion The results showed that supplementary irrigation increased the number of pods per plant and forage calcium content. But the highest rate and efficiency of photosynthetic materials remobilization and forage protein content were obtained in farming condition. Also, the number of pods per plant, the percentage of calcium and protein content of forage increased significantly due to the application of biological fertilizers. Thus, the combined application of mycorrhizal + Azotobacter treatment increased the number of pods per plant, and protein content of forage by 15.55% and 18.88%, respectively, as compared to the Control. While the highest rate and efficiency of photosynthetic materials remobilization were obtained in non-biofertilizer treatment (control). Supplementary irrigated vetch plants under combined application of mycorrhiza and Azotobacter, due to the having maximum amount of root colonization (63.45%) and relative water content (69.50%), had the highest number of seeds per plant (204.94) and 100 seed weight (4.47 g), which resulted in maximum seed yield (187.32 g/m2). Generally, the results of the experiment showed that in rainfed conditions, the amount of remobilization of photosynthetic materials increased. Subsequently, in this situation, the efficiency of the remobilization and also the remobilization share in grain filling increased, which probably reduced the filling time of the seeds. Thus, increase in the filling speed of the seeds, can partly compensate for the reduction of the material's transfer time to the seed. In the absence of water stress, more material is transferred to the seeds and the final weight of the seeds increases, and consequently the final yield of the seeds increases.   Conclusion Application of dual inoculation of mycorrhiza and Azotobacter could improve the uptake of yield and yield components in vetch under Agroforestry system. Therefore, according to the findings of this research, the combined use of biological fertilizers to increase yield and maintain long-term production in an agroforestry system under rain-fed conditions can be desirable for sustainable agriculture.