The Application of Plant Growth Promoting Microorganisms and Phosphate Fertilizers on Yield, Yield Components and Water Use Efficiency of Wheat at Levels of Irrigation Water

Water deficit and low soil fertility are the most important factors limiting plant growth and yield in arid and semiarid regions. The use of chemical fertilizers is the most common way to provide the necessary nutrients for plants including phosphorus. Due to the fixation of high amount of the phosphate fertilizers, especially in calcareous soils, overuse of these fertilizers in addition to their low efficiency, also causes environmental and economic problems.In addition to providing plant nutrients, use of beneficial soil microorganisms can increase tolerance to environmental stresses such as drought. Therefore, the aim of this study was to investigate the role of mycorrhizal fungi and phosphate solubilizing bacteria on yield and yield components of wheat and improving the efficiency of phosphate fertilizers at different levels of irrigation water.

This study was conducted as a factorial experiment in a randomized complete block design with three replications on wheat (Anfarm 4 cultivar) at the research farm of Faculty of Agriculture, Birjand University in crop year 2017-2018.Experimental treatments consisted of four levels of irrigation water (I0, I1, I2 and I3, 100%, 75%, 50% and 25% of field capacity (FC), respectively) and four levels of fertilizer treatment (F0, F1, F2 and F3, Control, plant growth promoting microorganisms (PGPM), 150 kg ha-1 triple super phosphate (TSP), and PGPM+ 75 kg ha-1 TSP, respectively). For determination of the plant height and tiller number, 10 plants were selected from each plot and then their numbers counted. Also, the spike number, spike length, number of seeds per spike, 1000-seeds weight, grain and biological yield, seed P concentration, root colonization and water use efficiency was recorded.

Results showed that with decreasing water use to 25% of FC, plant height (19%), tiller number (35%), spike number (22%), grain number (17%), 1000-grain weight (20%) and grain yield (35%) decreased, but the seed P concentration (42%) was increased. Water stress reduced grain yield more than biological yield. Application of irrigation water by 75%, 50% and 25% of FC, decreased grain yield by 25, 36 and 44% and biological yield by 21%, 30% and 38%, respectively. On the other hand, application of PGPM and chemical fertilizers increased the above parameters at various irrigation water levels. According to the results, there was no significant difference between TSP application and PGPM+ 50% TSP application at different levels of irrigation water for most of the studied indices such as spike number, seed number, 1000-seeds weight, grain yield and seed P concentration. Combined application of PGPM+ 50% TSP at irrigation water levels of 75, 50 and 25% of FC, increased grain yield by 79, 88 and 75% and biological yield by 57, 71 and 61%, respectively compared with the same irrigation water levels. The positive effect of PGPM on yield and yield components of wheat, especially under water deficit conditions,can be attributed to the production of auxin, organic acids and siderophore by bacteria, and the colonization of roots by fungi and access to more soil points, thereby increasing the uptake of nutrients such as phosphorus and water for the plant.

According to the results, although the application of chemical fertilizers had the most effect on most of the measured indices, the application of PGPM with 50% of chemical fertilizer was not statistically different from the full application of fertilizer. In other words, due to the environmental problems and high cost of chemical fertilizers, Therefore, the simultaneous application of chemical fertilizer and PGPM is recommended, especially in conditions of water scarcity in wheat production.