Effect of plant growth promoting micro-organisms on some vegetative characteristics and grain yield of rice (Oryza sativa L.) under different levels of potassium fertilizer

One of the aims of Iranian farmers is self-sufficiency in rice production. To purpose this aim according to the sustainable agricultural laws, it is important to use an appropriate agronomic management such as improving use of chemical fertilizers and or application of biofertilizers in both method; alone and or along with declined chemical fertilizers. Also, use of renewable inputs such as plant growth promoting microorganisms (PGPM; with the ability of biological nitrogen fixation, solubilize insoluble minerals like phosphorus and potassium, phytohormone production and or production of enzymes and organic acids) with high ecological benefits and low environmental damages is necessary today. Therefore, this study aimed to evaluate the efficiency of two PGPM on some vegetative characteristics and grain yield (GY) of rice (cv. ‘Tarom Mahali’) at different amounts of potassium sulfate fertilizer (PSF). A field experiment was conducted in a paddy field of Mazandaran province (Juybar city) as a split plot based on a randomized complete block design with three replications in 2016. Four levels of PSF (zero, 60, 120 and 180 kg ha–1) were used as the main plot and four levels of inoculation with PGPM (Pantoea ananatis and Piriformospora indica were applied individually and a co-inoculation with Pa. ananatis and Pi. indica (50:50) and non-inoculated as control) served as the sub plots. Based on the results of soil test, 50 kg ha–1 of triple super phosphate and all levels of PSF were used before transplanting time and 150 kg ha–1 of urea was applied twice (100 and 50 kg ha–1 at transplanting and heading stage, respectively). At anthesis stage, some vegetative characteristics including plant height (PH), total number leaves hill-1 (TNL), leaf area index (LAI), total tillers numbers hill-1 (TTN) and the time of beginning anthesis stage (BAS) were measured. GY was also determined at harvesting time by removing of 1 m–2 of rice plants from each plot. The results of this study indicate that all studied traits significantly affected by the simple effect of PSF and PGPM inoculations and also their interactions was significant at 0.01 and 0.05 probability level. As PSF increased from 0 to 120 kg ha-1, the significant increase in PH (from 142.1 to 150 cm), TTN (from 9.2 to 11.0 count), TNL (from 64.2 to 65.4 count), LAI (from 3.9 to 5.6) and GY (from 448.8 to 585.7 gr m-2) was 6, 20, 2, 41 and 30%, respectively, as compared to the control. In addition, BAS decreased significantly by 2.3% (from 57.6 to 56.2 days after transplanting), as compared to the control (without PSF). Although, an increasing of PSF from 120 to 180 kg ha-1 resulted in an increase in all studied traits, but differences were not statistically significant among treatments. In addition, single inoculations with Pa. ananatis, Pi. indica and co-inoculation treatment significantly increased PH by 4.4, 4.1 and 3.4%, TTN by 8.7, 8.7 and 22.7%, TNL by 2.8, 2.4 and 4.4%, LAI by 13.1, 15.0 and 27.2% and GY by 11.2, 11.2 and 19.4% and decreased significantly BAS by 2.0, 2.0 and 3.3%, as compared to the control (non-inoculation), respectively. Based on our finding the co-inoculation with Pa. ananatis and Pi. indica as the best treatment, improved the values of all studied traits when compared with the control condition. In general, application of this treatment resulted in decreasing PSF about 55 kg ha-1 (40 % lower than the control) and increasing GY about 79 gr m-2 (18.6% more than the control). Consequently, these PGPM can be used along with lower values of PSF as well as, particularly in sustainable rice cultivation systems.