Effect of plant growth promoting bacteria along with potassium fertilizer on yield and yield components of rice (cv. ‘Tarom Hashemi’)

Rice (Oryza sativa L.) is one of the most important tropical cereals which is a staple food for about 50% of population around the world, including Iran. The annual grain production of rice in Iran was 2.5 million tones which provided from an area of 0.59 million ha-1. Estimates indicate that rice yield should be enhanced about 65% in the world by the year 2020, especially in developing countries where it is the main food crop. The third macro-nutrient next to nitrogen (N) and phosphorus (P) is known as potassium (K). Potassium is absorbed by roots equal to N and or second after N in some plants like rice. However, it is available to plants about 1-2% of total K in the soil (K+, soluble forms) while 90-98% of this is unavailable for plant uptake, as a result of the strong binding force between K and other minerals such as mica and feldspar. Therefore, introduce alternative sources of fertilizer such as microbial activation can be an effective way to meet a sustainable agriculture and to decline the use of chemical fertilizers. For this purpose, plant growth promoting rhisobacteria (PGPRs) can be used in rice paddies field. PGPRs influence on plant growth and productivity using both direct (assisting in resource acquisition (nitrogen, phosphorus and essential minerals) or modulating plant hormone levels) and indirect (indirectly by decreasing the inhibitory effects of various pathogens on plant growth and development in the forms of biocontrol agents) mechanisms that are fully described in Ahemad and Kibret (2014).

A field experiment was conducted in a paddy field of Mazandaran province (Babol city) as a split plot arrangement based on randomized complete block design with three replications in 2016. Six levels of potassium sulfate fertilizer (PSF: 0, 25, 50, 75, 100 and 125 kg.ha-1) were used as the main plot and four levels of inoculations (non-inoculation as control, seed inoculation in the seedbed condition, seedling root inoculation before transplanting time and combined both previously methods) served as the sub-plots. The experiment was performed under optimal agronomic conditions. Plots were weeded by hand. If necessary, appropriate chemicals were applied to control pests and diseases. A water depth of 3–5 cm was applied in all plots from transplanting time until 2 weeks before harvest maturity (82 days after transplanting). Ten rice plants were randomly harvested at physiological maturity to measure yield components of rice. Actual paddy yield (PY) and biological yield (BY) were also determined at harvesting time by removing of 1 m–2 of rice plants from each plot. Potassium concentration in the grain was measured by the flame photometric method. 

The results indicated that all studied traits were significantly affected by PSF and various inoculation methods, except for panicle length and total number of grain per panicle, but the interaction effect between them were not statistically significant. Various inoculation methods significantly increased panicle number per hill, number of filled grain per panicle, PY, BY, harvest index, potassium uptake (PU) in the grain and PU in the straw of rice by 8.40-17.8, 3.50-8.30, 14.6-19.8, 8.71-13.2, 5.20-5.70, 15.9-18.9 and 3.45-13.2%, respectively, and the number of empty grain per panicle (NEGP) was decreased by 58.3-61.6% as compared to the control. Furthermore, values of all studied traits particularly PY (18.2% more than the control), except for NEGP which was decreased, increased with the addition of PSF from zero to 125 kg.ha-1.

The combined inoculation method improve yield components and potassium uptake by rice plant which was defined as the best method. Therefore, this method can be used in reduced potassium fertilizer condition (~25 kg.ha-1) to meet a sustainable rice system production.