Evaluation of biofertilizers on quality, yield and yield components of two potato (Solanum tuberosum) cultivars

Potatoes producers in Iran are widely use nitrogen, phosphorus and potash fertilizers for tuber production, but the tuber yield is less than the potential in desirable conditions. In this high cost and low efficiency farming system, soil microorganisms can play an important role in improving fertilizer efficiency and reducing costs. In addition to physical and chemical properties, soil quality has a close relationship with biological aspects. The aim of the present work was to evaluate the positive effects of potassium, phosphate solubilizing bacteria and nitrogen-fixing bacteria on potato growth, tubers yield and its dry matter, as well as saving the chemical fertilizers for healthier crop production. Materials and Methods This study was conducted as a split plot experiment in a randomized complete block design with three replications at Research Farm of Ferdowsi University of Mashhad, Iran in the 2016 cropping season. Treatments included nine fertilizer programs including; phosphate solubilizing bacteria (Phospho-powerbacter dayan), potassium solubilizing bacteria (Peta-powerbacter dayan), free-living nitrogen-fixing bacteria (Nitro-bacter dayan), phosphate solubilizing bacteria + Triple super phosphate fertilizer, potassium solubilizing bacteria + potassium sulfate fertilizer, free-living nitrogen-fixing bacteria+ nitrogen fertilizer with a source of urea 46%, phosphate solubilizing bacteria + potassium solubilizing bacteria + free-living nitrogen-fixing bacteria, phosphate solubilizing bacteria + potassium solubilizing bacteria + free-living nitrogen-fixing bacteria + triple super phosphate + potassium sulfate + nitrogen and control (without biological and chemical fertilizer) as main plots and two potato cultivars (Fontane and Sante) as subplots.

The highest leaf area index observed in Fontane cultivar and phosphate solubilizing bacteria + potassium solubilizing bacteria + free-living nitrogen-fixing bacteria. In Sante cultivar, tow treatments including free-living nitrogen-fixing bacteria alone and phosphate solubilizing bacteria + potassium solubilizing bacteria + free-living nitrogen-fixing bacteria showed the highest leaf area index. The highest Fontane shoot biomass was produced in phosphate solubilizing bacteria + potassium solubilizing bacteria + free-living nitrogen-fixing bacteria treatment and in Sante cultivar was observed in free-living nitrogen-fixing bacteria + Nitrogen fertilizer treatments. Application of phosphate solubilizing bacteria + potassium solubilizing bacteria + free-living nitrogen-fixing bacteria simultaneously caused an increase in the number of tubers per plant in both cultivars. Fontane in potassium solubilizing bacteria + potassium sulfate fertilizer produced the highest tuber yield, which it was 37% more than control treatment. The highest tuber yield in Sante cultivar was obtained by application of phosphate solubilizing bacteria + potassium solubilizing bacteria + free-living nitrogen-fixing bacteria + triple super phosphate + potassium sulfate + nitrogen, which was 36% more than control treatment. The highest of dry matter percentage, specific gravity and starch content in both cultivars were obtained in treatment of all bacteria with chemical fertilizers and the lowest of these characteristics was observed in control treatment. The lowest reducing sugars was obtained in the phosphate solubilizing bacteria + Triple super phosphate and phosphate solubilizing bacteria in Fontaneh and Sante cultivars, respectively. The best DPPH radical scavenging activity in Fontaneh was observed in treatment of all bacterias and in Sante cultivar in applying free-living nitrogen-fixing bacteria. The highest and lowest total phenol content was observed in control treatment and application of potassium solubilizing bacteria + potassium sulfate fertilizer with 75% difference, respectively.

In the present study, the application of bio fertilizers in potatoes showed that these fertilizers could improve physiological, yield and quality characteristics of potato cultivars by using less chemical fertilizers. Generally, application of phosphate solubilizing bacteria + potassium solubilizing bacteria + free-living nitrogen-fixing bacteria + triple super phosphate + potassium sulfate + nitrogen produced the highest potato tuber yield.