Studies on microbial isolates for potassium solubilization

Abstract

Potassium availability to crop plants in soil is generally low as nearly 98 per cent of total K in soil is in mineral forms.Application of locally available soil minerals such as mica, feldspar, and rock phosphate in combination with efficient potassium mobilizing bacterial strains as bio-fertilizers is urgently required to replace chemical fertilizers and for reducing the cost of crop cultivation. Although, many bacterial strains have been found to improve the growth of plants under pot culture conditions, the extent of growth stimulation by bacterial strains under field conditions usually remains unexplored. Therefore, effective potassium-solubilizing and plant growth promoting bacterium-plant systems must be tested under field conditions with specific crop experimental designs, keeping in consideration of the soil type, plant types grown, and the environmental factors. Thus, competitive and effective bacterial strains could be selected from the indigenous beneficial soil bacteria which could be adopted to the particular conditions of the inoculation site. The application of efficient strains of potassium-solubilizing bacteria is very crucial for their use in the amelioration of potassium-deficient soils, and to plan future research strategies. In current studies attempts were made to isolate potassium solubilizing bacteria from rhizosphere soil of different crops from various areas of Meerut-Muzaffarnagar district. A total of 36 potassium solubilizing isolates are isolated on Aleksandrov Agar media 33 out of which are bacterial isolates and 3 were fungal isolates. They were isolated for K solubilization and characterized upto genus level based on morphological and biochemical characters. The mechanisms involved in K soluiblization and other agronomical beneficial traits like solubilization of insoluble phosphate were analyzed for all thirty six isolates. After secondary screening ten bacterial isolates were selected from thirty three isolates for further studies that were able to solubilize higher amount of potassium mineral. Among them SS 7-6, SS 16-1, S-6, SS 5-3, PYS-19X, SS 9-2 and SS 7-1 were Gram negative, probably identified as Pseudomonas sp. as all gave blue fluorescence under UV light while SS-13,SS 7-7, and PYS-20A were Gram positive, and probably identified as Bacillus spas all Bacillus isolates showed positive results for Catalase, Oxidase and motility tests.. The highest solubilization efficiency was observed in case of SS7-6 i.e. 11.50 which was followed by SS-13 i.e. 11.30. All isolated KSB were checked for phosphorous solubilization (in separate studies) also as a result it was observed that the isolates SS 5-1, SS 5-2, SS 5-4, SS 7-1, SS7-4, S-6, SS-6, SS 9-1, SS 9-2, SS 9-3, PYS 19X, PYS-1, PYS-5B, PYS-5A, PYS-7C1 and PYS-20A efficiently solubilized phosphorous. Such results showed that they are responsible for both phosphorus and potassium solubilization capacity such ‘dual-soubilizers’ can utilize fixed potassium and phosphorous source in soil, this will ultimately enhance the plant growth and yield. Keeping in view the above results in future investigations can be done with above isolates to check if they are also solubilizing other fixed minerals in soil.Thus it can be inferred that potassium solubilizing bacteria have the potential to be efficiently used as bioinoculants in varios crops.