The main aim of this research was to study the dynamics of K release from waste mica inoculated with potassium solubilizing microorganism (Bacillus mucilaginosus) and to investigate its effectiveness as potassic-fertilizer using sudan grass (Sorghum vulgare Pers.) var Sudanensis as test crop grown under two Alfisols. Results revealed that application of mica significantly enhanced biomass yield, uptake and per cent K recoveries by sudan grass than control (no-K). Biomass yield, uptake and per cent K recoveries increased further when mica was inoculated with bacterial strain in both the soils than uninoculated mica. Alfisol from Hazaribag recorded higher yield, uptake and K recoveries than Alfisol from Bhubaneswar. The dynamics of K in soils indicated that K was released from mica to water-soluble and exchangeable pools of K due to inoculation of mica with Bacillus mucilaginosus in both the soils. Significantly greater amounts of water-soluble, exchangeable and non-exchangeable K were maintained in Alfisol from Hazaribag than Bhubaneswar. Release kinetics of K showed significant release of K from mica treated with bacterial strain.Significant correlation between biomass yield, K uptake by sudan grass and different pools of K in soils were observed. X-ray diffraction analysis indicates greater dissolution of mica due to inoculation of Bacillus mucilaginosus strain in both the soils. Thus, bio-intervention of waste mica could be an alternative and viable technology to solubilize insoluble K into plant available pool and used efficiently as a source of K-fertilizer for sustaining crop production and maintaining soil potassium.

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Soil needs simultaneous replenishment of various nutrients to maintain its inherent fertility status 22 under extensive cropping systems. Replenishing soil nutrients with commercial fertilizer is 23 costly. Among various fertilizers, deposits of potassium (K) ore suitable for the production of 24 commercial K fertilizer (KCl) are distributed in few northern hemisphere countries (Canada, 25 Russia, Belarus and Germany) which control more than 70% of the world's potash market. Naturally occurring minerals, particularly silicate minerals, could be used as a source of K, but not as satisfactorily as commercial K fertilizers. In this context, bio-intervention (in combination with microorganisms and/or composting) of silicate minerals has been found quite promising to improve plant K availability and assimilation. This is an energy efficient and environmentally friendly approach. Here we present a critical review of existing literature on direct application of silicate minerals as a source of K for plant nutrition as well as soil fertility enhancement by underpinning the bio-intervention strategies and related K solubilization mechanisms. An advancement of knowledge in this field will not only contribute to a better understanding of the complex natural processes of soil K fertility, but also help to develop a new approach to utilize natural mineral resources for sustainable and environmental friendly agricultural practices.

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A study was conducted to evaluate a waste rock powder collected from the Seaham quarry in New South Wales, Australia, as a source of potassium (K) in soil. The K supplying capacity of different size fractions of the mineral powder was evaluated by employing five chemical extractants as well as growing maize and holy basil in sand culture experiments. The K release by chemical extractants increased with decreasing particle size of the mineral powder. The amount of K released by different extractants followed the order :water <0.01 M calcium chloride <0.01 M citric acid<1 N ammonium acetate <1 N boiling nitric acid. The cumulative K release from the mineral powder in successive extraction procedure was recorded higher with organic and mineral acids, which suggested that the material was a slow release K source. A significant positive correlation was observed between K release by different chemical extractants and the biomass yield (r = 0.93; p<0.05) and K uptake(r = 0.96; p<0.05) by plants. Among the different chemical extractants, 1 N ammonium acetate and 1 N boiling HNO 3 showed higher correlations (r = 0.91 and 0.96, respectively) with plant K uptake values. Both the chemical and biological methods were able to extract only a portion (12-20%) of total K present in the mineral powder. The results indicated that the mineral powder could be used as a slow release K fertilizer in soils. Further studies in long term applications with exhaustive crops under field conditions are needed to assess its feasibility as a source of K in agriculture.