B. R. Maurya

Can Potassium-Solubilising Bacteria Mitigate the Potassium Problems in India?

The nutrients are one of the basic inputs for achieving increased crop productivity, and potassium is one of them. In a recently published nutrient budget, it has been shown that potassium became unbalanced through increased removal and increased system leakage, simplification (monoculture) and increased demand for rapid plant growth. Addressing this nutrient imbalance and shortages in developing countries, it would be required to enhance the world production of potassium fertiliser. India is not self-sufficient in producing potassium fertiliser. The entire quantities of potassium fertilisers are imported. Therefore efficient management in soil fertility is a prime concern to the scientist in view of the increasing gap between production and consumption of fertiliser with time. So, nowadays, crop nutrient stability is important to mitigate the exhaustion of soil nutrient stock for sustaining the crop yield and to reinstate the soil fertility. In these circumstances, it is suitable to study the present knowledge of substitutive sources of K. So this assessment imparts an opportunity to flourish native mineral sources of K as a substitute to impede costly remunerative fertilisers. So, bio-intrusion of potassium minerals with potassium-solubilising microorganism (KSM) would be a preferable and feasible technology to solubilise unavailable form of K minerals into available pool for plant uptake and efficiently used as a source of K fertiliser for maintaining the ecological balance and sustaining agricultural production and environmental quality.

Potassium-Solubilizing Microorganism in Evergreen Agriculture: An Overview

Increasing cost of the fertilizers with lesser nutrient use efficiency necessitates alternate means to fertilizers. Soil is a storehouse of nutrients and energy for living organisms under the soil-plant-microorganism system. These rhizospheric microorganisms are crucial components of sustainable agricultural ecosystems. They are involved in sustaining soil as well as crop productivity under organic matter decomposition, nutrient transformations, and biological nutrient cycling. The rhizospheric microorganisms regulate the nutrient flow in the soil through assimilating nutrients, producing biomass, and converting organically bound forms of nutrients. Soil microorganisms play a significant role in a number of chemical transformations of soils and thus, influence the availability of macro- and micronutrients. Use of plant growth-promoting microorganisms (PGPMs) helps in increasing yields in addition to conventional plant protection. The most important PGPMs are Azospirillum, Azotobacter, Bacillus subtilis, B. mucilaginosus, B. edaphicus, B. circulans, Paenibacillus spp., Acidithiobacillus ferrooxidans, Pseudomonas, Burkholderia, potassium, phosphorous, zinc-solubilizing microorganisms, or SMART microbes; these are eco-friendly and environmentally safe. The rhizosphere is the important area of soil influenced by plant roots. It is composed of huge microbial populations that are somehow different from the rest of the soil population, generally denominated as the “rhizosphere effect.” The rhizosphere is the small region of soil that is immediately near to the root surface and also affected by root exudates.

Towards the Soil Sustainability and Potassium-Solubilizing Microorganisms

Potassium (K) is needed in adequate quantities for a crop to achieve its maximum yield. The function of potassium in plant growth has not been clearly defined but it is associated with movement of water, nutrients and carbohydrates in plant tissue. When potassium is not adequate, the plants will have poor root development and will grow slowly, and their seeds will become small and have lower yields. About 5 million tonnes of potassic fertilizer requirement would be fulfilled through imports because India does not have commercial-grade sources of potash reserve. India is totally dependent on the import of potassic fertilizers. On the other hand, India has the largest reserve for low potassium-containing minerals. The depletion of potassium in soil has been started, and in future this will aggravate. In most of the soils, about 90–98 % of total K exists in relatively unavailable minerals such as feldspar, orthoclase and the micas (muscovite, biotite, phlogopite, etc.). These minerals are very resistant to decomposition and probably supply relatively smaller quantity of potassium to growing crops. Potassium in soil is present in four forms: water-soluble (solution K), exchangeable, non-exchangeable and structural or mineral forms. The fixed form of K minerals is solubilized by K solubilizers, and then acquisition or accumulation of potassium by crop plants certainly will be enhanced. For evergreen agriculture, production can only be fulfilled when the environment, its caretakers and surrounding communities are healthy, for this application of KSMs holds a key approach for K availability in soils. KSB increased K availability in soils and increased mineral nutrient specially K uptake by plant.

Can Bacillus Species Enhance Nutrient Availability in Agricultural Soils

One major challenge for the twenty-first century will be the production of sufficient food for the global human population. The negative impacts on soil–plant–microbes–environmental sustainability due to injudicious use of chemical fertilizer, pesticide, insecticide, etc. by the unaware farmers deteriorate soil and environment quality. One possible way to use efficient soil microorganisms to remediate nutrient deficiency in agricultural soils and other plant growth-promoting (PGP) activities that can be of help for plant growth and development. The Bacillus species is one the most dominant rhizospheric bacterial/rhizobacteria species like Bacillus subtilis, B. cereus, B. thuringiensis, B. pumilus, B. megaterium, etc. that can help enhance the plant growth and development by different mechanisms, which PGPR can inhibit phytopathogens is the production of hydrogen cyanide (HCN) and/or fungal cell wall degrading enzymes, e.g., chitinase and s-1,3-glucanase. Direct plant growth promotion includes symbiotic and non-symbiotic PGPR which function through production of plant hormones such as auxins, cytokinins, gibberellins, ethylene, and abscisic acid. Mitigate the challenge by adopting eco-friendly crop production practices. Some Bacillus species function as a sink for 1-aminocyclopropane-1-carboxylate (ACC), the immediate precursor of ethylene in higher plants, by hydrolyzing it into α-ketobutyrate and ammonia and in this way promote root growth by lowering indigenous ethylene levels in the micro-rhizo environment. Bacillus species also help in solubilization of mineral phosphates, potassium, zinc, and other nutrients; rhizobacteria retain more soil organic N and other nutrients in the soil–plant system, thus reducing the need for fertilizers and enhancing release of the nutrients from indigenous or mineral sources, enhancing the economic and environmental sustainability.