Elsevier

Pedosphere

Volume 33, Issue 1, February 2023, Pages 105-115
Pedosphere

Potassium sources, microorganisms and plant nutrition: Challenges and future research directions

https://doi.org/10.1016/j.pedsph.2022.06.025Get rights and content

Abstract

Until recently, potassium (K) has not received considerable attention because of the general belief that soils contain ample amounts of this element. In addition, low rates of K fertilizer application in agriculture have led to rapid depletion of K in the rhizosphere soil in many underdeveloped countries. This results in various negative impacts, including preventing optimum utilization of applied nitrogen and phosphorus fertilizers. To compensate for these losses, massive use of K fertilizers in agriculture has been suggested. Potassium fertilizers are manufactured from rock minerals, particularly sylvite (KCl) and carnallite (KCl·MgCl2·6H2 O). Unfortunately, to date, there is no cost-effective technology available for converting rock minerals into potassic fertilizers. Potassium-solubilizing microorganisms (KSMs) can release K from soil/minerals into plant-available forms, which could be a sustainable option. The possibility of using KSMs as efficient biofertilizers to improve crop production has been increasingly highlighted by researchers. In this review, the existing forms of K in soils and their availability and dynamic equilibrium are discussed. In addition, different K fertilizers and their advantages and disadvantages for crops are described. Furthermore, the microorganisms usually reported as K solubilizers, the research progress on KSMs, and future insights on the use of these KSMs in agriculture are reviewed. Screening and analyses of the published literature show that organic acid production is the common mechanism of K solubilization by bacteria and fungi. This review may serve as a proposal for the future research avenues identified here.

Section snippets

INTRODUCTION

Potassium (K) is one of the 16 elements essential for the growth and development of animals, humans, and plants. For plants, K is the third most important nutrient after nitrogen (N) and phosphorus (P) and is the most abundant nutrient after N in photosynthetic tissues of land plants. For some plant species, such as cotton and banana, the demand for K is higher than that for N and P (Mora et al., 2012). These latter are often added to soils through fertilization, whereas the K requirement of

K IN SOIL

Soil minerals from silt, clay, and sand are natural reservoirs of K. Based on their availability to crops, K is often subdivided into four fractions: solution K, exchangeable K, non-exchangeable or fixed K, and mineral K (K in primary mineral structure). These forms are in dynamic equilibrium (Fig. 1), which is controlled by the exchange properties, mineral makeup, and weathering rate of the soil. The relative abundances of the different forms of K are in the following order of mineral K (>

Root exudates and K availability

Plant roots exudate different compounds, including carbohydrates, organic acids, amino acids, phenolic compounds, enzymes, gaseous molecules (such as CO2 and H2), and inorganic ions such as HCO-3, OH, and H+ (Dakora and Phillips, 2002), which are directly or indirectly involved in K solubilization. For instance, Yang et al. (2019) showed that, under K-deficiency treatments, tobacco plants exudate a large amount of organic acids and activate a greater amount of K-bearing minerals. The organic

ISOLATION AND CHARACTERIZATION OF KSMS FROM RHIZOSPHERE SOILS

The Aleksandrov selective agar medium is generally used for the isolation and quantitative assessment of KSMs. The medium contains 5.0 g L–1 glucose, 0.5 g L–1 magnesium sulfate, 0.005 g L–1 ferric chloride, 0.1 g L–1 calcium carbonate, 2 g L–1 calcium phosphate, 2 g L–1 K-bearing minerals, and 3% agar (Aleksandrov et al., 1967). Inspired by the identification of P solubilizers using the Pikovskaya agar plate method, the plate assay has been developed for KSM isolation. The formation of a

MAJOR FUNCTIONS OF K IN CROP PRODUCTION AND QUALITY

Potash fertilizer ensures optimal plant growth, and the K+ requirement for plant growth changes with the developmental stage, crop species, and quantity of K+ available in soil. K is involved in many physiological processes that are vital to plant nutrient and water uptake. The optimal cytoplasmic concentration for enzyme activity is approximately 100–200 mmol L–1. Furthermore, K plays an important role in many fundamental physiological and metabolic processes, such as controlling ion

ADVANTAGES AND DISADVANTAGES OF K FERTILIZER APPLICATION

K in silicate structures can hardly be used by plants when added as fertilizer. Therefore, manufacturing K fertilizers is required for crop growth in soils depleted of available K. Currently, K fertilizers are obtained from sedimentary deposit rocks. The most frequently manufactured and used forms are KNO3, K2SO4, K2CO3, and KCl. Among these products, KCl (more than 95% of K fertilizer) is the most widely used form for agronomic crops. However, its application is subject to some precautions,

IMPROVING K USE EFFICIENCY

Annually, over 30 million tonnes of K fertilizers are applied to agricultural fields worldwide (Bahadur et al., 2016). The demand increased at a rate of 2.5% between 2014 and 2019 and was distributed as follows: 56% in Asia, 27% in America, 11% in Europe, and 6% in Africa (Basak et al., 2017). However, the excessive application of K from chemical fertilizers leads to environmental concerns without improving yield, whereas K deficiency results in reduced crop yields. In fact, K+ from fertilizers

APPLICATION OF KSMS TO CROP PRODUCTION

Several studies have indicated that using KSMs as bio-fertilizers can reduce agrochemical consumption while improving crop production. In this regard, Meena et al. (2016) reported that silicate-dissolving KSMs could free K from insoluble minerals and increase K availability from 84.8% in uninoculated soil to 127.9% in inoculated soil. Similarly, Singh et al. (2010) used waste mica as the sole source of K and showed that three KSMs (B. mucilaginosus, Azotobacter chroococcum, and Rhizobium spp.)

CHALLENGES FOR COMMERCIAL K BIOFERTILIZERS AT THE INDUSTRIAL LEVEL

To date, few biofertilizers based on KSMs are available on the market, and most of them are based on Frateuria species. For instance, Symbion-K, Green K, ABTEC Bio-Potash, UPTAKE, and K Soil B® are based on Frateuria aurantia and ADVEN is based on Frateuria sp., a K-mobilizing bacterium (Kore et al., 2020). Other products are based on Bacillus spp., such as POTAK, a liquid formulation of K-mobilizing Bacillus licheniformis. Overall, there are few biofertilizers based on K-solubilizing and/or

MULTIDISCIPLINARY RESEARCH CONTRIBUTIONS TO KSM BIOFORMULATION

Providing new formulations with the potential to fulfill their expectations requires exploring multidisciplinary research involving biotechnology, nanotechnology, agrobiotechnology, chemical engineering, and material sciences. At the crossroads of these diverse disciplines, several techniques have been developed, such as bioencapsulation, seed coating, and cell- or spore-lyophilized beads with cryoprotectants, such as mannitol, microcrystalline cellulose, granular inoculants, and dried

CONCLUSIONS

This review shows that the potential application of KSMs in agriculture is still under exploration, and studies are currently confined mostly to the laboratory scale. Most publications have shown that the main mechanisms of K solubilization are organic acid production and rhizosphere acidification. In addition, the literature analysis shows that the number of published articles related to K solubilization mechanisms is scattered and lower compared to that of K solubilization microbes. The

SUPPLEMENTARY MATERIAL

Supplementary material for this article can be found in the online version.

ACKNOWLEDGEMENT

We would like to thank Younes En-Nahli and Dr. Sitor Ndour for their support with the statistical analyses.

References (87)

  • C S Nautiyal

    An efficient microbiological growth medium for screening phosphate solubilizing microorganisms

    FEMS Microbiol Lett

    (1999)
  • F Pinzari et al.

    Fungal strategies of potassium extraction from silicates of different resistance as manifested in differential weathering and gene expression

    Geochim Cosmochim Acta

    (2022)
  • M V S Rajawat et al.

    A modified plate assay for rapid screening of potassium-solubilizing bacteria

    Pedosphere

    (2016)
  • J R Rogers et al.

    Mineral stimulation of subsurface microorganisms: Release of limiting nutrients from silicates

    Chem Geol

    (2004)
  • R Shin

    Strategies for improving potassium use efficiency in plants

    Mol Cells

    (2014)
  • S Supanjani et al.

    Nod factor enhances calcium uptake by soybean

    Plant Physiol Biochem

    (2006)
  • S Uroz et al.

    Mineral weathering by bacteria: Ecology, actors and mechanisms

    Trends Microbiol

    (2009)
  • C S Zhang et al.

    Isolation and identification of potassium-solubilizing bacteria from tobacco rhizospheric soil and their effect on tobacco plants

    Appl Soil Ecol

    (2014)
  • L L Zhou et al.

    Rhizosphere acidification of faba bean, soybean and maize

    Sci Total Environ

    (2009)
  • M A Abdel-Salam et al.

    Feldspar-K fertilization of potato (Solanum tuberosum L.) augmented by biofertilizer

    Am-Eurasian J Agric Environ Sci

    (2012)
  • A Ahmed et al.

    Nutrient accumulation and distribution assessment in response to potassium application under maize-soybean intercropping system

    Agronomy

    (2020)
  • V G Aleksandrov et al.

    Liberation of phosphoric acid from apatite by silicate bacteria

    Mikrobiolohichnyi Zhurnal (Kiev)

    (1967)
  • I P Anjanadevi et al.

    Rock inhabiting potassium solubilizing bacteria from Kerala, India: Characterization and possibility in chemical K fertilizer substitution

    J Basic Microbiol

    (2016)
  • G Archana et al.

    Pivotal role of organic acid secretion by rhizobacteria in plant growth promotion

  • M A Badr et al.

    The dissolution of K and P-bearing minerals by silicate dissolving bacteria and their effect on sorghum growth

    Res J Agric Biol Sci

    (2006)
  • D V Badri et al.

    Regulation and function of root exudates

    Plant Cell Environ

    (2009)
  • I Bahadur et al.

    Towards the soil sustainability and potassium-solubilizing microorganisms

  • B B Basak et al.

    Modification of waste mica for alternative source of potassium: Evaluation of potassium release in soil from waste mica treated with potassium solubilizing bacteria

    Nat Resour Res

    (2012)
  • B D Batista et al.

    Realities and hopes in the application of microbial tools in agriculture

    Microb Biotechnol

    (2021)
  • K Boubekri et al.

    The screening of potassium- and phosphate-solubilizing actinobacteria and the assessment of their ability to promote wheat growth parameters

    Microorganisms

    (2021)
  • I Cakmak

    Potassium for better crop production and quality

    Plant Soil

    (2010)
  • L C Carvalhais et al.

    Root exudation of sugars, amino acids, and organic acids by maize as affected by nitrogen, phosphorus, potassium, and iron deficiency

    J Plant Nutr Soil Sci

    (2011)
  • T Chaudhary et al.

    Techniques for improving formulations of bioinoculants

    3 Biotech

    (2020)
  • F D Dakora et al.

    Root exudates as mediators of mineral acquisition in low-nutrient environments

  • J S Dhillon et al.

    World potassium use efficiency in cereal crops

    Agron J

    (2019)
  • J A Dominguez-Nuñez et al.

    Mycorrhizal fungi: Role in the solubilization of potassium

  • H Etesami et al.

    Potassium solubilizing bacteria (KSB): Mechanisms, promotion of plant growth, and futurs prospects—a review

    J Soil Sci Plant Nutr

    (2017)
  • N K Fageria

    Absorption of magnesium and its influence on the uptake of phosphorus, potassium, and calcium by intact groundnut plants

    Plant Soil

    (1974)
  • M G Z Girgis et al.

    In vitro evaluation of rock phosphate and potassium solubilizing potential of some Bacillus strains

    AJBAS

    (2008)
  • K R Glowa et al.

    Extraction of potassium and/or magnesium from selected soil minerals by piloderma

    Geomicrobiol J

    (2003)
  • S Gopalakrishnan et al.

    Plant growth-promoting activities of Streptomyces spp. in sorghum and rice

    SpringerPlus

    (2013)
  • S N Groudev

    Use of heterotrophic microorganisms in mineral biotechnology

    Acta Biotechnol

    (1987)
  • H E Haeder et al.

    The effect of potassium on translocation of photosynthates and yield pattern of potato plants

    J Sci Food Agric

    (1973)
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