basak & biswas, plant and soil(2009)317;235-255

REGULAR ARTICLE

Influence of potassium solubilizing microorganism(Bacillus mucilaginosus) and waste mica on potassiumuptake dynamics by sudan grass (Sorghum vulgare Pers.)grown under two Alfisols

B. B. Basak & D. R. Biswas

Received: 13 May 2008 /Accepted: 6 October 2008 /Published online: 5 November 2008# Springer Science + Business Media B.V. 2008

Abstract The main aim of this research was to studythe dynamics of K release from waste mica inoculatedwith potassium solubilizing microorganism (Bacillusmucilaginosus) and to investigate its effectiveness aspotassic-fertilizer using sudan grass (Sorghum vulgarePers.) var Sudanensis as test crop grown under twoAlfisols. Results revealed that application of micasignificantly enhanced biomass yield, uptake and percent K recoveries by sudan grass than control (no-K).Biomass yield, uptake and per cent K recoveriesincreased further when mica was inoculated withbacterial strain in both the soils than uninoculated mica.Alfisol from Hazaribag recorded higher yield, uptakeand K recoveries than Alfisol from Bhubaneswar. Thedynamics of K in soils indicated that K was releasedfrommica to water-soluble and exchangeable pools of Kdue to inoculation of mica with Bacillus mucilaginosusin both the soils. Significantly greater amounts ofwater-soluble, exchangeable and non-exchangeable Kwere maintained in Alfisol from Hazaribag thanBhubaneswar. Release kinetics of K showed significantrelease of K from mica treated with bacterial strain.

Significant correlation between biomass yield, Kuptake by sudan grass and different pools of K in soilswere observed. X-ray diffraction analysis indicatesgreater dissolution of mica due to inoculation ofBacillus mucilaginosus strain in both the soils. Thus,bio-intervention of waste mica could be an alternativeand viable technology to solubilize insoluble K intoplant available pool and used efficiently as a source ofK-fertilizer for sustaining crop production and main-taining soil potassium.

Keywords Waste mica . Alfisol . Sudan grass .

Bacillus mucilaginosus . Pools of K .

X-ray diffraction analysis

Introduction

Potassium (K) is the third major essential nutrient forplant growth. It plays an essential role for enzymeactivation, protein synthesis and photosynthesis. Theissue of sustainable management of potassium in soilhas partly been ignored during the last decades whenthe focus was aimed with potent environmentalimpact on use of nitrogen and phosphorus. However,in recent years there is a growing awareness amongall concerned regarding the importance of potassiumin crop production in several parts of India. There aremany reports in recent past that Indian soils do showK deficiency because available soil K levels havedropped due to rapid development of agriculture

Plant Soil (2009) 317:235255DOI 10.1007/s11104-008-9805-z

Responsible Editor: Philippe Hinsinger.

B. B. Basak :D. R. Biswas (*)Division of Soil Science and Agricultural Chemistry,Indian Agricultural Research Institute,New Delhi 110 012, Indiae-mail: [email protected]

B. B. Basake-mail: [email protected]

without replenishing it and application of potassiumfertilizer to those soils gives positive response.

Potassium in soil is present in water-soluble(solution K), exchangeable, non-exchangeable andstructural or mineral forms. Potassium from water-soluble and exchangeable pools is directly availablefor plant uptake. At low levels of exchangeable K incertain soil types, non-exchangeable K can alsocontribute significantly to the plant uptake (Memonet al. 1988; Sharpley 1989). Exchangeable K oravailable K is held by negative charge clay mineralsand organic matter in soils, while non-exchangeableK consists predominantly of interlayer K of non-expanded clay minerals such as illite and lattice K inK-minerals such as K-feldspars. The bulk of total soilK is in the mineral fraction (Sparks and Huang 1985;Sparks 1987). There are dynamic equilibrium andkinetic reactions between the different forms of soil Kthat affect the level of soil solution K at any particulartime, and thus, the amount of readily available K forplants. Levels of soil solution K are determined by theequilibria and kinetic reactions between the otherforms of soil K (Sparks 1987). The rate and directionof reactions between solution and exchangeable formsof K determine whether applied K will be leachedinto lower horizons, taken up by plants, convertedinto unavailable forms, or released into availableforms (Sparks 2000). The fate of applied K in soil isalso governed by clay content and clay mineralogy ofsoil, and the nature of crops grown. Release of non-exchangeable K to the exchangeable form occurswhen levels of exchangeable and solution K aredecreased by crop removal and/or leaching andperhaps by large increases in microbial activity(Sparks 1987). Mineral K is generally assumed to beonly slowly available to plants (Sparks and Huang1985); however, the availability is dependent on anumber of factors, including the level of other formsof K, namely, solution, exchangeable and non-exchangeable, and the degree of weathering of theK-bearing minerals like feldspar and micas (Sparks1987).

Potassium is added to soil in the form of potassicfertilizers. India ranks fourth after USA, China, andBrazil as far as the total consumption of K-fertilizersin the World is concerned (FAI 2007). However, thereis no reserve of K-bearing minerals in India forproduction of commercial K-fertilizers and the wholeconsumption of K-fertilizers are imported in the form

of muriate of potash (KCl) and sulphate of potash(K2SO4) which leads to a huge amount of foreignexchange. These necessitate to find an alternateindigenous source of K for plant needs and maintainK status in soils for sustaining crop production. In thisrespect, India is fortunate to have the worlds largestdeposit of mica mines distributed in Munger districtof Bihar and Koderma and Giridih districts of Jhark-hand. During the dressing of raw micas largequantities of waste mica are generated (about 75%of total mica mined) which are not used in agricultureas source of potassium though contains significantamount of K (812% K2O) and dumped near the micamines (Nishanth and Biswas 2008). These are mostlywhite mica and categorized as muscovite mica. Theyhave flake-like sheet structure, insoluble in water andhydrochloric acid (HCl), but can be solubilized bydigesting with phosphoric acid (H3PO4) at 300350Cfor about an hour. These materials can effectively beused as a source of potassium, if modified or alteredby some suitable chemical or biological means. Oneof the possible means of utilizing waste mica is bymobilizing their K through composting technologywhere unavailable K is converted into plant availableform because of the acidic environment prevailingduring composting (Nishanth and Biswas 2008).

The results of the few experiments done elsewhereon the K-releasing capacity of a range of crushedrocks and minerals as source of K-fertilizer has beeninvestigated (Hinsinger et al. 1996; Sanz Scovino andRowell 1988; Bakken et al. 1997, 2000). Although itis concluded that a substantial part of the K bound incrushed rocks and mine tailings containing biotite,K-feldspar and nepheline is plant available, theserock/mineral products weathered too slowly to re-plenish the native pool of plant available K. Groundrock has been proposed as a slow release K-fertilizerfor highly weathered soils and leaching environmentswhere soluble fertilizers may be easily dissolved andleached (Coroneos et al. 1996; Hinsinger et al. 1996;Sanz Scovino and Rowell 1988). Nutrients fromground rock under leaching conditions may bereleased at a rate that allows them to remain in thetop-soil and utilized by plants (Coroneos et al. 1996).Ground silicate rocks are also considered as slowrelease K-fertilizer in situations where leaching ratesof conventional fertilizers are particularly high, e.g. insandy soils under wet climatic regimes (Harley andGilkes 2000). However, the effectiveness of silicate

236 Plant Soil (2009) 317:235255

rock fertilizers in agricultural practices has beenfound very poor because of low solubility of silicaterocks and the subsequent low availability of nutrientsto plants as well as the practicality of applying largeamounts of ground rock to agricultural land (Hinsingeret al. 1996; Bolland and Baker 2000; Harley andGilkes 2000). Fused potassium silicate, which con-tains K2Ca2Si2O7, has been prepared and used as aslow-releasing potassium fertilizer (Yao et al. 2003).Such result suggests the involvement of K priming,a process by which the addition of K fertilizersenhances plant K uptake from the soil.

Some microorganisms in the soil are able tosolubilize unavailable forms of K-bearing minerals,such as micas, illite and orthoclase, by excretingorganic acids which either directly dissolves rock Kor chelating silicon ions to bring the K into solution(Bennett et al. 1998; Barker et al. 1998). Thesemicroorganisms are commonly known as potassiumsolubilizing bacteria (KSB) or potassium dissolvingbacteria or silicate dissolving bacteria. Some researchhas been made about the use of potassium dissolvingbacteria, known as biological potassium biofertilizer(BPF), particularly in China and South Korea toinvestigate the bio-activation of soil K-reserves so asto alleviate the shortage of K-fertilizer. It was shownthat KSB increased K availability in soils andincreased mineral uptake by plant (Sheng et al.2002, 2003). Therefore, application of KSB holds apromising approach for increasing K availability insoils. However, information on mobilization of K inwaste mica and their use as K-fertilizer for cropproduction is lacking. The objectives of this studywere (i) to see the dynamics of potassium releasefrom waste mica as influenced by potassium solubi-lizing microorganism (Bacillus mucilaginosus) and(ii) to investigate its effectiveness as K-fertilizer usingsudan grass (Sorghum vulgare Pers.) var Sudanensisas test crop grown under two Alfisols.

Materials and methods

Waste mica

Waste mica, a K-bearing mineral, was obtained fromthe surroundings of mica mines located at Kodermadistrict of Jharkhand, India. The waste mica isgenerated during the dressing of raw mica blocks,

which is generally used as electrical insulator. Thiswaste material is dumped near the mica mines and notused in agriculture as such. It belongs to muscovitemica, which has the theoretical composition of(OH)4K2(Si6Al2)Al4O20. The waste mica has a flake-like structure. It was ground in a Wiley mill and passedthrough 2-mm sieve before further use. The groundwaste mica contained 10.0% total K and had 30.0 mgkg1 of water-soluble K. The amounts of exchangeableand non-exchangeable K in the ground waste micawere 157.5 mg kg1 and 260.0 mg kg1, respectively.

Bacterial strain

Biological potassium fertilizer (BPF), a carrier basedbiofertilizer product containing Bacillus mucilaginosusstrain was obtained from the Hebei Research Instituteof Microbiology, Hebei Academy of Science, BaodingCity, Hebei Province, P.R. China with due permissionfrom the Government of India, Ministry of Agriculture,Department of Agriculture and Cooperation, Directorateof Plant Protection, Quarantine & Storage, Faridabad,Haryana, India. The BPF product is widely used aspotassium solubilizing biofertilizers in China. Theactive bacterial strain was isolated from the BPFmaterial using nutrient agar medium and subsequentlymultiplied for further use. The composition of thenutrient agar medium were: beef extract 3.0 g; peptone5.0 g; agar 15.0 g; distilled water 1000 ml; pH 6.67.0.The isolated strain was maintained on potato-dextroseagar slants in a refrigerator at 4C.

The Bacillus mucilaginosus strain was multipliedby standard technique. Broth culture medium of thebacteria was prepared according to the proceduresuitable for potassium solubilizing bacteria (Shenget al. 2002; Wu et al. 2005; Sheng and He 2006). Thecompositions of the broth culture medium used were:sucrose 5.0 g; sodium hydrogen phosphate (Na2HPO4)2.0 g; magnesium sulphate (MgSO4.7H2O) 0.5 g;ferric chloride (FeCl3) 0.005 g; calcium carbonate(CaCO3) 0.1 g; waste mica (potassium source) 1.0 g;distilled water 1000 ml; pH of the medium wasadjusted to 7.5 using dilute acid and/or alkali. All theingredients except mica were dissolved in 1000 mldistilled water. The contents were transferred into fourconical flasks of 500 ml capacity each and waste mica(2-mm size) was added. The flasks were plugged withcotton and sterilized at 120C and 0.1 MPa for 20 minin an autoclave. Sterilized medium was kept at

Plant Soil (2009) 317:235255 237

ambient temperature (251C) in a dust-free environ-ment for another 7 days to produce sufficient numberof bacterial cells in broth culture for further use.

Soils

Two surface soil samples (015 cm depth) wereobtained from the research farm of (i) OrissaUniversity of Agriculture and Technology (OUAT),Bhubaneswar, Orissa; and (ii) Central Rainfed UplandRice Research Station, Hazaribagh, Jharkhand, India.These two soils were selected taking into accounttheir variable amounts of different pools of K,particularly low in available potassium (K-deficient)as well as their varying mineralogical compositions.Both the soils are categorized as Alfisol (TypicHaplustalfs). The soil of Hazaribag is clay loam intexture with illite and montmorillonite as the dominantclay mineral, while soil of Bhubaneswar is sandy loamin texture with kaolinite and illite dominated clay.

Soil analysis

Soil samples were air-dried and passed through a 2-mmsieve before laboratory analyses. The particle sizeanalysis was determined by hydrometer method(Bouyoucos 1962) after dispersing the soil in sodiumhexametaphosphate solution. Soil pH and electricalconductivity were measured in soil: water ratio of 1:2(Richards 1954). The organic carbon content of soilwas determined by rapid titration method (Walkleyand Black 1934). Cation exchange capacity (CEC) ofsoil was determined as per the procedure outlined byJackson (1973). Easily oxidizable N as an index ofavailable N was determined by the alkaline perman-ganate method as outlined by Subbiah and Asija(1956). Available P was extracted following themethod of Bray and Kurtz (1945), where soil wasextracted by shaking with solution of 0.03 N NH4F+ 0.025 N HCl for 30 min using a soil solution ratio of1:20. Phosphorus in the extracts was analyzedspectrophotometrically using ascorbic acid as reduc-tant (Watanabe and Olsen 1965). Water-soluble K wasextracted by shaking soil samples with distilled waterusing a soil solution ratio of 1:5 (Page et al. 1982).The exchangeable K was extracted by shaking neutral1 N NH4OAc solution for 5 min using a soil solutionratio of 1:5 (Hanway and Heidel 1952). Non-exchangeable K was extracted by adding 25 ml of

1 N HNO3 to 2.5 g of soil and boiling for 15 min(Page et al. 1982). The total K was determined by themethod as described by Jackson (1973), whichinvolved digesting soil (0.1 g) in a mixture of HFand HClO4. Potassium fixation was determined as perthe procedure outlined by Jackson (1973). Potassiumin the extracts was determined by a flame photometer.The important physicochemical properties of the soilsare presented in Table 1.

Crop

Sudan grass (Sorghum vulgare Pers.) var Sudanensiswas selected as the test crop for greenhouse experi-ment. This crop was selected because of its quickgrowing nature. It is known as a K-exhausting crop asit requires high amount of K for its growth. Moreover,since it is a perennial grass, there is a possibility toaccumulate K in excess of its own requirementsdepending upon the availability of K in soil andpotassium added through fertilizers. Sudan grass hasshown promise as a fodder crop particularly innorthern India. During its growth multiple cuttingscan be obtained to supply fodder for a longer period.

Greenhouse experiment

The experiment was carried out in greenhouse in rabiseason, November 2006 to April 2007 at the IndianAgricultural Research Institute (IARI), New Delhi,located at 28 3728 39 N latitude and 77 97711 E longitude, at an altitude of 220 m above sea level.The climate of the study area is semi-arid subtropicalregion showing hot summers and cold winters with amean annual maximum and minimum temperature of40.5C and 6.5C, respectively and total annual rainfallof 760 mm (approximately) occurring mostly duringthe months of July to September.

Sixteen treatments consisting of factorial combi-nations of four rates of waste mica (M0, M1, M2 andM3 corresponding to 0 mg K kg

1, 50 mg K kg1,100 mg K kg1 and 200 mg K kg1 soil), two bacterialcultures (without and with Bacillus mucilaginosus) andtwo Alfisols (Bhubaneswar and Hazaribag) were used.The experiment was laid out in a completely random-ized design (CRD) with three replications for this study.

Processed soil (

containing about 1.01071.5108 cfu) were addedto soil as per the treatment combinations and mixedthoroughly. A basal dose of nitrogen (50 mg N kg1

soil) and phosphorus (50 mg P kg1 soil) through ureaand sodium di-hydrogen orthophosphate (NaH2PO4),respectively were applied as in solution form to eachpot and mixed thoroughly with the soil. Adequateamount of water was added so as to raise the moisturecontent of soil to field capacity. The soil treated withfertilizer materials were finally placed in the polyethylene-lined earthen pots having 25 cm upper diameter and30 cm depth.

Twenty seeds of sudan grass were sown in each poton 21st November 2006, which after germination(7 d) was thinned to retain eight healthy plants per potto ensure enough dry matter production and nutrientremoval from the soil. The pots were kept weed-freeand maintained in an optimum soil moisture regime,approximately at 60% water holding capacity of thesoil throughout the experiment by irrigating the crop ona regular basis to ensure that water was not a limitingfactor. The crop was harvested by cutting sample at 810 cm above soil surface in each cutting so as toregenerate the biomass for next cutting. Altogether fivecuttings of biomass were obtained with an interval of1 month each (30 day, 60 day, 90 day, 120 day and150 day after sowing) and recorded the respectivebiomass yield after drying at 651C. The oven-dried

plant samples were mixed well, ground by a Wiley mill(5-mm size) and digested (0.5 g) with di-acid mixture(8 ml) containing HNO3:HClO4:: 9:4 on an electric hotplate (Piper 1967). Potassium content in the acid digestwas determined by a flame photometer and uptake ofK was computed. Per cent K recovery by crop wascomputed by the relationship as given below:

Per cent K recovery 100 UKt UKc =Awhere, UKt=Uptake of K in fertilizer treated pot (mg Kpot1); UKc=Uptake of K in control pot (mg K pot

1);A=Amount of K applied (mg K pot1).

Measurement of the different pools of K in soilswas carried out after drawing sub-sample of soil fromeach pot with the help of soil auger (015 cm depth)after each cutting of the crop to investigate the Kdynamics of the soil. Air-dried soil samples werepassed through 2-mm sieve and analyzed for water-soluble K (Page et al. 1982), exchangeable K (1 NNH4OAc extractable K) (Hanway and Heidel 1952)and non-exchangeable K (1 N boiling HNO3 extract-able K) (Page et al. 1982). Potassium in the extractswas determined by a flame photometer.

Kinetics of K release

Kinetics of K release from waste mica as influencedby Bacillus mucilaginosus strain was carried out and

Table 1 Some physicochemical properties of the experimental soils

Characteristics Values Method/Reference

Bhubaneswar Hazaribagh

pH (soil: water:: 1:2) 5.64 6.13 Richards (1954)EC (soil:water::1:2) (dS m1) 0.21 0.23 Jackson (1973)Mechanical analysis Bouyoucos (1962)Sand (%) 67.7 63.4Silt (%) 12.4 11.7Clay (%) 17.9 24.9Textural class Sandy loam Clay loamOrganic carbon (g kg1 soil) 4.1 4.7 Walkley and Black (1934)CEC [cmol(p+) kg1 soil] 8.93 9.45 Jackson (1973)Available N (mg kg1 soil) 86.3 91.1 Subbiah and Asija (1956)Available P (mg kg1 soil) 4.87 5.54 Bray and Kurtz (1945)Different pools of KWater-soluble K (mg kg1 soil) 8.44 14.1 Page et al. (1982)Exchangeable K (mg kg1 soil) 19.7 47.3 Hanway and Heidel (1952)Non-exchangeable K (mg kg1 soil) 51.2 112.7 Page et al. (1982)Total K (g kg1 soil) 4.50 11.25 Page et al. (1982)Potassium fixing capacity (%) 68.8 74.5 Jackson (1973)

Plant Soil (2009) 317:235255 239

the rate of release of K was computed. To computethe rate of release of K, the data generated in potexperiment were fitted into the kinetics equation.There are many equations employed by differentworkers including first-order, Elovich, parabolicdiffusion, zero-order and power function equation todescribe the kinetics of K release pattern in soils(Sparks et al. 1980; Feigenbaum et al. 1981; Martinand Sparks 1983; Jardine and Sparks 1984; Havlinet al. 1985; Sparks 1987; Dhillon and Dhillon 1990).These equations have been used to determine reactionorder and rate coefficients between the different poolsof soil K. In this study we used the best-fitted equationas tested by larger correlation (r) value and least squareregression analysis to determine which equation is bestdescribed the K release from waste mica. Based onthis, we employed the best-fitted simple first-orderequation of Jardine and Sparks (1984) as given below:

ln ap ln a ktwhere, ln = natural logarithm; a = exchangeable K(mg pot1) present initially in soil; p = K (mg pot1)released at a particular timet (d) plus mean K uptakeby plant in that stage; (a-p) = nutrient present finallyin soil; and k = rate constant.


In the present study to see the structural changes ofmica, if any, as affected by potassium solubilizingmicroorganism (Bacillus mucilaginosus), another set oftreatments were selected for conducting pot experimentusing same soils used in earlier experiment. To achievethis objective one rate of mica (100 mg K kg1 soil)was used with and without inoculation of bacterialbroth culture (Bacillus mucilaginosus) and applied intwo soils. There were four treatments consisting of twomica (without bacterial culture and with bacterialculture) and two soils (Hazaribag and Bhubaneswar)for this pot study, which were replicated three times.The experiment was laid out in a completely random-ized design. Processed soil (

mica compared to control (17.4 g pot1) in both thesoils. The biomass yield increased (P

mica application in both the soils (Fig. 1). Both thesoils exhibited a similar trend in increasing cumulative Kuptake in each cutting. In general, the trend in cumulativeuptake was linear up to fourth cutting (120 d) and thenthere was a steep increase in the fifth cutting (150 d),irrespective of treatments. Inoculation with Bacillusmucilaginosus resulted in further increase in cumulativeK uptake by sudan grass. This is true for both theAlfisols (Fig. 1). The cumulative K uptake was muchhigher in Alfisol from Hazaribag than that of Alfisolfrom Bhubaneswar.

Per cent K recovery

Per cent K recoveries by sudan grass grown in twoAlfisols (Table 4) showed that treatment receivingmica @ 50 mg K kg1 soil recorded the highestrecoveries in both the soils, while the lowest Krecoveries were obtained with treatment receivingmica @ 200 mg K kg1 soil. Thus, over all Krecoveries decreased with the increase in rates of micaapplied either alone or inoculated with Bacillusmucilaginosus strain. It was observed that withoutbacterial strain, application of mica @ 50 mg K kg1

soil recorded 20.5 and 40.5 per cent K recoveries inAlfisol from Bhubaneswar and Hazaribag, respectively.

On the other hand with bacterial inoculation, thesevalues were 48.3 and 90.4 per cent, respectively. Ingeneral, the K recoveries in Alfisol from Hazaribagwere much higher than Alfisol from Bhubaneswar at aparticular rate of mica application.

Dynamics of K in soils

Water-soluble K

There was a general increase inwater-solubleK (Fig. 2) insoils up to second cutting (60 d), thereafter it decreasedgradually during the remaining period of greenhouseexperiment. Lowest amount of water-soluble K wasfound in control where no K was added compared totreatments receiving mica as source of K after eachcutting of crop, irrespective of bacterial inoculation andsoils. Significantly greater amount of water-solubleK was obtained with increase in rate of mica up to100 mg K kg1 soil application, thereafter it was at par.Alfisol from Hazaribag recorded significantly greateramount of water-soluble K than Alfisol from Bhubanes-war across the rates of mica application, inoculation ofbacterial strain and stages of cuttings. Treatments receiv-ing mica along with bacterial strain Bacillus mucilagino-sus enhanced water-soluble K in both the soils.

Table 3 Effect of waste mica as influenced by Bacillus mucilaginosus strain on potassium uptake (mg pot1) by sudan grass (sum offive cuttings) grown in two Alfisols

Treatment Microbial culture Soils Mean

Without Bacillusmucilaginosus

With Bacillusmucilaginosus

Alfisol fromBhubaneswar

Alfisol fromHazaribag

Rate of mica (mg K kg1 soil)M0 (0 mg K kg

1) 240.0 397.7 137.8 499.9 318.8M1 (50 mg K kg

1) 308.5 458.4 178.7 588.2 383.5M2 (100 mg K kg

1) 336.1 531.2 192.2 675.2 433.7M3 (200 mg K kg

1) 335.0 559.1 184.8 709.4 447.1SoilsAlfisol from Bhubaneswar 134.4 212.4Alfisol from Hazaribag 475.5 760.9Mean 304.9 486.6 173.4 618.2LSD (P=0.05)Rate of mica 38.3Bacterial culture 73.0Soil 73.0Rate of micaBacterial culture 54.2Rate of micaSoil 54.2Bacterial cultureSoil 103.0Rate of micaBacterial cultureSoil NS

242 Plant Soil (2009) 317:235255

Exchangeable K

Data in Fig. 3 showed that after first cutting of sudangrass, exchangeable K increased significantly with

addition of mica compared to control. In case ofAlfisol from Bhubaneswar, the exchangeable Kincreased up to third cutting (90 d), then decreaseddrastically at the fourth cutting (120 d) and then

1a. Without B. mucilaginosus

0

50

100

150

200

250

30 60 90 120 150Stage of cutting (d)

Cum

ulat

ive

K up

take

(mg/p

ot)

M0M1M2M3

1b. With B. mucilaginosus

0

50

100

150

200

250


Cum

ulat

ive

K up

take

(mg/p

ot)

M0M1M2M3

Alfisol from Bhubaneswar

1c. Without B. mucilaginosus

0

100200

300

400

500600

700

800900

1000


Cum

ulat

ive

K up

take

(mg/p

ot)

M0M1M2M3

1d. With B. mucilaginosus

0

100200

300

400

500600

700

800900

1000


Cum

ulat

ive

K up

take

(mg/p

ot)

M0M1M2M3

Alfisol from Hazaribag

* M0 = Mica @ 0 mg K kg-1 soil; M1 = Mica @ 50 mg K kg

-1 soil;

M2 = Mica @ 100 mg K kg-1 soil; M3 = Mica @ 200 mg K kg

-1 soil.

Fig. 1 Effect of waste micaas influenced by Bacillusmucilaginosus strain oncumulative potassium up-take by sudan grass(mg pot1) grown in twoAlfisols

Table 4 Per cent recoveries of potassium by sudan grass in two Alfisols as affected by application of different rates of micainoculated with Bacillus mucilaginosus strain

Rate of mica (mg K kg1 soil) Without Bacillus mucilaginosus With Bacillus mucilaginosus





M0 (0 mg K kg1) - - - -

M1 (50 mg K kg1) 20.5 40.5 48.3 90.4

M2 (100 mg K kg1) 10.9 31.9 29.5 73.2

M3 (200 mg K kg1) 4.1 17.0 14.4 56.5

Plant Soil (2009) 317:235255 243

slowly after fifth cutting (150 d), irrespective of ratesof mica application and inoculation of bacterial strain,which resulted in less K being available for plants. Incase of Hazaribag soil, the exchangeable K increasedup to second cutting (60 d), and then decreased inthird cutting (90 d), thereafter no significant changes inexchangeable K were noticed till fifth cutting (150 d),which was reflected well in higher K uptake by thecrop because of effective absorption of K by plants.The exchangeable K was much lower in Bhubaneswarsoil than Hazaribag soil across the rates of micaapplication, inoculation of bacterial strain, and stagesof cuttings. Application of mica increased exchange-able K up to 100 mg kg1 soil throughout the cropstages. Treatments receiving mica along with bacterial

strain Bacillus mucilaginosus consistently maintainedthe higher exchangeable K than uninoculated mica inboth the soils and after each cutting of crop.

Non-exchangeable K

The non-exchangeable K decreased gradually fromfirst to fifth cuttings of the crop in Alfisol fromBhubaneswar (Fig. 4). On the other hand, in case ofAlfisol from Hazaribag, the non-exchangeable Kdecreased gradually up to third cutting (90 d). Thenon-exchangeable K, thereafter, increased gradually tillthe end of fifth cutting (150 d) across the rate of Kapplication and inoculation of bacterial strain. Lowestamount of non-exchangeable K was observed in control


0

5

10

15

30 60 90 120 150

Stage of cutting (d)

Wa

te

r-s

olu

ble

K

(m

g/k

g s

oil)

M0

M1

M2

M3


0

5

10

15

30 60 90 120 150


Wa

te

r-s

olu

ble

K

(m

g/k

g s

oil)

M0

M1

M2

M3



0

5

10

15

20

25

30 60 90 120 150


Wa

te

r-s

olu

ble

K

(m

g/k

g s

oil)

M0

M1

M2

M3


0

5

10

15

20

25

30 60 90 120 150


Wa

te

r-s

olu

ble

K

(m

g/k

g s

oil)

M0

M1

M2

M3


* M0 = Mica @ 0 mg K kg-1 soil; M1 = Mica @ 50 mg K kg-1 soil; M2 = Mica @ 100 mg K kg-1 soil; M3 = Mica @ 200 mg K kg-1 soil.

** Initial water-soluble K: 8.44 and 14.1 mg K kg-1 soil in Bhubaneswar and Hazaribag, respectively.

Fig. 2 Changes in water-soluble K (mg kg1) in soilsafter each cutting of sudangrass grown in two Alfisolsas affected by different rateof mica inoculated withBacillus mucilaginosusstrain

244 Plant Soil (2009) 317:235255

treatment where no mica was added, and it increasedwith increase in rates of mica up to 100 mg K kg1 soilapplication in both the soils. Increase in non-exchange-able K in soils was observed due to inoculation ofbacterial strain Bacillus mucilaginosus. In general, thenon-exchangeable K pool was two to three timeshigher in Alfisol of Hazaribag than Bhubaneswar.

Correlation matrix

Data on Pearsons correlation matrix in Alfisol fromBhubaneswar (Table 5) showed that biomass yield ofsudan grass was significantly and positively correlated(P

cantly but negatively correlated with exchangeable(r=0.315**) as well as non-exchangeable K(r=0.370**). Water-soluble K was significantly andpositively correlated with exchangeable K (r=0.373**)and non-exchangeable K (r=0.287**), while ex-changeable K was significantly and negatively corre-lated with non-exchangeable K (r=0.219*).

Potassium release kinetics

Data generated in the present experiments werefitted into a kinetics equation and rate of releasekinetics of K from waste mica as affected bybacterial inoculation in soils were computed.Accordingly, a release curve of ln (a-p) versus

time was plotted for different treatments. In case ofAlfisol from Bhubaneswar (Fig. 5), no significantrelease of K from mica was found up to third cutting(90 d), thereafter released K at a faster rate up to fifthcuttings, irrespective of treatments. On the otherhand the release kinetics of K in Alfisol fromHazaribag showed that irrespective of treatments,significant amount of release of K from mica wasnoticed up to third cutting (90 d) of the crop; theamount of release of K decreased thereafter up tofourth cutting (120 d). The release of K increasedsubstantially till the end of last cutting. Treatmentsreceiving mica along with Bacillus mucilaginosusreleased significantly higher amounts of K overuninoculated mica.


0

25

50

75

100

125

150


Non

-exc

hang

eabl

e K

(mg/k

g soil

)

M0M1M2M3


0

25

50

75

100

125

150


Non

-exc

hang

eabl

e K

(mg/k

g soil

)

M0M1M2M3



0

50

100

150

200

250

300

350

400

450


Non

-exc

hang

eabl

e K

(mg/k

g soil

)

M0M1M2M3


0

50

100

150

200

250

300

350

400

450


Non

-exc

hang

eabl

e K

(mg/k

g soil

)

M0M1M2M3



-1 soil;


-1 soil.

** Initial non-exchangeable K: 51.2 and 112.7 mg K kg-1 soil in Bhubaneswar and Hazaribag,

respectively.

Fig. 4 Changes in non-exchangeable K (mg kg1) insoils after each cutting ofsudan grass grown in twoAlfisols as affected by dif-ferent rate of mica inoculatedwith Bacillus mucilaginosusstrain

246 Plant Soil (2009) 317:235255


4.5

5.0

5.5

6.0

6.5

7.0

7.5

30 60 90 120 150Days after sowing (d)

ln(a-

p)

M0M1M2M3


4.5

5.0

5.5

6.0

6.5

7.0

7.5


ln(a-

p)

M0M1M2M3



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6.0

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7.0

7.5

8.0

8.5


ln(a-

p)

M0M1M2M3


5.5

6.0

6.5

7.0

7.5

8.0

8.5

30 60 90 120 150Days after sowing (a)

ln(a-

p)

M0M1M2M3


M0: Y = -0.108 X + 7.58 M1: Y = -0.041 X + 7.10 M2: Y = -0.019 X + 7.21 M3: Y = -0.049 X + 7.39

M0: Y = -0.058 X + 7.47 M1: Y = -0.029 X + 7.32 M2: Y = -0.106 X + 7.59 M3: Y = -0.064 X + 7.17

M0: Y = -0.233 X + 7.10 M1: Y = -0.347 X + 7.21 M2: Y = -0.365 X + 7.42 M3: Y = -0.391 X + 7.44

M0: Y = -0.344 X + 7.26 M1: Y = -0.331 X + 7.26 M2: Y = -0.486 X + 7.61 M3: Y = -0.717 X + 7.73


-1 soil;


-1 soil.

Fig. 5 Release kinetics ofpotassium from waste micaby sudan grass grown intwo Alfisols as affected byBacillus mucilaginosusstrain

Table 5 Pearsons correlations matrix between biomass yield, K uptake by sudan grass and different pools of K after each cutting ofcrop grown in Alfisol from Bhubaneswar and Hazaribag

Parameter Biomass yield Potassium uptake Water-soluble K Exchangeable K Non-exchangeable K

Alfisol from BhubaneswarBiomass yield 1.00 0.953b 0.280b 0.562b 0.502b

Potassium uptake 1.00 NS 0.355b 0.483b

Water-soluble K 1.00 0.447b NSExchangeable K 1.00 0.315b

Non-exchangeable K 1.00Alfisol from HazaribagBiomass yield 1.00 0.931b NS 0.289b NSPotassium uptake 1.00 NS 0.315b 0.370b

Water-soluble K 1.00 0.373b 0.287b

Exchangeable K 1.00 0.219a

Non-exchangeable K 1.00

a Correlation is significant at P=0.05 level (2-tailed), b Correlation is significant at P=0.01 level (2-tailed)

Plant Soil (2009) 317:235255 247


X-ray diffraction patterns of the residue of micamineral left after the crop harvest showed noticeablestructural changes due to uninoculated and inoculatedtreatment from those of the original unused fresh mica(Table 6). The values of Pk position (2) due touninoculated and inoculated treatments were statisti-cally non-significant (P

Bennett et al. 1998). Many workers have reported thatproduction of carboxylic acids and capsular polysac-charide is associated with solubilization of feldspar byapplication of K solubilizing microorganisms viz.,Bacillus mucilaginosus and Bacillus edaphicus (Linet al. 2002; Sheng and Huang 2002). Malinovskayaet al. (1990) opined that a mixture of polymers andlow molecular weight ligands had a synergistic effecton mineral weathering by Bacillus mucilaginosus.Bennett et al. (2001) reported that microorganismsproduced various organic ligands during their metabo-lism. These includedmetabolic byproducts, extracellularenzymes, chelates and both simple and complex organicacids, which helped in dissolution of feldspar bydecreasing the pH of the environment. Increase inbiomass yield may also be attributed to plant growthpromoting activity of Bacillus mucilaginosus strain,which has an ability to convert potassium fromunavailable to available form through biological pro-cesses. The present results corroborate the finding ofother workers (Sheng 2005; Wu et al. 2005).

The other possible hypotheses/mechanisms tomobilize soil K reserve are due to biofilms formationon the rhizospheric mineral surfaces by certainbacterial strains (Balogh-Brunstad et al. 2008). Bio-films are known to protect the microbial communityfrom various environmental effects and even fromantibiotics, regulate transport of heavy metals andpossibly other cations and nutrients to the microbes,and isolate mineral weathering and nutrient uptake bybacteria from bulk soil processes. They reported thatectomycorrhizal hyphal networks and root hairs ofnon-ectomycorrhizal trees, embedded in biofilms(microorganisms surrounded by extracellular poly-mers), transferred nutrients to the host. These resultssuggest that biofilms help to accelerate weathering ofminerals like biotite and anorthite, thereby increaseplant nutrient uptake.

Role of root derived organic acids in the mobiliza-tion of nutrients from the rhizosphere has been evalu-ated (Jones and Darrah 1994; Jones et al. 1996; Jones1998). Jones et al. (2003) reported that organic acidshave been hypothesized to perform many functions insoil including root nutrient acquisition, mineralweathering, microbial chemotaxis and metal detoxifi-cation. Calvaruso et al. (2006) reported the significantimpact of plant root hairs on mineral weathering anddemonstrated that a bacterial isolate, Burkholderiaglathei PML1(12), significantly improved biotite

weathering by a factor of 1.3 for Mg and 1.7 for Kand promoted plant growth, mainly because of itseffect on mineral weathering. In addition, theyobserved a significant positive effect of differentbacterial strains on pine growth and on root morphologylike number of lateral roots and root hairs. Similarly, theimpact of Douglas-fir and Scots pine seedlings onplagioclase weathering in a laboratory experiment underacidic conditions was reported by Bakker et al. (2004).Their results thus underline the importance of takinginto account biotic and abiotic environments, like thecomposition of root exudates, the presence of ectomy-corrhizal fungi, and soil properties (pH, aeration, andphysicochemical characteristics), when characterizingthe weathering effect of a given bacterial strain becausethese parameters may influence the expression of theweathering ability of the bacteria. Another possibilityof increase in weathering is due to a synergistic effect,which could result from three hypothetical processes:(i) the fragmentation of the mineral caused by rootactivity increases the direct positive effect of thebacteria on mineral weathering by increasing thereactive surfaces; (ii) the root exudates indirectlyprovide the substrates required for the production ofweathering metabolites by the bacteria, or (iii) theproduction of growth phytohormones by the bacteria,in addition to weathering agents, stimulates rootdevelopment and modifies root physiology and rootexudation, which improves mineral weathering andnutrient uptake (Gahoonia et al. 1997). Leyval andBerthelin (1989) showed that ectomycorrhizal fungiwere able to solubilize K, Fe, Mg and Al fromphlogopite within the rhizosphere of beech. Thepotential for dissolution of silicate rock powders isenhanced through the removal of nutrients and theaddition of acids by mycorrhiza. It is also reported thatsome rock-eating fungi (ectomycorrhizal fungi) havethe capacity to exude low molecular weight organicanions (LMWOA) to an extent that forms microscopictunnels through exuded at hyphal tips within mineralslike feldspar and hornblende grains in soils therebyweathering rates are significantly increased (van Schllet al. 2008).

In the case of nutrients such as P, the primarymechanisms of solubilization of rock phosphateattributed are H+ excretion and organic acid production.Excretion of H+ by plant roots into the rhizosphere iscaused by a higher uptake of cations relative to anions(Hinsinger et al. 2003). Phosphate solubilizing micro-

Plant Soil (2009) 317:235255 249

organisms are known to produce organic acids, namelycitric, oxalic, tartaric, acetic, lactic, gluconic, -ketogluconic, etc. (Babana and Antoun 2006; Vassilevet al. 2006). These acids are sources of H+ ions able todissolve the mineral phosphate and to make it availablefor the plant. In addition to pH reduction, organic acidanions can solubilize rock phosphate through chelationreactions (Reyes et al. 2006).

With regard to the experimental soils, the biomassproduction was much higher in Alfisol from Hazaribagthan that of Bhubaneswar, irrespective of rates of micaand inoculation of bacterial strain. The poor perfor-mance in Alfisol from Bhubaneswar may be attributedto higher acidity (pH 5.64) as against lower acidity(pH 6.13 in Hazaribag soil) as well as lower initialfertility status (low available N, P and K) thanHazaribag soil.

Bacillus mucilaginosus influences on K uptakeand recoveries

Bio-intervention of waste mica with Bacillus mucila-ginosus performed significantly in enhancing Kuptake by sudan grass in both the soils. The resultsconfirm the findings of earlier workers where theyreported greater total uptake of K by crop when K-bearing minerals were inoculated with potassiumsolubilizing bacteria (Sheng and Huang 2002). Sheng(2005) also reported significant increase in shoot androot dry yield as well as greater uptake of K by cottonand rape due to application of K-bearing mineral(illite) inoculated with potassium releasing strainBacillus edaphicus NBT. It leads to generalizationthat the potassium dissolving bacteria play an impor-tant role in plant nutrition through the increase in Kuptake by the plant. Significantly higher uptake of Kby wheat grown in a K-deficient yellow-brown soil inNanjing, China were reported by a wildtype bacterialstrain Bacillus edaphicus NBT and their mutants MPs(+) and MPs(+)1 (Sheng and He 2006). Han et al.(2006) also reported the beneficial effect of Bacillusmucilaginosus on mobilization K from potassiummineral, and nutrient uptake and growth of pepper andcucumber on an Inceptisol from Korea. Han and Lee(2005) reported the synergistic effects of soil fertiliza-tion with rock P and K materials and co-inoculationwith phosphate solubilizing bacteria (PSB) Bacillusmegatherium and potassium solubilizing bacteria(KSB) Bacillus mucilaginosus KCTC 3870 on the

improvement of P and K uptake by eggplant grownunder limited P and K soil in greenhouse.

The higher mobilization of K from mica and itssubsequent uptake by sudan grass due to inoculationwith Bacillus mucilaginosus could be attributed toincrease population of bacteria in the root andrhizosphere soil. Lin et al. (2002) and Egamberdiyevaand Hoflich (2003) demonstrated that bacterial inoc-ulation resulted in growth promotion and higher Kcontents of plant components. As successful plantgrowth promoting inoculants, bacteria must be able torapidly colonize the root system during the growingseason (Defreitas and Germida 1992). Sheng (2005)demonstrated that Bacillus edaphicus NBT was ableto colonize the rhizosphere soil and root of cotton andrape. The inoculated bacterium was able to establishlarger population on the root and the rhizosphere soilof cotton and rape up to 5-weeks after sowing.

Per cent K recoveries by sudan grass showed thattreatment receiving mica at the lowest level recordedthe highest recoveries of K in both the soils, while thelowest K recoveries were obtained with the highestlevel of K applied either alone or inoculated withbacterial strain Bacillus mucilaginosus. In general, therecoveries of K in Hazaribag soil were much higher thanBhubaneswar. This may be attributed to higher biomassproduction due to greater amount of different pools of K(water-soluble, exchangeable, non-exchangeable andtotal K content) as well as better physicochemicalproperties like higher organic carbon, pH, CEC, andavailable N and P status in the initial soil of the former.

K dynamics

There was a general trend in increase in water-solubleK in soils up to second cutting (60 d) then decrease inthis pool till the end of the greenhouse experiment.The initial increase in this pool of K may be due torelease of K from exchangeable and non-exchange-able pools of K, which was utilized by the crop duringtheir growth period resulting in decrease in this pooltowards the end of the crop. The treatment in whichwaste mica was incorporated was found to increasewater-soluble, exchangeable and non-exchangeable Kcontent in soils than control receiving no mica. This isobvious because of low available potassium (water-soluble and exchangeable K) in both the soils. It isreported that the effectiveness of silicate rock powdermay increase when initial nutrient levels in soils are

250 Plant Soil (2009) 317:235255

low (Hinsinger et al. 1996; Sanz Scovino and Rowell1988). Further, water-soluble K as well as exchangeableK increased significantly when mica was inoculatedwith Bacillus mucilaginosus strain in both the soils,which can be attributed to solubilization of non-exchangeable and structural K by the microbe throughproduction of organic acids like oxalic and citric acids.The results of the present study corroborate thefindings of other workers (Barker et al. 1998). Thereis much evidence showing that mineral K can bedirectly utilized by crops. Frequently, in continuouscropping systems, the removal of soil K by crops isincomparable to depletion in the soil available and thenon-exchangeable K pool, which indicates that therelease of mineral K contributes some proportion of Ktaken up by crops (Wang et al. 2000). The work byCoroneos et al. (1996) indicates that water soluble KClis much more effective for immediate plant growth, butthey stress that the non-exchangeable fraction of Kfrom granite may be beneficial for plant growth inleaching environments.

Greater water-soluble and exchangeable K wasobserved in Hazaribag soil than Bhubaneswar in thisstudy, which can be attributed to inherently higher Kstatus in the former soil. It can also be due to highersolubilization of non-exchangeable pool to exchange-able pool of K. In general, the exchangeable K increasedup to 90 days, then decreased drastically in Alfisol fromBhubaneswar, while in Hazaribag soil, the exchangeableK increased up to second cutting (60 d), then decreasedtill third cutting (90 d), and thereafter no significantchanges were noticed till the end of the experiment(150 d), which was reflected well in higher K uptakebecause of efficient absorption of K by the crop.

With the progress of crop growth, non-exchange-able K in Alfisol from Bhubaneswar decreasedgradually. It may be due to crop uptake of K fromavailable pool, because as stressed by the crop demandsome parts of non-exchangeable K might have beenconverted to exchangeable form. While in case ofAlfisol from Hazaribag, the non-exchangeable Kdecreased gradually up to third cutting (90 d), becauseof either crop uptake or due to conversion intoexchangeable K. The non-exchangeable K, thereafter,increased gradually till the end of fifth cutting (150 d)across the rate of K application and inoculation ofbacterial strain, which can be attributed to fixation ofwater-soluble and exchangeable K to unavailable K i.e.fixed or structural K.

In general, the values of exchangeable and non-exchangeable K for M0 treatment were greater than theinitial values of both the soils. This is because someamount of mineral K or structural K might have beenconverted first into non-exchangeable K and then ex-changeable K during the crop growth. This is reflectedwell by the fact that the amount of K taken by plant islargely higher than the sum of the modification ofexchangeable and non-exchangeable K in soils.

Non-exchangeable K reserves were in general highin Alfisol from Hazaribag, while Alfisol fromBhubaneswar maintained low levels. The abundanceof non-exchangeable K in the former soil than latterbroadly followed the same trend as their total K.Larger non-exchangeable K reserves in Alfisol fromHazaribag could be due to the presence of largeramounts of illite/mica in this soil. Lower non-exchangeable K in Alfisol from Bhubaneswar couldbe due to the presence of the major portion of total Kin the form of K feldspars, which are highly resistant;thus, a major portion of total K is not dissolved inboiling 1 N HNO3 (Subba Rao et al. 1988). Variationin amounts of total K and non-exchangeable K couldbe attributed to amounts of clay, silt, and sand andvariations in mineralogical composition of the threeparticles (Sekhon et al. 1992).

Hinsinger et al. (1992, 1993) reported that disso-lution of phlogopite (a trioctahedral mica) structureoccurred in the rhizosphere of ryegrass and rapeprobably due to proton excretion by roots andvermiculitized after root induced release of interlayerK, which implies K in solid framework forms couldbe a source of K for plants. This verifies that some rockscontaining K-bearing minerals have some potential forbeing used as K fertilizer, as demonstrated for granite byCoroneos et al. (1996) and Hinsinger et al. (1996). Therelease of non-exchangeable K from feldspar has alsobeen attributed to exudation of acids, especially citricand oxalic acids, from roots (Song and Huang 1988;Wang et al. 2000; Moritsuka et al. 2004).

Soil 2:1 clay minerals play an important role forsoil K availability. Indeed, several studies showed thatthe presence of such clay minerals, even in subsidiaryquantities, increases effective soil K availability. It isreported that illitic 2:1 clay minerals behave as arenewable K reservoir (Barr et al. 2008). The fillingor emptying of this reservoir could be followedefficiently through X-ray measurements of materialsformed under field conditions. This reservoir is likely

Plant Soil (2009) 317:235255 251

to have a key role for K cycle in soils. The mostevident implications are that it could obviously supplyshort term K for plant needs and preserve long-termecosystem productivity by reducing K leaching. Theparticular importance of such clay layers relies ontheir ability to adsorb and release K+ ions from 2:1clay mineral interlayer sites (Hinsinger 2002).

Correlation matrix

Significant correlation (P

Conclusion

We conclude that application of waste mica inoculatedwith potassium solubilizing microorganism (Bacillusmucilaginosus) has a significant effect on biomassyield, potassium uptake and recoveries by sudan grassgrown under two Alfisols due to higher solubilizationof K. Similarly, bacterial intervention of mica improvesthe water-soluble, exchangeable and non-exchangeableK pools in soils, thereby influences the K dynamics insoils into those pools which are relatively moreavailable to plant. X-ray diffraction analysis indicatesthat dissolution of some portion of mica at the edgesoccurred due to the action of microbial culture duringthe growing period of sudan grass, resulting morereleases of the structural K from mica. Thus, bio-intervention of waste mica could be an alternative andviable technology to solubilize insoluble K into solubleform and could be used efficiently as a source of K-fertilizer for sustaining crop production and maintain-ing soil potassium. Further studies are needed to seethe effect of the new fertilization method tested ispromising for big scale field application.

Acknowledgements The senior author is grateful to IndianCouncil of Agricultural Research (ICAR) for providingfinancial support as Junior Research Fellowship during hisresearch work and Head, Division of Soil Science andAgricultural Chemistry, Indian Agricultural Research Institute(IARI), New Delhi for providing facilities for successfulcompletion of the research works.

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Plant Soil (2009) 317:235255 255

Influence...AbstractIntroductionMaterials and methodsWaste micaBacterial strainSoilsSoil analysisCropGreenhouse experimentKinetics of K releaseX-ray diffraction analysisStatistical analysis

ResultsBiomass yieldPotassium uptakePer cent K recoveryDynamics of K in soilsWater-soluble KExchangeable KNon-exchangeable K

Correlation matrixPotassium release kineticsX-ray diffraction analysis

DiscussionBacillus mucilaginosus strain influences on biomass accumulationBacillus mucilaginosus influences on K uptake and recoveriesK dynamicsCorrelation matrixK release kineticsStructural changes of waste mica

ConclusionReferences

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basak & biswas, plant and soil(2009)317;235-255

Documents

inoculation of mica

uninoculated mica

keywords waste mica

indian soils

available soil

maintaining soil potassium

division of soil science

higher yield