What you always wanted to know about "BioFertilizers in Organic Agriculture"

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  • 1. Journal of Phytology 2010, 2(10): 42-54 ISSN: 2075-6240 An Open Access Journal Available Online: www.journal-phytology.com REVIEW ARTICLE BIO-FERTILIZERS IN ORGANIC AGRICULTURE S. Sheraz Mahdi1*, G. I. Hassan2, S. A. Samoon3, H. A. Rather4, Showkat A. Dar5 and B. Zehra6 1Divisionof Agronomy, Sher-e Kashmir University of Agricultural Sciences and Technology of Kashmir, Shalimar, Srinagar, J & K-India-19112112Division of Pomology, Sher-e Kashmir University of Agricultural Sciences and Technology of Kashmir, Shalimar, Srinagar, J & K-India-191121 3Division of Floriculture, Sher-e Kashmir University of Agricultural Sciences and Technology of Kashmir, Shalimar, Srinagar, J & K-India-191121 4Faculty of Forestry, Sher-e Kashmir University of Agricultural Sciences and Technology of Kashmir, Shalimar, Srinagar, J & K-India-191121 5Division of Entomology, Sher-e Kashmir University of Agricultural Sciences and Technology of Kashmir, Shalimar, Srinagar, J & K-India-191121 6Faculty of Horticulture, Sher-e Kashmir University of Agricultural Sciences and Technology of Kashmir, Shalimar, Srinagar, J & K-India-191121SUMMARY Experiencing the adverse effects of synthetic input dependent agriculture the concept of organic agriculture is gaining momentum. Almost 31 million hectares of land are currently managed organically by more than 6, 00, 000 farmers worldwide, constitutes 0.7 per cent of agriculture land. India had brought more than 2.5 m ha land under certification of organics. In these systems production is based in synergism with nature, which makes systems of unending life i.e. sustainable. Deteriorative effects of synthetic chemical inputs are obvious, but, at the same time we need to revive soil health and living which support to sustainable production system. Soil environment needs to be made congenial for living of useful microbial population, responsible for continuous availability of nutrients from natural sources. Bio-fertilizers being essential components of organic farming play vital role in maintaining long term soil fertility and sustainability by fixing atmospheric dinitrogen (N=N), mobilizing fixed macro and micro nutrients or convert insoluble P in the soil into forms available to plants, there by increases their efficiency and availability. Currently there is a gap of ten million tonnes of plant nutrients between removal of crops and supply through chemical fertilizers. In context of both the cost and environmental impact of chemical fertilizers, excessive reliance on the chemical fertilizers is not viable strategy in long run because of the cost, both in domestic resources and foreign exchange, involved in setting up of fertilizer plants and sustaining the production. In this context, organic manures (bio-fertilizers) would be the viable option for farmers to increase productivity per unit area. The mycorrhizal associations (VAM) in alleviating Al toxicity, increasing N, P and micronutrient uptake, maintaining soil structure by the production specific protein called “Glomulin” has been repeatedly demonstrated. Liquid bio-fertilizer technology now, shares more advantage over conventional carrier based bio-fertilizers and can be considered as a breakthrough in field of Bio-fertilizer technology and should find greater acceptance by farmers, extension workers and commercial bio-fertilizer manufactures. In this review, the established facts observed and the work carried out by many researchers on bio-fertilizers is discussed.Key words: Bio-fertilizers, Crop growth, Sustainability, VA-mycorrhizaeS. Sheraz Mahdi et al. Bio-fertilizers in Organic Agriculture. J Phytol 2/10 (2010) 42-54*Corresponding Author, Email: sheerazsyed@rediffmail.com
  • 2. S. Sheraz Mahdi et al./J Phytol 2/10 (2010) 42-541. Introduction considerable opportunity for organic farming Organic farming has emerged as an due to least utilization of chemical inputs. Itimportant priority area globally in view of is estimated that 18 million hectare of suchthe growing demand for safe and healthy land is available in the NE that can befood and long term sustainability and exploited for organic production. With theconcerns on environmental pollution sizable acreage under naturallyassociated with indiscriminate use of agro- organic/default organic cultivation, Indiachemicals. Though the use of chemical inputs has tremendous potential to grow cropsin agriculture is inevitable to meet the organically and emerge as a major suppliergrowing demand for food in world, there are of organic products in world’s organicopportunities in selected crops and niche market (Venkatashwarlu. 2008a) The reportareas where organic production can be of Task Force on Organic Farming appointedencouraged to tape the domestic export by the Government of India also observedmarket. that in vast areas of the country, where Bio-fertilizers are being essential limited amount of chemicals are used andcomponent of organic farming are the have low productivity could be exploited aspreparations containing live or latent cells of potential areas to develop into organicefficient strains of nitrogen fixing, phosphate agriculture. Arresting the decline of soilsolubilizing or cellulolytic micro-organisms organic matter is the most potent weapon inused for application to seed, soil or fighting against unabated soil degradationcomposting areas with the objective of and imperiled sustainability of agriculture inincreasing number of such micro-organisms tropical regions of India, particularly thoseand accelerate those microbial processes under the influence of arid, semiarid andwhich augment the availability of nutrients sub-humid climate. Application of organicthat can be easily assimilated by plants. Bio- manures particularly bio-fertilizers is thefertilizers play a very significant role in only option to improve the soil organicimproving soil fertility by fixing atmospheric carbon for sustenance of soil quality andnitrogen, both, in association with plant roots future agricultural productivity (Ramesh,and without it, solubilise insoluble soil 2008).phosphates and produces plant growthsubstances in the soil. They are in fact being Why to explore bio-fertilizers:-promoted to harvest the naturally available, Indiscriminate use of synthetic fertilizersbiological system of nutrient mobilization has led to the pollution and contamination of(Venkatashwarlu, 2008a). The role and the soil, has polluted water basins, destroyedimportance of biofertilizers in sustainable micro-organisms and friendly insects,crop production has been reviewed by making the crop more prone to diseases andseveral authors (Biswas et al. 1985; Wani and reduced soil fertility.Lee, 1995; Katyal et al. 1994). But the • Demand is much higher than theprogress in the field of BF production availability. It is estimated that bytechnology remained always below 2020, to achieve the targetedsatisfaction in Asia because of various production of 321 million tonnes ofconstraints. food grain, the requirement of It may be noted, only 30 % of India’s total nutrient will be 28.8 million tonnes,cultivable area is covered with fertilizers while their availability will be onlywhere irrigation facilities are available and 21.6 million tones being a deficit ofthe remaining 70 % of the arable land, which about 7.2 million tones.is mainly rain fed, very negligible amount of • Depleting feedstock/fossil fuelsfertilizers are being used. Farmers in these (energy crisis) and increasing cost ofareas often use organic manures as a source fertilizers. This is becomingof nutrients that are readily available either unaffordable by small and marginalin their own farm or in their locality. The farmers.North- Eastern (NE) region of India provides
  • 3. S. Sheraz Mahdi et al./J Phytol 2/10 (2010) 42-54 • Depleting soil fertility due to needed to restore the population of effective widening gap between nutrient strains of the Rhizobium near the rhizosphere removal and supplies. to hasten N-fixation. Each legume requires a • Growing concern about specific species of Rhozobium to form environmental hazards. effective nodules. Many legumes may be • Increasing threat to sustainable modulated by diverse strains of Rhizobia, but agriculture. growth is enhanced only when nodules are Besides above facts, the long term use of produced by effective strains of Rhizobia. It isbio-fertilizers is economical, eco-friendly, thus extremely important to matchmore efficient, productive and accessible to microsymbionts prudently for maximummarginal and small farmers over chemical nitrogen fixation. A strain of Rhizobia thatfertilizers (Venkataraman and nodulates and fixes a large amount ofShanmugasundaram, 1992). nitrogen in association with one legume species may also do the same in associationEstimated demand and supply of some with certain other legume species. This mustimportant bio-fertilizers in India be verified by testing. Leguminous plants The annual requirement and production that demonstrate this tendency to respondof different bio-fertilizers have clearly shown similarly to particular strains of Rhizobia aretremendous gap in this area. Thus a strategy considered “effectiveness” group (Wani andfor judicious combination of chemical Lee 2002).fertilizers and biofertilizers will beeconomically viable and ecological useful. It Azospirillum: belongs to familyshould be recommended that biofertilizers Spirilaceae, heterotrophic and associative inare not a substitute, but a supplement to nature. In addition to their nitrogen fixingchemical fertilizers for maximizing not only ability of about 20-40 kg/ha, they alsothe yield but also agro system stability. produce growth regulating substances. Although there are many species under this genus like, A.amazonense, A.halopraeferens,2. Potential characteristic features of A.brasilense, but, worldwide distribution andsome bio-fertilizers benefits of inoculation have been provedNitrogen fixers mainly with the A.lipoferum and A.brasilense.Rhizobium: belongs to family Rhizobiaceae, The Azospirillum form associative symbiosissymbiotic in nature, fix nitrogen 50-100 kg/ with many plants particularly with thoseha. with legumes only. It is useful for pulse having the C4-dicarboxyliac path way oflegumes like chickpea, red-gram, pea, lentil, photosynthesis (Hatch and Slack pathway),black gram, etc., oil-seed legumes like because they grow and fix nitrogen on saltssoybean and groundnut and forage legumes of organic acids such as malic, aspartic acidlike berseem and lucerne. Successful (Arun, 2007a). Thus it is mainlynodulation of leguminous crops by recommended for maize, sugarcane,Rhizobium largely depends on the availability sorghum, pearl millet etc. The Azotobacterof compatible strain for a particular legume. colonizing the roots not only remains on theIt colonizes the roots of specific legumes to root surface but also a sizable proportion ofform tumour like growths called root them penetrates into the root tissues andnodules, which acts as factories of ammonia lives in harmony with the plants. They doproduction. Rhizobium has ability to fix not, however, produce any visible nodules oratmospheric nitrogen in symbiotic out growth on root tissue.association with legumes and certain non-legumes like Parasponia. Rhizobium Azotobacter: belongs to familypopulation in the soil depends on the Azotobacteriaceae, aerobic, free living, andpresence of legume crops in the field. In heterotrophic in nature. Azotobacters areabsence of legumes, the population present in neutral or alkaline soils and A.decreases. Artificial seed inoculation is often chroococcum is the most commonly occurring
  • 4. S. Sheraz Mahdi et al./J Phytol 2/10 (2010) 42-54species in arable soils. A. vinelandii, A. BGA forms symbiotic association capable ofbeijerinckii, A. insignis and A. macrocytogenes fixing nitrogen with fungi, liverworts, fernsare other reported species. The number of and flowering plants, but the most commonAzotobacter rarely exceeds of 104 to 105 g-1 of symbiotic association has been foundsoil due to lack of organic matter and between a free floating aquatic fern, thepresence of antagonistic microorganisms in Azolla and Anabaena azollae (BGA). Azollasoil. The bacterium produces anti-fungal contains 4-5% N on dry basis and 0.2-0.4% onantibiotics which inhibits the growth of wet basis and can be the potential source ofseveral pathogenic fungi in the root region organic manure and nitrogen in ricethereby preventing seedling mortality to a production. The important factor in usingcertain extent (Subba Rao, 2001a). The Azolla as biofertilizer for rice crop is its quickisolated culture of Azotobacter fixes about 10 decomposition in the soil and efficientmg nitrogen g-1 of carbon source under in availability of its nitrogen to rice plantsvitro conditions. Azotobacter also to known to (Kannaiyan, 1990). Besides N-fixation, thesesynthesize biologically active growth biofertilizers or biomanures also contributepromoting substances such as vitamins of B- significant amounts of P, K, S, Zn, Fe, Mbgroup, indole acetic acid (IAA) and and other micronutrient. The fern forms agibberellins. Many strains of Azotobacter also green mat over water with a branched stem,exhibited fungi static properties against plant deeply bilobed leaves and roots. The dorsalpathogens such as Fusarium, Alternaria and fleshy lobe of the leaf contains the algalHelminthosporium. The population of symbiont within the central cavity. AzollaAzotobacter is generally low in the can be applied as green manure byrhizosphere of the crop plants and in incorporating in the fields prior to riceuncultivated soils. The occurrence of this planting. The most common speciesorganism has been reported from the occurring in India is A. pinnata and same canrhizosphere of a number of crop plants such be propagated on commercial scale byas rice, maize, sugarcane, bajra, vegetables vegetative means. It may yield on averageand plantation crops, (Arun, 2007a). about 1.5 kg per square meter in a week. India has recently introduced some species of Blue Green Algae (Cyanobacteria) and Azolla for their large biomass production,Azolla: These belongs to eight different which are A.caroliniana, A. microphylla, A.families, phototrophic in nature and produce filiculoides and A. mexicana.Auxin, Indole acetic acid and Gibberllic acid,fix 20-30 kg N/ha in submerged rice fields as Phosphate solubilizersthey are abundant in paddy, so also referred Several reports have examined the abilityas ‘paddy organisms’. N is the key input of different bacterial species to solubilizerequired in large quantities for low land rice insoluble inorganic phosphate compounds,production. Soil N and BNF by associated such as tricalcium phosphate, dicalciumorganisms are major sources of N for low phosphate, hydroxyapatite, and rockland rice. The 50-60% N requirement is met phosphate. Among the bacterial genera withthrough the combination of mineralization of this capacity are pseudomonas, Bacillus,soil organic N and BNF by free living and Rhizobium, Burkholderia, Achromobacter,rice plant associated bacteria (Roger and Agrobacterium, Microccocus, Aereobacter,Ladha, 1992). To achieve food security Flavobacterium and Erwinia. There arethrough sustainable agriculture, the considerable populations of phosphate-requirement for fixed nitrogen must be solubilizing bacteria in soil and in plantincreasingly met by BNF rather than by rhizospheres. These include both aerobicindustrial nitrogen fixation. Most N fixing and anaerobic strains, with a prevalence ofBGA are filamentous, consisting of chain of aerobic strains in submerged soils. Avegetative cells including specialized cells considerably higher concentration ofcalled heterocyst which function as micro phosphate solubilizing bacteria is commonlynodule for synthesis and N fixing machinery. found in the rhizosphere in comparison with
  • 5. S. Sheraz Mahdi et al./J Phytol 2/10 (2010) 42-54non rhizosphere soil (Raghu and Macrae, genera of fungi that contain species, which2000). The soil bacteria belonging to the are known to produce Arbuscular mycorrhizalgenera Pseudomonas and Bacillus and Fungi fungi (AMF) with plants. Two of these genera,are more common. The major Glomus and Sclerocytis, producemicrobiological means by which insoluble-P chlamydospores only. Four genera formcompounds are mobilized is by the spores that are similar to azygospores:production of organic acids, accompanied by Gigaspora, Scutellospora, Acaulospora andacidification of the medium. The organic and Entrophospora. The oldest and most prevalentinorganic acids convert tricalcium phosphate of these associations are the arbuscularto di- and- monobasic phosphates with the mycorrhizal (AM) symbioses that firstnet result of an enhanced availability of the evolved 400 million years ago, coincidingelement to the plant. The type of organic acid with the appearance of the first land plants.produced and their amounts differ with Crop domestication, in comparison, is adifferent organisms. Tri- and di-carboxylic relatively recent event, beginning 10, 000acids are more effective as compared to years ago (Sawers et al. 2007).mono basic and aromatic acids. Aliphaticacids are also found to be more effective in P- Zinc solubilizerssolubilization compared to phenolic, citric The nitrogen fixers like Rhizobium,and fumaric acids. The analysis of culture Azospirillum, Azotobacter, BGA and Phosphatefiltrates of PSMs has shown the presence of solubilizing bacteria like B. magaterium,number of organic acids including citric, Pseudomonas striata, and phosphatefumaric, lactic, 2-ketogluconic, gluconic, mobilizing Mycorrhiza have been widelyglyoxylic and ketobutyric acids. accepted as bio-fertilizers (Subba Roa, 2001a). However these supply only major nutrientsPhosphate absorbers but a host of microorganism that canMycorrhiza (an ancient symbiosis in transform micronutrients are there in soilorganic agriculture) that can be used as bio-fertilizers to supply The term Mycorrhiza denotes “fungus micronutrients like zinc, iron, copper etc.,roots”. It is a symbiotic association between zinc being utmost important is found in thehost plants and certain group of fungi at the earth’s crust to the tune of 0.008 per cent butroot system, in which the fungal partner is more than 50 per cent of Indian soils exhibitbenefited by obtaining its carbon deficiency of zinc with content must belowrequirements from the photosynthates of the the critical level of 1.5 ppm of available zinchost and the host in turn is benefited by (Katyal and Rattan, 1993). The plantobtaining the much needed nutrients constraints in absorbing zinc from the soilespecially phosphorus, calcium, copper, zinc are overcome by external application ofetc., which are otherwise inaccessible to it, soluble zinc sulphate (ZnSO4). But the fate ofwith the help of the fine absorbing hyphae of applied zinc in the submerged soil conditionsthe fungus. These fungi are associated with is pathetic and only 1-4% of total availablemajority of agricultural crops, except with zinc is utilized by the crop and 75% ofthose crops/plants belonging to families of applied zinc is transformed into differentChenopodiaceae, Amaranthaceae, mineral fractions (Zn-fixation) which are notCaryophyllaceae, Polygonaceae, Brassicaceae, available for plant absorption (crystallineCommelinaceae, Juncaceae and Cyperaceae. They iron oxide bound and residual zinc). Thereare ubiquitous in geographic distribution appears to be two main mechanisms of zinc-occurring with plants growing in artic, fixation, one operates in acidic soils and istemperate and tropical regions alike. VAM closely related with cat ion exchange andoccur over a broad ecological range from other operates in alkaline conditions whereaquatic to desert environments (Mosse et al. fixation takes by means of chemisorptions, (1981). Of 150 species of fungi that have been chemisorptions of zinc on calcium carbonatedescribed in order Glomales of class formed a solid-solution of ZnCaCO3), and byZygomycetes, only small proportions arepresumed to be mycorrhizal. There are six
  • 6. S. Sheraz Mahdi et al./J Phytol 2/10 (2010) 42-54complexation by organic ligands (Alloway, effects on plant yields. The effect of2008). Azotobacter chroococcum on vegetative growth The zinc can be solubilized by and yields of maize has been studied bymicroorganisms viz., B. subtilis, Thiobacillus numerous authors (Hussain et al., 1987;thioxidans and Saccharomyces sp. These Martinez Toledo et al., 1988; Nieto andmicroorganisms can be used as bio-fertilizers Frankenberger, 1991; Mishra et al., 1995;for solubilization of fixed micronutrients like Pandey et al., 1998; Radwan, 1998), as well aszinc (Raj, 2007). The results have shown that the effect of inoculation with this bacteriuma Bacillus sp. (Zn solubilizing bacteria) can be on wheat (Emam et al., 1986; Rai and Gaur,used as bio-fertilizer for zinc or in soils 1988; Tippanavar and Reddy, 1993,where native zinc is higher or in conjunction Elshanshoury, 1995; Pati et al., 1995; Fares,with insoluble cheaper zinc compounds like 1997a).zinc oxide (ZnO), zinc carbonate (ZnCO3) Alkaline phosphatase activity in theand zinc sulphide (ZnS) instead of costly zinc peach roots was highest with Azotobactersulphate (Mahdi et al. 2010). chroococcum + P fertilizer (Godara et al., 1995). Results of a greenhouse pot experiments3. Potential role of bio-fertilizers in with onion showed that application of G.agriculture fasciculatum + A. chrooccocum + 50% of theNitrogen-fixers (NF) and Phosphate recommended P rate resulted in the greatestsolubilizers (PSBs) root length, plant height, bulb girth, bulb The incorporation of bio-fertilizers (N- fresh weight, root colonization and P uptakefixers) plays major role in improving soil (Mandhare et al. 1998). Inoculation withfertility, yield attributing characters and Azotobacter + Rhizobium + VAM gave thethereby final yield has been reported by highest increase in straw and grain yield ofmany workers (Subashini et al. 2007a; wheat plants with rock phosphate as a P-Kachroo and Razdan, 2006; Son et al. 2007). fertilizer (Fares, 1997a). Elgala et al. (1995)In addition, their application in soil improves concluded that with microbial inoculationsoil biota and minimizes the sole use of rock phosphate could be used as cheapchemical fertilizers (Subashini et al. 2007a). source of P in alkaline soils and that Under temperate conditions, inoculation combined inoculation could reduce the rateof Rhizobium improved number of pods of fertilizer required to maintain highplant-1, number of seed pod-1 and 1000-seed productivity.weight (g) and thereby yield over the control. It is an established fact that the efficiencyThe number of pods plant-1, number of seed of phosphatic fertilizers is very low (15-20%)pod-1 and 1000-seed weight (g) recorded due to its fixation in acidic and alkaline soilswere 25.5, 17.1 and 4.7 per cent more over the and unfortunately both soil types arecontrol, respectively which was statistically predominating in India accounting moresignificant Bhat et al. (2009). In rice under low than 34% acidity affected and more thanland conditions, the application of BGA+ seven million hectares of productive landAzospirillum proved significantly beneficial in salinity/alkaline affected (Yawalkar et al.,improving LAI and all yield attributing 2000). Therefore, the inoculations with PSBaspects. Grain yield and harvest index also and other useful microbial inoculants inexhibit a discernable increase with use of bio- these soils become mandatory to restore andfertilizers (Dar and Bali, 2007). Afzal, (2006) maintain the effective microbial populationsfound that seed and straw yield of green for solubilization of chemically fixedgram increased significantly up to single phosphorus and availability of other macroinoculation with Rhizobium under 20 kg N + and micronutrients to harvest good45 kg P2O5 ha-1 fertility level. Field trials sustainable yield of various crops.carried out in different locations have Commercial exploitation of phosphaticdemonstrated that under certain microbial inoculants can play an importantenvironmental and soil conditions role particularly in making the direct use ofinoculation with azotobacteria has beneficial abundantly available low grade phosphate
  • 7. S. Sheraz Mahdi et al./J Phytol 2/10 (2010) 42-54possible. Among the bacterial genera with consists of a wider physical exploration ofthis capacity are pseudomonas, Bacillus, the soil by mycorrhizal fungi (hyphae) thanRhizobium, Burkholderia, Achromobacter, by roots. A speculative mechanism to explainAgrobacterium, Microccocus, Aereobacter, P uptake by mycorrhizal fungi involves theFlavobacterium and Erwinia. production of glomalin. Glomalin contains Beside N-fixation and P-solubilization, very substantial amounts of iron (up to 5% ofthe incorporation of nitrogen fixing bacteria the glomalin pool, Lovelock et al., 2004).(Azotobacter spp.) under the commercial Assuming 0.5 mg glomalin g-1 soil with 1%name ‘cerealien’ and phosphate dissolving iron, and assuming that this iron wasbacteria (Bacillus megaterium) ‘phosphorien’ derived initially from unavailable Fe–Phas shown the highest degree in inducing the forms in the NaOH-Pi fraction, thedegree of the physiological tolerance to destabilization of this bond could havesalinity which enables the stressed plants of released 1.75 mg P per pot, comparable to thethe Seets cultivar of wheat to be adapted and 2.01 mg NaOH-Pi that was taken up. Bolan etkeep better performance against all applied al. (1987) had already proposed thatlevels of salinity (3000, 6000 and 9000 ppm). mycorrhizal fungi may break the bondThis performance was reflected by the between Fe and P, but they did not suggest aincrease in growth, dry matter accumulation, mechanism. Further research into theyield as well as chemical constituents. All physiological and ecological roles ofchemicals constituents including N, P, K+, glomalin is needed to address this question.sugars, proline and were increased as AM plants have been reported to improvecompared to their control treatments in the nutrition of the other macronutrients N andcultivar Seets. Mohmoud and Mohamad, K. In acid soils, AM fungi may be important2008. for the uptake of ammonium (NH4+), which Mycorrhizae is less mobile than nitrate (NO3-) and where The fungi that are probably most diffusion may limit its uptake rate. Althoughabundant in agricultural soils are arbuscular nitrate is much more mobile thanmycorrhizal (AM) fungi. They account for 5– ammonium (uptake is regulated through50% of the biomass of soil microbes (Olsson mass flow). Because of their small size, AMet al., 1999). Biomass of hyphae of AM fungi fungal hyphae are better able than plantmay amount to 54–900 kg ha-1 (Zhu and roots to penetrate decomposing organicMiller, 2003), and some products formed by material and are therefore better competitorsthem may account for another 3000 kg for recently mineralized N (Hodge, 2003). By(Lovelock et al., 2004). Pools of organic capturing simple organic nitrogencarbon such as glomalin produced by AM compounds, AM fungi can short-circuit thefungi may even exceed soil microbial N-cycle.biomass by a factor of 10–20 (Rillig et al., It is also reported that the AM- fungi also2001). The external mycelium attains as increases the uptake of K, and concentrationmuch as 3% of root weight (Jakobsen and of K has been found more in mycorrhizalRosendahl, 1990). Approximately 10–100 m than non-mycorrhizal plants (Bressan et al.,mycorrhizal mycelium can be found per cm 2001). Apart from this, the AM-fungi alsoroot (McGonigle and Miller, 1999). increases the uptake and efficiency of The mineral acquisition from soil is micronutrients like Zn, Cu, Fe etc. byconsidered to be the primary role of secreting the enzymes, organic acids whichmycorrhizae, but they play various other makes fixed macro and micronutrientsroles as well which are of utmost important: mobile and as such are available for the plant.Improved nutrient uptake (Macro andmicronutrients) Better water relation and drought tolerance The improvement of P nutrition of plants AM fungi play an important role in thehas been the most recognized beneficial water economy of plants. Their associationeffect of mycorrhizas. The mechanism that is improves the hydraulic conductivity of thegenerally accepted for this mycorrhizal role
  • 8. S. Sheraz Mahdi et al./J Phytol 2/10 (2010) 42-54root at lower soil water potentials and this hyphae of the latter over those of AM fungiimprovement is one of the factors (Klironomos and Kendrick, 1996; Gange,contributing towards better uptake of water 2000). In addition, AM fungi produceby plants. Also, leaf wilting after soil drying, glomalin (12-45 mg/cm3), a specific soil-did not occur in mycorrhizal plants until soil protein, whose biochemical nature is stillwater potential was considerably lowered unknown. Glomalin is quantified by(approx. 1.0 M. Pa). Leaflets of Leucaena measuring several glomalin related soil-plants inoculated with VA mycorrhizae did protein (GRSP) pools (Rillig, 2004). Glomalinnot wilt at a xylem pressure potential as low has a longer residence time in soil thanas -2.0 MPa. Mycorrhiza induced drought hyphae, allowing for a long persistenttolerance can be related to factors associated contribution to soil aggregate stabilization.with AM colonization such as improved leaf The residence time for hyphae is consideredwater and turgor potentials and maintenance to vary from days to months (Staddon et al.,of stomatal functioning and transpiration, 2003) and for glomalin from 6 to 42 yearsgreater hydraulic conductivities and (Rillig et al., 2001). Steinberg and Rillig (2003)increased root length and development. demonstrated that even under relatively favorable conditions for decomposition, 40%Soil structure (A physical quality) of AM fungal hyphae and 75% of total Whereas the role of mycorrhizal glomalin could be extracted from the soil 150associations in enhancing nutrient uptake days after being separated from their host.will mainly be relevant in lower input agro- Glomalin is considered to stably glue hyphaeecosystems, the mycorrhizal role in to soil. The mechanism is the formation of amaintaining soil structure is important in all ‘sticky’ string-bag of hyphae which leads toecosystems (Ryan and Graham, 2002). the stability of aggregates.Formation and maintenance of soil structurewill be influenced by soil properties, root Enhanced phytohormone activityarchitecture and management practices. The activity of phytohormones like The use of machines and fertilizers are cytokinin and indole acetic acid isconsidered to be responsible for soil significantly higher in plants inoculated withdegradation. The specific adsorption of P by AM. Higher hormone production results infunctional groups can affect the charge better growth and development of the plant.balance and cause dispersion of particles(Lima et al., 2000). Soil aggregation is one Crop protection (Interaction with soilcomponent of soil structure. Mycorrhizal pathogens)fungi contribute to soil structure by (1) AM fungi have the potential to reducegrowth of external hyphae into the soil to damage caused by soil-borne pathogeniccreate a skeletal structure that holds soil fungi, nematodes, and bacteria. Meta-particles together; (2) creation by external analysis showed that AM fungi generallyhyphae of conditions that are conducive for decreased the effects of fungal pathogens. Athe formation of micro-aggregates; (3) variety of mechanisms have been proposedenmeshment of micro aggregates by external to explain the protective role of mycorrhizalhyphae and roots to form macro aggregates; fungi. A major mechanism is nutritional,and (4) directly tapping carbon resources of because plants with a good phosphorusthe plant to the soils (Miller and Jastrow, status are less sensitive to pathogen damage.1990, 2000). This direct access will influence Non-nutritional mechanisms are alsothe formation of soil aggregates, because soil important, because mycorrhizal and non-carbon is crucial to form organic materials mycorrhizal plants with the same internalnecessary to cement soil particles. Hyphae of phosphorus concentration may still beAM fungi may be more important in this differentially affected by pathogens. Suchregard than hyphae of saprotrophic fungi non-nutritional mechanisms includedue to their longer residence time in soil, activation of plant defense systems, changesbecause fungivorous soil fauna prefers in exudation patterns and concomitant
  • 9. S. Sheraz Mahdi et al./J Phytol 2/10 (2010) 42-54changes in mycorrhizosphere populations, sterilization (while using autoclave, limeincreased lignification of cell walls, and mixed lignite is filled up to two thirdcompetition for space for colonization and capacity of steel trays for 1-2 hours for threeinfection sites (Kaisamdar, et al. 2001). It is days and sterilized at 121 0C ) for carrieralso reported that increased production and material.activity of phenolic and phytoalexiencompounds with due to AM-inoculation Mutation during fermentationconsiderably increases the defense Bio-fertilizers tend to mutate duringmechanism there by imparts the resistance to fermentation and thereby raising productionplants. and quality control cost. Extensive research work on this aspect is urgently needed to4. Constraints in bio-fertilizer use eliminate such undesirable changes.Production Constraints Despite significant Market level constraintsimprovement/refinement in BF technology Lack of awareness of farmersover the years, the progress in the field of BF Inspite of considerable efforts in recentproduction technology is below satisfaction years, majority of farmers in India are notdue to the followings:- aware of bio-fertilizers, their usefulness in increasing crop yields sustainably.Unavailability of appropriate and efficientstrains Inadequate and Inexperienced staff Lack of region specific strains is one of Because of inadequate staff and that toothe major constraints as bio-fertilizers are not not technically qualified who can attend toonly crop specific but soil specific too. technical problems. Farmers are not givenMoreover, the selected strains should have proper instructions about the applicationcompetitive ability over other strains, N- aspects.fixing ability over a range of environmentalconditions, ability to survive in broth and in Lack of quality assuranceinoculants carrier. The sale of poor quality bio-fertilizers through corrupt marketing practices resultsUnavailability of suitable carrier in loss of faith among farmers, to regain the Unavailability of suitable carrier (media faith once is very difficult and challenging.in which bacteria are allowed to multiply)due to which shelf life of bio-fertilizers is Seasonal and unassured demandshort is a major constraint. Peat of a good The bio-fertilizer use is seasonal andquality (more than 75% carbon) is a rare both production and distribution is donecommodity in India. Nilgiri peat is of poor only in few months of year, as suchquality (below 50% carbon). According to the production units particularly private sectorsavailability and cost at production site, are not sure of their demand.choice is only with lignite and charcoal inIndia. As per the suitability the order is peat Resource constraint>lignite > charcoal > FYM > soil >rice husk. Limited resource generation for BF productionGood quality carrier must have good The investment in bio-fertilizermoisture holding capacity, free from toxic production unit is very low. But keeping insubstances, sterilisable and readily adjustable view of the risk involved largely because ofPH to 6.5-7.0. Under Indian conditions where short shelf life and no guarantee of off take ofextremes of soil and weather conditions bio-fertilizers, the resource generation is veryprevail, there is yet no suitable carrier limited.material identified capable of supporting thegrowth of bio-fertilizers. Better growth ofbacteria is obtained in sterile carrier and the Field level constraintsbest method is Gamma irradiation of Soil and climatic factors
  • 10. S. Sheraz Mahdi et al./J Phytol 2/10 (2010) 42-54 Among soil and climatic conditions, high based bio-fertilizers (1000 times). Since thesesoil fertility status, unfavorable PH, high are liquid formulations the application in thenitrate level, high temperature, drought, field is also very simple and easy. They aredeficiency of P, Cu, Co, Mo or presence of applied using hand sprayers, powertoxic elements affect the microbial growth sprayers, fertigation tanks and as basaland crop response. manure mixed along with FYM etc.Native microbial population Antagonistic microorganism already 5. Conclusion and future strategiespresent in soil competes with microbial Identification/ selection of efficientinoculants and many times do not allow location/ crop/soil specific strainstheir effective establishment by out- for N-fixing, P, Zn- solubilizing andcompeting the inoculated population. absorbing (mycorrhizal) to suitFaulty inoculation techniques different agro climatic conditions. Majority of the marketing sales Strain improvement throughpersonals do not know proper inoculation biotechnological methods.techniques. Bio-fertilizers being living Exchanging the cultures betweenorganisms required proper handling, countries of similar climatictransport and storage facilities. conditions and evaluating their performance for better strain forLiquid Bio-fertilizers (Break through in BF- particular crop. Checking the activityTechnology) of cultures during storage to avoid Liquid bio-fertilizers are special liquid natural mutants.formulation containing not only the desired Use of sterile carriers and installingmicroorganisms and their nutrients but also centralized unit of gamma chamberspecial cell protectants or chemicals that facilities at different locations to usepromote formation of resting spores or cysts by private and governmentfor longer shelf life and tolerance to adverse manufacturers in the case of use ofconditions. (Hegde, 2008). carrier based inoculants till the Bhattacharyya and Kumar (2000), states development of alternate formulation.that, bio-fertilizers manufactured in India are Identifying two or three commonmostly carrier based and in the carrier-based carrier materials in different(solid) bio-fertilizers, the microorganisms countries based on availability andhave a shelf life of only six months. They are recommends them to the producers.not tolerant to UV rays and temperatures Developing suitable alternatemore than 30 0C. The population density of formulations viz., liquid inoculants /these microbes is only 108 (10 crores) c.f.u/ml granular formulations for allat the time of production. This count reduces bioinoculants, to carrier basedday by day. In the fourth month it reduces to inoculants. Standardizing the media,106 (10 lakhs) c.f.u/ml and at the end of 6 method of inoculation etc., for themonths the count is almost nil. That’s why new formulations.the carrier-based bio-fertilizers were not Employing microbiologists ineffective and did not become popular among production units to monitor thethe farmers. These defects are rectified and production. Developing cold storagefulfilled in the case of Liquid bio-fertilizers. facilities in production centers.The shelf life of the microbes in these liquid Technical training on the productionbio-fertilizers is two years. They are tolerant and quality control to the producersto high temperatures (55 0C) and ultra violet and rendering technical advice andradiations. The count is as high as projects to manufacturers.109 c.f.u/ml, which is maintained constant Organizational training to theup to two years. So, the application of 1 ml of extension workers and farmers toliquid bio-fertilizers is equivalent to the popularize the technology.application of 1 Kg of 5 months old carrier Dissemination of information
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