Cyanobacterial Biofertilizer Research Articles

Metabolomic and gut-microbial responses of earthworms exposed to microcystins and nano zero-valent iron in soil

The earthworm-based vermiremediation facilitated with benign chemicals such as nano zero-valent iron (nZVI) is a promising approach for the remediation of a variety of soil contaminants including cyanotoxins. As the most toxic cyanotoxin, microcystin-LR (MC-LR) enter soil via runoff, irrigated surface water and sewage, and the application of cyanobacterial biofertilizers as part of the sustainable agricultural practice. Earthworms in such remediation systems must sustain the potential risk from both nZVI and MC-LR. In the present study, earthworms (Eisenia fetida) were exposed up to 14 days to MC-LR and nZVI (individually and in mixture), and the toxicity was investigated at both the organismal and metabolic levels, including growth, tissue damage, oxidative stress, metabolic response and gut microbiota. Results showed that co-exposure of MC-LR and nZVI is less potent to earthworms than that of separate exposure. Histological observations in the co-exposure group revealed only minor epidermal brokenness, and KEGG enrichment analysis showed that co-exposure induced earthworms to regulate glutathione biosynthesis for detoxification and reduced adverse effects from MC-LR. The combined use of nZVI promoted the growth and reproduction of soil and earthworm gut bacteria (e.g., Sphingobacterium and Acinetobacter) responsible for the degradation of MC-LR, which might explain the observed antagonism between nZVI and MC-LR in earthworm microcosm. Our study suggests the beneficial use of nZVI to detoxify pollutants in earthworm-based vermiremediation systems where freshwater containing cyanobacterial blooms is frequently used to irrigate soil and supply water for the growth and metabolism of earthworms.

Cyanobacterial biofertilizer inoculation has a distinctive effect on the key genes of carbon and nitrogen cycling in paddy rice

Cyanobacterial biofertilizer inoculation has a distinctive effect on the key genes of carbon and nitrogen cycling in paddy rice

Foliar application of cyanobacterial formulations stimulates plant growth and fruit quality in tomato under protected cultivation

ABSTRACT Cyanobacterial biofertilizers enhance plant and soil productivity across crops, through soil-seed application at the field level; however, their use as foliar treatment is less investigated. This study evaluated the role of foliar sprays, initiated 4 weeks after transplantation of nursery-raised seedlings in beds, and effected at weekly intervals for a period of eight weeks. towards enhancing plant growth, yield and quality of tomato grown in a climate-controlled polyhouse. Sprays were composed of aqueous formulations of carrier alone, and those amended with the formulations of plant-growth-promoting cyanobacterium Anabaena laxa (A. laxa) or biofilm Anabaena torulosa -Trichoderma viride (An-Tr) or suspension of 100 µM Fe EDTA. A. laxa brought about a significant increase in nitrate reductase and glutamine synthetase activity in leaves by 13%–17%, along with 3-fold stimulation in carbonic anhydrase activity. Cyanobacterium-amended foliar agents significantly enhanced soil dehydrogenase, urease activity, along with increments in organic carbon, Fe, Zn in soil and stimulated yield, fresh weight and quality of fruits. Both cyanobacterial formulations were promising in enhancing plant growth, fruit yield and quality, however, A. laxa also significantly improved microbiological activity and nutrient enrichment in soil. Future research is focused towards optimising the dose and storage life of such foliar agents for protected horticulture.

Azolla Biofertilizer Is an Effective Replacement for Urea Fertilizer in Vegetable Crops

Azolla spp. is a water fern that hosts Anabaena azolla, an N-fixing cyanobacterium, in its dorsal leaf cavities. Azolla occurs naturally in freshwater bodies in warm-temperate and tropical regions, and they have commonly been grown in rice paddies as a living fertilizer, providing N to the rice crop. We evaluated the potential use of Azolla harvested from freshwater bodies and applied as a biofertilizer to dryland vegetable crops. Two-thirds of the greenhouse gas emissions from crop production is attributed to N fertilizer, including fossil fuels used in fertilizer production and transportation. Azolla grown in on-farm ponds could remove CO2 from the atmosphere and minimize the use of fossil fuels in fertilizer production and transport. A 140-d laboratory incubation was used to compare the N mineralization of Azolla biofertilizer with compost and cyanobacterial biofertilizer treatments. Azolla treatments had the greatest N availability at the end of the incubation (73.0%), with compost demonstrating the least N availability (15.5%), and the cyanobacterial biofertilizers moderate in N release (31.6%). A greenhouse study evaluated the N uptake and yield of kale (Brassica oleracea) receiving Azolla biofertilizer compared to urea and organic fertilizers. The nitrogen uptake by kale followed the same pattern as in the incubation study, with the Azolla treatments highest among the organic fertilizers, and urea the greatest overall. Compost yielded better than the control but was the lowest yielding among the fertilizer treatments. Finally, we compared the agronomic effect of Azolla biofertilizer with urea and manure applied at the same N rates to spinach (Amaranthus cruentus) and radish (Raphanus sativus) crops grown in the field on alluvial and peat soils. Fertilizer treatments affected the spinach yield at both locations but did not affect the radish yield. The manure treatment resulted in the highest spinach yields (18–27 t ha−1), and the Azolla treatment applied at the same N rate as the manure yielded the same as the manure treatment on the peat soil and had the highest leaf and branch numbers. Azolla shows promise as a biofertilizer for dryland vegetable crops; however, an economic feasibility analysis is needed prior to encouraging the widespread adoption of on-farm Azolla production and use.

Climate mitigation potential and soil microbial response of cyanobacteria‐fertilized bioenergy crops in a cool semi‐arid cropland

AbstractBioenergy carbon capture and storage (BECCS) systems can serve as decarbonization pathways for climate mitigation. Perennial grasses are a promising second‐generation lignocellulosic bioenergy feedstock for BECCS expansion, but optimizing their sustainability, productivity, and climate mitigation potential requires an evaluation of how nitrogen (N) fertilizer strategies interact with greenhouse gas (GHG) and soil organic carbon (SOC) dynamics. Furthermore, crop and fertilizer choice can affect the soil microbiome which is critical to soil organic matter turnover, nutrient cycling, and sustaining crop productivity but these feedbacks are poorly understood due to the paucity of data from certain agroecosystems. Here, we examine the climate mitigation potential and soil microbiome response to establishing two functionally different perennial grasses, switchgrass (Panicum virgatum, C4) and tall wheatgrass (Thinopyrum ponticum, C3), in a cool semi‐arid agroecosystem under two fertilizer applications, a novel cyanobacterial biofertilizer (CBF) and urea. We find that in contrast to the C4 grass, the C3 grass achieved 98% greater productivity and had a higher N use efficiency when fertilized. For both crops, the CBF produced the same biomass enhancement as urea. Non‐CO2 GHG fluxes across all treatments were low and we observed a 3‐year net loss of SOC under the C4 crop and a net gain under the C3 crop at a 0–30 cm soil depth regardless of fertilization. Finally, we detected crop‐specific changes in the soil microbiome, including an increased relative abundance of arbuscular mycorrhizal fungi under the C3, and potentially pathogenic fungi in the C4 grass. Taken together, these findings highlight the potential of CBF‐fertilized C3 crops as a second‐generation bioenergy feedstock in semi‐arid regions as a part of a climate mitigation strategy.

Ameliorative effects of endogenous and exogenous indole-3-acetic acid on atrazine stressed paddy field cyanobacterial biofertilizer Cylindrospermum stagnale

Across the world, paddy fields naturally harbour cyanobacteria that function as biofertilizers and secrete various compounds like Indole-3-acetic acid (IAA) that help organisms in regulating their growth. Also, paddy field farming utilizes large amounts of pesticides (e.g. atrazine); but their continued application in the agricultural field causes toxicity in non-target cyanobacterial species that hinder their performance as a biofertilizer. Hence, the current study is an attempt to ameliorate the atrazine stress in cyanobacterium Cylindrospermum stagnale by addition of IAA (1 mM each) under different atrazine levels (0, 60, 80, 100, 120, 140 µg/l). Atrazine toxicity affected C. stagnale in a dose-dependent manner further experiments revealed that both the exogenous and endogenous IAA mitigated the detrimental effects of atrazine. It reduced MDA content and simultaneously increased chlorophyll content, total protein content, and multiple antioxidant enzyme activities [superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX)] at 140 µg/l. A molecular docking study revealed that the pesticide binds to the D1 protein of the photoelectric chain in photosynthesis. Hence, the application of IAA or cyanobacterial biofertilizer that secretes a sufficient amount of IAA may assist sustainable agriculture in counteracting the atrazine toxicity.

Mitigative effect of biosynthesized SeNPs on cyanobacteria under paraquat toxicity

Increasing population has resulted in increased food demand. Pesticides like paraquat (PQ) have been used indiscriminately to increase the growth and yield of crops. However, this has adversely affected a wide spectrum of non-target organisms like cyanobacteria that are used as a bio-fertilizer in the rice field. In the present study, biogenic- Gloeocaspa gelatinosa NCCU -430 mediated selenium nanoparticles (SeNPs) were synthesized and characterized using different techniques including UV–Visible spectroscopy, XRD, FTIR, TEM and SEM-EDX for their use as PQ toxicity mitigator in cyanobacterial biofertilizer (Anabaena variabilis NCCU-442). Therefore, a comparative study was performed among control, PQ, SeNPs and SeNPs+PQ to check the efficacy of SeNPs in mitigation of PQ induced toxicity. Supplementation of SeNPs in PQ treated culture enhanced antioxidant enzymes activity i.e., SOD (7.55%), CAT (57.94%), APX (17.45%) and GR (14.72%) as compared to only PQ treated culture. The outcomes of the present study suggested that SeNPs can ameliorate the PQ induced stress that may be used in sustainable rice cultivation needed for filing the gap between requirement and supply.

A Review on Cyanobacterial Biofertilizer for Organic Rice Cultivation: Technology, Improvement and Future Prospects

A Review on Cyanobacterial Biofertilizer for Organic Rice Cultivation: Technology, Improvement and Future Prospects

BIORECLAMATORY STUDIES ON SALT AFFECTED SOIL BY USING CYANOBACTERIAL BIOFERTILIZERS

In the present investigation, three strains of cyanobacteria isolated from agricultural fields near to salt mine were used as biofertilizer individually and in consortia. Farm yard manure was also used along with cyanobacterial biofertilizers to see the ameliorative effect on soil physical, chemical and biological properties. The algalization experiment was conducted in pots in the glass house of the department for 240 days. There was an improvement in carbon, nitrogen, phosphate, potassium, magnesium, calcium, zinc, iron, copper and manganese with biofertilizers treatment whereas sodium ion, EC and pH were found to be decreased. Soil microbial activities and plant growth parameters were found to be improved. Thus, the cyanobacterial species show promise in effective exploitation for phytoremediation and improved productivity of saline soils.

Aboveground and belowground responses to cyanobacterial biofertilizer supplement in a semi‐arid, perennial bioenergy cropping system

AbstractThe need for sustainable agricultural practices to meet the food, feed, and fuel demands of a growing global population while reducing detrimental environmental impacts has driven research in multi‐faceted approaches to agricultural sustainability. Perennial cropping systems and microbial biofertilizer supplements are two emerging strategies to increase agricultural sustainability that are studied in tandem for the first time in this study. During the establishment phase of a perennial switchgrass stand in SW Montana, USA, we supplemented synthetic fertilization with a nitrogen‐fixing cyanobacterial biofertilizer (CBF) and were able to maintain aboveground crop productivity in comparison to a synthetic only (urea) fertilizer treatment. Soil chemical analysis conducted at the end of the growing season revealed that late‐season nitrogen availability in CBF‐supplemented field plots increased relative to urea‐only plots. High‐throughput sequencing of bacterial/archaeal and fungal communities suggested fine‐scale responses of the microbial community and sensitivity to fertilization among arbuscular mycorrhizal fungi, Planctomycetes, Proteobacteria, and Actinobacteria. Given their critical role in plant productivity and soil nutrient cycling, soil microbiome monitoring is vital to understand the impacts of implementation of alternative agricultural practices on soil health.

Exogenous salicylic acid mediated herbicide (Paraquat) resistance in cyanobacterial biofertilizer Microchaete sp. NCCU-342.

Paddy field farming remains the dominant form of growing rice in modern times as the rice is the staple food for over half the world's population and is closely associated with food security and political stability of many countries. Record increase in rice production have been observed since the start of the Green Revolution. India is one of the largest paddy producer and exporter in the world. However, constant use of chemical herbicide like paraquat had shown adverse impact on the rice yield. Non-target organisms of the habitat including cyanobacterial paddy biofertilizer face the herbicide toxicity and are unable to perform efficiently their role as biofertilizer. Therefore, in the present study, an attempt has been made to enhance the paraquat resistance in rice biofertilizer (Microchaete sp. NCCU-342) by exogenous addition of salicylic acid. Paraquat showed toxicity in Microchaete sp. NCCU-342 in a dose-dependent manner. Concentration of paraquat >1.0 μM exhibited lethal effect since the beginning. Through successive narrow range experiment, LD50 value of paraquat was obtained as 0.6 μM. Biomass exposed to paraquat (LD50 value) and salicylic acid (0.3 mM) showed mitigation in free radical production (2.20 % MDA and 1.69 % H2O2) and enhancement in the activity of the antioxidant enzymes activity, i.e. SOD, CAT, APX (137.76 %, 87.45 %, 118 %, respectively) and osmolytes (3.8 % proline and 21.51% sucrose). Thus, for sustainable agricultural practice, especially for paddy field cyanobacterial biofertilizer, application of salicylic acid or organism with higher salicylic acid production ability may be an alternative to overcome the paraquat toxicity.

Cyanobacterial biofertilizers as an alternative to chemical fertilizers in paddy fields: a review.

In India, rice is the most significant crop in terms of the total area of cultivation and fertilizers. Distributed in 44.7 million hectares, it accounts for 31.8% (5.34 million tons) of the net use of the chemical fertilizer. Continuously using chemical fertilizers in agricultural production poses a severe environmental risk. The cost of chemical fertilizers is expensive and contributing to less crop yield. There is a need to adopt alternatives for chemical fertilizers in paddy fields. Cyanobacteria are abundant in paddy fields, and it presents remarkable contribution in producing the rice crop. It fixes atmospheric nitrogen, increases the accessibility of available phosphorus, and produces innumerable plant growth-promoting factors. It requires sunlight as the source of energy for carbon and nitrogen fixation in the soil. It represents remarkable potential as a biofertilizer and thereby decreases fuel demand for chemical fertilizer production. Cyanobacterial biofertilizers are inexpensive, simple to use, and do not harm the environment. This review focuses on the potential application of cyanobacterial biofertilizers in paddy fields.

Cartap hydrochloride induced stress response in Anabaena variabilis ARM 441

Cartap hydrochloride is a moderately hazardous nereistoxin analogue insecticide that is predominantly applied in paddy fields of India, at a recommended dose of 10 μg ml−1 to kill chewing and sucking insect pests of rice crop. Toxicity of cartap hydrochloride was studied on non-target free-living nitrogen fixing cyanobacterium Anabaena variabilis ARM 441 commonly used as algal biofertilizer in rice cultivation. Anabaena sp. could tolerate commercial grade insecticide up to 30 μg ml−1. However, at the recommended dose of 10 μg ml−1, it caused reduction in algal growth, total nitrogen and heterocyst frequency by 47.28, 24.29 and 17.72% respectively, as well as photosynthetic pigments under pure culture conditions. Scanning electron micrographs revealed cell rupture and breakage in filaments due to cartap exposure with the formation of akinetes. Cartap hydrochloride induced stress, since level of superoxide dismutase, peroxidase and catalase were increased by 108.57, 187.5 and 117% respectively. Generation of superoxide radicals and hydrogen peroxide were also increased by 152.48 and 34% respectively. Lipid peroxidation was increased by 31.03%, whereas there was decline in ascorbate content by 48.45%, however the glutathione content was increased by 128.57%. Increase in osmolytes such as proline from 8.6 to 32.8% and sucrose from 61.22 to 90.13% indicates their possible role in overcoming cartap induced oxidative stress and can be helpful in assessing its detrimental effect on Anabaena variabilis ARM 441, since cyanobacterial biofertilizers are purposely used in paddy fields as nitrogen contributors.

Influence of Cyanobacterial Biofertilizer on the Response of Zea mays Plant to Cadmium-stress

CADMIUM (Cd) pollution is a thoughtful problem that alters crop yield and agricultural soils worldwide. Cyanobacteria are emerging candidates as eco-friendly biofertilizers. The present study evaluates the capability of super blue green biofertilizer (cyanobacteria biofertilizer (CB); Nostoc sp. and Anabaena sp.) to alleviate the Cd toxicity on 21 d-old Zea mays plants (applied as 2 and 10mM CdSO4). Application of CB significantly improved maize growth and reduced Cd-accumulation. Cadmium-induced oxidative stress indicated by increment of malondialdehyde (MDA), H2O2 contents and electrolyte leakage (EL) was diminished upon application of CB. Cd-stress significantly induced L-phenylalanine ammonia-lyase (PAL) specific activity and phenolics accumulation in the leaves and roots of maize plants. The results revealed that Cd-stress markedly enhanced GSH/GSSG ratio, gltuthione reductase (GR), superoxide dismutase (SOD) and catalase (CAT) specific activities, while it decreased that of ascorbate peroxidase (APx) and guaiacol peroxidase (GPx) and insignificantly increased polyphenol oxidase (PPO). The isozyme pattern of peroxidase was changed upon Cd-exposure. CB application significantly reduced both of the Cd-induced accumulated phenolics content and reduced glutathione (GSH) while it increased total glutathione (TG). CB application significantly induced all tested antioxidant enzymes. The data revealed that CB application could reduce Cd toxicity in maize plants.

Optimizing a cyanobacterial biofertilizer manufacturing system for village-level production in Ethiopia

A series of experiments in laboratory and hoop house environments was conducted to develop a cyanobacteria-based biological N fertilizer source that can be produced in Ethiopian villages, thus providing an alternative to expensive, imported urea. In the laboratory, factorial combinations of four Anabaena species strains (E-2, E-3, E-5, and E-9) isolated from Ethiopian soils and three water sources (river, lake, and ground water) were laid out in a complete randomized design in a light box constructed for this purpose with three replications. Factorial combinations of two pond-lining materials (transparent and black plastic sheets) and two aeration intervals (1-hour and 30-min intervals) were laid out in a complete randomized design with three replications in a hoop house using small ponds (1 m × 2 m × 0.25 m). Cyanobacteria strain E-3 performed best in the river water and was selected based on significantly higher values of optical density, growth rate, heterocyst frequency, and total Kjeldahl nitrogen than the other strains. DNA sequencing showed that clones of E-3 shared 99% similarity with Anabaena oscillariodes. Moreover, transparent plastic–lined ponds with a 1-hour aeration interval provided the best growing conditions for the E-3 strain based on its significantly higher dry biomass, optical density, and growth rate under these conditions as compared with ponds lined with black plastic or aerated in 30-min intervals. Therefore, transparent plastic–lined ponds with 1-hour aeration intervals are recommended for the mass production of A. osciolloides strain E-3 for use as a biofertilizer.

Cyanobacterial biofertilizer’s successful journey from rural technology to commercial enterprise: an Indian perspective

This paper discusses the outcome of a study on the transition of cyanobacterial biofertilizer technology from laboratory to small-scale production to large-scale commercial use. The nitrogen-fixing ability of cyanobacteria helps to reduce the dose of chemical nitrogen fertilizer (urea) needed, so they are immensely important for paddy crops, especially in Southeast Asian nations, where soil quality is deteriorating and where large groups of farmers cannot afford the use of more costly chemical fertilizers. Inundated water is required for this technology to be effective in paddy crops and is also imperative for good paddy crop; fortunately, this is exactly how paddy is grown on the Indian subcontinent. This study elaborates the whole cyanobacterial biofertilizer technology chain and its development process, the triggering role played by industry partners, and industry’s dissemination of the technology to farmers’ doorsteps.

Cyanobacteria: A sustainable and commercial bio-resource in production of bio-fertilizer and bio-fuel from waste waters

Abstract The indiscriminate increasing the human population and development has posed extra burden on the soil and water resources. Micro-algae and cyanobacteria compared to other organisms are eco-friendly, larger cell size and efficient biomass production, makes them best and sustainable solution for the problems related to soil fertility and available water resources. Compared to chemical fertilizers, the cyanobacterial bio-fertilizer can act as supplements to fertilizer N contributing up to 30 kg N ha−1. These bio-agents are also considered as potential candidate for lipid content production because of their rapid biomass production efficiency. The micro-algae biomass can be used to produce biofuels. Large scale biomass production and harvesting of cyanobacteria and micro-algae in waste water or their integration cultivation in sewage and effluent treatment plants could be very useful for waste water treatment. There is the need to find out how the cyanobacterial technology can be applied cheaply enough at the local-village level while still being effective alternatives options for the chemical fertilizers. The micro-algae, adapted to local water and soil conditions, test ponds and soils should be being seeded with these bio-agents which are naturally occurring in local native habitats. The goal should be for farmers to be able to produce the efficient biomass producing micro-algal agents on-site to use in their own fields as bio-fertilizers and bio-fuel production. This review article reveals use of cyanobacteria and micro-algae in waste water treatments, slow release bio-fertilizer for sustainable agriculture and also as feed stock for eco-friendly bio-fuels generation.

English

Although chemical fertilizers have long been used to meet the high demand of nitrogen (N), the most common limiting nutrient to plant growth, the frequent use of this fertilizer gradually deteriorates soil fertility in addition to its high cost, lower supply and agronomic use efficiency in Ethiopia. Nevertheless, N-fixing cyanobacterial biofertilizers are eco-friendly, and currently considered important to support the developing organic agriculture. Therefore, this study was conducted to evaluate the potential of cyanobacterial biofertilizer for the growth and yield of three commonly growing crops in Ethiopia: maize, kale, and pepper under Alfisol and Andosol, and to investigate the potential contribution of cyanobacteria biofertilizer in selected soil fertility parameters. Three independent factorial experiments were conducted simultaneously in the greenhouse. Each experiment included a factorial combination of four nitrogen fertilizer sources applied at recommendation rate for each crop (control, urea, dried cyanobacteria, and liquid cyanobacteria,) and two soil types with acidic and alkaline pH (Alfisols and Andosols, respectively) arranged in a complete randomized design (CRD) with three replications. Application of dried and liquid cyanobacterial biofertilizer treatments significantly improves the soil N, soil organic carbon (SOC) and available P, Fe and Zn. Cyanobacteria treatments were also found to reduce or maintain the mean soil pH. Accordingly, maximum values of all the vegetative growth attributes of kale, and maize were obtained from the application of two comparable-fertilizer treatments: air-dried cyanobacteria and urea while for pepper crops only dried cyanobacteria. Concentrations of N, P, Zn, and Fe in leaves of kale, pepper, and maize were also significantly increased by air-dried cyanobacterial biofertilizer. Overall, dried cyanobacteria improved the growth and yield of the three crops, and the fertility of the soils. Therefore, the use of dry cyanobacterial biofertilizer could be recommended as a supplementary N source to inorganic fertilizer for kale, pepper and maize production in both study sites. Key words: Alfisols, andosols, biofertilizers, cyanobacteria, N-fixing.

Heavy metal accumulation from coal fly ash by cyanobacterial biofertilizers

ABSTRACTBioleaching of heavy metals (Cu, Zn, Cr and Pb) from coal fly ash by cyanobacterial strains (Nostoc muscorum, Anabaena variabilis, Tolypothrix tenuis and Aulosira fertilissimia), that are commonly used as biofertilizers in rice cultivation was studied to assess utilization of fly ash while mitigating its environmental metal toxicity. Cyanobacteria were grown at different concentration of fly ash at 0, 5, 10, and 20% was treated with different blue green algal strains (Nostoc muscorum, Anabaena variabilis, Tolypothrix tenuis, and Aulosira fertilissimia) in suitable growth medium (BG-11) and distilled water to observe their growth and metal accumulation. Nostoc muscorum (ARM 442 mg g−1) showed maximum uptake of Cr (3.65 mg g−1), Pb (2.12 mg g−1) at BG 11(-N) medium amended with 10% fly ash, respectively. Anabaena variabilis (ARM 441) showed maximum uptake of Cu (0.313 mg g−1) and Pb (2.01 mg g−1) in BG 11 (–N) medium amended with 5% fly ash whereas Cr uptake (1.21 mg g−1) at 10% fly ash and Zn uptake (0.697 mg g−1) at 20% fly ash grown in BG 11(-N) medium. Increased accumulation of metals in blue green algae biomass grown in BG 11(-N) medium amended fly ash confirms that metal concentration was balanced between the algal strains.

Developments in Cyanobacterial Biofertilizer

Rice is the world’s most important food crop as more than 40% of the world’s population depends on rice as a major source of calories. Rice yield in India is about 1990 kg/ha against a maximum of 3346 kg/ha in Punjab. Though the rice yields in Punjab is highest in the country, it is quite low compared to China (5807 kg/ha). Such diversity in yields is due to insufficient use of fertilizer nitrogen. Nitrogen is present as elemental nitrogen in the atmosphere and constitutes more than 79 per cent of total gases. However, crop plants cannot utilize nitrogen in elemental form. On global level, out of 180 million tonnes of nitrogen added annually on the earth’s surface, 2/3 is through biological processes, largely microbial activities. Cyanobacteria colonize rice fields and provide biologically fixed nitrogen to the rice crop to the extent of 25-30 kg nitrogen per hectare. In India, on an average, cyanobacteria accounts to about 33% of total algal flora of Indian rice field soils [66], whereas in some of the southern and eastern states this reaches up to 50%. Virtually all the dominant cyanobacteria in rice fields are nitrogen fixing. Apart from increase in yield and saving of fertilizer nitrogen, cyanobacterial inoculation improves the physico-chemical properties of soil, gradual build-up of residual soil nitrogen and carbon, improvement in soil pH and electrical conductivity. The grain quality in terms of protein content was improved. Our recent studies have shown that the cyanobacteria ( Nostoc and Anabaena ) were capable of forming associations with wheat roots grown in liquid culture. Probably, such cyanobacteria contribute nitrogen and growth promoting substances to plants in the rhizosphere.