Start a Blue Green Algae Biofertiizer Plant

(196) Start a Blue Green Algae Biofertiizer Plant
     
1.0 Product and its applications

Blue Green Algae (BGA) find a favourable abode in the waterlogged conditions of rice fields. These cyanobacteria provide inexpensive nitrogen to plants besides increasing crop yield by making the soil fertile and productive. BGA biofertilizer in rice popularly known as ‘Algalization' helps in creating an environment – friendly agroecosystem that ensures economic viability in paddy cultivation while saving energy intensive inputs. Under favourable conditions, BGA have been found to contribute up to 25- 30 kg N per hectare per season and increase the crop yield by 10-15%. These have also been recognized as important agents in the stabilization of soil, add organic matter, release growth promoting substances, improve soil physico-chemical properties and solubilize the insoluble phosphates. The technology can be easily adopted by farmers for multiplication at their own level.

The improved production technology developed by Indian scientists includes a) indoor production of algal biomass under near pure state and in semi-controlled conditions b) a suitable and inexpensive growth medium for faster growth of the organisms and c) mixing with a suitable carrier material in desired quantities

2.0 Advantages of BGA

On an average, BGA contribute 20-30 kg N / ha / season which means that chemical nitrogen fertilizer to that extent could be saved through these organisms. Application of BGA biofertilizer leads to increased productivity of rice by 10-15%. BGA improve soil health and maintain a continuous supply of crop nutrients. It improves water holding capacity of soil and increases soil aggregation. BGA leads to population build up and enhances the microbial activity. Algalization induces early grain setting and maturity. It checks weeds proliferation by blocking nutrient supply and light. It is economical and easily adaptable by small and marginal farmers. BGA biofertilizer is eco-friendly and non-polluting to the environment.          


5.0 TECHNICAL ASPECTS
5.1 Location

Indoor production can be undertaken in polyhouse or glass house. The dimensions and number of such production units are variable depending on the turnover. The production unit should be located (North- South) in an open area away from shade so as to receive maximum sunlight during the day throughout the year.

5.2 Salient Features of Process / Technology

The BGA multiplication units can be made of RCC, brick and mortar or polythene lined pits.. The life of polythene lined shallow pit on ground is about 6 months, whereas other structures are permanent. The smallest recommended size of pits of RCC or brick and mortar is 1.7m x 0.9m x 0.3m (l x b x d). The dimensions of length and breadth may vary so as to utilize the maximum available space with operational management and convenience. The multiplication units are filled with suitable medium to provide essential nutrients like potassium, phosphorus and magnesium in an economical manner. The pH should be near neutral.

Each pit is inoculated with actively growing culture (12 – 15 days old) equivalent to 20 - 25 g fresh biomass per unit. BGA is allowed to grow for 5-8 days depending upon the ambient temperature, light intensity and humidity till enough biomass is produced so as to cover the surface of medium. The algal culture is agitated manually 2-3 times a day during its multiplication. Once fully grown, the culture is harvested, mixed with carrier (presoaked clay or Multani mitti) and sun dried. The sun dried material is finely ground to 200 mesh and packed in 500 g capacity polythene bags and sealed, Store at a cool dry place in the room and do not mix with any chemical fertilizers or pesticides.

Method of Application : One packet (500 g) of ready to use multani mitti based BGA biofertilizer is recommended for one acre of rice growing area. The packet is opened and mixed with 4 kg dried and sieved farm soil. The mixture is broadcast on standing water 3-6 days after transplantation. Use of excess algal material is not harmful; instead it accelerates the multiplication and establishment in the field. The field should be kept waterlogged for about 10-12 days after inoculation to allow good growth of BGA.

If the farmer is using self produced soil based BGA biofertilizer, 12-15 kg/ha is used by broadcasting the mixture on standing water 3-6 days after transplantation. Similarly, the field should be kept waterlogged for 10-12 days after inoculation to allow good growth of BGA. When nitrogenous fertilizers are used, reduce the dose by one-third and supplement with BGA. Normal pest control measures and other management practices do not interfere with the establishment and activity of BGA in the field. Apply BGA for at least four consecutive seasons to have cumulative effect. One may not need to apply BGA further as these will establish in the field and reappear as and when the condition becomes favourable.

Precautions: When fertilizer or pesticides (e.g. weedicides.) are applied in the field; the algal application should be followed after a gap of 3-4 days. Application of a small dose of phosphate fertilizer after BGA inoculation accelerates BGA multiplication. However, this quantity should be considered in the total application dose for rice corp.

Tips: Growth of BGA can be periodically examined using a micro-scope. The iodine test can also be used to differentiate between green and blue-green algae. The green algae turn dark violet or black with iodine. Alkaline conditions with pH around 8.0 prevent contamination with green algae to an appreciable extent. For commercial purpose, the tank dimensions can be increased or decreased to make maximum use of the space available. Provide enough space between the tanks for operational convenience. Production units should be constructed in such a way to have maximum light and allow more surface area for algal growth. Addition of superphosphate should be split into two or three doses. Under ideal conditions, the algal biomass production reaches 100 g/m 2 /day. Since the wet algal biomass contains more than 90 per cent water and it is mixed with equal amount of clay.
            

1. Introduction: The global energy crisis and dwindling mineral oil reserves have widened the gap between supply and demand of nitrogenous fertilizers. An introduction of fertilizer responsive high yielding crop varieties has further increased the demand of this important crop nutrient. This has resulted in further burden on small and marginal farmers, especially in developing countries. This has become necessary to look for alternative sources to meet atleast a part of nitrogen requirement of crop production.
In India, rice is cultivated on about 40 million hectares of area, which constitutes about 37-40% of total area under cereals. Though, rice cultivation is an age-old practice in our country, the average production is only about 1.7 t/ha. This is because more than 85% of the total area of rice is owned by small and marginal farmers. These farmers cannot afford to use various inputs needed to harvest maximum yield of rice. They do not get full returns/unit nitrogenous fertilizers in their fields because of high nitrogen losses in the ecosystem.
The past few decades have widened remarkable advancement in harnessing some of the potentially useful micro-organisms to build up the fertility of the soil to increase the crop yield. In recent years, blue-green algae, a group of soil micro-organisms have been shown to be agriculturally important, particularly in tropical rice field soils. This is because of capacity of some of the algae to synthesize organic substances and also to fix atmospheric nitrogen.
Submerged conditions of a rice field provide congenial habitat for blue green algae where they form most efficient system providing biologically fixed nitrogen to the crop. The importance of blue-green algae was first recognised by De (1936) who reported that these micro-organisms are responsible for spontaneous fertility of tropical rice field soils. Since then series of reports have been appeared emphasising their role in nitrogen cycle in general and rice field in particular. The propagation of blue green algae will not only enrich the nitrogen status of the soil by their fixation process but also provide organic matter and biologically potent substances for plant growth. These algae form a living constituent of the soil biotype and continue their activity year after year. Besides they release oxygen for the paddy roots and increase soil phosphate. Some of them prevent the loss of soil ammonia and leaching out of nitrates by converting them into organic nitrogen. Blue green algae also produce a surface humus after death and exert a solvent action on certain minerals – maintaining a reserve supply of elements in a semi-available form for higher plants either by ecretion or upon death and decomposition.
2. Distribution of blue green algae in rice field soils: Blue green algae have been found in almost all the conceivable habitats. They are widely distributed throughout the tropical, subtropical and temperate regions. However, the frequency of their occurrence was more prominent in Southern than in Northern regions. Tropical soils harbour comparatively higher population of blue green algae.
In Southeast Asia including Japan the presence of species Tolypothrix, Nostoc, Cylindrospermum, Calothrix, Anabaena, Plectonema and Anabaenopsis was found prominent. In Senegal, the dominant species reported were Nostoc and Anabaena, whereas, Scytonema and Calothrix were respectively found in 50 and 15 percent area. In Indonesia Cylindrospermum, Anabaenopsis, Nostoc and Nodularia were found to be common. In North Australia blue green algae flora was dominated by Nostoc and Anabaena. The dominant species in Philippines weree Nostoc and Anabaena. In Russia, Nostoc and Anabaena were found most common.
In India, a general prodominance of blue green algae except in acidic soils of Kerala, Assam and parts of Tamil Nadu. Forms like Anabaena, Nostoc and Calothrix were found to be widely distributed throughout rice growing tracts of India.
Other forms like Cylindrosporum, Tolypothrix, Scytonema and Aulosira had localised distribution. The distribution of soils harbouring blue green algae in India varies from as low as 7 to as high as 80 percent in different States. Uttar Pradesh soils are rich in Aulosira and Mastigocladae is found in Gujarat. Westiella is found very dominant in Maharashtra and Cylindrospermum in Karnataka and Calothrix in Punjab soils of Vidharbha and Konkan of Maharashtra are dominated by blue green algae.
During recent years, quantitative studies showed consistent presence of N2 fixing blue green algae at high densities in soils under rice cultivation in countries like India, Malaysia, Philippines, Portugal, Nostoc sp. Was dominant followed by Anabaena and Calothrix. Blue green algae occurred at densities from 1.0 x 10^-2 to 8.0 x 10^-6 CFU/cm^-2 and their abundance was correlated to pH and available `P’ content of soil.
3. Strain variation: Biological N₂ fixation in nature or agricultural ecosystem is rarely limited by a lack of N₂, fixing micro-organisms. Nevertheless, very little nitrogen fixed in nature. Apart from the ecological stresses the efficiency of strains themselves may play an important role. Therefore great differences in the amount of nitrogen fixed by various genera and sometimes by the same species from different localities. The need for wide collection, culturing and testing for the relative efficiency of different strains is, therefore, obvious. The possible reasons for the reported differences in their efficiency in fixing nitrogen may be due to variations in the cultural conditions like light, temperature, nutrient deficiences, etc. It is also known that the secrete of increasing nitrogen fixing capacity lies in the adequate supply of trace elements like molybdenum.
Likewise, the influence of genetic constitution might also play a vital part in determining the capacity to fix nitrogen. Apart from the natural inherent variations, combined nitrogen and various agrochemicals play a vital role in determining the nitrogen contribution by the added blue green algae in field. This offers an opportunity to select strains for specific ecosystem.
4. Strain competition: The successful induction of a micro-organism in an ecosystem depends upon its ability to adopt and compete with the indegenous biotypes. For the positive introduction of an effective blue green algae strain in an area depends upon its ability to survive and compete with the native flora for establishment, growth and effective nitrogen fixation.
Prior to seeding, the paddy field water may be sprinkled with lime powder, which will be effective in suppressing the growth of other algae and at the same time will lower the acidity of water to a favourable level. It is possible that antagonistic effects of other organisms may affect the successful survival of particular algae strain. Similarly, possibilities for the presence of algophages cannot be ruled out. There is a great deal of indirect evidence to show that some algae can liberate antibiotic substances. There are reports that there was no marked difference in the total amount of nitrogen fixed and bacteria under water logged conditions. Thus nitrogen fixation is essentially, an algae process and the part played by bacteria is relatively unimportant. The decomposition of blue green algae is enhanced by the presence of bacteria in an adequate quantity. Besides fertilizing action of nitrogen fixing blue green algae in the field is considerably improved by bacterial flora.
5. Strain selection: The Production of strains, likely to be superior, in nature to those which already exist, is daunting challenge. First it is essential to select N₂ fixing strains capable of rapid growth. Well studied Cynobacteria such as Anabaena cylindrica are relatively slow growing with a generation time of 16 – 24 hours. Anacystis nidulans, which was doubling time of 2 hours does not fix nitrogen. However, with improved culture media and methods of obtaining axenic cultures, the selection of rapidly growing N₂fixing strains has a reality.       
   
   
   
   

Secondly, Cyanobacteria should be selected which can fix N₂ equally well under aerobic, micro aerobic and anaerobic conditions, so that they can tolerate the very wide range of oxygen tension found in rice fields. The heterocystous and certain unicellular forms satisfy these conditions. However, N₂ fixing unicellular forms which can tolerate Oxygen extremes and high light intensities and grow rapidly are not yet available. Heterocystous forms are currently better alternatives.

Third, it is important to choose Cyanobacteria that fix N₂ under Photoautotrophic, Phoheterotrophic and chemoheterotrophic conditions. These Cyanobacteria include species of Anabaena, Anabaenopsis, Nostic and Tolypothrix.

Fourth, strain that show little or no H₂ evolution should be selected. The extent of H₂ production varies in different N₂ fixing Cynabacteria and it is important to select strains that little show such production and ATP wastage.

Fifth, the selection of strains that possess non-repressible nitrogenase could possibly be important.

In Cyanobacteria nitrogenase is inhibited by high level of NHX4 –N and it is thus important to obtain strain in which this does not occur.

Sixth, strains should be selected that not only liberate extracellular Nitrogen but liberate it in substantial amounts, exceeding the requirement of Cyanobacteria for optimal growth and is released it in a form that can be readily assimilated.

Seventh, the way in which glutamine synthetase regulated is of importance in Nitrogen fixing Cyanobacteria.

Blue green algae, biofertilizer has been proved to be most efficient source of organic nitrogen in low level Paddy.

N₂ from blue green algae

Nitrogen constitutes in general 1-2 per cent of total dry weight of plants and in unfertilized soils this often limits crop production. Use of chemical fertilizers during 1960-1970 was preferred by farmers due to its cheapness and easiness of application. Later on these fertilizers become most expensive and hence farmers were unable to use these fertilizers as required by crops. The production of N-fertilizer is the energy intensive process and this energy is provided from fossil fuels to convert Nº NÕ NH₃. However, with the energy crisis of the late 1970 the cost of chemical fertilizer was escalated. Hence it was necessary to search for alternative source to maintain the production level of grains to feed the increasing population.

The most inexhaustible energy source is the solar radiation thus there is particular interest in those organisms which can use this energy within their protoplasm to produce ammonia from nitrogen. There are two groups of microorganisms viz. Cyanobacteria (blue-green algae) and photosynthetic bacteria.

Blue green algae (BGA) are photosynthetic procaryotic micro-organisms. Their main photosynthetic pigments are chlorophyll-a carotenes. Xanthophylls, together with phycobiliproteins, c-phycocyanin (blue) and e-phycoerythrin (red). Due to the presence of these latter pigments and mucilage, the colour of BGA in nature ranges from dirty yellow, through various shades of blue-green to brown or black.

Some blue green algae can fix atmospheric nitrogen because they contain an O₂ sensitive enzyme nitrogenase. The term algal biofertilizer was coined in early sixties to embody such blue green algae which have the capacity to metabolize the molecular nitrogen and bring about an addition to the nitrogen content of soil. The conversion of elemental nitrogen to ammonia was the monopoly of heterocystous blue green algae till the findings of Whyatt and Silvey in 1961 who reported nitrogen fixation by a unicellular algaeGloeocapsa. Since then more than a dozen non-heterocystous genera of blue green algae have been found to fix air nitrogen.

Heterocysts

Some blue green algae have empty looking thick walled structures in their trichomes, known as heterocysts. These specialised cells lack pigment system-II and as such there is no endogenous evolution of oxygen. The oxygen from air cannot diffuse through their thick walls. The anaerobic conditions are so created inside the heterocysts keep nitrogenase active in them. Thus, under aerobic conditions only the heterocysts blue green algae can fix nitrogen.

The nitrogenase in the vegetative cells also can become active if the entire trichome is transferred to microgerobic or anaerobic conditions. The non-heterocysts blue green algae find such an environment in the subsoil region and soil water interphase in a rice field where they add substantial amount of nitrogen through nitrogen fixation.

Growth promoting effects of blue green algae

In addition to contributing about 30kg N/ha /season, blue green algae help in maintaining the soil fertility by way of liberating growth promoting substances like auxin, vitamins. They add organic matter because of their photolithotrophic nature. They also solubilize insoluble phosphate and improve physical and chemical properties of soil.

Blue green algae have been found to synthesize and liberate biologically potent substances into the medium. The liberation of auxins, vitamin B₁₂ and amino acids has been found to be maximum during the stationary phase of the growth. The substances benefit the crop growth and enable plants to utilize more of the applied nitrogen.

Photosynthesis by blue-green algae

Blue green algae possess permanent property of metabolizing both elemental nitrogen and carbondioxide from the atmosphere simultaneously. The process of photosynthesis in these organisms meets the entire energy requirement including the power needed for reducing nitrogen to ammonia. As such these algae form a completely independent system and they don’t dwell upon soil organic matter for energy supply. As a consequence of algal growth, organic matter is added to the soil. But because of high nitrogen content and high rate of decomposition in the water logged conditions no appreciable addition to the organic matter content in soil is observed. The presence of organic matter in the soil has been found to favour the growth of the blue green algae. This is attributed to the increased availability of carbon dioxide for the process of photosynthesis.

The polysaccharidic sheath present around the trichomes of these algae binds the soil particles and increases the particle size. This improvement in soil aggregates formation increases aeration and water holding capacity. Some saprophytic algae like Calothrix, Tolypothrix and Scytonema grow on moist soil surface forming a velvety growth and protect the soil from erosion.

Iron toxicity

Algae have been found to grow in the subsoil zone upto a depth of about 20cm. Being photosynthetic in nature they liberate oxygen in this zone which helps in bringing down oxidizable matter content of soil. This has an important implication in areas where 2 to 3 crops of rice are taken in one year. In these areas continuos water-logging conditions create reducing conditions which results iron toxicity. The oxygen liberated by the blue green algae in the microaerobic or anaerobic zones of a rice field converts Fe⁺⁺ to Fe⁺⁺⁺. The later being insoluble gets participitated and iron content of the water is reduced. Iron, if present beyond 5 ppm, is known to adversely affect the cell permeability.

Phosphate solubilization

Many algae have been found to solubilize the insoluble phosphate to the extent of 2.27mg P₂O₅/ml/15 days. This attains importance in view of the fact that most of the phosphatic fertilizer, when applied to soil, is immediately converted into insoluble calcium phosphate and becomes unavailable to the plants.

Response of BGA to various external stresses

Algae when introduced in the field are subjected to physical, chemical and biotic stresses. The physical stress is exerted by soil texture, temperature and moisture. Chemical properties of the soil, pH, fertilizers and various agricultural chemicals constitute the chemical stresses. Variety of micro-organisms present in soil exert antagonistic and synergistic effects on the introduced algae.

Physical stresses

Heavy soils rich in organic matter and with higher water holding capacity support good algal growth. Saline alkali soils with higher water table and poor drainage harbour rich flora of blue green algae. Conversely, sandy soils have a poor algal growth. Blue green algae can grow at temperature range of 30 to 45⁰C. Blue green algae essentially true hydrophytes, although many of them exist in sub-aerial and terrestrial habitats. Although water-logged conditions favour the growth of BGA, quite a few of them grow as true saprophytes. In such forms no significant reduction in growth and nitrogen fixation was observed even when water was present upto 50% of the total water holding capacity of soil. Increased humidity coupled with high temperature and shade favour luxurious growth of algae in rice fields.

Chemical stresses

Soil pH plays an important role in distribution and predominance of algae. Acidic soils show a higher incidence of green algae while neutral to slightly alkaline soils support a rich blue green algae flora. The ideal pH range for luxuriant growth of blue green algae is 6.5 to 8.5.

Use of chemical fertilizers and pesticides has become an integral part of the present day agriculture. In the presence of fertilizers nitrogen blue green algae are expected to "shut off" the process of nitrogen fixation. This effect is more pronounced in presence of NH₄⁺ than NO₃^- nitrogen. However, upto 40 ppm ammonium nitrogen, no significant reduction in nitrogen fixation by blue green algae occurs.

The blue green algae have been found to accumulate pesticides within their cells, in concentrations several folds higher than that of surroundings. At the recommended field application doses, most of the pesticides do not have any adverse affects on the activity of algae.

Biotic stresses

Variety of micro-organisms inhabit the soil. In an undisturbed soil ecosystem, there always exists an equilibrium. A disturbance in this is likely to be met with resistance. The capacity of introder to withstand, overcome and adjust to the new environment qualifies the organisms to be used as inoculum. Fungi like Alternaria and Cephalosporium have synergistic effect on algae. Antibiotics producing organisms are expected to have a regulatory effect on algae. Protozoa, mosquito larvae and snails are common grazers of algae in rice fields.

Blue green algae (Part C)

Algal Production Technology

The success of any technology usually depends upon its techno-economic feasibility. The algal production technology developed and reported by different Algologists is very simple in operation and easy in adaptability by Indian farmers. The technology has got potential to provide an additional income from the sale of algal biofertilizer. In general, there are four methods of algal production have been reported viz, (a) trough or tank method, (b) pit method, (c) field method and (d) nursery cum algal production method. The former two methods are essentially for individual farmers and latter two are for bulk production on a commercial scale.

1. Trough method:

1. Prepare shallow trays (2mx1mx23 cm) of galvanised iron sheet or permanent tank. The size of the tank can be increased if more material is to be produced.
2. Spread 4 to 5kg of river soil and mix well with 100g of superphosphate and 2g Sodium molubdate.
3. Pour 5 to 15cm of water in the trays. This will depend upon local conditions i.e. rate of evaporation. Mix the ingredients properly.
4. In order to avoid the nuisance of mosquitoes and insects add 10 to 15g Furadon granules or malathion, or any other suitable granules.
5. The mixture of soil and water will settle within 8-10hours. At this time, add 200 to 250g mother culture of blue green algae to the surface of water. Then don’t disturb water.
6. The reaction of the soil should be neutral. If the soil is acidic then add CaCo₃ in order to bring the pH of the soil to neutral.
7. If sunlight and temperature are normal then within 10-15 days the growth of the blue green algae will look hard flakes on the surface of the water/soil. Similarly, water level will be reduced due to evaporation.
8. This way water in the tray/pit is allowed to evaporate and the growth of the algae flakes is allowed to dry.
9. If soil is dried the algal growth is separated from soil. These pieces of algal growth are collected and stored in plastic bags. In this way from one sq.m.tray or/pit about half tonnes kg blue green algal growth is obtained.
10. Again add water to trays and stair the soil well. Then allow the algae to grow in this way. This time it is not necessary to add mother culture of algae or superphosphate. In this manner one can harvest growth of algae 2-3 times. After this effect of superphosphate and soil is reduced.

1. Pit method:
This method of production of blue green algae does not differ from the one described above i.e. trough method. Instead of troughs or tanks pits are dug in the ground and layered with thick polythene sheet to hold the water or one half cement plastered tanks. Other procedure is the same as in the trough method. This method is easy and less expensive to operate by small farmers.
2. Field scale method:

The field scale production of blue green algae is really a scaled up operation of trough method to produce the material on a commercial scale. This type of method of algal production is more common amongst farmers of south India.

1. Demarcate the area in the field for algal production: - The suggested area is 40m². No special preparation is necessary although algal production is envisaged immediately after crop harvest, the stubble is to be removed and if the soil is loamy it should be well puddled to facilitate water logging conditions.
2. Prepare a bund with earth so as to store the water.
3. Flood the area with water to a depth of 2.5cm. In trough or pit methods flooding is done only in the beginning, while in field scale method flooding is repeatedly needed to keep the water standing.
4. Then apply superphosphate 12kg/40m².
5. To control the insect-pests attach, apply carbofuran (3% granules) or Furadon 250g 40m².
6. If the field has received previously algal application for at least two consecutive cropping seasons no fresh algal application is required. Otherwise apply the composite algal culture of 5kg/40m².
7. In clayey soils, good growth of algae takes place in about two weeks in clear, sunny weather, while in loamy soils it takes three to four weeks.
8. Once the algae have grown and formed floating mats they are allowed to dry in the sun in the field and the dried algal flake, are then collected in sunny bags for further use.
9. One can continually harvest algal growth from the same area by reflooding the plot and applying super phosphate and pesticides. In such situations an addition of algal innoculum for subsequent production is not necessary.
10. During summer months (April-June), the average yield of algae per harvest ranges from 16-30kg/40m².

1. Nursery cum algal production:

Farmers can produce algae alongwith seedlings in their nurseries. If 320m² of land are allotted to prepare a nursery, an additional 40m² alongside can be prepared for algal production as described above. By the time rice seedlings are ready for transplantation about 15-20kg of algal material will be available. This much quantity of algal mass will be sufficient to inoculate one and half hectares of area. If every farmer produces the algal material required to inoculate his own land then he will reduce the cost of algal innoculum required to be purchased. So also one can cut the cost of chemical fertilizers to be applied as recommended.

Recommendation of algal biomas for field application:

1. If mineral nitrogen fertilizers are not used, apply blue green algae biofertilizer in order to gain the benefits of 30-40kg Nitrogen/ha.
2. Broadcast the dry algal material over the standing water in the rice field at a rate of 10-15kg/ha one week after transplanting the seedlings.
3. Addition of excess algal material is not harmful and will accelerate the multiplication and establishment in the field.
4. The sun dried algal material can be stored for a long time in a dry state without any loss in viability.
5. Do not store the algal material in direct contact with chemical fertilizers or other chemicals.
6. Apply algae for atleast three consecutive seasons so that there will be sufficient algal innoculum found in the field.
7. Recommended pest control measures and other management practices don’t interfere with the establishment and activity of algae in the field.

Blue green algae (Part D)

Algalization and crop yield

The significance of algal biofertilizer lies in the fact that unlike the chemical fertilizers, these are not directly utilized by the crop. Only the products of their activity are used. During the crop growth cycle, the algae grow, multiply, fix atmospheric nitrogen and make it available to the crop by way of excretion and autolysis. During unfavourable season, they form perennating bodies which germinate with the onset of congenial conditions. Thus, there is a possibility to build up populations of these algae in the soil, through superimposed inoculations for 3-4 consecutive seasons. Algalization of rice crop has been found to supplement nitrogenous fertilizers to the extent of 30-40 kg N/ha/season.

Successful establishment of desired algae in the rice fields has been found to form a source of slow release of nitrogen for the crop plants. They have also been found to protect a part of the applied fertilizer nitrogen from being lost. Studies using N¹⁵ have been shown that the nitrogen fixed by the blue green algae is actually taken up by the crop plants.

Algalization in problematic soils:

Saline-alkali soils are generally unsuitable for raising crops. Blue green algae have been shown to help in reclamation of such soils. This is because of the preferential absorption or adsorption of sodium by them. The growth of these blue green algae in saline –alkaline habitats reduces salinity by 25-30%, pH, electrical conductivity and exchangeable sodium. It also increases aggregation, hydraulic conductivity, soil nitrogen and permeability.

However, we still don’t know the mechanism by which the blue green algae scavanges Sodium. Attempts are to be made to investigate as to what happens to this absorbed/adsorbed sodium. It is also essential to develop an adaptable technology which can be used to grow and multiply the salt tolerant algal strains in such areas.

Acidic soils pose another problem in getting good results from algalization. Majority of blue green algae have a wide pH range of 6.5 to 8.5. However, some algal species are delicate. Quite a few of them have been found to be true acidic forms showing optimum growth only when the pH is below 5.0. On the other hand, there are forms, which prefer only alkaline pH. Thus, it is possible to isolate pH specific algal forms from the natural algal flora which can be used in acidic soils without any soil amendments.

Fertilizers nitrogen and pesticides effect:

Combined sources of nitrogen, which are commonly used in rice production, constitute an important stress on microbial systems. The fact that blue green algae are able to revert back to nitrogen fixing mode, when exogenous nitrogen is depleted. This indicates that a cyclic process of fertilization by these organisms can be used as an adjacent to the linear fertilization by the chemical fertilizers. Strains of blue green algae capable of absorbing and growing at higher fertilizer nitrogen levels will be more useful. They increased biomass in presence of combined nitrogen which is expected to bring about increased addition to nitrogen through nitrogen fixation when exogenous nitrogen is depleted. If we can develop strains with depressed nitrogenase, which can continue to function in presence of high level of combined nitrogen, the algal supplementation effect can be considerably increased.

Pesticides have no adverse effect on the growth of blue green algae when pesticides are used at recommended doses. Some pesticides have been found to accelerate the growth of blue green algae.

Results of field trials

The results from extensive field trials conducted in different agroclimatic regions of our country during the last two decades have shown that the effect of algal inoculation in terms of increased crop yield was satisfactory. Studies with algal inoculation at different levels of fertilizer nitrogen have shown that the supplementation effect is more pronounced at low level of nitrogen. This effect does not change with the soil type and rice variety. The subdued effect in acidic soils can be enhanced by the application of appropriate quantities of lime.

In long term experiment, there was a gradual increase in organic carbon due to algal inoculation but the amount remained steady at end of 3 years.

An increase of organic matter, water holding capacity and exchangeable Ca was reported to from medium to high level. Due to algalization of saline and alkaline soils. Algalization was also reported to increase available phosphorus in the soil, possibly because of excretion of organic acids by the blue green algae. The blue green algae have been found to solubilize the unavailable phosphate sources like Missouri rock phosphate.

Induced variability

The process of photosynthesis provides energy and carbon skeletons for nitrogen fixation. This is evidenced by evolution of oxygen under nitrogen fixing conditions. The nitrogen fixation is drastically reduced in dark because of depleting supply of photosynthates. The strains with very high rate of photosynthesis and ability to store the photosynthetes will be capable of fixing nitrogen for a comparatively longer period in the dark.

It is known that under certain conditions, nitrogenase can act as ATP dependent hydrogenase systems. An understanding and enzymology of this hydrogen evolution will enable us to train this system to evolve hydrogen from water at the expense of solar energy. This is expected to reduce our dependence on the fuel energy especially in the manufacture of fertilizer nitrogen.

Another approach to achieve this can be through the development of ammonia leaking strains. Anabaena azollae actually makes available the nitrogen fixed by it to Azolla as ammonia. Algal mutants with the defect in the regulation of the enzyme glutamine synthetase (GS) can be made to liberate ammonia. The ammonia excreted into the medium can be harvested and used for various purposes.

The efficiency of inoculum can also be increased if it contains a heavy load of the perennating bodies like akinetes and hormocysts. Many species of Anabaena and Nostoc form a long chains of spores and sometimes the entire trichome gets transformed into spores. A culture containing such organisms will multiply faster when inoculated into the field. Genetic engineering can be used to clone together, the properties of growth, nitrogen fixation and spore formation in addition to the tolerance to fertilizer nitrogen and pesticides.

Although, use of algae has been restricted to mainly rice especially low level rice cultivation successful results have been reported in sugarcane, jute, vegetables, tomatoes, fruit trees, banana, etc.

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