Rise in the food demand is one of the major issues and a global concern. Security of food has also become a concern with increase in populations and limited lands for cultivation. This is a major result of industrialization and urbanization. On the arrival of green revolution, concentrated agricultural practices came into existence comprising the use of disease-resistant crop varieties, high-yielding and continuous input of agrochemicals like pesticides, chemical fertilizers and more. However, application of chemicals is unfavorable as it affects the dynamic equilibrium of soil and also affects the agro biodiversity by finishing nontarget useful flora & fauna of soil.

Rice is

Rise in the food demand is one of the major issues and a global concern. Security of food has also become a concern with increase in populations and limited lands for cultivation. This is a major result of industrialization and urbanization. On the arrival of green revolution, concentrated agricultural practices came into existence comprising the use of disease-resistant crop varieties, high-yielding and continuous input of agrochemicals like pesticides, chemical fertilizers and more. However, application of chemicals is unfavorable as it affects the dynamic equilibrium of soil and also affects the agro biodiversity by finishing nontarget useful flora & fauna of soil.

Rice is one of the most important food items in the world as half of the population of world depends on rice as staple food. It is registered around 742 Mn tons of production as rice market monitoring accompanied by FAO. However, various coordinated efforts for growth in rice production comes into existence to meet the demand of rising population in support of research & development units. Efforts are helping in increasing the opportunities in employment, rise in the income of farmers and inspiring access of rice to poor populations worldwide. The approach is sustainable agricultural practices comprising of application of biofertilizer to improve the content of soil nutrient resulting in better productivity. It is reported that nitrogen deficiency affects the productivity of rice in various ways like production of dwarf plants, underdeveloped growth & development, lower yield and yellowing of leaves. In many of the cropping system recovery efficiency is almost less than 60%. In addition, large amount of nitrogen is lost because of leaching, volatilization, soil erosion and denitrification. Although, algae with universal presence in all the terrestrial environments is the characteristic organism on Earth having probable application in agriculture as bio fertilizers and nutrition as food supplements. However, heterocystous, filamentous, photosynthetic cyanobacteria and nitrogen fixing is the part of tropical paddy field ecosystem assuming the outstanding source of nitrogen economy of rice fields and embracing as replacement to agrochemicals with important environmental and economic advantages. Hence, cyanobacterial strains are differentiating heterocyst in nitrogen-deprived condition and engage both diazotrophy & photoautotrophy, needing mineral nutrients, water, light & carbon dioxide for survival.

Appearance of Algae as Biofertilizer:

Hence, plant nutrients, mostly phosphorous and nitrogen are the factors responsible for agricultural yield. However, in Haber-Bosch procedure, an artificial nitrogen fixation procedure is consuming around 1-2% of annual energy supply on Earth is industrial phenomenon for production of nitrogen for plants. It’s an irony that nitrogen is the most necessary elements in high amounts of crops. Hence, the availability is low to crop plants in spite of abundant profusion in atmosphere. Hence, the fact that many of the crop plants without the anticipated trait to blend in the atmospheric nitrogen. Therefore it requires the production of artificial nitrogen fertilizers. Thus, the production of chemical fertilizers depend on decreasing the nonrenewable resources and not able to gratify the requirement of nitrogen of crop plants. Additionally, production costs is prohibiting the poor farmers using synthetic fertilizer. Hence, synthetic nitrogen fertilizers manufactured and used in the agricultural practices are capable of feeding almost one-third of world population. Destructive use of the synthetic fertilizers is leading to soil erosion, improved water demand, constraining crop productivity and deprivation of local ecosystem opening gates for diseases & pests. These fertilizers are known to participate towards the emission of greenhouse gas as production depends on fossil fuels where use of chemicals is predictable to meet the increasing demand for food. Appearance of organic farming is significant area of priority of increasing demand for long-term sustainability and healthy food. Biofertilizers are evolving as best substitute to synthetic fertilizers. Whereas, biofertilizers includes living microorganisms on which the application take over the rhizosphere or interior of plant, seed surfaces or plantlet or soil, promoting the growth by escalating the obtainability of nutrients for hosting plant.

Diversity of Algae in Paddy Fields:

Examination of paddy fields in various countries such as Thailand, Japan, China, Bangladesh, Philippines & India reveals that cyanobacteria is registering the dominance on other organisms. However, rice paddy field is distinguished in three compartments on the basis of chemical and physical soil condition, anoxic bulk, oxic surface and rhizosphere with rhizoplane. Because of the high habitat diversity, a clear longitudinal and chronological heterogeneity can be observed, and is accountable for the development of separate ecological niches. However, the anoxic bulk is methanogenic. Therefore, oxic compartment is occupied by diazotrophic cyanobacteria and controlled by Anabaena, Phormidium and Nostoc. However, salinity is accountable for shifts in diversity in paddy fields, less salinity favors growth of heterocystous cyanobacteria, while high salinity is supporting the growth of nonheterocystous genera.

Outcome on soil biochemical and physico-chemical properties:

Several kinds of soil indicators are useful in assessing the properties of fertilizers. Many of them are using soil physical & chemical properties where others are concentrating on biochemical properties that are reflecting the activity & size of soil microbial biomass. 

Algae- Biofertilizer impacts soil porosity and soil aggregation:

Substantial rise in dehydrogenase, soil polysaccharides, phosphatase activities and urease was recorded. Enhancement in oil aggregation was seen, where stable soil aggregates are necessary to soil fertility. However, soil polysaccharides is the main component accountable for soil stabilization. As a result, enhancement in soil aggregation is following the incubation with BGA, providing the healthier water holding capacity to soil. However, algal proteoglycans are possessing the adhesive properties that are easily fastening the cells to solid surfaces and combined soil particles. Hence, soil aggregation & arrangement of soil combinations is significant affecting aeration, temperature & infiltration rates of soil, enhancing the physical environment of crop.

Consequence on Soil pH & Chelation of Soil Elements:

Soil pH is recognized as being affected by algal biofertilizers. Primary increase in pH of soil, reporting the substantial reduction in pH and hydraulic conductivity, soil aggregation and electrical conductivity. Cyanobacteria is known for ability to state trace elements from the insoluble materials. However, Zn, Mn and Fe is known for influencing in rice fields by the cyanobacterial growth. Although, Sargassum (brown alga) is serving as soil conditioner because of the presence of soluble alginates accelerating the breakdown of organic matter by bacteria. Thus, algal biofertilizers are influencing soil properties by aggregation of soil particle, trace and phosphate element released from the insoluble minerals, slow release and N storage.

Impact on Microbial Community:

As many of the workers are studying the effect of algal biofertilizer on the microflora of soil known about the changes in soil microbial community resulting in inoculation of blue-green algae. Although, four logarithmic unit enhances in heterotrophic bacteria, algal, fungal propagules and actinomycetes & three logarithmic unit develops in fungal mycelia after the inoculation of burnt soils with cyanobacteria.

Conclusion:

Algal species are having the potential in biofertilizer technology on the basis of eco-friendly soil binders, cost effectiveness, amelioration of sodic soil as the natural occurrence in paddy fields. In addition, secretion of bioactive substances and exopolysaccharides by cyanobacteria and algae is proving the role in recuperating mobilization and soil nutrients of insoluble forms of inorganic phosphates. Hence, expansion of genetically modified stress-tolerant cyanobacteria is having the outlook as biofertilizer & transfer the stress coping genes in crop plants having great future.