Microalgae are promising tools in improving soil fertility and agricultural production in the era of increased population and the need for food security, which is mostly hindered by climate change. The microbes have the ability to sequester atmospheric carbon dioxide, produce metabolites with many applications in addition surviving and growing in harsh environmental conditions. In this chapter, microalgae species of the cyanobacteria and green algae groups are established as good soil biofertilizers and conditioners which are crucial in nutrient cycling, improved soil structure, and increased soil microbial activity. These are requirements for better crop production. Microalgae are also crucial biocontrol agents that suppress and kill plant pathogens and pests, regulate the production of phytohormones, and in bio-remediation of polluted soils. Their use is therefore a road map to sustainable agriculture and food security. To ensure their optimal use, extensive research is necessary to understand the mechanisms of action behind the benefits.
TopIntroduction
Modern day faces a challenge in meeting the food demands through sustainable agricultural activities despite the growing global population and other agricultural issues. While the need to increase food and biomass productivity is urgent, climate change is also predominant and therefore, innovative technologies and products that facilitate increased crop productivity, yield and quality and at the same time reducing the resultant carbon footprint from agricultural activities must be sought (Ronga et al., 2019). Traditional agricultural activities are heavily influenced by non-renewable inputs such as pesticides and fertilizers (Chiaiese et al., 2018). The introduction of these agrochemicals however poses environmental and human health threats in addition to extra costs considering the increased nutrient mining during intensified agricultural activities (Costa et al., 2019). Furthermore, there is mounting public concern to regulate the use of these agrochemicals using stringent legal frameworks and hence their application is limited in optimizing agricultural production (Renuka et al., 2018).
Microalgae have been identified as potential alternatives to conventional agrochemical inputs. They are categorized based on their cell structure, life cycle and pigmentation. Existence literature has estimated the number of microalgae species to be approximately 800, 000 while only about 50, 000 have been described (Suganya et al., 2016). These microbes have diversified uses and it is possible to choose varied strains that have specific biochemical composition and the capacity to grow under different environmental conditions. Generally, algae are categorized into 1) multicellular, 2) filamentous, 3) colonial and 4) unicellular algae according to biologists (Nabti, Jha, & Hartmann, 2017). From the four categories, algae can be micro or macro based on size. The latter are macroscopic with a maximum length of at least 60 m and are multicellular while microalgae are microscopic and have a size ranging from approximately 1 to 900 µm (Ronga et al., 2019). Microalgae grow in fresh and marine water and are photosynthetic in nature. They can also be grown in wastewater, which reduces their production costs. The dominating microalgae species that are available commercially include Dunaliella spp., Arthrospira spp., Chlorella spp., Chaetoceros spp. and Isochrysis spp (Priyadarshani & Rath, 2012).
Microalgae consist of a variety of components including carbohydrates, proteins, pigments and lipids in addition to biomass that make them suitable for use in crop, pharmaceutical, animal feed, food and fuel production. Some of the components of the microbes are as shown in Figure 1. The current and emerging applications of microalgae are also shown in the representation. For purposes of agricultural production, microalgae comprises of micro- and macro-nutrients essential for plant growth and production. It is for this reason that microalgae have been used as biofertilisers and biostimulants (Garcia-Gonzalez & Sommerfeld, 2016; Khan et al., 2009; Shaaban, 2001; Shaaban, 2001). These microbes are gaining significant attention towards sustainable agriculture (Renuka et al., 2018). This book chapter explores the uses of microalgae for improved soil and agricultural production towards food security and greener ecosystems.
Figure 1. Composition of microalgae and its current and emerging applications
TopTechnologies For Microalgae Production
Microalgae are eukaryotic and prokaryotic microorganisms that have the capacity to produce lipids, proteins and carbohydrates through photosynthesis. They are fast maturing and can survive in harsh terrestrial and aquatic environs owing to their simple multicellular and unicellular structure. Some of the common examples include diatoms (Bacillariophyta), green algae (Chlorophyta), golden algae (Chrysophyceae) and cyanobacteria or blue-green algae (Cyanophyceae) (Mostafa, 2013). In agricultural applications cyanobacteria and blue-green algae species are commonly applied. Arable land, nutrients, water and sunlight are the growth requirements for algae and the organisms can fix CO2 ten times better than terrestrial plants. Apart from growing them, microalgae species can be produced due to their commercial and economic applications from preserving water, recovering nutrients and wastewater (Ronga et al., 2019). The conventional approach uses open or raceway ponds to produce microalgae while the modern approach uses closed photobioreactors or hybrid systems (Khan et al., 2009).