The fundamental differences of chemical and bio- fertilisers

Introduction

Cyprus is facing significant agricultural problems which can influence the quality of life and economy of the country. Problems such as low economic incentive for agricultural practices, aging agricultural labor force and low labor productivity have been slowly eroding the agricultural sector of Cyprus over the years.

However, environmental and climate issue have worsen the condition of the agricultural sector significantly. High temperatures, low water supply, overuse of traditional synthetic/animal excrement fertilizer and overall, the insularity trend of the Cypriot people have diminished the capabilities of Cypriot soil to hold significant agricultural practices. The heavy reliance οn synthetic fertilizers have led to significant environmental concerns that include nutrient loss, greenhouseemissions and the depletion of important resources like phosphorous and potassium. These issues are not only found in Cyprus but in the whole of Europe thus, research into sustainable alternatives, amongst them being microalgae and cyanobacteria, are gaining significant attention.    

Microalgae are a diverse group of photosynthetic organisms that can be either prokaryotic cyanobacteria such as spirulina or eukaryotic such as Chlorella vulgaris. Microalgae are rich in various compounds that are beneficial to both plant and soil health and growth. The utilization of microalgae as a biofertilizer/biostimulant for this compounds can be extremely beneficial to the agricultural sector.

Essential Nutrients:

Microalgae can provide essential macronutrients such as nitrogen (N), phosphorus (P) and potassium (K) to plants and the soil itself. However, the concentration of the macronutrients is low compared to chemical fertilizers, ranging from 6-8% N, and 1-3% P and K, other essential and extremely beneficial microelements are present in significantly greater quantities.  Micronutrients such as calcium (Ca), magnesium (Mg), sulphur(S), boron (B), zinc (Zn), iron (Fe) and manganese (Mn) are present in microalgae biofertilizers. These micronutrients are crucial for plants growth, health and development. Furthermore, depending on the application method of the biofertilizer, both the micro and macronutrients are released gradually, which helps prevent nutrient losses and increases nutrient absorption from the plant.  

Organic Matter and Polysaccharides:

Microalgae contribute significantly to soil organic matter content. They fix atmospheric CO2 and convert it into organic biomass through photosynthesis. This organic carbon enrichment is vital, especially considering the depletion of soil organic carbon in croplands. Microalgae biomass is a source of proteins, carbohydrates, and lipids. They also excrete extracellular polymeric substances (EPS), which are polysaccharides. These EPS help increase organic carbon levels, enhance soil aggregation, and improve soil stabilisation and moisture retention. Polysaccharides derived from microalgae are recognised as potential biostimulants

Biostimulatory Compounds:

Microalgae are a rich source of various compounds that can directly enhance plant growth and other physiological processes. Compounds such as phytohormones, proteins, amino acids and polypeptides have been shown to influence various aspects of plants development such as shoot growth, root elongation, biomass accumulation and stress resistance. Furthermore, these compounds can be a direct and easily assimilated source of nutrition for plants and other organisms in the soil, boosting their development.

Vitamins and antioxidants:

Microalgae are capable of synthesizing various vitamins, such as vitamin B, C, E and K3 which can promote plant growth and immunity. Intriguingly, land plant such as crops often lack vitamin B12 which is provided by  microorganisms in the soil such as microalgae, thus by adding microalgae based fertilizer and can fill the vitamin gap that our current crops are lacking. Furthermore, microalgae contain antioxidants and polyphenols which further contribute to plant health and stress tolerance.

Enzymes and biocontrol compounds:

Microalgae produce various enzymes and compounds that can aid in nutritional cycling between plants. Furthermore, studies have shown that specific enzymes and compounds such as hydrolytic enzymes, siderophores and free fatty acids (FFAs) can suppress the growth of pathogenic organisms such as fungi, bacteria and nematodes.

Effect on soil and plants:

Microalgae have been shown to increase soil fertility by increasing the quantity and quality of organic matter, enhancing soil structure, increase water retention and aeration. Furthermore, the soil can become less compact, making the easier for plant roots to penetrate the soil thus allowing for larger root systems and therefore nutrient acquisition. Moreover, microalgae enzymes and organic matter can positively influence the microbial populations in the soil, supporting beneficial and crucial bacteria and fungi species.

Different essential molecules such as nitrogen in the form of ammonium and nitrate cannot be absorbed by plants alone and it is done by bacteria and cyanobacteria, which are a type of microalgae, via nitrogen fixation. This adds nitrogen in usable form directly into the soil which can then be freely absorbed and utilized by plants.

Biomass or extract from microalgae can enhance plant growth, development and overall yield by positively influencing plant shoots, roots, step, vigor, biomass accumulation and fruit development. Furthermore, these effects, due to the slow release of biological compounds from the microalgae, can be present for large periods of time.

Phyohormones and polysaccharites have been shown to increase the resilience of plants to various abiotic factors such as droughts, high/low temperatures and salinity. This is done by compounds stimulating the plant’s own defense responses.

Comparison with chemical fertilizers:

Environmental pollution: The intensive use of chemical/synthetic fertilizers can lead to significant pollution in the soil. Furthermore, chemical fertilizers are associated with nutrient loss through runoff and leaching which increases water pollution not just near the farming area but in general.

Soil degradation: Use of chemical fertilizers causes the quality of the soil the decrease over time due to changes in soil pH, increasing salinity, reducing the capacity of the soil to hold water, and finally killing beneficial soil microbes.  

Greenhouse gas emissions: Nitrogen based chemical fertilizers have been shown to greatly contribute to the increase of greenhouse emissions. This is done by the release of large amounds of nitrous oxide (N2O) from the chemical fertilizers which are then processed by the microorganisms in the soil which release significant amounts of CO2. This can also be done indirectly via nitrogen runoff that is common when using chemical fertilizers. Furthermore, the production of chemical fertilizers can release large amounts of CO2 in the atmosphere.

Resource depletion: The production of chemical fertilizers relieon resources such as phosphorus and potassium deposits, which leads to a depletion of these resources and an increase in the cost of chemical fertilizers.

Human health issues: The excessive use of chemical fertilizers in the soil increases the accumulation of hazardous heavy metals such as lead, arsenic and cadmium. These chemicals can pose risks to human health as crops containing heavy metals are eaten.

While chemical fertilizer consist of high concentration of synthetic macronutrients such as nitrogen, phosphorous and potassium, and provide rapid nutrient supply, they often lack essential micronutrients found in organic sources. Microalgae based fertilizers on the other hand can also provide the plant and soil with essential macronutrients , though at lower concentrations. Nevertheless, they are rich in a wide spectrum of micronutrients like calcium, iron, manganese, zinc, copper and boron, often in higher amounts that in chemical fertilizers.

Moreover, microalgae fertilizers contain organic matter and bioactive compounds including proteins, carbohydrates, lipids, phytohormones, vitamins polysaccharides, amino acids  andenzymes.

Chemical and microalgae fertilizer comparison:

While chemical fertilizers offer a quick nutrient boost, their systematic usage degrades the soil, pollutes the environment and increases the risks of heavy metal  poisoning in humans. In contrast, microalgae biofertilizers may have lower levels of primary macronutrients compared to synthetic options, they can improve the overall long-term quality of the soil, increasing it fertility and structure. This is achieved by providing organic matter to the oil and promoting the growth of beneficial microbes. Furhtermore, they provide a slow and sustained release of nutients, enchancing nutrient availability through microbial interaction and enzymes production while supplying crucial micronutrients and bioactive compounds that synthetic fertilizers lack. The composition of microalgae fertilizers promote a stronger plant growth, increase stress tolerance the environment and pathogens/pests, while contributing positivelyto the environment by absorbing CO2 and reducing greenhouse gas emissions, unlike in the use and production of chemical fertilizers which greatly contribute to this problem.