Invisible creatures that help the plant thrive
With light, water and about 20 other elements, plants can support all their biochemical needs. These essential elements can be divided into two groups: macronutrients and micronutrients.
Macronutrients are the nutrients the plants require in large amounts; calcium, carbon, hydrogen, magnesium, nitrogen, oxygen, phosphorus, potassium, and sulphur. Micronutrients or trace elements are present in very small quantities, they include boron, chlorine, cobalt, copper, iron, manganese, molybdenum, nickel, silicon, sodium, and zinc
The main three nutrients a plant needs are nitrogen (N), phosphorus (P) and potassium (K), the well-known and often used NPK fertilizer.
Microorganisms can also provide these nutrients to plants. The group of beneficial microbes that can be used for this are Biofertilizers. They are defined as substances that contain microbes that help promote the growth of plants by increasing the supply of essential nutrients to the plants. These microbes have the ability to colonize the rhizosphere and enhance plant nutrient uptake.
Nitrogen is essential for plant growth and chlorophyll synthesis. Nitrogen is one of the most abundant elements on earth, but nitrogen deficiency is probably the most common nutritional problem affecting plants worldwide. A very high percentage of the total nitrogen found in soil is in organic form, this nitrogen form is not directly available to plants. Plants can take up nitrogen from the soil in the form of nitrate (NO3-) and ammonium (NH4+). Nitrogen is also the most abundant element in the earth's atmosphere, but plants are not able to get their nitrogen directly from the air.
Nitrogen is one of the most abundant elements on earth, but nitrogen deficiency is probably the most common nutritional problem
Several microorganisms can be used to help plants with the uptake of nitrogen. In legumes Rhizobium can be used to help the plant with nitrogen uptake. Root colonization of Rhizobium results in the formation of root nodules, were they convert atmospheric nitrogen into ammonia.
Other microorganisms that can be used for nitrogen fixation are e.g., Azotobacter, Azospirillum, and Bacillus. The advantage of these microorganisms is that they work on a wider range of crops and are not limited to legumes.
Phosphorus is a vital component of adenosine triphosphate (ATP) which is the energy form the plant uses. Phosphorus also stimulates root development, increases stem length and improves crop quality.
Phosphorus (P)Phosphorus is often deficient in natural soils because it is fixed as for instance iron phosphates or calcium phosphates dependently on the soil type. Microorganisms like Bacillus, Aspergillus and Penicillium secrete organic acids that lower the soil pH, resulting in the breakdown of fixed phosphate in soil. Some bacteria like Bacillus and Pseudomonas can solubilize insoluble inorganic phosphates such as di-calcium phosphate and tri-calcium phosphate.
Mycorrhizal fungi can help the plant with the uptake of phosphorus. Arbuscular mycorrhizae form a symbiotic relationship with the host plant, in exchange for carbon and sugars they provide water and nutrients to the plant.
Potasium (K+)Potassium is essential for plant growth and reproduction; it is also responsible for the activation of numerous enzymes. Most of the potassium in the soil is in the form of mineral potassium and is unavailable for plant uptake. Minerals containing potassium are mica and feldspar.
Potassium solubilization is done by for instance by Paenibacillus spp, Bacillus mucilaginosus and Bacillus edaphicus.
(The above-mentioned microbial genera all consist of a wide variety of species and strains. The precise beneficial effects of these microbes depend on the specific species and strain that is used)