Bio-Sustain™ contains PGPR, but what are they?

Plant Growth Promoting Rhizobacteria (PGPR) are a group of bacteria that colonize roots or rhizosphere soil and are referred to as plant growth promoting rhizobacteria (PGPR). Microorganisms found in the rhizosphere are able to produce substances that regulate plant growth and development. These microbes have direct mechanisms that facilitate nutrient uptake or increase nutrient availability by nitrogen fixation, solubilization of mineral nutrients, mineralize organic compounds and production of phytohormones. The mechanisms of PGPR include regulating hormonal and nutritional balance, inducing resistance against plant pathogens, and solubilizing nutrients for easy uptake by plants.

Nitrogen fixation:
Nitrogen is an essential element for all forms of life and it is the most vital nutrient for plant growth and productivity. Nitrogen, which is needed for the synthesis of amino acids and proteins, is the most limiting nutrient for plants.
Phosphate solubilization: Phosphorus is the most important key element in the nutrition of plants, next to nitrogen (N). It plays an important role in virtually all major metabolic processes in plant including photosynthesis, energy transfer, signal transduction, macromolecular biosynthesis and respiration.
Plant growth promoting rhizobacteria present in the soil employ different strategies to make use of unavailable forms of phosphorus and in turn also help in making phosphorus available for plants to absorb.
Potassium solubilization (K) is the third major essential macronutrient for plant growth. The concentrations of soluble potassium in the soil are usually very low and more than 90% of potassium in the soil exists in the form of insoluble rocks and silicate minerals.
Plant growth promoting rhizobacteria are able to solubilize potassium rock through production and secretion of organic acids. Potassium solubilizing to release potassium in accessible form from potassium bearing minerals in soils.

Phosphate solubilizing Bacteria (PSB)
Due to immobilization of phosphate by mineral ions such as Fe, Al and Ca and organic acids, the rate of available phosphate in soil is well below plant needs. Chemical fertilizers are also immobilized in the soil, immediately so that only 20% of added fertilizer is absorbed by plants. PSB converts insoluble phosphate compounds such as rock phosphate, bone meal and basic slag particularly the chemically fixed soil phosphorus into available form. PSB can cause a large amount of soluble phosphate to be released and in excess of 50 Kg/ ha of P2O5. Phosphorus solubilizing activity is determined by the ability of microbes to release metabolites such as organic acid (lactic acid, malic acid, glutamic acid, acetic acid etc). Inorganic phosphorus is solublized by action of organic and inorganic acids secreted by PSB and which maintain soil pH. The pH of rhizosphere is lowered through the release of bio-carbonates (anions/cation balance) and oxygen/carbon oxide gaseous exchange. Phosphorus solubilizing ability of PSB has direct correlation with pH of the medium.

Potassium solubilizing microorganisms (KSM)
Potassium (K) is the third major essential macronutrient for plant growth. The concentrations of soluble potassium in the soil are usually very low and more than 90% of potassium in the soil exists in the form of insoluble rocks and silicate minerals. Plant growth promoting rhizobacteria are able to solubilize potassium rock through production and secretion of organic acids. Potassium solubilizing to release potassium in accessible form from potassium bearing minerals in soils.

Soil microbes and cycling of elements:
The biogeochemical process through which organic compounds are broken down to inorganic compounds or their constituent elements is known “Mineralization”, or microbial conversion of complex organic compounds into simple inorganic compounds & their constituent elements is known as mineralization.
Soil microbes plays important role in the biochemical cycling of elements in the biosphere where the essential elements (C, P, S, N & Iron etc.) undergo chemical transformations. Through the process of mineralization organic carbon, nitrogen, phosphorus, sulfur, Iron etc. are made available for reuse by plants.