Bacteria flourish dramatically when readily available nutrients are added to the soil. These actively metabolising bacteria need nutrients provided from outside sources for their rapid growth, but the supply is quickly exhausted. In other words, bacteria respond promptly to soil amendments, become and remain numerous as long as the nutrients are available, then decline once their food source is depleted.
Environmental conditions affect the density and composition of bacterial flora. The primary environmental variables that influence soil bacteria include: moisture, aeration, temperature, organic matter, pH and inorganic nutrient supply.
Highly acidic or alkaline conditions inhibit many common bacteria; the optimum pH range for most species is about 6.4 to 6.8. Generally, the greater the hydrogen ion concentrations (the higher the acidity), the smaller the size of the bacterial community.
Bacteria and fungi play an essential role in decomposition, but they are also crucial to life on Earth because of their exclusive ability to perform key bio-chemical changes.