Injection of phosphorus nutrient sources under acid conditions for subterranean microbial processes

In a process for injecting microbial nutrients into a subterranean formation wherein microorganisms are provided a phosphorus nutrient source, the improvement which comprises introducing as said phosphorus nutrient source a solution of an inorganic phosphate wherein said inorganic phosphate solution is acidified by the addition of an acid in an amount sufficient to achieve a pH in the range of about 1.0 to about 5.5, and then injected into said formation.