The limiting factor in nitrogen fixation of soil is

Answer: ASolution: Extreme of soil pH affects nodulation by reducing the colonisation of soil and the legume rhizosphere by rhizobia. Highly acidic soils $\left(pH<4.0\right)$ frequently have low levels of phosphorus, calcium and molybdenum and high concentration of toxic elements while highly alkaline soils $\left(pH>8.0\right)$ tend to be high in sodium chloride, bicarbonate and borate, and are often associated with high salinity which reduce nitrogen fixation.