Relationship Between Soil pH and Available Phosphorus: A Quantitative Analysis Across pH Gradients

Soil pH is among the most influential factors influencing the availability of phosphorus (P) in soils, and has an effect on the chemical form and the mobility of P. The present research evaluated the relationship between the soil pH and the available phosphorus within a wide pH (3.0-10.0) span. In order to give uniformity to the analysis, repeated values were reduced to several pH intervals. The findings showed that there was a high change in the availability of phosphorus according to soil pH. The relationship between the pH and the available phosphorus in strongly acidic soils (pH 3-5) was insignificantly negative (r = -0.210), indicating low availability due to fixation by iron and aluminum. In the pH range of 5 to 6, a positive association though slightly positive (r = 0.389), was observed with more phosphorus availability with a lower acidity of the soil. Nevertheless, this relationship was very weak in nearly neutral soils (pH 6-7) (r = 0.024) which suggests comparatively constant phosphorus concentrations. At slightly alkaline conditions (pH between 7 and 8) the correlation was weakly negative (r = -0.053), but at the pH between 8 and 9, a very weak relationship was positive (r = 0.046). A further increase in pH made the relationship negative again (r = -0.209), presumably because phosphorus was precipitated with the calcium compounds. Overall, the results show that even though soil pH influences the availability of phosphorus, this correlation is weak to moderate and is affected by pH ranges. This implies that soil properties other than pH are of significance in the control of phosphorus. The study further says that the availability of phosphorus and efficiency of nutrient use can be improved by maintaining the soil pH nearly at the neutral level, which is significant in the production of crops.