Soil pH Sample Clauses

Soil pH. Scope and Application pH is a measure of the relative acidity or alkalinity of a soil solution in equilibrium with soil particles. Mathematically, pH is the negative log10 of the activity of H+ ions in solution. A pH probe uses the difference in electric potential that results from variations in chemical potential as H+ activity varies. Soil pH can be measured in a saturated paste, 1:1 or 1:2 soil to water ratio, or in a solution of 0.01M calcium chloride CaCl2. pH is a considered a primary factor in soil characterization because it impacts sorption and the relative availability of nutrients. Alternatively, the exchangeable acidity (measure of H+ and Al3+) can be measured in a 0.1M CaCl2 solution to determine the total concentration of acid cations that occupy the cation exchange sites. Generally, the reproducibility of pH measurements is considered to be ± 0.07pH units. Summary Soil pH can be measured at either a 1:1 or 1:2 soil to water ratio. Because of the use of the log scale, the two ratios typically provide similar results. A soil with high clay or organic matter may require a 1:2 or even 1:5 ratio to allow for enough fluid to make a measurement. A sample that will also have the lime requirement measured will be measured with a 1:1 ratio when possible. With either method, the soil and water are placed in a tube and shaken for 15 minutes. A calibrated probe accounting for temperature is used for the measurement. One CAL standard sample is included in each batch. Equipment and Materials  Xxxxx HI5522 with pH and temperature probe  Falcon tube with cap or small beaker with glass stir rod  Reciprocating shaker Reagents  pH calibration standards (4.01, 7.01, 10.01)  DI water or 0.01M CaCl2 Procedure