Water, Salt, and Buffer pH

Increased awareness of different lab methods to measure extractable nutrients has been positive to help understand variations in soil test data from various regions of the country and why they may be different.  Like extractable nutrients there are various lab methods for testing soil pH.

Soil pH - Water vs. Salt

There is 1:1 water which uses equal parts distilled/deionized water and soil to make a slurry for pH determination. This is the common method in most of the eastern US. In drought conditions natural salts can accumulate in the soil that interfere with the pH probes used to measure the pH of the soil and water slurry. This interference can lead to a 0.2 to 0.6 drop in soil pH readings. This drop is also common in arid regions of the Western US. The severity of the drop is based on the salt levels in the soil. To overcome this issue in the arid western regions, low concentration salt water is used to stabilize the readings at 0.5 to 0.6 pH units lower than 1:1 water pH. The target pH is different for 1:1 water vs salt pH.

Buffer pH

Buffer pH is used to determine how much lime application rates. This is similar to soil pH in that it is a a buffer is added slurry of soil and water that strips all of the hydrogen from the CEC of the soil. The more hydrogen on the CEC the greater amount of reserve acidity in the soil leads to a greater decrease in the buffering solution. The greater the decrease of the buffer solutions after stripping the hydrogen from the soil indicates higher lime application rates. There are several buffer solutions that start at different pH’s and result in different buffer pH’s. Common Buffer solutions include:

• SMP
• Sikora
• Woodruff
• Adam Evans
• Mehlich

At ALGL our standard methods are 1:1 water pH and Sikora buffer pH.