buffer ph on a soil test

Demystifying Buffer pH on Your Soil Test Report

Soil tests provide critical information for monitoring and amending your soil to optimize plant growth. Along with pH essential nutrients and organic matter, most lab reports also include something called buffer pH. What does this value mean and how can you use it? This guide breaks down everything you need to know about interpreting buffer pH from your soil analysis.

What is Buffer pH?

Buffer pH provides an estimate of your soil’s inherent resistance to changes in pH, also known as acid buffering capacity. It measures the ability of your soil to neutralize acids and resist shifts up or down the pH scale.

Soils with higher clay content and more organic matter have a greater buffering capacity and resistance to pH change Sandy soils with little organic material are much less buffered and can experience wider pH swings

How is it Measured?

Buffer pH is determined in the lab by adding a strong base to lower the pH of an acidified soil sample, then measuring the pH change. More lime is required to increase pH in highly buffered soils, so they end up with a higher buffer pH reading.

Soils that take less lime to neutralize and raise the pH have a lower buffer pH, indicating they have less ability to resist pH changes up or down. Most productive soils in the U.S. fall between 6.0 and 7.0 buffer pH.

Relating Buffer pH to Total Acidity

Buffer pH correlates to your soil’s total acidity – the amount of acid molecules bound to the soil particles plus any free hydrogen ions in the soil water.

Soils with higher buffer pH can store more acidity on particle surfaces before the soil water pH shifts down. A lower buffer pH means there is less acidity bound to particles keeping the soil water pH stable.

Think of buffer pH as an indicator of your soil’s capacity to hold acids in reserve. The higher the buffer pH, the greater your soil’s inherent acid storage capacity.

Buffer pH and Lime Requirements

One of the primary uses of the buffer pH reading is to determine how much lime is required to raise the pH of acidic soils to a target level.

Soils with higher buffer pH can neutralize more acidity, so they need larger lime applications to change the pH. Low buffer pH soils reach the desired pH with much less lime because they have less acidity to overcome.

Let’s look at two scenarios to demonstrate:

Soil A has a pH of 5.8 and a high buffer pH of 6.8. To reach the ideal pH of 6.5, it would need a hefty lime application of 2 tons of ECCE lime per acre.

Soil B has a pH of 5.8 but a low buffer pH of just 6.2. It only requires 1 ton of ECCE lime per acre to get to the same target of 6.5 pH, because its lower buffer pH indicates less acidity to neutralize.

The lab report will provide lime recommendations based on the soil properties, or you can reference soil test calibration tables. Pay attention to both pH and buffer pH when planning your liming needs.

Buffer pH Over Time

For acidic soils, monitoring buffer pH over successive years provides useful trend information. Here are some patterns you may observe:

• Falling buffer pH – Indicates the soil is losing some of its acid buffering capacity and becoming more vulnerable to pH fluctuations. Time to limit acidifying inputs.

• Rising buffer pH – The soil is accumulating more acidity on particle surfaces. A higher lime requirement is likely next time pH drops.

• Unchanging buffer pH – Acidity bound to soil particles is at equilibrium. Lime needs to maintain target pH will be consistent.

Routine testing every 2-4 years will allow you to track buffer pH trends and adjust soil amendments accordingly.

Ideal Buffer pH Range

Most productive agricultural soils will fall between 6.0 and 7.0 buffer pH, with an average around 6.5. Here are some general guidelines for interpreting your soil’s buffer pH:

• Below 6.0 – The soil has very low acid buffering capacity and is vulnerable to acidification. Limit acidifying fertilizers and closely monitor pH trends.

• 6.0 to 6.5 – Less buffering capacity exists to maintain pH. Liming needs will be lower and pH can change faster.

• 6.5 to 7.0 – This is the typical range for most properly managed soils. Substantial buffering capacity provides pH stability.

• Above 7.0 – High clay and organic matter give the soil a large buffering capacity against pH shifts. Liming needs to reach target pH will be higher.

• 7.5+ – Very high buffering suggests poor internal drainage. Excess sodium may be an issue. Remediation may be needed beyond liming.

Remember your soil’s texture, drainage class and organic matter levels all influence the ideal buffer pH range. Assess trends with your field’s characteristics in mind.

Improving Buffer pH

While the inherent mineralogy largely determines buffer pH, building organic matter through cover crops, manure additions, reduced tillage, and rotational grazing can help improve buffering in weaker soils.

Deep rooted plants and maintaining soil structure with minimal disruption also promote acidity storage on soil particles. Healthy biological activity cycles acids to reinforce buffer pH.

Hopefully this breakdown gives you a better grasp of buffer pH and how it complements the standard pH reading in your soil test report.

Monitor your soil’s buffer pH over time to track your soil’s acidity storage capacity. Compare buffer pH trends to pH fluctuations and lime response to see the connection.

Use the buffer pH to help refine lime application rates when raising pH is warranted. Remember soils with high buffer pH require more lime to reach the target than low buffer pH soils at the same starting pH.

Think of buffer pH as an indicator of your soil’s inherent ability to store and supply acids that influence the soil water pH you measure. Understanding this relationship will lead to more informed soil management.