When it comes to proper soil fertility management, maintaining proper soil pH is key.

The relative acidity or alkalinity of soil is indicated by its pH. The pH scale runs from 0 to 14. Any pH reading below 7 is acidic and any pH above 7 is alkaline. Consequently, soils are often described as acidic (sour) or alkaline (sweet.) A pH of 7 indicates a neutral soil.

Soil pH is important because it influences the availability of essential nutrients. The majority of crops will grow satisfactorily in soils with a pH between 6 and 7.5.

Dr. Tryston Beyrer, a crop nutrition lead at the Mosaic Company, spoke with Country Folks about how farmers should approach the pH balance of their soils.

How do farming practices impact soil pH?

Soil parent material and geography are primary factors that influence soil pH. Higher rainfall geographies leach more hydrogen ions and salts from the soil while limestone-based parent material in subsoils are usually more alkaline. Higher rates of ammonium nitrogen can decrease soil pH. Legumes generally require more calcium and magnesium (a higher pH).

What effect does tillage have? Or prescriptive tillage?

No-till farming often stratifies pH more, where the top couple of inches could be more acidic from repeated nitrogen applications and acidification from plant roots. When engaging in no-till farming, you should test the top two inches and then separately test a deeper core to see if this has occurred.

Periodic or prescriptive tillage is often a beneficial way to mix acidic topsoil with more alkaline subsoil.

Do you recommend the use of lime applications?

Yes, when soil pHs are low. When liming soil, mixing the lime throughout the soil will react more quickly, especially at deeper depths.

The importance of soil pH testing

Can you describe the banding process, and how it affects soil pH?

Banding fertilizer involves placing fertilizer in “bands” alongside or beneath a row of planted crops. This is opposed to the “broadcast” method of application, which spreads fertilizer evenly over a field. Banding most fertilizers will acidify the banded zone. This is often beneficial in the root zone as many nutrients are taken up more efficiently when root exudates acidify the area around the rhizosheath (a layer of adhering soil particle on the root surface) to facilitate greater nutrient uptake.

Some growers have considered adding a pelletized lime source in with fertilizer, but caution needs to be taken since adding calcium will often bind with other nutrients (like phosphate) and make less plant available nutrients (like calcium phosphate). The most common recommendation is to move the band over time and, when lime applications are needed, they are broadcast and mixed throughout the soil tillage depth.

Are there any other tips or best practices you’d like to mention?

Routine soil testing every two to four years will best help monitor changes in soil pH. If lime applications have recently been made, you should give it time, at least two years, to start to neutralize the soil. Soil pH is one of the very first items I recommend looking at on a soil test. Correcting soil pH increases the efficiency of any nutrients you may apply.

by Enrico Villamaino