Home Lifestyle Soil calcium, magnesium and potassium — straight talk about nutrient ratios

Soil calcium, magnesium and potassium — straight talk about nutrient ratios

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RALEIGH — Now that harvest is complete, the focus for many growers turns to soil sampling and formulating nutrient management plans for next season. For some, it is a time to reflect on yields and if goals were not met, ponder different strategies.

One concept that farmers may hear about and be enticed to implement is supplying soil with a balanced ratio of calcium, magnesium and potassium. These nutrients are called bases in soils as opposed to soil constituents that are acid — hydrogen and aluminum. Hence, the basic cation saturation ratio concept recommends an ideal balance of calcium, magnesium and potassium to achieve maximum yield.

Recommendations are made to keep these ratios at optimum or ideal levels no matter what traditional soil test levels are. Over the past 50 to 70 years, varying ratios have been proposed by different soil scientists but there is not universal agreement about what is best. For growers considering this concept, this lack of agreement might best be taken as a red flag to proceeding in this direction.

A 2017 American Society of Agronomy journal article titled, “Historical Perspective of Soil Balancing Theory and Identifying Knowledge Gaps: A Review,” summarizes that seven peer-reviewed research publications (1980s — late 2000s) on study and evaluation of specific ratios to optimize crop yields or positive impacts on crop production refute the concept as valid.

Additionally, according to Dr. Luke Gatiboni, an associate professor in Crop and Soil Science at N.C. State University, “it is well known that nutrient interactions occur in soils, meaning that the amount of one nutrient such as potassium if in excess can negatively impact root uptake of other nutrients such as calcium and magnesium; research has validated this. However, supplying calcium, magnesium and potassium in ideal ratios that exceed plant requirements may indeed create nutrient imbalances and deficiencies.”


Lastly, there is a physical component of soils that farmers think about referred to as soil structure. Good soil structure is achieved by maintaining organic matter that is often referred to as the “glue” that forms stable aggregates with sand, silt and clay soil mineral particles.

The BCSR concept asserts better soil structure is achieved by maintaining higher levels of calcium than magnesium. Undoubtedly, good soil structure is needed for optimum entry of water into soils, supply of plant-available water to crops, and maintenance of adequate drainage. However, the ASA article reports research showing that good soil structure can be maintained over a wide range of ratios of calcium to magnesium, with no scientific evidence to support a specific balance. Some North Carolina growers have embraced the use of gypsum, a calcium supplement, for this purpose but no research supports this use in our soils.

As growers consider their yields this year and strive for higher yields ahead, it is important to remember that soil fertility is just one component of yield. Growers know that variety selection, planting dates, weather and many other factors determine final yield.

“Use our Agronomic Division’s traditional soil testing service as a solid foundation for lime recommendations to correct soil acidity and to supply calcium and magnesium along with potassium fertilizers based on soil test levels and crop needs,” said Agriculture Commissioner Steve Troxler. “This will help keep our No. 1 industry — agriculture — profitable.”

David H. Hardy is chief of soil testing for the N.C. Department of Agriculture and Consumer Services.

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