The Relationship of Potassium and Magnesium in Soil

Primary and Secondary Nutrients

• When discussing soil nutrients, scientists tend to draw a distinction between primary nutrients and secondary nutrients. The primary nutrients--nitrogen, potassium and phosphorus--are the most critical to healthy plant growth and thus are of chief concern when growing any kind of plant; soil amendments are primarily used to supplement these nutrients in soil. The secondary nutrients--calcium, magnesium and sulfur--while still crucially important to plant growth, typically already exist in sufficient amounts in soil. Secondary nutrients are usually introduced to soil when a grower adds lime to soil to adjust the soil's pH.

Potassium

• With the exception of nitrogen, plants tend to absorb larger amounts of potassium than any other nutrient. Plants use potassium to build proteins; it is also essential to the process of photosynthesis. Potassium also plays a key role in deciding the size and quality of the fruit yield of fruit-bearing plants and in fighting plant diseases. Numerous plant diseases are either caused or exacerbated by potassium deficiencies or by an over-abundance of potassium in soil.

Magnesium

• Magnesium is one of the key components of the chlorophyll that gives plants their green color. Magnesium also plays a critical role in the process of photosynthesis and activates plant enzymes without which the plant would not be able to add any new growth. The most common sources of magnesium for enhancing a magnesium-deprived soil are soil minerals, organic material, fertilizers and dolomitic limestone.

Atagonism

• To define how these nutrients relate to one another is very complex, since soil nutrients tend to inter-relate in myriad and diverse ways. The University of Wisconsin-Madison Department of Soil Science, for example, finds that "application of high rates of potassium or ammonium fertilizer often heightens magnesium deficiency," a phenomenon known as antagonism. Antagonism is one of the most commonly occurring phenomena associated with the relationship between magnesium and potassium in soils, but there are many such phenomena that depend on the unique blend and concentrations of these and other nutrients in soil.