For Release January 26, 1999

Know Your Nutrients

by Chuck Otte, County Extension Agent

All growing organisms need nutrients. People need nutrients, usually called food, as do pets, livestock and plants. Many of our soils in Kansas are deficient in one or more of the principal nutrients. In plant growth we have macronutrients, those that are needed in large quantities and micronutrients, those needed in much smaller quantities.

Macronutrients are general considered to be elements like nitrogen, phosphorus and potassium. These just happen to be the three numbers that you always see on bags of fertilizer and they indicate the percent of nitrogen, phosphorus and potassium (in that order) in the fertilizer. If you have a ten pound bag of 13-13-13 then that ten pounds of fertilizer contains 1.3 pounds of nitrogen (13% times ten pounds), 1.3 pounds of phosphorus and 1.3 pounds of potassium. Macronutrients may be needed in quantities of 10 to over 200 pounds per acre

The list of micronutrients can be quite extensive and includes elements like boron, copper, iron, manganese, zinc and magnesium. The amount per acre needed by plants of these elements can range from a couple of pounds down to just a few ounces. Most soils, if they contain good amounts of organic matter, can provide these micronutrients in adequate amounts so fertilizer is not needed. But, if they are deficient, the effects on the plant can be very obvious and very damaging.

In recent years we’ve also discovered that a couple of elements that we used to call micronutrients may be needed in larger amounts, but still not enough to call them macronutrients. We have long known that sulfur and chloride were needed by plants. One of the reasons we seldom saw deficiency symptoms was that many of our fertilizer sources had fair amounts of sulfur and chlorine as contaminants or "tag alongs" with other nutrients. However, in the last 25 years the fertilizers that we’ve used have become so highly refined and our soil testing and fertilizer application have become so much more precise that soils that had built up levels of these two elements have become depleted. These secondary nutrients, placing them between macro and micronutrients, are often needed at rates of 5 to 25 pounds per acre.

We can easily test for most soil nutrients to know how much nutrient a soil has and how much needs to be applied, if any. Unfortunately, application and ultimately plant uptake are not so straight forward. Nutrients like nitrogen, potassium and chloride are very water soluble. These fertilizers can be applied on the soil surface and rainfall will carry them into the soil to the roots. Heavy rainfall, though, can leach these nutrients through the soil and carry them below where plant roots can get them. The plant ends up underfed and the nutrients wind up in the ground water or surface water.

Elements like phosphorus are not very water soluble. For many crops we need to place the phosphorus an inch or two into the soil. Many grass and forage crops can develop surface roots and gather phosphorus off the surface. But heavy rains can wash phosphorus off the surface depositing this nutrient in rivers and lakes. Then, to further complicate matters, soils with acid or alkaline pH can make nutrients more or less available to plants.

It doesn’t matter if you are growing an agricultural crop, a vegetable or flower garden or a yard, every plant needs nutrients and they all have different needs. It comes down to the grower needing to know and learn what their soils have, and what their plants need. It’s sometimes a challenge and sometimes a frustration. That’s where I come in. Together we can determine how much of which fertilizers to insure good growth, yet minimize the cost and negative environmental impact.


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