Are You Applying Enough Sulfur?

The majority of sulfur present in soils is in the organic form. Organic matter has to be broken down for nutrients like sulfur to become plant available. Many areas of the U.S. and Canada may never experience sulfur deficiency because of the sulfur supply from organic sources. As soil temperatures warm up, soil mineralization occurs, converting organic matter into sulfate, which is then available for plant uptake.

Some states and provinces use organic matter content and soil test values in making sulfur fertilizer application rates. However, the rates of mineralization can vary widely and since sulfate is highly mobile within the soil profile, both values can be misleading to make recommendations.

For this reason, the best estimate for determining sulfur application rates for a specific crop is usually based on removal rates and total uptake. There is a difference between uptake needs and removal rates. Plant uptake is the amount of each nutrient a plant needs to maximize yields and take up over the growing season. Removal rates are what is taken up and stored in either the grain or tissue and removed with harvest. When tissue and grain are harvested, those nutrients leave the field and what remains can be recycled in the soil.

Both the uptake and removal rates are used to calculate nutrient harvest index. Nutrient harvest index provides insight to the proportion of the nutrients taken up that are being removed. For example, a corn crop yielding 230 bushels per acre will take up 23 pounds of sulfur and remove 13 pounds in harvested grain. The calculated sulfur harvest index is 57 percent and thus, a little over half of the sulfur taken up is removed in grain harvest. It is important to know the percentage removed as well as the total amount of nutrients needed to maximize production (i.e. 23 pounds for a 230 bushel corn).

If roughly 23 pounds of sulfur are required for plant uptake, not all of that is taken up at the same time. Half of the sulfur taken up by corn occurs after the plant enters reproductive stages with the greatest rates being taken up during grain fill. Since sulfur is immobile within the plant from older tissue, it is critical that a supply of sulfur is available during grain fill.

Smart Nutrition™ MAP+MSTĀ® is a slow release fertilizer. The sulfur is present in the elemental form as micronized sulfur technology (MST), which requires oxidation to sulfate to become plant available. The slow release protects the sulfur from leaching potential as sulfate is relatively mobile within the soil profile with large rainfall events.

Consider Smart Nutrition MAP+MST as part of your fertilizer program to meet your sulfur application needs. Thinking about a fall application? See our application recommendations or contact your local rep.