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Sulfur, Part 2: Application Rates & Timing

 By: Glen Howell

In Midwestern agriculture, there are primarily 4 fertilizers that are actively used for meeting sulfur nutritional needs. They are listed from highest to lowest sulfur concentration.  Also listed is their overall analysis & type of product composition:

Elemental Sulfur-90%S; (0-0-0-90S); dry product; sulfur is not in plant available form
Ammonium Thiosulfate (ATS)-26% S; (12-0-0-26S); liquid product
Ammonium Sulfate (AMS)-24% S; (21-0-0-24S); dry product
Potassium Magnesium Sulfate (langbeinite)-21% S; (0-0-21-21S-11Mg); dry product
Calcium Sulfate (SuperCal SO4; CaSO4; gypsum)-17%S; (0-0-0-17S-21Ca); dry product
Potassium Sulfate (SOP)-17% S; (0-0-50-17S); dry product

Crop need for sulfur

Crops need varying amounts of sulfur to complete their life cycle.  Much of what is needed for growth is recycled to the soil with plant residues, but there is a net loss with the crop removed. Organic matter (O.M.) in soil is a great sulfur source—each 1% contains 140# of sulfur—but it may not always be available when the crop needs it. 

Crop         Unit of Measure        # Sulfur/Unit of Measure        Yield-# Sulfur Removed                                                                 (Crop removal)

Corn (grain)        Bushel                   0.08#                               200 Bushels-16# S

Corn (silage)      Ton                        1.1#                                 30 Ton-33# S

Soybean (grain)  Bushel                   0.18#                                60 Bushels-10.8# S

Alfalfa/Forages  Ton                        5.4#**                   &nb


Sulfur-Part 1: Solubility & Leaching

 By: Glen Howell


I have received several calls this week on sulfur.  They focused on solubility/leaching potential, application rates, application timing, and product comparisons.  We will discuss solubility & leaching potential in this part.

The solubility of any fertilizer or soil amendment is critical to a successful outcome.  In order for plants to utilize a nutrient, it must be in soil solution (the water surrounding the soil particles).  Until a nutrient dissolves & goes into this solution, it is unavailable for plant growth.  This is why applying fertilizer does not immediately result in improved plant growth, but takes time (usually days) for the material to dissolve, go into soil solution, & be taken up by plant roots, before 

Corn showing sulfur deficiency

resulting crop growth occurs.  Leaching can happen if a product is too soluble, & unfavorable weather conditions occur.  This is typically associated with heavy rains, especially during the growing season, but is possible at other times also.  We are most often concerned about leaching nitrogen, but sulfur can leach almost as easily.  

Soil particles have both positive (+) and negative (-) charges on their exchange sites.  Younger, unweathered soils, such as those found in the Midwest, have a prevalence of positive sites, referred to as cation exchange capacity (CEC), while older, highly weathered soils have more anion exchange capacity (AEC).  Opposite charges are attracted to each other, so Midwestern soils with good CEC values, can hold significant quantities of beneficial nutrients such as Calcium (Ca++), Magnesium (Mg++), Potassium (K+) & the ammonium form of Nitrogen (NH4+). Unfortunately, nitrogen does not stay in the ammonium form for long, & instead changes to the nitrate form (NO3-), which is why nitrate leaching is such a huge concern (; Sulfur must be in the sulfate form (SO4--) for plants to use it, so conditions favorable for nitrate leaching will also favor the loss of sulfates.

In the next part, we will look at application rates for sulfur fertilizers.

Other references:


Glen Howell is a contributing writer to Yield Starts Here, a blog for farmers, focusing on increasing yield and profitability by focusing on the soil.  His other interests include severe weather & old farm tractor


Soil pH

pH defines the relative acidity of alkalinity of a substance. The scale ranges from 0 being acid to 14 being alkaline. A pH value of 7.0 is neutral.

Acids are substances that release hydrogen ions (H+). The more H+ held in the soil, the greater it's acidity. Basic ions such as calcium (C++) make soils more alkaline.

Soil pH simply measures H+ activity and is expressed in logarithmic terms. This simply means that each unit change on the scale is a tenfold change in the acidity or alkalinity. A soil with a pH of 6 is ten-times more acid than a soil with a pH of 7. A soil that has a pH of 5 is 100 times more acidic than a soil with a pH of 7. A soil with a pH of 4 is 1000 times more acidic than a soil with a 7 pH.

How nitrogen fertilizers affect soil acidity

The nitrification process converts ammonium to nitrate. This process releases H+ ions. Nitrate furthers increases acidity by leaching calcium, magnesium (N never takes Mg), and potassium with it. As these alkaline ions are removed more hydrogen can be replaced in the soil.

How lime reduces soil acidity

One Ca++ ion from lime replaces two H+ ions on the soil exchange site. This process creates water (H20) and carbon dioxide (CO2). As the H+ concentration is lowered soil acidity decreases.

There are other factors that affect soil acidity. Excessive rainfall can leach basic ions. Nitrogen fixation of legumes, crop removal, and organic matter decomposition also increase acidity. As the alkaline ions (Ca++, Mg++, K+) are removed they will need to be replaced or H+ will steadily increase, lowering pH.

Calcium Products, lower input costs, higher yields, neutral soil pH


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