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 (http://cornandsoybeandigest.com/crop-chemicals/keep-nitrates-where-they-make-you-money-pointers-keeping-your-nitrogen-where-you-bene; http://www.ipm.iastate.edu/ipm/icm/2007/5-14/nitrogenloss.html). 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.
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