Sulfur (S) has often been coined the “fourth most essential nutrient” following closely behind N, P, and K. However, in recent years the booming growth of sulfur deficiencies has many asking more pointed questions, why are sulfur applications more important now than in previous years and how can we solve the issue.
Roles of Sulfur in Crop Growth
To understand its importance, we must first understand the role sulfur plays in crop production. Some significant roles include:
- Protein Synthesis: Sulfur is found in some amino acids–protein building blocks–and a majority of sulfur absorbed by plants is used for protein synthesis.
- Improved Chlorophyll Stimulation & Photosynthetic Processes: Sulfur is essential in an enzyme required for the chlorophyll molecule formation.
- Metabolization of Nitrogen: Sulfur aids in metabolizing N within the plant, making it vital to utilizing N inputs.
- Oil Synthesis: Sulfur, especially in oil crops such as legumes, forages and some vegetables, is needed as much as phosphorus for healthy development of crop oil.
Causes for Loss of Sulfur
Sulfur deficiencies continue to arise at staggering rates for a number of reasons. To name a few:
- As power plant and other burning fuel emissions have decreased due to EPA and other clean air action, free sulfur previously deposited via rainfall has declined dramatically. Many areas of the Midwest receive 10-20 lb. per acre less S from this source than in previous years with fewer environmental restrictions.
- Higher crop yields remove more S from our soils, requiring higher levels of need and replacement.
- Fewer sulfur-containing pesticides are used in today’s agricultural industry.
- The movement to reduce tillage reduces the mineralization of S into our soil (due mainly to unseasonably cooler temperatures).
The main source of sulfur for crops, other than inorganic fertilizers, comes via the mineralization of soil’s organic matter–the utilization of sulfur already in your soil’s profile by the result of microbial activity. Healthy soil microbes help to mineralize and mobilize sulfur into compounds readily available for plant uptake. However, even after mineralization, the soil only releases a limited amount of S via mineralization of organic matter.
With all the work happening below ground to produce usable sulfur to the plant, how do you ensure that with over 50% of S demand in late-season (post-flowering) production that S is still available at those peak times, especially with the reduction of sulfur-deposited rainfall?
Foliar Applications of Plant-Available Sulfur
Foliar applications of supplemented sulfur post-flower in its readily available form works to offset and/or protect from sulfur deficiencies later in the growing season when the damage is harder to reverse. Using available-sulfur products, like AgXplore’s SulPak™ with added absorption technologies, in a foliar application also allows to feed the plant with grain-filling energy that helps to boost yield potential.