Sulfur, an often overlooked but important nutrient

According to your soil test results; nitrogen, phosphorus and potassium are nutrients that we supply year after year to our corn crop; however, there is one nutrient that we might be overlooking when applying fertilizer.

Sulfur is considered the fourth most important nutrient needed by plants. With reduced sulfur emissions from industrial and transportation sources, atmospheric deposition of sulfur is much lower, leading to an increase in sulfur-deficient corn. Adequate sulfur supply to crops is important to maintain a high yielding crop.

A sulfur deficiency in the field is often seen as a yellow band with veins remaining green. A quick search for “sulphur deficiency in corn” will yield useful images for comparison.

Sulfur is used by the plant for protein synthesis; it is also used to produce chlorophyll which is needed by the plant to perform photosynthesis. In other cultures, it is used for the formation of nodules (soya) and the quality of cereal proteins (wheat). Sulfur is not mobile in plant tissues, which often explains deficiency symptoms in younger leaves.

Most of the sulfur in the soil is found in organic matter and crop residues; however, it is not readily available until it is converted into a soluble form of sulfate; this mineralization process depends on temperature, humidity and other environmental factors. Sulphate in soil is soluble and will easily move to the root with soil water; however, it will also overrun the root zone in the event of rain or excessive irrigation.

There are many different fertilizer options when it comes to providing sulfur. Manure is generally a good source of sulphur. Some readily available options include ammonium sulphate (AMS; 21% N and 24% S), gypsum (22% CaO and 17% S), potassium sulphate (50% K20 and 18% S), sulphate Zinc (36.4% Zn and 24%% S), Elemental Sulfur (90% S), MicroEssentials ((MESZ; 12% N, 40% P2O5, 10% S and 1 Zn), (MES10; 12% N , 40% P2O5 and 10% S), or (MES15; 13% N, 33% P2O5 and 15% S)); as well as other sources.

Each of these sources varies in the type of sulfur: soluble or insoluble. The soluble source is readily available for plants to use; however, if applied in the fall, soluble sources can leach past the root zone and become unusable by the plant. Insoluble elemental sulfur must be converted to sulfate before plant roots can absorb the nutrient, which can take weeks to years.

Favorable environmental conditions and an appropriate pH can help accelerate this conversion; the size of the elemental sulfur particles may also play a role in the process. Some fertilizer products are composed of both soluble and insoluble sulfur providing an immediate source; as well as a later season source.

Field screening and tissue sampling are often the best practices for identifying sulfur deficiency. For assistance with identification, tissue sampling procedures, or application rates, contact your local extension educator for assistance.

About Marco C. Nichols

Check Also

Profit Watch: Effects of High Inputs | Profitability

This year’s harvest is not over yet. There’s still plenty of harvest in the northern …