In recent years, sulfur (S) deficiency in wheat has become more common in many areas of Kansas, particularly in no-till wheat. The likely reasons for this are a reduction in sulfur additions to the crop from atmospheric deposition (there is less S in the air now) and cooler soil temperatures as a result of no-till, which slows S mineralization in the soil. Some crops in the rotation, such as soybean, can also take up significant amounts of S, resulting in an S deficit for the following wheat crop. Most of the crop's S needs will occur after spring green-up when the crop goes through stem elongation.
Historically, S deficiency was most common in high-yielding crops grown on irrigated, sandy soils that are low in organic matter and subject to leaching. However, due to the reasons discussed above, an increasing number of finer-textured soils have shown S deficiency in recent years.
Generally, S-deficient wheat is yellow and stunted and is observed in patches in the field, especially in areas with previous soil erosion or movement. The patchy S-deficient areas of the field are often found on hilltops or side slopes where erosion has occurred, and soil organic matter is reduced or where leaching is more pronounced. Wheat in areas where topsoil was removed or significant cuts were made (i.e. terraced or leveled fields) also commonly shows symptoms.
Sulfur deficiency in growing crops is often mistaken for nitrogen (N) deficiency. However, unlike N deficiency, where older leaves show firing and yellowing, with S deficiency, the pale-yellow symptoms often appear first on the younger or uppermost leaves. Wheat plants with S deficiency eventually become uniformly chlorotic (yellow leaf tissue).
Sulfur deficiencies in wheat have been showing up early in the spring, shortly after green-up, before organic S is mineralized from soil organic matter and before wheat roots can grow into the subsoil to utilize any available S (sulfate) accumulations. Deficiencies of S are often difficult to identify because the chlorosis is not always obvious. Crops lacking S also may be stunted, thin-stemmed, and spindly. In the case of wheat and other cereal grains, maturity is delayed.
If any of your fields have had a known history of S deficiency and you have not applied any S yet. Rather than waiting for symptoms to appear in the spring, farmers may want to consider a winter top-dress application of S as a preventive measure.
There is a soil test for available sulfate-S in the soil profile. Soil texture, soil organic matter, the crop to be grown, and the expected yield level should all be considered when interpreting this soil test. Accurate estimates of S needs cannot be made from a surface sample alone. Since sulfate is mobile, sampling to a 24-inch depth is important. However, due to the relatively high demand for S during the rapid vegetative growth phase of wheat and relatively shallow rooting by the wheat crop at this time, the S measured in the deeper subsoil levels by the test may not be available to wheat in the early spring, especially where soils are cold. Now is a good time to collect soil samples and assess S levels as we plan for topdressing.
Leaf tissue tests can be useful, particularly when determining the exact cause of yellow wheat. A representative sample can be made by collecting the newest mature leaves from 30+ plants throughout the area where deficiency symptoms are observed (“bad” areas). A similar sample from a “good” area (no deficiency symptoms) should also be collected. This will allow direct comparisons between “good” and “bad” areas.
There are several S-containing fertilizer materials both dry and liquid. Supplemental resources: Sulfur in Kansas (MF 2264), http://www.ksre.ksu.edu/bookstore/pubs/MF2264.pdf For estimations of required application rates of S - Soil Test Interpretation and Fertilizer Recommendations, (MF2586) http://www.ksre.ksu.edu/bookstore/pubs/mf2586.pdf