Sulfur Deficiency In wheat

With the increased rate of growth in wheat in parts of Kansas following the precipitation received in early April, sulfur deficiency is beginning to be seen again. During this past week, we have seen or gotten reports of fields of pale yellow wheat in parts of central, north central, and northeast Kansas. The cause is sulfur (S) deficiency.

Sulfur deficiency symptoms in wheat can appear similar to nitrogen deficiency, with a general chlorosis or yellowing of the leaves. However, S deficiency does differ from nitrogen (N) deficiency in that the whole plant is pale, with a greater degree of chlorosis in the young leaves. The reason is S is not mobile in the plant like N, so the lower leaves do not “fire” and show more severe deficiency symptoms than the upper leaves, as is the case with N deficiency.

The uniform nature of the yellowing on the plants is one means of diagnosing S deficiency in wheat. Another common difference compared to N deficiency is the pattern in the fields. Sulfur deficiency often occurs first on slopes, eroded areas, on coarser soils, or wherever organic matter levels are lowest. Therefore, deficiencies are usually limited to only certain areas of the field.

Soil and plant analysis are good tools for diagnosing or confirming sulfur deficiencies. Wheat plants at jointing should have more than 0.20 percent S in the plant. Plants with S levels less than 0.15 percent are clearly S deficient, and would likely respond to applications of a sulfate-S fertilizer.

Plant available S is primarily derived from mineralization of soil organic matter and atmospheric deposition. It also can occur from weathering of some minerals. Sulfur is retained on soil mineral surfaces much like P, but much less strongly attracted. It does accumulate in the subsoil of many medium and heavier textured soils, which is why a 2-foot profile soil sample is used for sulfur soil tests. Sulfate (the plant available form of S) is mobile, especially in sandy soils, leaching below the root zone with excess rainfall. Soil testing at the 0-6 inch depth for sulfate-S has not been considered reliable because of this mobility.

Warm moist soils promote mineralization, so S deficiencies are more likely to be seen when soils are cold in the spring and plants begin to grow rapidly. But S deficiencies can also be evident during the remainder of the growing season, particularly in soils prone to S deficiency. During the period of residue buildup in no-tillage, S mineralization may also be limited. Efforts to reduce sulfur deposition and improve air quality have been successful over the past 25 years in the U.S., decreasing the amount of S available to crops in many states. In Kansas, these efforts have reduced deposition by nearly 50 percent. This is likely one of the reasons S deficiencies appear to be more common today.

Including S in a fertilizer program to avoid S deficiency is more efficient and less costly than correcting a S deficiency once it occurs. Applications should be made based on a preplant soil test. Typically soil applications of 15-25 pounds of sulfate-S per acre are sufficient to correct or prevent S deficiency. Blending ammonium sulfate (21-0-0-24 S) or calcium sulfate (gypsum) with broadcast phosphorus in the fall is a convenient and cost-effective ways to provide S. Other useful sources include elemental S; however this source is not available to the crop immediately and should be applied in time to allow conversion to sulfate-S.

Source: ksu.edu