The Role of Sulphur on Wheat
As the wheat has fully broken dormancy and it is starting to green up, it is a great time to get out in the wheat fields and do a stand assessment prior to any nitrogen application. The previous Wheat News Plus articles on Soft Red and Hard Red nitrogen options illustrate the methods to complete a stand assessment. I cannot stress doing a stand assessment enough! The wheat overwintered very well which is absolutely fantastic, however we did not lose any tillers. There are some fields with 3-4 stems per plant and 15-20 plants per foot of row. This sets us up for 700-1000 heads per square yard which is a big red flag for lodging risk. Last year there were many fields with similar stand counts, however we missed some rain and it stayed cool through critical grow stages which meant the stems thickened up and the wheat stayed short which mitigated the lodging risk.
In some parts of the province the first shot of nitrogen has already gone on. Once the fields dry up, nitrogen will be going on full bore. As part of a systems approach to wheat management, it is critical that a source of sulphur is added to the mix during the first application.
The messaging around sulphur on wheat is becoming more common every year. Since we do not get sulphur for “free” through acid rain anymore, sulphur is becoming a limited nutrient to most field crops across the province. Sulphur is a critical component in protein production as well as it increases the nitrogen use efficiency. As a result, when we raise the nitrogen rates to push for higher yields, the sulphur rates should also be increased. The standard rule of thumb for Ontario is (10:1). This means for every 10lbs N add 1lb S. Whether you use ammonium thio sulfate or ammonium sulphate, they are both excellent sources of sulphur for the plants.
Areas in the field that will show sulphur deficiency first are the coarse textured low organic matter soils. The easiest way to distinguish sulphur from nitrogen deficiency is that S deficiency shows up on the new growth first whereas N deficiency shows up on the old growth first.
Every year the response to sulphur varies. Temperature and soil moisture levels influence mineralization of S making it plant available. Ontario research shows a positive response to sulphur applications, however the rate of return changes every year. The best thing to do is add a check strip to evaluate it on an individual field basis.