Assess sulphur needs on irrigated land
By Bruce Barker
In years of high rainfall and low irrigation, sulphur fertilization may be necessary.
The long-held belief is that sulphur (S) is not required under irrigation in Saskatchewan or Alberta because irrigation water carries adequate amounts of naturally occurring S for crop development. However, over the last few years, Gary Kruger, provincial irrigation agrologist with Saskatchewan Agriculture at Outlook, Sask., has noticed a few instances when crops were lacking in S.
“We haven’t seen sulphur deficiencies at the Canada-Saskatchewan Irrigation Diversification Center (CSIDC) at Outlook, but when we look at producer fields, we have seen some fields where sulphur deficiencies were showing up,” says Kruger.
The CSIDC is structured as a partnership between Agriculture and Agri-Food Canada, the Saskatchewan Ministry of Agriculture, the Irrigation Crop Diversification Corporation, the Saskatchewan Irrigation Projects Association, and the University of Saskatchewan to support irrigation-based economic development and environmental sustainability.
Kruger says the first reports of S deficiency he received occurred in 2010. That year was set up with high rainfall and a very low requirement for irrigation. About 25 per cent of the usual irrigation water was applied to meet water demand, with irrigation occurring during three weeks in late-July and early-August. Kruger explains that because most S uptake occurs prior to heading in cereals and bolting in canola, supplemental S that is normally applied through irrigation water was not applied during the critical nutrient uptake stages. Compounding the lack of supplemental S applied through irrigation water was that heavy rainfall during the prior fall and the 2010 growing season likely leached the sulphur lower in the rooting profile.
Another example of S deficiency came from soil testing and plant tissue analysis of a hay sample from an Irrigation Crop Diversification Corp. project in the Chesterfield Irrigation District in 2011. The fifth year alfalfa crop was found to have inadequate S nutrition. Alfalfa and canola are both heavy users of S.
Kruger says producers should be assessing S needs on a year-to-year basis, supported with soil testing. His experience is that upward water movement via capillary action will carry sulphate-sulphur upwards into the rooting zone to replenish the S supplies during dry autumn weather. In these cases, there may be adequate S in the soil to act as a hedge for years when irrigation water is not applied early in the season.
However, Kruger adds that a good practice is to include a small quantity of sulphate-sulphur in fertilizer blends at seeding. He recommends a blend of 5 lb S/ac for cereals and 10 lb S/ac for canola and alfalfa.
“Canola and alfalfa are most likely to benefit from this practice, but cereals would also respond in years when frequent rainfall leaches sulphate from the upper horizons of the soil profile such as in 2010,” says Kruger.
To gain a further understanding of the S needs of crops, a research project was initiated in 2013 looking at the phosphorus (P), potassium (K) and S fertilizer needs of a new alfalfa stand. The project is being led by Sarah Sommerfeld, regional forage specialist with Saskatchewan Agriculture at Outlook. The alfalfa stand was established in the spring of 2013 and will be managed for three production years. In 2013, eight fertilizer treatments were implemented including P, K and S; a ninth treatment including zinc (Zn) was added in the fall of 2013 when plant tissue analysis indicated a Zn deficiency.
Fertilizer treatments were applied on October 10 as a banded application using a small plot disc drill on eight-inch row spacing. Plant stand assessments took place this spring to determine the level of winter injury and the impact of fertilizer on stand survival. Yield and forage quality analysis will be collected later this season and into the fall. Top Crop Manager will report on the project’s results in future issues of the magazine.