When I first started working in the agriculture industry I spent the entire month of May blending fertilizer. At this point in time when a grower came in and asked for a “34-17-0” blend, I was a pretty happy guy. It meant less work and less chance of screwing up, win-win for me as an 18 year old trying to make a few bucks at my first summer job. Nowadays, when someone asks for that blend, I cringe.
Having a proper fertility package is one of the most important things when starting off your crop in the spring, but it is very often overlooked. I like to put it into terms of us as people. We have three essential macro-“nutrients,” those being protein, carbohydrates and fat. If we were only to eat carbohydrates and proteins, we would begin to run into a whole world of problems due to malnutrition from lack of fat.
The same imbalance occurs with canola as well, even if we don’t see obvious deficiency symptoms. Plants limited by a nutrient may be weaker and losing yield even without showing obvious signs. Liebig’s Law of the Minimum shows us that a plant/crop can only produce as much its most limiting factor will allow it. If we only have sulfur in the soil for 30 bushels of canola, you will be hard pressed to get any more out of that crop due to the lack of sulfur, regardless of how much nitrogen and phosphorus you throw at it.
More farmers are highly aware of the sulfur needs of canola, thanks to groups like the Canola Council of Canada and agronomists and retailers. It’s one hting to know that canola is a high sulfur user, but let’s explore WHY the crop needs so much more than others. Many growers never ask, and a lot of individuals that promote sulfur don’t always explain the specifics behind why canola is a higher user than other crops.
If we under fertilize sulfur on a canola crop, these compounds begin to be broken down by an enzyme so the plant can use the sulfur elsewhere in the plant, meaning the plants defense system is taking a back seat to other basic physiological processes
The family canola belongs to, brassicaceae, is generally a higher sulfur user (this family also includes mustards and vegetables like cabbage and cauliflower). This family of plants has secondary metabolism compounds known as glucosinolates. These compounds are made up of a lot of sulfur as well as nitrogen. The main reason these compounds are important is due to their ability to increase a plants defense system/stress tolerance against pathogens or insects. If we under fertilize sulfur on a canola crop, these compounds begin to be broken down by an enzyme so the plant can use the sulfur elsewhere in the plant, meaning the plants defense system is taking a back seat to other basic physiological processes. This can open your crop up to increased disease or insect risk and increased susceptibility to stress. There is more that sulfur does in canola as well, but this is the quick and dirty version. Remember, the ratio of nitrogen to sulfur is important as well — you need to maintain about a 5:1 (N:S) ratio. For every 5 lb of N, the canola plant will use one pound of S under ideal conditions to achieve maximum yield.
Source: Marschners Mineral Nutrition of Higher Plants
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