Navigating the confusing world of crop nutrition
Dec. 25, 2019
In the Crop Production Costs — 2020 guideline document recently released by Manitoba Agriculture, the assumed fertilizer cost for canola is more than $80 an acre, with hard red spring wheat at nearly $64. The only big break is on nitrogen-fixing crops, such as soybeans and peas, where the assumed fertilizer cost is in the $13 to $17 range.
Fertilizer prices since spring have been stagnant to lower, but fertilizer costs might still increase in the next growing season even if prices don’t. That’s because producers have been steadily increasing fertilizer rates as they chase higher yields.
A report recently prepared for the National Farmers Union advises farmers to cut their nitrogen expenditures as a way to make more money. Most producers see that as ludicrous. Global Ag Risk Solutions, a company that provides production cost insurance, has data showing that increasing input spending, on average, increases farm profitability.
It is true, however, that optimum fertilizer rates are a matter of interpretation. Different soil test labs will give you different results on the level of nutrients in your soil and then agronomists will interpret those numbers differently.
While an estimate can be made of how much water is in the soil at the time of sampling, no one knows how much moisture will fall during the growing season. Do you assume average precipitation or do you fertilize for an above average crop?
Nitrogen, phosphate, sulfur and potassium still form the basis for most fertility programs, but the offering of alternative forms of the major macronutrients is more diverse than ever. And there’s a big push on micronutrients such as zinc, boron and copper applied in various forms.
All the companies have trial results and convincing testimonials designed to drive sales. Some of the products have merit while others have merit only in certain circumstances. Some are a waste of money.
In extreme cases, some companies promote soil science principals that appear to come from some sort of parallel universe. They’ve invented their own jargon and while it sounds convincing, it has little basis in science.
The newest craze is biologicals. It is possible for micro-organisms including mycorrhizal fungi to work with plant roots to more effectively access nutrients in the soil. It’s an interesting area worthy of more study. However, we should realize that more effective plant uptake does not create soil nutrients.
When you harvest a crop and ship away the grain, you’re shipping away a large amount of nutrients. Unless you think the soil has an endless supply of what plants need, nutrients somehow need to be replaced.
The one exception is legume crops that work with rhizobium bacteria to produce soil available nitrogen. This is a truly additive impact — fixing nitrogen from the air.
Most farmers don’t have formal training in soil science and even for those who do, it’s difficult to scrutinize the explosion of crop nutrition offerings. How do we make good decisions when so much money is on the line?
Personally, I like hiring companies that interpret soil test results and provide advice but aren’t in the business of selling any of the inputs. Paying a little bit for an unbiased recommendation beats paying for questionable crop nutrition products.
By Kevin Hursh
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