Prairie farmers are used to being flexible, always on the lookout for new recommendations for fertility applications — and when it comes to growing corn, they have to be. Corn is an expensive crop with high nutritional requirements. And every farmer’s land requires something slightly different.
Morgan Cott, field agronomist for Manitoba Corn Growers Association, says that corn has two major fertility needs, nitrogen and phosphorous, and that generous application is required to get high yields. “What each field needs depends on the soil type. Lighter soils will tend to leach nitrogen more if conditions are right,” she explains. “However, over-applying in a dry year will just cost the grower more money. Nitrogen is very mobile in the soil and corn doesn’t need the bulk of its requirements until V4 to V8 staging, so over-applying nitrogen early on will just lead to losses.” (V4 refers to the fourth Vegetative Growth Stage, the point where the collar of the fourth leaf is visible. At Vegetative Growth Stage 8, the collar of the eighth leaf is visible.)
Cott also says that corn benefits from a complete blend of fertilizer, including potassium and sulfur, and soil sampling should be done to assess the soil’s needs. “Corn also loves micronutrients, but you need to sample for these to know if they are needed or not,” she says.
According to John Heard, crop nutrition specialist for Manitoba Agriculture, Food and Rural Development, and recipient of this year’s International Certified Crop Advisor (CCA) of the year award from the American Society of Agronomy, farmers should be “spoon-feeding” the crop at the rate it requires, but also managing time of application. If farmers apply fertilizer at the wrong time, they’ll need to bump the rate of application to account for possible losses. It’s a tricky balance, and one that growers have to figure out for themselves.
“In each individual situation I hope the farmers are getting good advice and experience and will tailor rate based on the equipment they have for whatever time and placement system they have,” he says.
New types of fertilizer application
Cott says Manitoba farmers are adapting to new methods of fertilizer application. “It used to be that all the fertilizer went down at the same time, but now we have the ability to do split applications of nitrogen, or add fertilizer safeners such as ESN, a nitrogen product, so that it can be placed in larger amounts and closer to the seed without burning,” she says.
One common problem she’s noticed with fertilizer application, Cott says, is that growers sometimes float on the fertilizer before incorporating it, or they apply the fertilizer with an air seeder drill and plant afterward. “The concerns I have with these methods are that they require multiple passes over the field, and that there may be too much fertilizer-to-seed contact and create burn,” she explains.
Cott is also concerned about farmers who may be over-fertilizing. “Are you capable of getting 150 bushel yields, or just 110? Sometimes we push for a yield that just isn’t possible for our area that we farm in, so don’t be fertilizing for a pipe dream — it’s a waste of money,” says Cott. “On the flip side, if you can get 150 plus bushels, you need to be fertilizing for that capability. Don’t skimp and expect to get those yields year after year because you’ll end up mining the soil and wind up spending more in the long run.”
If farmers wish to self-assess the appropriateness of their fertilizer application, they can take the corn stock nitrate test, says Heard. While it will be too late to make fertilizer changes for the current year, it will give farmers valuable information for future years.
Zero-tillers need less N
This summer, North Dakota State University unveiled a new set of corn fertility recommendations, this time with separate suggestions for no-till soil. According to the North Dakota experts, farmers who have been continuously no-till for six years or longer require 40 to 50 pounds less nitrogen per acre than growers with tilled fields.
David Franzen, North Dakota State University extension soil specialist, led the effort to develop the recommendations. “I was able to run a statistical analysis to determine whether the responses of corn to nitrogen were the same in both tillage systems. They were not,” he emphasizes. “The response curve of the no-till sites was flatter (less response to nitrogen) and the economic optimum for long-term no-till was about 50 pounds of nitrogen per acre less than for conventional tillage.”
The difference, he says, is similar to that seen in 2010’s North Dakota spring wheat and durum recalibration project.
Franzen’s theory is that in long-term no-till soil, the diversity of biology takes up a large percentage of nitrogen and uses it to increase population multiplication and residue decomposition. “The nitrogen is excreted as intermediate nitrogen containing compounds that seem to act like a natural slow release nitrogen. Conventional tillage systems do not have this type of biology, or at least not nearly as much, and so the nitrogen is much more exposed to losses to leaching/denitrification,” he says.
Manitoba’s John Heard cautions that the new recommendations should be taken with a grain of salt, especially for farmesr who have only been zero tilling for a short time. “The zero-till corn function does not always have a lower nitrogen recommendation,” he says of the NDSU’s fertility calculator. “For the first five years the zero-till corn needs more nitrogen, presumably to deal with nitrogen immobilization by crop residue until an new nitrogen cycle equilibrium is established,” he explains. “Then the nitrogen rate is reduced.”
The new recommendations out of North Dakota will only be of passing interest to Prairie growers, who have by and large not yet adopted zero-till farming, according to both Cott and Heard. However, the results are highly applicable to Manitoba growing conditions. “Nine of the Manitoba Corn Grower Association sponsored studies conducted by myself during the last decade were included in the NDSU dataset to develop the calculator,” he says.
Heard also points to another study led by Curtis Cavers of Agriculture and Agri-Food Canada based in Portage la Prairie which is analyzing nitrogen management in corn at three sites for the next three years. “The study looks at different nitrogen rates, sources such as urea, ESN and UAN, timings, both pre-plant and in-crop, and placement, including broadcast and incorporated, surface broadcast and side dress injected. This data should help us validate the guidelines published by NDSU,” says Heard.