LETHBRIDGE – The high cost of nitrogen fertilizer makes it more important for producers to know their crops’ growth cycles and when nitrogen is most needed.
Ross McKenzie told the recent Agronomy Update in Lethbridge that it’s important to understand the relationship between nitrogen and crop production before finalizing cropping decisions.
“Crops take up a lot of their nitrogen early in their growth cycle. A cereal crop would take up about 70 percent of its nitrogen by late tillering, yet that’s only about 30 percent of the dry matter that it will actually produce. Therefore, making sure nitrogen fertilizer is available and placed well for efficient uptake is critical,” said McKenzie, a soil scientist with Alberta Agriculture in Lethbridge.
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“It’s important to have the nitrogen there, ready for uptake, early in the growth cycle. If that nitrogen releases later in the season, it may have less effect on yield and more effect on grain protein.”
McKenzie said yields gradually increase as nitrogen is added, eventually reaching an optimum level once enough nitrogen is added. Protein, on the other hand, will dip down after the first nitrogen is added.
“We’re increasing our vegetative growth, but if we don’t put on enough nitrogen, our protein will go down a little bit before it starts to increase,” he said.
“When we’re at sufficient nitrogen for yield, we still haven’t got sufficient nitrogen for optimum protein. It’s important to understand those two relationships with nitrogen, in yield and protein.”
McKenzie said durum and hard red wheat growers want nitrogen for higher protein, but malting barley and soft wheat growers don’t want their protein levels to become too high.
Because it’s a mobile nutrient, nitrogen loss can be a concern for farmers. It can leach into the lower soil profile out of the root zone, or it can be lost to the atmosphere as a gaseous form.
The nitrification process speeds up if soil is warm and moist because it’s more suitable for microbial conditions. For volatilization, McKenzie said conditions are most favourable when soil temperatures are above 5 C and air temperatures are above 10 C. Moist soil surface also increases risk.
“Especially if we have cooler temperatures at night, we have a dew, it warms up in the day and we get some wind, then we have prime conditions if urea is on the soil surface,” he said.
“To minimize the volatilization of urea, broadcast the urea when soil temperatures are less than 5 C. If you’re going to broadcast nitrogen onto grass or winter wheat, you want to do it as early as you can in the spring when things are cool and the soil surface is dry. If you can time that before some rain or wet snow, it will do even better.”
McKenzie said denitrification is where some of the greatest losses occur.
“When the soil is at or near field capacity, the micropores are full of water, nitrate is present, oxygen is absent – that’s when the microbes are stripping oxygen off the nitrate and we’re going to lose nitrogen. That can be a big loss of nitrogen from our soils, particularly when you have wet June conditions or when we have rains in September when soils are still relatively warm.”
McKenzie said urea, anhydrous ammonia and liquid urea ammonium nitrate are the three forms of nitrogen available to prairie farmers.
“We have a few different options with urea. We can get the ESN (Environmentally Smart Nitrogen) form, which is polymer coated, to protect it from loss, or there’s Agrotain, a urease inhibitor product.”
McKenzie said while side banding may be a preferred method of applying nitrogen, many farmers are interested in how much can be applied with the seed.
“The two things we have to be careful of are the salt effect and toxicity. There’s two very different things that can go on,” he said.
“If we put urea with the seed and it converts to ammonia, that can be toxic to the seed. An example of a salt effect would be with ammonium sulfate – 21-0-0-24 – which has a high salt index. If you put that with the seed with canola, because you want to get some sulfur in, that can have quite a negative effect. Both can kill the plants before they even emerge.”
To solve these problems, McKenzie said producers should make sure they spread seed and fertilizer across the seed bed. Then they can put more fertilizer with the seed. Scientists have developed charts for western Canadian conditions, dealing with soil type, seed bed use and safe fertilizer levels for various fertilizer types on different crops.
“There’s another way we can put more fertilizer with seed – using a urease inhibitor like Agrotain, but you must make sure that the fertilizer is completely coated. If it’s not completely coated, you’re not going to have the protection you think you have. Agrotain will give you 10 to 12 days of protection, so you can put more fertilizer with the seed,” McKenzie said.
“The other option is going to ESN, the Agrium fertilizer called Environmentally Smart Nitrogen. It’s a urea fertilizer coated with a plastic polymer to prevent it from quick release. It allows the fertilizer to release over a 20 to 50 day period, with the majority released between 30 and 40 days.”
ESN can be broadcast on the soil surface or placed in the soil. The release rate depends on moisture and temperature.
“What happens is, the polymer doesn’t break down itself,” he said.
“It stays intact, is permeable to water and allows water to diffuse through the membrane to the granule. The urea dissolves, converts to ammonia and ammonium, then diffuses back out.”
Without the coating, under optimum conditions, McKenzie said urea might be all converted to nitrate in 14 days, but the coated urea slows that conversion down. The only down side is the extra cost.
