It’s an agricultural conundrum – crops need nitrogen but too much too close can be toxic.
Granular urea is the most cost effective form of synthetic nitrogen fertilizer. Its high level of nitrogen and relatively low costs of production, transportation and storage make it a competitive product for farmers.
But if too much of it is placed too close to the seed, seedlings will suffer before they can take advantage of its proximity.
Single shoot placement with the seed is the desirable choice for producers, but achieving this goal is challenging unless the young plants can be protected from the nitrogen.
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“Ideally you need to be putting more than 40 kilograms of N in the ground per hectare (about 35 pounds per acre) for your cereal crop. Likely 60, (55 lb. per acre) and we can often benefit from even much higher rates,” said Viterra fertilizer research agronomist Rigas Karamanos.
“This is where we begin to treat the product to delay its release and avoid the damage.”
Ross McKenzie of Alberta Agriculture said toxicity is a danger, especially for canola.
“But unless you feed the crop, you won’t get the desired yield,” he said.
Damage to canola seedlings starts at seed-placed rates as low as 28 lb. per acre.
Brian Beres of Agriculture Canada in Lethbridge said even crops such as durum and winter wheat begin to suffer at these rates.
“Controlled release urea systems can help avoid these problems,” he said.
“For seed-placed situations, polymer coated urea was shown to be superior to controlled release forms such as urease inhibitor systems.”
McKenzie’s research has shown that Agrium’s Environmentally Smart Nitrogen (ESN) can be seed placed at relatively high levels without creating phytotoxicity problems in most crops.
McKenzie stressed that care has to be taken when handling coated urea prills because the coating is all that prevents the urea from damaging crop seedlings.
Alberta research published in 2007 showed that ESN was safe when seed placed or side banded in winter wheat at rates as high as 106 lb. per acre. Uncoated urea began to damage crops at rates higher than 25 lb. per acre.
The urea prills did not reduce grain protein benefits.
Beres’s research indicates that producers using the coated product should be able to safely seed place ESN with winter wheat and canola at rates three times higher than what is recommended for uncoated urea.
“But the way the product is handled is critical. If you damage that coating, you are now seed placing plain urea,” he said.
“Think about how many times it has been handled. The plant where it was coated, the dealer and on the farm, then into the seeder’s meter and then through its air delivery system. At any point that coating could become damaged.”
McKenzie said producers should examine samples of the coated material at the seeding tool’s boot and assess the amount of damage there. If damage levels are unacceptable, take a sample at the truck and at the farm’s bin and as far back as the dealer if necessary.
Beres has found that farm handling typically results in 20 percent release of nitrogen, which has no significant effect on crop yields or maturity.
“We’ve found that the most damage occurs when the product is transferred in equipment that has scaly fertilizer deposits, where it is top dressed by boom application equipment and where air seeders have header manifold junction boxes running very high fan speeds,” he said.
“Retailers should run 10 tonnes of potash through their loading equipment before they handle ESN. Drill fills on the farm should be treated the same way.”
Beres said header manifold air seeder systems, such as the Flexicoil Easy Flow, may not be amenable to coated products unless care is taken to avoid high fan speeds.
