GHGMP Project Reports by Region

Tests may help fine tune nitrogen requirements in corn

Standard fertilizer recommendations may be more than the crop needs and more than the environment can handle

Evaluation of different soil nitrogen tests and different nitrogen application rates over the next couple years may help Ontario farmers reduce both fertilizer costs and the amount of surplus nutrients, which can negatively impact the environment.

The project launched at nine Ontario sites in 2003 is being continued through the 2004 and 2005 growing seasons, says Brian Hall, a field crops specialist with the Ontario Ministry of Agriculture and Food, based in Stratford.

Results from the 2003 trials indicate the optimum fertilizer rate is something less than the standard recommendations followed by most corn producers, says Hall. "It may mean producers are able to reduce nitrogen rates and in doing so, there could be a lower risk of surplus nitrogen being leached through the soil or lost to the atmosphere." The project, partially funded by the federal Greenhouse Gas Mitigation Program for Canadian Agriculture (GHGMP), should provide more conclusive answers over the next couple years.

Hall is working with several producer/co-operators such as Tim Borho, who farms in south Bruce County, near Walkerton. About six acres of a corn field on his farm is divided into half-acre replicated plots for research purposes. Several tools are being used to measure the amount of nitrogen in the soil before, during and after the growing season, as well as the amount of nitrogen used by the crop. Plots at all locations were treated with nitrogen rates ranging from zero to 150 pounds per acre.

Fertilizer limit

"There was no improvement in yield at the higher fertility rates," says Borho, referring to nitrogen application in 100 to 150 pound per acre range. "There was reduced yield when no supplemental nitrogen was applied, but we achieved maximum yield at nitrogen rates between 50 and 100 pounds per acre. It showed there was a limit to how much good higher rates of nitrogen does."

To get a better handle on nitrogen levels and crop nutrient requirements, Hall is applying four different nitrogen tests. He's using a pre-plant nitrogen soil analysis; an in-crop test known as a pre-side dress soil nitrogen test; a test that measures nitrogen in corn plant tissue near the end of the growing season, known as the corn stalk nitrogen test; and, a fall soil test analysis.

Nitrogen testing at the various stages over the growing season will provide a clearer picture of the amount of nitrogen actually available and used, says Hall.

"Right now most producers are following provincial recommendations for crop nutrient requirements and are also taking into account how much nitrogen is in the manure that's being applied," he says. "What most producers are not taking into account is the amount of organic nitrogen that's mineralized in the soil during the growing season."

A producer may apply 100, 130 or 150 pounds of actual nitrogen just prior to seeding, when in fact those rates may be too high considering the amount of nitrogen mineralized in the soil. "That's where the pre-side dress nitrogen test may play a role," says Hall.

Little-used test

The pre-side dress soil test is done at the four to six leaf crop stage. It indicates the amount of available nitrogen in the soil. While the test is known, it isn't widely used by corn producers.

The potential, if the pre-side dress test is deemed accurate, means producers could eliminate application of higher rates of nitrogen prior to seeding. The crop could be seeded with a lower rate starter fertilizer, then the pre-side dress nitrogen test could recommend the amount of nitrogen needed in-crop to support the corn over the balance of the growing season. In this research project, side dress nitrogen in the form of 28 percent UAN liquid nitrogen was applied with an applicator equipped with fluted coulters. Fertilizer was pumped into the soil through tubes attached to knives following behind the coulters. Fertilizer was applied at about the mid-point between corn rows.

Near the end of the growing season at the black layered stage (maturity) the corn stalk nitrogen test, which is used in some areas of the United States, is used to determine if fertility during the growing season was adequate for the crop to achieve yield potential, says Hall.

As well, a fall soil test will show how much residual nitrogen is in the soil at the end of the growing season.

Several benefits

"Checking nitrogen levels at these various points over the next couple of years will tell us if standard recommendations are correct, if the pre-side dress test is accurate, and how much surplus nitrogen is left in the soil at various fertilizer rates," says Hall. "The tools may help producers reduce application rates and input costs, as well as the amount of surplus nitrogen in the soil."

Reducing residual nitrogen is important from an environmental standpoint. Nitrogen can leach from soil affecting the quality of groundwater. And, under waterlogged soil conditions, the nitrogen can be converted to ammonia in a process known as denitrification and lost to the atmosphere as nitrous oxide, a harmful greenhouse gas.

"As producers, it's important that we have a better handle on soil nutrient levels," says Borho. "Along with reducing input costs, it's also better for the environment. If we don't pay attention to these issues we may not have a choice in the future."

Regional reports will be posted as information becomes available. Please check back regularly for updates.