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Changing Weather Patterns Impact Nitrogen Management

Changing Weather Patterns Impact Nitrogen Management

Iowa State University climatologist Elwynn Taylor believes we are entering a 25-year period of greater volatility of both weather and corn yields.

From flood to drought, the nation's breadbasket has had to contend with great weather extremes in recent years. In general, the Midwest is experiencing a period of warmer winters, higher minimum temperatures, higher dew points, greater moisture variability and more intense weather events, according to climatologists studying weather trends.

Peter Scharf, nutrient management specialist at the University of Missouri, estimates that 2 billion bushels of corn were lost due to nitrogen deficiency in corn from 2008 to 2011, when there was widespread, excessive rainfall in the Midwest.

For example, North Dakota's growing season has lengthened by 12 days since 1879 and Iowa has 50% more days with measurable precipitation now than it did in the 1900s. This past year, Iowa began the season with widespread drought followed by the wettest spring in 140 years of recordkeeping and a droughty summer. This is the third year that science faculty and research staff from Iowa's universities and colleges signed a statement warning that climate change has profoundly disrupted ag production and is projected to be more harmful in coming decades.

Looking at long-term trends, Elwynn Taylor, Iowa State University climatologist, believes we are entering a 25-year period of greater volatility of both weather and corn yields. "Our climate goes through wet, dry, hot and cold cycles of about 40 years," Taylor says. "Since 1865, there has been a trend of 18 years with fairly consistent weather and corn yields in the Corn Belt followed by 25 years of highly variable weather and corn yields. This cycle has been repeated four times. It appears that 2012 was year one of the next 25 years of extremes."

While there may be debate about the cause of climate change, there is no doubt that farmers will need to adapt to changing weather patterns that affect growing seasons, crop diseases and pests, water availability and nutrient management. "Climate is changing in our own backyards, and it's changing at a pace that is startling," says Mark Seeley, University of Minnesota climatologist. "We are seeing profound consequences already. The need to adapt is very much present."

Strategies to protect nitrogen
Nitrogen is a key crop nutrient that is significantly affected by weather. With increased annual precipitation, more heavy rainfall events, higher temperatures and increased humidity, there is greater chance of losing nitrogen from leaching, volatilization and denitrification.

Peter Scharf, nutrient management specialist at the University of Missouri, estimates that 2 billion bushels of corn were lost due to nitrogen deficiency in corn from 2008 to 2011, when there was widespread, excessive rainfall in the Midwest. The land area in the Midwest with 16 inches or more of rainfall in the spring (April – June) has dramatically increased in the last 25 years from less than 80,000 square miles to nearly 200,000 square miles in 2013. Drew Lerner, senior agricultural meteorologist and president of World Weather, Inc., forecasts another wet and cold spring for the eastern half of the country in 2014.

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Changing weather patterns make nitrogen management more important than ever. "As Midwestern weather warms up and gets wetter, nitrogen will leach, denitrify and volatilize more rapidly," says Ron Heiniger, professor of cropping systems, North Carolina State University. "We're used to these conditions on the eastern seaboard. That's why we split-apply nitrogen and include a nitrogen stabilizer. 

"We want to slow down the nitrogen conversion reactions so the target plant can take up the nitrogen. In our work with NutriSphere-N Nitrogen Fertilizer Manager, we observed more nitrogen being taken up by the plant. We also observed better early growth," says Heiniger.

 Synchronize N with plant uptake
"As we have more variable rainfall, too much or too little, we can no longer expect to rely on a single application of nitrogen," says Tony Vyn, Purdue University professor of agronomy. "The way to deal with higher occurrences of extreme weather events is to move toward split-nitrogen applications as a standard practice. Farmers should also accept the fact that even with split applications at preplant and early sidedress, they may need to consider late-season applications where excessive nitrogen losses occurred in saturated soils or sandy soils," Vyn indicates.

Changing weather patterns will also influence fall nitrogen decisions. In northern Corn Belt states, warmer winters mean that farmers must wait longer for soil temperatures to drop below the recommended 50 degrees Fahrenheit for fall application. Wetter springs mean more delayed planting and that leaves fall-applied nitrogen vulnerable to loss for a longer period, which is one reason why Vyn expects a move away from fall applications in the western Corn Belt. Other reasons include nitrogen losses associated with warmer winters, concerns about water quality and the environment and regulatory concerns. Since modern hybrids take up more than 30% of their total nitrogen after silk emergence, there is a growing farmer focus on meeting nitrogen needs later in the growing season.

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