Farmers attempt to manage light and water to maximize grain yields. No sweat until the numbers change. The forecast from the Intergovernmental Panel on Climate Change (IPCC) report of a 9° F increase over the next century affects row crop agriculture in the following ways, scientists say:

Warmer night temperatures will greatly affect corn yields. In Indiana, for example, 95% of the annual yield variation (2008-2014 excluding 2012) can be attributed to variation in average July night temperatures, according to Jeff Volenec, Purdue agronomy professor. Higher night temperatures reduce carbon uptake, interfering with corn’s pollen viability, fertilization and grain formation, says the IPCC report. If Midwestern night temperatures rise by 9 degrees by 2100, as many climate scientists predict, the corn yield/July temperature relationship from Indiana suggests a yield decrease of 2.1 bushels per acre for every degree Fahrenheit increase, adds Purdue’s Volenec. “This translates to about 20 bushels per acre—in some cases this represents a farmer’s profit,” Volenec says from producers’ response to this data.

“More global precipitation and increased global surface temperature,” according to the IPCC report.

Higher carbon dioxide levels will increase corn yield much less than it will soybean yield, due to fundamental differences in their photosynthesis, Volenec says.

Warmer temperatures, heavy downpours and flooding in the Midwest, says Mark Seeley, Minnesota Extension climatologist/meteorologist. “This tendency has begun: For example, 31% of the Great Lakes region’s precipitation now falls in extreme weather events,” he adds.

An increase in weather volatility means that bacteria and other microorganisms can become more active earlier than normal. “We might get this really warm weather that we usually don’t have where the soil temperature goes up into the 50s in December,” says Elwynn Taylor, Iowa State University climatologist and agronomist. “Microorganisms in the soil can begin to convert nitrogen (N) to a form that can be lost.”

More Midwestern rainfall in the first half of the year, with more extreme wet years and extreme dry-year variability, says Gene Takle, director of the Iowa State University Climate Science Program.

More frequent and amplified climate extremes in the western Great Lakes region, Seeley says. For example, annual precipitation amounts in Faribault, Minn. (southern Minnesota) has increased by 31% since the 1921-1950 time span, and by 21% in the western Minnesota town of Milan, Minn.

More precipitation falls as violent storms, with more accumulation per event.  For example, the frequency of Minnesota 2-inch thunderstorm rains has doubled since 1990, according to state records.

More flash flooding will require a need to re-evaluate tile drainage, runoff management and soil erosion management, Seeley says.

Longer growing seasons, Seeley says.

Later fall dipping of soil temperatures below 50 degrees, leaving a smaller window for fall chores, Seeley says.

Midwestern soil will remain frozen longer and to greater depths, Seeley says.

We have more freeze-thaw cycles each year.

Weather patterns linger for longer periods in the Midwest before moving on.

Crop pests, pathogens and insects will survive longer, according to the IPCC report and Iowa Extension Weed Specialist Mike Owen. You will have more pests and weeds to combat, for longer parts of the season.

Later fall N application, Seeley says, and a greater potential for N loss from extreme precipitation events, Taylor says.

Crop residues will break down more rapidly, Seeley says.

Higher dew points will make summers feel hotter and extend some pathogens’ virulence and lifespan, say Seeley and Takle. “Crops will increasingly experience temperatures above the optimum for their reproductive development,” says the IPCC report.

Higher carbon dioxide levels partially closed stomata, the tiny leaf pores that allow gaseous exchange, Volenec says. This results in increased leaf temperatures during the day, exacerbating already overheated plants. This response was observed at most field locations globally where carbon dioxide fertilization (raising carbon dioxide from its current 400 ppm level to 500-600 ppm) in the field was used to measure crop responses and yield, he adds.

“In some locations increased summer air temperatures may also reduce relative humidity,” Volenec says. “Plants’ water-use efficiency declines as more water exits stomata into the warmer, lower humidity air (transpiration). Partial stomata closure to reduce water loss results in leaf temperature increases as evaporative cooling declines.

 “Modest temperature increases (e.g., from 82 F to 97F) have been shown to greatly increase plant evapotranspiration rate,” Volenec says. “Warmer air is less humid, and that pulls water from plant leaves, lowering plants’ water-use-efficiency and increasing irrigation needs.”

The most invasive weeds will migrate northward, fueled by more atmospheric carbon dioxide, the IPCC report says.

The controversy

These predictions come from 2,000 of the best minds in the world on climate change, says Purdue’s Volenec. “They run 20-30 different models and use the best data. This is the best wisdom we have on climate change. If we get this wrong, there are incredibly serious consequences.”

Editor’s note: The Intergovernmental Panel on Climate Change report is at www.ipcc.ch.

Night temps affect corn yield

Corn’s growth and yields are better in years with cool nights, “other things being equal,” says Jeff Volenec, Purdue agronomy professor. They reduce corn respiration rates. But scientists predict a 9-degree F night temperature increase by 2100. He’s documented a 2.8-bushel per acre yield hit for each 1 degree F increase in (Indiana) night temperature. “This translates to about 20 bushels per acre – in some cases this represents a farmer’s profit,” Volenec says, based on producer response to this data. “The helpful thing about this data is that other factors, like crop genetics, have not changed markedly in that seven-year period,” he adds.

Credit: www.nws.noaa.gov/climate/index.php?wfo=ind and Jeff Volenec, Purdue

What Iceland teaches us

Naturally occurring Icelandic high-carbon dioxide vents have emitted 790 ppm carbon dioxide for 100 years. (We are at 400 ppm now.) When plants downwind from the vents are compared to those upwind (i.e., normal carbon dioxide concentrations) these differences reflect how plants adapted from living more than 100 years in this setting:

Credit: Cook et al, 1998

Fewer days to plant; more to harvest

In the last 16-30 years, Illinois and Iowa have 11-12% fewer hours in a week suitable for planting on average than its farmers had between 1980 and 1994. That’s a half day. In Indiana, that’s actually 1 less day per week. This data comes from Purdue University Agricultural Economics Associate Professor Ben Gramig.

More rain in the early growing season, and in higher amount amounts is to blame – all well documented by climate-change scientists.

Illinois farmers had 4.1 days of weather suitable for planting per week on average between 1995 and 2010 – down from 4.6 suitable days per week between 1980 and 1994, the data show.

Indiana farmers had an average of just 3.7 days per week suited to planting between 1995 and 2010, compared to 4.9 days in 1980 and 1994 – a 24% drop!

Iowa farmers had an average of 4 days per week suitable for planting between 1995 and 2010, compared to 4.5 days between 1980 and 1994, an 11% drop.

Good information to weigh when planning equipment and manpower needs, or choosing fertilizer application timing. No wonder larger planters are popular. These numbers should help with planning equipment and manpower needs, or to weigh fertilizer application options.

Your harvest weather window has expanded by about the same amount lost during planting, over the same time period.

Illinois, Indiana and Iowa gained another half-day of harvesting weather per week on average.