farmgate: Sinks, Cycles, and Laughing Gas
The Cornbelt is ready for Mother Nature to warm up and dry out in the short term so corn can be planted. But in the long term, warming up and drying out would not be your preferred forecast. The idea of global warming has become a lightning rod issue that has polarized many people, including some in agriculture. Whether you believe that mankind is responsible for rising temperatures or they are part of a periodic change in climate is your own decision. But any change in the climate will have an impact on agriculture and that is where we are going today.
For millions of years the Earth has been warming up, then cooling off, then warming up again. The average cycle fluctuates about 18-22 degrees Fahrenheit, which typically happens over thousands of years and is not noticeable without scientific data. A collector of that is Eugene Takle, meteorology researcher at Iowa State University. He and ag economist Don Hofstrand have created a series of report in the Ag Decision Maker.
In the February newsletter they report global warming over the past 15,000 years and expect a gradual decline over the next 70-80,000 years and they say carbon dioxide and methane concentrations go up and down with the temperature. Based on the concentrations of those gases as found where nature collects them, temperatures had been declining over the past 1,000 years, but began a rapid climb upward about 100 years ago. Solar sunspot activity has contributed to warming and volcanic activity has contributed to cooling; but concentrations of greenhouse gases in the atmosphere have added to the warming since 1960. Takle and Hofstrand say, “By themselves the natural factors do not account for the rise in global temperatures since 1960. Only when they are combined with the (human origins) of greenhouse gases and sulfate does the model predict relatively accurately the actual temperature levels. This leads us to believe that (human origin) factors have a significant role in the recent increase in global temperature.”
Takle and Hofstrand say in the March newsletter that warmer global temperatures “will have a profound impact on global agriculture.” But they are unsure of the impact on the Midwest. Their focus is on role of greenhouse gases, which include carbon dioxide, nitrous oxide, methane, and water vapor being the most prevalent. Recalling your high school science class on the carbon cycle, keep in mind that it fluctuates over time from the carbon dioxide in the atmosphere to carbon locked in the ground from growing plants that absorb it. As the plant dies, microbes break it down, combine the carbon with oxygen and it is returned to the atmosphere. The use of coal and oil for energy production also returns carbon dioxide to the atmosphere.
Each of the greenhouse gases stays in the atmosphere varying amounts of time and also has a varying ability to warm the atmosphere. Takle says levels of the gases in the atmosphere are increasing, and he believes the atmosphere contains more carbon dioxide than at any time in the past 420,000 years. If the current trend continues, which began at 310 parts per million in 1960, the carbon dioxide content in the atmosphere will be about 950 parts per million by the end of this century. Based on its ability to cause higher temperatures, the carbon dioxide in the atmosphere will cause temperatures to rise as well. Takle estimates it will rise as much as 4 degrees by 2030, and as much as 18 degrees over the next 100 years. But he says the increase will not be distributed evenly around the Earth, and the warming tends to be concentrated in the Northern Hemisphere, interspersed with ocean regions that cooled somewhat.
The April newsletter says the electric power industry creates over 33% of greenhouse gas emissions, followed by 28% for transportation, 19% for industry, and 8% for agriculture. But how does agriculture emit greenhouse gas? Takle and Hofstrand point to several sources:
1) Nitrous oxide makes up about 60% of the greenhouse gases originating from agricultural sources. And you probably are thinking, “Where does laughing gas used by my dentist originate on my farm?” Nitrous oxide is produced by soil microbes which break down nitrogen fertilizers into a form usable by your corn crop. While nitrogen is required for profitable corn production, more efficient management of application practices can reduce the nitrous oxide that is emitted into the atmosphere.
2) Methane is produced as part of the normal digestive process of livestock. Microbes ferment the feed and methane is released in the rumen of cattle. Iowa State says generally, lower quality feed and higher feed intake lead to higher methane emissions.
3) Methane is also produced during the decomposition of manure in lagoons, tanks, or pits where there is no oxygen present. On a field, the manure will decompose with oxygen and methane is not produced. With improved application technology, manure can be spread on fields with reduced methane production. Or the alternative is to capture the methane produced by manure pits, and burned as an energy source.
4) The use of diesel fuel and gasoline in tractors, combines, trucks, and other farm power equipment burns fossil fuel, and releases carbon. An increased reliance on alternative fuels will reduce carbon dioxide emissions.
5) The flooding of rice paddies restricts underwater decomposition to the anaerobic system described in the section on manure. That decomposition at the bottom of a flooded rice paddy will produce methane.
A carbon sink is the storage of carbon in another form. Underground coal veins and crude oil deposits are carbon sinks formed when plant material was buried, and the decomposition did not allow carbon to be emitted into the air. Carbon sinks can be formed with the development of forests, since the wood in the tree contains carbon. Burning the wood or letting it decompose puts the carbon back in the air, but using the wood for building material converts the carbon into the structure for a home.
A different carbon sink is the organic matter in the topsoil created from prairie grasses. Conventional tillage allows the carbon to oxidize and be released into the air. However, increased conservation tillage has allowed equilibrium to be reached between release of carbon and depositing the carbon from crop residue. This practice allows farmers to obtain payments from carbon credits that are sold to emitters of carbon such as power plants.
Summary:
The release of carbon dioxide and other greenhouse gases has the potential to increase the atmospheric temperature over time. While agriculture is a relatively low emitter of greenhouse gases, there are a number of practices that can be undertaken to reduce those emissions, and even convert agriculture into a carbon storage industry which could generate revenue for farms.
Posted by Stu Ellis on April 28, 2008 12:43 AM to farmgate