Soil Scientist Jeremy Dennis pushes the soil sample out of the 100cm sampling tube. He and Steve Alspach will evaluate, measure and describe the soil, store segments of the sample in plastic bags then send the samples to Temple, Texas to be processed further.
Soil Scientist Steve Alspach uses a coffee can and a specific measure of millet to help describe the volume of the section of the sample that has too sandy of a texture to hold a specific shape. The millet is easy to measure and easy to separate from the sample before it is stored.
There are three rules of rapid carbon testing that anyone can pick up rather quickly. Don’t stand behind the guy with the truck when he’s moving from flag to flag, don’t stand downwind of the guy with the knife, and even though it is called rapid carbon testing – you’ll need to wear a hat because you’ll be in the sun for more than just a few minutes. The rest takes a quite a bit more expertise. A good day for sampling might be a little windy but with sun shining so you can see the horizons more clearly.
Soil survey offices around the country are in the second year of a two year project to collect information about how much carbon is stored in the ground. The Oklahoma’s NRCS Soil Scientists Steve Alspach and Jeremy Dennis are finishing up the sites randomly selected for testing in the area. They are surveying sites in southern Kansas, Oklahoma and northern Texas. Most of the landowners are generally already cooperating with one of the NRCS programs so it is not too difficult to get permission to sample, however, many are not and one of the hardest parts of the study is locating absentee landowners or convincing resistant landowners of the need for the information for this product.
Hundreds of samples in this area, thousands across the country will help generate a map, grouped by similar properties, land uses, agricultural management, and ecosystems, that will tell organizations, businesses and individuals which types of soils are capable of storing the most carbon and where. Carbon data will be used to determine the effects of conservation practices on soil carbon stocks for global carbon accounting and create improved maps and inventory about the distribution of U.S. soil carbon stocks. It will help create reliable soil survey databases that can be accessed by the public for model development and validation. It is possible the information could be used in the carbon markets to help evaluate how much carbon can potentially be stored in the soil in any given location based on the land use and management changes.
Dennis uses a bull probe to drive a long metal tube into the wheat field in 4 different places 100 feet from an initial sample site. The sample they are taking is from a wheat field that lies in a flood plain. This is one of several types of uses of land the study is looking at. The sampling here can take about two hours to complete if they get an initial sample that is typical of the land use. It takes longer to sample in a wooded area because they have to do most of the work by hand. Sampling in sandy soils can take longer as well because sandy soils don’t hold the shape as well and have to be measured differently.
When the tube slides out of the ground, inside is a 100 centimeter soil sample. When they look at the sample they see different colors of dirt from one end of the sample to the other. Every place the soil changes color significantly indicates a new ‘horizon,’ or layer of activity of some sort. Further down in the sample is dark brown soil that can have very small clay like structure. Most of the soil closer to the top of the sample is more reddish, like Oklahomans are used to seeing when we look out the window. Ninety percent of the carbon that exists in the soil is in the top 5 cm.
Further down in the soil, carbon is attached to other molecules which form solid particles called carbonates. After the soil has been exposed to the air the carbonates look like small white streaks of chalk. Cultivation tilling breaks through the top layer of soil and releases carbon gas into the air. If enough of the soil is disturbed the carbonates can react to oxygen and be released into the atmosphere as gas as well. That is why no-till practices are encouraged. Plants need carbon to grow. When plant material is allowed to break down naturally, the soil it creates holds that carbon where it can be useful to plants. When the material is plowed under any benefit of carbon that was held in the top layer disappears into the atmosphere.
The soil sample they take is, in most cases, about the size of a soda can. One can sized section of each horizon is placed in a plastic bag, described according to color and characteristics (worms, plant materials, sand texture, carbonate threads) and the textures the scientists can feel in it. Once they have the sample, Dennis records the descriptive information and punches it in to the computer mounted in the truck. The computer allows him to upload the data directly to the national database instead of having to intermediate on paper first and then enter it when he gets back to the office.
Christopher Hobbs, soil scientist, is visiting from the Woodward, Okla. Soil Survey Office and getting to know the process they use at the state office so that he can learn techniques that are different from the ones they use in Woodward. Hobbs notices what he thinks is a clay film. Alspach and Dennis stop, look closely at the sample and discuss the characteristics. They tell Hobbs the difference between what he thinks he sees and what they see – which is consistent with soils in the area. They give Hobbs a reference for material that describes what they are talking about. Soil can vary greatly in depth of horizons, composition and even structure in one 100 foot radius. They tell Hobbs that an important factor to take into consideration when he thinks he sees something he might not usually see is the context of the place where he is standing.
The team brings the samples back to the lab. The ‘lab’ is a small room off their office space that has a sink, a scale and about 15 buckets full of soil samples in bags that are in sets that represent the sites they tested. They weigh the sample to see how much the soil weighs with the water in it. It doesn’t take long to weigh the samples. They have to weigh them soon after they take the sample because the soil starts to condensate on the plastic storage bag and that changes the weight and texture of the soil which are important factors in the process.
They will send the samples to Temple, Texas. Where they will let the samples air dry, weigh them again and then “bake” them to dry them out completely and be able to assess at that point how much carbon is in various levels of the soil.