Life in the Soil BusinessWritten by Cameron Clark
By Cameron Clark, supervisory soil scientist in the Saratoga Soil Survey office, USDA Natural Resources Conservation Service
At 5:30 on a typical morning last summer the crew starts to filter in. It’s been a hot one, not record heat, mind you, but 85 degrees is still plenty warm when you are working outside all day. Between the dirt stains, the sweat, the smeared sunscreen, the bug-spray cologne and the wind-styled hair, we are all a sight to behold. For scientists, it is a far cry from a laboratory and a clean white coat, but most of us never wanted that, anyway. In Wyoming it is a blessing to work outdoors in the summer and be a soil scientist.
This summer’s crew consisted of two Saratoga-based soil scientists and two more on loan from other states, along with a student intern. Emiliano and I work full-time out of the Saratoga office. Laura came to us from the Kansas NRCS. Andrew came from the NRCS in Florida. Joxelle, our intern, came all the way from Puerto Rico! The latter three tended to roll their eyes whenever I joked about our intense heat, which was nothing compared to where they came from. Perhaps they should pay us for the privilege to map with us during our beautiful summers.
Laura maps with a one-ton truck equipped with a special Giddings probe, which allows her to drill soil cores using gas power rather than shoulder power. The power auger lets her sample more quickly and with less strain than a shovel would. On a good day, she can drill, analyze and record soil properties from 10 separate locations. That’s a big help because in Carbon County our field season is short and we need to cover about a thousand acres each day.
Andrew and the rest of us use more primitive tools. We specialize in using shovel (sharpshooter and spade) and hand auger. The hydraulic “bull” probes that make our trucks look unique work in certain areas and at certain times of the year but are hit or miss on dry and rocky soils. On those soils, the probe goes in a few inches, stops and then proceeds to jack the truck up. What can you do but break out the hand tools?
So, what exactly is it that we are trying to accomplish by looking at the soils? The short answer is that we are working on the Carbon County Soil Survey. That may or may not mean much to you unless you have farmed or ranched or otherwise stirred the soil in one of the nearly 3,000 counties that already have a published soil survey. It’s that thick white book with aerial photos in the back and lots of soils information in the front.
The soil survey is a detailed review of the soil types and associated plant communities found in a particular county. The scale and level of detail will vary from survey to survey, depending on the intensity of land use and the resources available to conduct the survey. On Wyoming rangeland, we typically map at what we call “Order III” level.
At this level, we delineate areas of similar soil/vegetation/landform characteristics ranging from as small as 40 acres to as large as several thousand acres. These delineations are drawn as polygons on aerial photographs at the same scale as a topographic map (1:24,000). The land user can locate their property on the map, find the map unit number(s) that cover the area of interest and then look up the soil properties, vegetation communities, production estimates and engineering properties associated with those map units.
A typical map unit will consist of a “complex” or blend of two or three different soil series along with a few minor anomalies. This complex will occur on certain landforms and will have specific native vegetation communities (or ecosites) associated with them.
Additionally, each map unit will be used on numerous polygons with similar characteristics throughout the survey area. Otherwise, we would end up with well over 20,000 map units and a survey the size of bookshelf.
Soils are a dynamic entity, often morphing into one another, rather than having precise characteristics with sharp boundaries. Picture two different colored cans of paint (blue and green) spilling on the floor and running into each other. You will have a blue area and a green area, but in between will be shades of aqua or turquoise or blue-green. It is hard to say exactly where the blue stops and the green starts.
Thus a soil survey map provides a good indication of the performance and management considerations at the scale of a field or a ranch but not an exact prediction of what you will find at any one spot. To stretch the color analogy a bit, if your 80-acre field falls within the “Blue-Green complex” map unit, you can expect to find blue and green tones, not reds, yellows or purples. However if you look at any one spot, it might be a blue-green shade, rather than a pure color.
There are more precise levels of mapping soils, such as Order I or Order II surveys, but they take longer and cost more to complete. In the end you want a level of detail appropriate for the level of management. For example, if you are estimating stocking rates on a section of rangeland with a single perimeter fence, you hope to arrive at a single value for the entire area. It would be cumbersome to average the values for 50 or 100 different polygons to get the carrying capacity for the section. On the other hand, if it is productive ground and you plan on splitting it up into five-acre paddocks for rotational grazing, a closer investigation would be profitable so that you could estimate the performance of each individual paddock.
This survey has been a long time coming. Parts of Carbon County have been mapped in the past by a variety of entities, including the BLM, the NRCS, the National Forest Service and private contractors but the data has not been correlated and significant areas were left unmapped. This is common with many of the sparsely populated counties in the West, where completion was not given high priority until recently. Here we resumed mapping in 2007 and should have the last unmapped areas completed next summer. From there we will correlate the data and begin proofing the earlier surveys, in order to produce a consistent soils map across the entire county.
Right now, summer is over, the office is quieter and the leaves are turning. We will still map until muddy roads or frozen soils keep us out sometime in November. As always, there will be plenty of data work to do in the long winter season. At least we are safe from any more heat waves!