Learn to estimate soil texture-by-feel, with the aid of a new computer program

Healthy soils and their efficient management are key to any society's long-term survival. Soils cycle carbon, nitrogen, nutrients and help produce energy in the form of biomass. But there is only a handful of soil scientists around who can help us make the most of this important natural resource. In fact, a lot damage can be done to soils by non-experts working them on a daily basis. And many land-use decisions would be changed if knowledge about soils was put into practise more often. Some basic soil science techniques and skills can be learned by anyone willing to put in some effort, though. An interesting article in the Journal of Natural Resources and Life Sciences Education explains how you can learn to estimate soil texture-by-feel. A new computer program will help you acquire the necessary skills.

Many soil properties depend largely on soil texture, and texture impacts most land-use decisions. Soil texture strongly influences the nutrient holding ability of a soil, the amount of water the soil can store, the amount of this water that is available to plants, how fast water moves through the soil, the effectiveness of soil in cleaning up waste water, the shrink-swell nature of soil, and many other properties.

D.P. Franzmeier and P.R. Owens of Purdue University write about how soil texture can be determined by using the texture-by-feel method.

Soil texture can be determined in the field using the texture-by-feel method or the samples may be sent to a laboratory for particle-size analysis. The laboratory option is more accurate, but it is more expensive and slower because it can take weeks or months to get the results. - P. R. Owens, lead author

The field method is less accurate than the lab method, but much faster. Soil scientists use texture-by-feel to provide quick reliable estimates of soil texture in the field. This method is used by researchers where numerous samples are required to capture variability, developing soil surveys, and consultants for sizing on-site wastewater disposal systems.

When the texture-by-feel method is used, the estimator takes a soil sample about the size of a marble up to the size of a golf ball. The person estimates the texture by rolling, squeezing, flattening, and pressing the soil between his fingers. Each person develops his own technique for estimating texture. The important point is that while learning the technique, he must always compare his results with laboratory data.

A computer program assesses student performance for estimating particle-size distribution and soil texture. If the estimate coincides exactly with laboratory results, the score is 100%. If the estimate and laboratory results are as far apart as possible, at opposite corners of the texture triangle (click to enlarge), the score is zero:
energy :: sustainability :: biomass :: agriculture :: soil :: water :: nutrients :: soil texture :: land-use ::

Students appreciate the fairness of grading. Also, we can use the method to let a student or professional know if their estimates are consistently above or below the laboratory values, which helps them calibrate their fingers. - Owens

Franzmeier adds that they have used this tool to help registered soil scientists improve their field skills and that they seem to enjoy the challenge.

The program is available on the IRSS website: http://www.isco.purdue.edu/irss/. Select Resources, then Texture Estimate Calculator.


Today's educators are looking to the Journal of Natural Resources and Life Sciences Education for the latest teaching techniques in the life sciences, natural resources, and agriculture. The journal is continuously updated online during the year and one hard copy is published in December by the American Society of Agronomy.

The Soil Science Society of America (SSSA) is a progressive, international scientific society that fosters the transfer of knowledge and practices to sustain global soils. Based in Madison, WI, and founded in 1936, SSSA is the professional home for 6,000+ members dedicated to advancing the field of soil science. It provides information about soils in relation to crop production, environmental quality, ecosystem sustainability, bioremediation, waste management, recycling, and wise land use.

SSSA supports its members by providing quality research-based publications, educational programs, certifications, and science policy initiatives via a Washington, DC, office.

SSSA is the founding sponsor of an approximately 5,000-square foot exhibition, Dig It! The Secrets of Soil, which opened on July 19, 2008 at the Smithsonian's Natural History Museum in Washington, DC.


Chart: soils are classified by analysing their texture, which depends on the amount of clay, sand and silt they contain. Pictured here is the U.S. classification system. There are other systems with some important differences, but the classification principles and the techniques to measure soil texture are the same. Credit: USDA.

References:
D. P. Franzmeier and P. R. Owens, "Soil Texture Estimates: A Tool to Compare Texture-by-Feel and Lab Data" [*.pdf], Journal of Natural Resources and Life Sciences Education, N° 37 (2008).

Soil Science Society of America.