May 18th, 2005 - Spring Celebration!

Daffodils2

Don Ross
Research Associate Professor,
Department of Plant & Soil Science
University of Vermont, gave a presentation on
  "A Brief History of Soil Chemistry and Soil Testing"

McCardell Bicentennial Hall
Middlebury College
On May 18th Don Ross, Research Associate Professor, Department of Plant & Soil Science, University of Vermont gave us “a brief history of soil chemistry and soil testing”. This well attended event was hosted by the Chemistry Department at Middlebury College, who made us very welcome.

The text-book definition of soil is “the unconsolidated mineral or organic material on the immediate surface of the earth that serves as a natural medium for growth of plants” – but soil is also a complex biological and chemical entity including a host of microscopic animals. There are a range of different soil types in the USA. For example, the Mollisols of the Great Planes have a deep, dark, nutrient rich surface layer. The red-colored clay-enrighed Ultisols found in the southeast are much lower in nutrients. The colorful Spodosols (Don’s favorite soils) are quite common in Vermont, they have a light grey surface, above a redish, aluminium and/or iron enriched layer. They commonly grow coniferous trees. Also found here are the Tunbridge Soils (in fact this is the Vermont State Soil!), these are loamy, well drained soils, with a very dark brown surface above a light grey subsurface. They are particularly good at growing white ash, beech, birch, hemlock and red spruce, and of course, maple trees.

Tunbridge soil profile
Tunbridge Soil - the Vermont State Soil!
  • Surface layer: very dark brown, partially decomposed organic material
  • Subsurface layer: gray fine sandy loam
  • Subsoil - upper: dark brown fine sandy loam
  • Subsoil - lower: brown channery fine sandy loam
  • Bedrock: schist

Typical Landscape for Tunbridge - Vermont State Soil

Fact sheet: ftp://ftp-fc.sc.egov.usda.gov/NSSC/StateSoil_Profiles/vt_soil.pdf
Soil science (and soil chemistry) has a long history. Early researchers such as Leonardo da Vinci, J. B. van Helmont and Robert Boyle observed that, if watered, a plant will grow in a pot without significantly lessening the weight of the soil (for example, when Boyles willow tree grew to 200lbs, only two ounces of soil were consumed). They concluded that plants were made entirely from water! Later it was realized that plants absorbed CO2 from the atmosphere (in fact, all plant carbon is derived from the air); and John Woodwards observation that plants grew better when watered with London Thames river water was the first suggestion that dissolved solids and organic matter were also important. Much of the work in the early and mid 20th Century focused on the structures and ion-exchange behavior of the inorganic clays. More recently the focus has moved to the organic matter, and the analysis of the surfaces of inorganic particles using new techniques such as EXAFS, XANES and atomic force microscopy. Don’s group has been involved the detailed analysis of soils from many parts of Vermont. They have studied the effects of nitrogen (from acid rain) on forest soils and bog ecosystems, and the interaction between soil manganese oxides and heavy metals. For example, old paint from Vermont buildings can create significant local lead contamination (there are examples of this on the UVM campus). The group has been investigating methods for dealing with this problem. They have also studied the dynamic behavior of this living system. As soon as you remove soil from its natural environment it starts to change – posing a challenge for soil testing, particularly testing for nitrogen content.

The pH of garden soil (an important thing to know) may be determined by diluting soil 1:1 or 1:2 in distilled water and measuring with a pH meter; although the addition of 0.1 M KCl slightly lowers the original pH, the KCl assists in stabilizing pH measurements. Most analyses of soil focus on the N, K, and P content. These are required nutrients. P and K are found in most modern day fertilizers – the amounts reported on the packet are actually the quantities of the oxides, P2O5 and K20. Soil scientists in the 1700s believed that the purest form of elements were the oxides – as Don commented, some things take a long time to change!


Bio:  Don is a member of the ACS Green Mountain Local Section. He completed both his M.S. (1980) and PhD (1990) under Rich Bartlett, Emeritus Professor of Soil Chemistry.  The latter was done while running the UVM soil testing lab.  While he was actually writing this bio for us he recieved a phone call informing him that he has been promoted to Research Associate Professor. Congratulations Don!