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A Growing Concern
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Prework for Unit 4
- (3 pts) Read the 'Introduction' Soil Organic Matter and define SOM and describe its role in supporting plant growth. (A full credit answer will provide a definition and at least three important roles/functions of SOM).
- Compare the figures below showing the relative amounts of soil organic matter and the major physiographic regions in the United States.
Soil Organic Matter, from Hargrove and Luxmore, 1988, released to USDA.
Physiographic Divisions, from Fenneman and Johnson, 1948
- (3 pts) Does the amount of soil organic matter generally relate to physiographic region? (A full credit answer will describe similarities or differences between at least three regions on the maps).
- (3 pts) Based on the reading, what are the two controls on the amount of SOM? How might these controls relate to physiographic regions? (A full credit answer will discuss 2 agents that impact the amount of SOM in the soil and relate these agents to physiographic regions).
- Soils are mapped at distinct spatial scales. Soil scientists interpolate, or approximate, boundaries between soil units (pedons). The resolution of a soil study is known as the order of the soil survey. The scale of each order is given in hectares (ha). One ha is equivalent an area of 100 m X 100 m (10,000 m2). Soils are classified by identifying soil properties at depth. These are characterized examining physical (e.g. texture, color) and chemical properties (e.g. SOM) to a depth of National soils are mapped by soil scientists and provided through STATSGO and SSURGO (Soil Survey Geographic Database). STATSGO surveys represent a 1:250,000 scale. SSURGO surveys are more detailed with a scale of 1:24,000 or less. Note that STATSGO surveys represents ~2.5 soil sample sites per 10 ha and SSURGO scale represents ~2.5 soil sample sites per ha.
Order of Soil Survey, Soil Survey Staff, 1993
- (2 pts) Based on the table what planning activities/management decisions might the STATSGO and SSURGO soil surveys assist with?
(1 pt) What activities might require even more detailed sampling than available through SSURGO?
- Figure 1: Hargrove, W.W. and R.J. Luxmore. 1988. Soil organic matter content across the United States,From: A New High-Resolution National Map of Vegetation Ecoregions Produced Empirically Using Multivariate Spatial Clustering, released to the USDA, public domain.
- Figure 2: The major physiographic divisions of the 48 conterminous United States. Map based on public domain data from the USGS
- Table 1: Order of soil survey. Soil Survey Staff. 1993. Soil Survey Manual 18, US Govt, Printing Office, Washington, DC.