Marginality Principle - Principles of Sustainable Soil Management in Agroecosystems - page 20

image of the diversity of soils across a landscape, and if we walk across a field, there
are likely to be noticeable differences in color, texture, and vegetative growth. If we
were to dig a pit in these soils, there would be a vast array of differences below the
soil surface. A county soils map as shown in the following diagram demonstrates
the diversity of soils within a relatively small area of the world, and a picture of a
soil profile provides a glimpse into the complex nature of the soil system (Figures
2.1 and 2.2).
The characteristics of each soil series affect the functional uses and ecosystem ser-
vices they have the capacity to provide. A primary function is the soil's ability to grow
crops to meet human needs for food, fiber, and fuels. Another critical function is the
regulating of the ecosystem directly and indirectly via nutrient filtration, retention,
and cycling as well as carbon retention and sequestration and regulation of the water
balance—all of which affect vegetative growth and the nitrogen, carbon, and water
cycles (Collins et al. 2011). Karlen et al. (1997) elaborate on soil functions as follows: “1)
Sustaining biological activity, diversity, and productivity; 2) Regulating and partitioning
water and solute flow; 3) Filtering, buffering, degrading, immobilizing, and detoxifying
organic and inorganic materials, including industrial and municipal by-products and
atmospheric deposition; 4) Storing and cycling nutrients and other elements within the
earth's biosphere; and 5) Providing support of socioeconomic structures and protection
for archeological treasures associated with human habitation.” County soil maps are

Section: 15

1 mi.

Delaware
County

Soil texture
Clay loam
Fine sandy loam
Loam
Loamy sand
Loamy fine sand
Loamy v. fine sand

Sand
Sandy loam
Silt loam
Silty clay loam
Silty clay
Muck

Iowa

FIGURE 2.1 Map of soils for Delaware County, Iowa, showing the variation at the county
level with an inset for an individual landscape (USDA NRCS).