Landscape and field-level evaluations: To understand the state of soil in a field or set of fields, we may want to start with some straightforward evaluations of its characteristics in the landscape, such as:
- Is the soil deep or shallow? Digging a hole somewhat deeper than the soil is plowed or hoed can reveal if there is rock or other parent material close to the surface, or whether the soil is deep. Farmers may already have knowledge and experience in characterizing their own fields and the differences in soil depth as a source of variability in productivity, so this topic should be pursued in conversations with farmers about a given field.
- What is the long-term history of the soil? Was it just converted from grassland or forest, in which case it may be quite fertile? Or has it been cropped continuously for over fifty years, in which case the fertility levels may depend on the management during that time.
- What is the recent management history of the soil? Typically, asking about how the previous three years management was conducted may help to understand the typical practices without over-taxing the ability of farmers to remember this management. Was it cropped continuously twice a year with a cereal, and thus hoed or plowed constantly to plant and or manage weeds? Or perhaps there was a more diverse rotation, or several years of fallow or a perennial forage crop? Was only fertilizer added, or manure, or nothing? This approach is expanded below using the idea of a nutrient balance.
- Geographic factors such as slope, elevation, and aspect (the direction that the slope faces) can be helpful in interpreting the more detailed characterization of the soil below. Is it high up in the local topography, and thus especially shallow, or perhaps part of a stable, deep soil on a plateau? Is it in a depression and prone to wet conditions, but high in organic matter? This is an area where farmers may be keenly aware of how geographic position affects the soil’s behavior.
- Stoniness. Often a sample taken from the site will have stones removed. However, especially for very stony soils, stoniness can have a big impact, for example, reducing water holding capacity and the total stock of organic matter a soil can hold, but sometimes increasing a soil’s resistance to water and wind erosion.
S. Vanek