Soil Testing: A Management Tool
Soil analysis can guide farmers and gardeners in making soil amendment and soil management decisions. Making soil sampling an annual event will allow for tracking management practices and influencing future soil amendment decisions. This fact sheet presents a comprehensive, yet affordable, procedure for implementing an annual soil-testing program for farms with diverse vegetable crops. The reader will learn when to sample, where to sample, how to take a sample, and finally how to use sample results to improve farm management.
The Importance of Soil Testing
Soil testing results can indicate nutrient deficiencies or excesses, nutrient-holding capacity, organic matter content, and soil alkalinity or acidity. The value and reliability of this information depends on how a sample is taken and what area of the farm the sample represents. Trying to represent too large an area with one sample is counterproductive, especially if crops with different nutrient requirements will be planted within the same area.
If soil testing is done carefully and consistently over several years, soil test data can be used to determine the timing and amounts of fertilizer, compost, manure, lime, or other amendments aimed at improving crop response. Soil testing can also be used to evaluate soil improvement strategies, such as cover cropping. Finally, a soil test can be used to evaluate fertilizer efficiency.
The Challenges to Implementing a Soil-Testing Program
The variability in soil properties across the farm creates a challenge for farmers who want to describe their farm’s soil properties. Soils vary because of geological changes over time and because of landscape position, vegetation, soil organisms, and past management. In addition to the differences in soil properties, the diversity of farm plantings also makes it difficult to describe and manage soil. Each contiguous area that is planted, fertilized, and otherwise managed together can be seen as a management zone. Farms with a wide variety of crops tend to have many management zones.
Divide The Farm by Landscape Position, Soil Type, and Management History
Soil properties, such as texture, drainage, and topography, will vary across the farm and even within a field (Collins et al. 2011). For example, soil in one field may be “heavier” at the western end, indicating greater clay content toward the west and less toward the east. In another example, low areas in a field may drain poorly and produce less than other areas. Management history also has an effect. For instance, an area formerly used as pasture or a feedlot will likely have different properties and soil management needs than the rest of the field. Sometimes, an area may produce poorly, although no cause is apparent. Soil analysis may reveal the reason for this poor production.
A practical first step in soil testing is to create a detailed map of the farm that includes landscape position (including boundaries and elevations), soil type, and management history. To do this, begin with an aerial photograph of the farm, and then add further details to it. If necessary, use a topographical map to delineate hilltops, slopes, bottom lands, and other landscape features (Figure 1) (U.S. Geological Survey 2011).