Soil Testing: A Guide for Farms with Diverse Vegetable Crops

Soil Testing: A Guide for Farms with Diverse Vegetable Crops

EM050E
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Douglas Collins, Small Farms Extension Specialist, Center for Sustaining Agriculture & Natural Resources, Puyallup, WA.
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.
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Soil Testing: A Management Tool

Introduction

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.

Soil-Testing Methods

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).

Consult the Natural Resources Conservation Service (NRCS) soil maps, available through the Web Soil Survey (NRCS 2011), to find information on the variation of soil types across the farm (Figure 2).

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Copyright 2012 Washington State University

Published July, 2012

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