Soil Sampling Guide for Crops Matt Yost, Grant Cardon, Megan Baker, Jody Gale, Earl Creech, Mike Pace, Kalen Taylor, Cody Zesiger, Tiffany Evans, and Rhonda Miller
Why Sample? Why conduct soil sampling for crops? The answer is simple and intuitive for most involved in agriculture. Regular soil sampling, testing, and associated guidance on fertilization and soil amendments help develop and maintain more productive and healthy soils. Soil tests can indicate whether plant nutrients are deficient and, if so, what amounts are needed for optimum growth. Soil testing is also a useful diagnostic tool to identify problems related to excessive levels of nutrients and salts, sodicity, high pH, low organic matter, and poor drainage. Soil is one key factor that determines crop productivity levels. Proper soil testing often helps optimize investments in fertilizer and amendments and influences several other agricultural inputs.
What to Sample? Many soil properties can be measured, with some being more practical than others for making crop management decisions. Soil properties can be broken into three broad categories: chemical, physical, and biological. Each category includes many properties, with some properties having multiple procedures for testing. Below are some of the most common properties measured for agricultural applications: •
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Chemical – for fertilizer and amendment management (examples include macro and micronutrients, pH, salinity, and sodium absorption ratio). Macronutrients generally include nitrogen, phosphorus, potassium, sulfur, calcium, and magnesium. Micronutrients include zinc, boron, manganese, copper, iron, and chlorine. Physical – for soil health and irrigation management (examples include texture, bulk density, available water holding capacity, soil surface hardness, and aggregate stability). Biological – for soil health and fertilizer/amendment management (examples include organic matter, soil protein, soil respiration, Figure 1. Soil Sampling Near active C, potentially mineralizable nitrogen, and phospholipid Logan, UT fatty acid [PLFA]).
More detailed descriptions of each of these properties can be found in the fact sheet, Measuring and Building Soil Health (Yost et al., 2019) or the Natural Resources Conservation Service publication Recommended Soil Health Indicators and Associated Laboratory Procedures (Stott, 2019).