Soil Analyses

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Soil Analyses
College of Agriculture and Life Sciences
Revised 10/11
AZ1412
This publication provides information on techniques of soil sampling and analysis for horticulture and agriculture. Soils are sampled to determine physical conditions, fertility (nutrient) status, and chemical properties that affect their suitability as plant growing media. Through a combination of field and greenhouse research, analytical methods have been developed which provide quantitative estimates of plant-available nutrients. Field research determines the optimum soil test levels for various nutrients for specific soil and crop combinations. Optimum fertilizer practices can be determined by knowing the optimum test level of each nutrient for a specific crop and soil, and by knowing how much fertilizer is required to change soil test values. Soil testing is comprised of four steps:

▪ Collection of a representative soil sample
▪ Laboratory analyses of the soil sample
▪ Interpretation of analytical results
▪ Management recommendations based on interpreted analytical results This publication focuses on the first two of these steps. The reader should gain an understanding of the proper methods for collecting soil samples, and of the potentials and limitations of soil testing. Soil Sampling

The first and most critical step in soil testing is collecting a soil sample. A soil analysis can only be as good as the sample sent to the laboratory. It is important to recognize what a tiny portion of a field is actually analyzed in the laboratory. For example, a 1 lb soil sample collected from a 5 acre field represents just 1/10,000,000 of the field! Therefore, it is vital that the soil sample be representative of the entire field. The most common and economical method for sampling an area is composite sampling, where sub-samples are collected from randomly selected locations in a field, and the sub-samples are composited for analysis. The analytical results from composite sampling...
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