Page 97 - Nutrient Management Planning Guide

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Soil Sampling

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A list of labs that analyze soil samples is included in the Appendices.

Random Composite Sampling

Random composite sampling involves taking samples in a random pattern across a field, while avoiding unusual or problem soil areas (Figure 3.3.4). This strategy is most appropriate for fields less than 30 ha (80 ac), that have been uniformly cropped in the recent past and have little natural variation. This is the most common method of sampling presently used in Alberta.

For random sampling, collect cores from 15 to 20 sites and separate each core by depth (see General Soil Sampling Guidelines) to obtain representative bulk samples for each depth.

Figure 3.3.4 Random Composite Sampling Pattern.

Directed Random Sampling

Directed or managed random sampling is a modified version of a random sampling strategy (Figure 3.3.5). This pattern is suited to fields or areas where it is difficult to identify a single dominant area that would represent most of the field.

Sub-divide the field into management zones based on unique characteristics. For instance, if there are noticeable differences in yield throughout a field, management zones might be comprised of below- average, average and above-average yielding areas. Take 15 to 20 cores (see General Soil Sampling Guidelines) randomly from each management zone. A single field may require several bulk samples depending on the number of management zones.

This strategy might also be appropriate for areas with more than one soil type, fields with hummocky (rolling) landforms, and fields under strip-crop management.

Figure 3.3.5 Directed Random Sampling Pattern

Benchmark Sampling

Benchmark sampling involves selecting a small (30 m by 30 m) representative site on a field (Figure 3.3.6). This site is used as a guide for fertilizing that entire field. Select probe sampling sites in a grid pattern within the benchmark area and prepare a composite sample for each soil depth. Sampling from the same small area each year reduces sampling variability and better reflects changes in soil nutrient level from year to year. Benchmark sampling sites should be marked with a GPS or by other means.

Figure 3.3.6 Benchmark Sampling Pattern