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Soil Sampling

Important Terms

Table 3.3.1 Key Terms and Definitions

Term Definition

Fallow

The practice of leaving the land uncropped and weed free by means of tillage or chemical vegetation control.

Immobile Nutrients Nutrients having a very low mobility due to low solubility. Legume

A plant of the botanical family Leguminosae (e.g., pea), which has the ability to fix atmospheric nitrogen through a symbiotic association with Rhizobium . Nutrient Transformation

The process where by a nutrient is changed from one form to another form (e.g., NH

4

+ changed to NH

3

). Remote Sensed Image

The term generally refers to images (e.g., photos, color infrared, maps) that are generated through the use of instruments aboard aircraft and spacecraft.

Residue or Crop Residue The portion of plant material remaining in the field after harvest (e.g., straw, roots, stems)

Proper soil sampling is required for accurate soil analyses and reliable nutrient recommendations. Soil analysis provides a “snapshot” of nutrient reserves in the soil, and can be a guide for nutrient applications. Soil samples submitted for analysis should be representative of the field. Obtaining representative samples can be difficult because of soil variability. To get a representative soil sample consider:

Timing of sampling • Sampling tools • Sampling depth • Sampling frequency • Sampling strategy or parts of fields to sample • Appropriate handling of samples •

Timing of Sampling

The ideal time to assess soil nutrient status is just before a crop is actively growing and needs soil nutrients. Use the following guidelines to select an appropriate time to sample:

For spring-sown annual crops collect samples early •

in spring as soon as the soil has thawed or in the fall once soil temperatures have dropped below 5 to 7 °C (e.g., late October).

For establishing perennial or fall-sown crops, •

collect samples about a week prior to seeding and fertilizing. In fields with established perennials, sample •

annually in the spring before active growth begins.

Fall Sampling

If spring sampling is not possible, sample in the previous fall after soil temperatures drop below 5 to 7°C. When soils cool to this range, soil microbial processes that affect crop available nutrients (e.g., mineralization) slow down. Consequently, further changes in plant available nutrient levels are minor. Fall sampling allows time to properly process samples, and get test results and nutrient recommendations to develop nutrient application strategies.

In most areas of Alberta, it is generally safe to begin fall sampling by the middle of October. Fall sampling in forage fields can begin anytime after September 1 st .