Northeast Region Certified Crop Adviser (NRCCA) Study Resources

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In This Section

• Introduction
• PO 15 Fertilizer analysis conversions
• PO 16 Soil sampling
• PO 17 Variability in soil test results
• PO 18 Fertilizer recommendations
• PO 19 Soil test interpretation
• PO 20 Soil sampling strategies
• PO 21 Pre-sidedress nitrogen test
• PO 22 Plant tissue analysis
• PO 23 Plant nutrient level
• Summary

Competency Area 3: Soil Testing and Plant Tissue Analysis

PO 16. Recognize how the following affect soil sampling methods.

1. Method of previous fertilizer application
2. Tillage system
3. Nutrient stratification
4. Within-field soil and crop variability

Anything that induces variability in the field will increase the amount of sub-samples that must be taken. This reduces the likelihood that the results of a given composite sample will be skewed by a sub-sample taken from a non-representative area of the field.

The method of previous fertilizer application can change the nutrient profile of a field.  Banding fertilizer and manure spreading are known to increase spatial variability within a field. As not all areas receive the same amount of fertilizer or manure, the nutrient availability differs throughout the field. The more variability there is, the more sub-samples should be taken. If the location of the fertilizer bands is known, samples should NOT be taken directly from the band.

Tillage systems impact the distribution of nutrients over a field and over depth. Deep tillage, zone tillage, etc. will differ in thoroughness of mixing and thus in nutrient variability. The more tillage there is, the less variable the nutrient distribution, and the minimum recommended sub-sampling guidelines can be followed.

Nutrient stratification, or irregularities in where nutrients are located throughout the soil profile, is influenced primarily by tillage. In no-till situations, nutrient stratification is usually greater than for conventionally tilled fields. Consistent sampling to the recommended depth is critical.  For soil pH in no-till systems, two soil samples will be needed: 0-1 inch (for seeding), and 0-6 inches. If the surface sample pH is lower than 6, a limestone application should be made, even if the deeper sample does not call for liming.

Within-field soil and crop variability encompasses other uncontrollable differences within a field. Thus, there are a minimum recommended number of sub-samples to be taken, and recommendations on the areas those samples should be taken from.

• Take 2-3 sub-samples per acre and then combine. One composite sample should not represent more than 10 acres, unless past sampling shows minimal differences.
• The area to be sampled should be fairly uniform: similar soil properties and past management.
• If there are known significant differences within the area (such as old fence rows, manure or lime stockpile areas, wet spots, etc), then a modified sampling strategy should be followed.
• If the areas are too small to manage separately, avoid taking any sub-samples from these areas.
• If the areas are large enough for the farmer to practically manage them separately, take separate samples from these areas.