ACCURATE SOIL SAMPLING

Step by Step on on how to collect soil samples for testing
ACCURATE SOIL SAMPLING

Accurate sampling is absolutely critical to a successful soil management plan as all recommendations are based on the samples submitted to labs.

SELECTING SAMPLE AREAS
The actual size of the sample area is determined by certain factors. Areas that differ in any of the following must be sampled separately:

Soil type, previous cropping, previous lime or fertilizer applications, slope, drainage

Where very large areas of land are uniform, divide the land into areas that would be treated as a unit (i.e. one field), and sample these areas individually.

One sample should not represent more than one field, as individual fields will have had different treatments in the past. Large fields can be divided for sampling purposes into two or three smaller sections

Sampling depth Depth of sampling is critical because tillage and nutrient mobility in the soil can influence nutrient levels in different soil zones. Sampling depth depends on the crop, cultural practices, tillage depth and the nutrients to be analyzed.

Plant roots, biological activity and nutrient levels occur mainly in the surface layers (0-25 cm) hence most of the soil samples are collected within this layer. For tree crops, samples from 30 – 50 cm can also be collected.

Sampling Procedure One sample should consist of between 20 - 30 cores taken from the set area. It is recommended that the cores be taken from the area in a zigzag pattern as shown in the field figure 2

ONCE IN THE FIELD CARRY OUT SAMPLING AS FOLLOWS:

1) Divide your field into areas which have the same soil type, color, slope, fertilizer and crop history Figure 3 ( source Crop Nutrition Laboratories)

2) Scrape away surface litter and crop residues and sample the whole core from the true soil surface to 25 cm depth

3) Take between 20-30 cores from each uniform soil area. Place each core in a bucket and mix them thoroughly once you have taken all the cores.

4) Fill the soil sample bag half full (500g) from this mixed representative sample.

5) Several different tools such as a soil sampling tube, soil auger, or spade may be used in taking soil samples. Label the bag carefully with you company name, farm name, field name, sample depth and crop to be grown.

6) Avoid taking samples from areas such as lime piles, fertilizer spills, gate areas, livestock congregation areas, poorly drained areas, dead furrows, fertilizer bands, old fence rows, or any other unusual areas.

7) Do not use galvanized, soft steel or brass equipment if trace metal analyses are desired.

Sample handling and dispatch to lab If possible soil samples that are moist should be air dried on site away from dust contamination and not in direct sunlight.