UNIT NAME: SOIL SCIENCE PRINCIPLES

TOPIC: SOIL SAMPLING

Definition of Terms

Sample- a small quantity or part of something taken to be used as evidence of the quality of the whole.

Soil sampling- is the random collection of soil samples from the land for laboratory testing and analysis.

Soil testing-the practice of examining the soil t be able to determine its fertility status.

Sample areas- specific areas marked out for collecting the soil samples.

Sampling depth- the vertical distance downwards from the soil surface in which a soil sample is collected.

Nursery bed- a special piece of land prepared for raising seedlings which are later transferred into the main field.

Procedure- a particular method for performing a task.

Logbook- a book in which soil farm events and practicals are recorded.

Soil Sampling Procedure

Soil sampling refers to the process of taking a small sample of soil, which is then sent to a laboratory to determine the soil nutrient content. Soil sampling and testing is essential for building sustainable soil fertility and fertilizer management programs for your farm, to increase your crop yields and reduce your input costs. Accurate sampling is absolutely critical to a successful soil management plan as all recommendations are based on the samples submitted to the lab.

Soil sampling methods

There are three major methods of soil sampling namely:

Ø  Random method

Ø  Zigzag method

Ø  Traverse method.

How to take a soil sample in a field crop

Equipment/materials Needed

1. Sample bags (khaki)
2. Soil Auger or shovel
3. Bucket
4. Sample submission forms
5. Field logbook 
6. Labels or marker pens

Selecting Sample Areas

When you are selecting areas to sample you must remember that there is no set size but it is recommended to take more samples for areas greater than 20 Ha. The actual size of the sample area is determined by certain factors. Areas that differ in any of the following should be sampled separately: 

a)      Soil type.

b)      Soil colour.

c)      Previous cropping history.

d)     Previous lime or fertilizer applications.

e)      Slope.

f)       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 represent one field, as individual fields will have had different treatments in the past. As mentioned, it is recommended that one soil sample should not represent more than 20 hectares regardless of apparent field uniformity. This is because non-uniformity is usually difficult to assess over

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:

1. Crop.
2. Cultural practices.
3. Tillage depth.
4. Nutrients to be analyzed.

Plant roots, biological activity and nutrient levels occur mainly in the top soil (0-25 cm) hence most of the soil samples are collected within this layer. For tree crops and other deep rooted crops, samples from the sub soil (25–50 cm) should also be collected.

Sampling Procedure

Procedure

One sample should consist of about 20 cores taken from the set area.

1.      It is recommended that the cores be taken from the area in a zigzag pattern as shown below:

2. Put the soil cores in a bucket and mix thoroughly. 

3. Label the sample bag carefully with your company name, farm name, field name, sample depth and date, and crop to be grown. Fill the soil bag half full (500g), from this mixed representative sample.

4. Different tools such as a soil sampling tube, soil auger, or spade may be used to take soil samples. Do not use galvanized, soft steel or brass equipment if analysis for trace metal analyses is desired. Clean all tools between sampling.

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

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

After collecting the samples should be packed in sampling khaki bags with the following information given:

v  Name and address of the farmer or locality of the farm

v  History of land use/ cultivated crops

v  History of fertilizer or manure use

v  Crop to be grown

v  Special features on the land.

Soil testing

Soil is tested for the following reasons:

Ø  To determine fertility status of the soil

Ø  To find out the PH of the soil

Ø  To find out the amount and type of fertilizer or liming material needed

Ø  To determine a suitable crop for the land

Ø  To give projections of the yield expected based on the recommendations.