The purpose of soil testing is to identify the soil fertility that the plants or crop, in a given area will experience. The soil area and volume could be a large field, a small garden, or simply the root zone of a single tree or shrub. The most difficult step in soil testing is accurately representing the desired area of soil. A laboratory cannot improve the accuracy of a sample that does not represent the area.
In most soils, it takes more than one year to make significant changes to the soil test levels. As the soil improves with better fertility programs, subsequent crops or plant growth should show increasing rates of improvement. Soils are formed over thousands of years, and are not easily changed in a short time.
For soil sampling, different items are considered for taking samples which include:
Sampling Methods
For soil sampling, different sampling techniques is applied which include cluster, base soil, and core and grab sampling which are introduced in detail.   
Sampling Instruments
For sampling each environment, different tools and instruments are required are completely introduced. In addition, the other information such as size and type of materials is available.

The goals of your soil sampling plan should be to:
1. Goal for soil type and moisture availability
2. Identify manageable sized fields with similar characteristics.
3. Accurately and cost-effectively determine the nutrient status of those fields.
4. Highly variable soil fertility levels across a field can make it difficult to collect a good soil sample. With planning, representative soil samples can be obtained from your pasture. Careful, comprehensive soil sampling pays dividends in smarter management decisions and efficient use of fertilizer nutrients
5. management and control of wind and water erosion
6. the soil acidity (pH)

Soil sampling methodology
Getting a good sample
Soil sampling is the most important step in soil testing. The sample you take should be representative of the field. A well-taken sample will result in appropriate fertilizer and lime recommendations. A poorly taken sample will result in under- or over-application of nutrients and limestone.
The area to be sampled should not be greater than 20 acres in size. Sample areas may be delineated by soil color, soil texture, slope, cropping history, limestone, fertilizer and manure applications, and old farmsteads or feedlots. Many farmers are beginning to sample their fields more intensively and develop soil fertility maps.
Soil samples should be taken to a depth of 6 to 7 inches. Traveling in a zigzag pattern, take 15 to 20 soil cores for each sample.  Mix these cores together in a plastic bucket and either fill a soil sample box with the soil or bring about 1 pint of the sample to your local University Extension center. An information sheet will need to be filled out on each soil sample. Come prepared with the following information: test desired (regular, zinc, sulfur, micronutrients, pHsalt, pHwater), last crop grown, cropping plans and yield goals. For agronomic purposes, fields should be retested every 3 to 4 years to monitor changes in soil fertility.
Yield goal is an important part of fertilizer recommendations for nitrogen, phosphorus and potassium. The yield goal determines the nutrient demand of the crop within the nutrient recommendation system. The magnitude of the yield goal has a large effect on the amount of fertilizer recommended, particularly for nitrogen recommendations.
The purpose of this section is to introduce methods, instruments and tools used for soil sampling.