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The main objective of soil sampling is to collect a small amount of soil weighing about one kilogram (kg), that is a representative of a large land area. Since only a small amount of soil sample is to be used during the analysis, the accuracy of the results heavily depends on the correctness of the soil sampling procedure performed.
Therefore, the following steps should be strictly observed and carried out:
1. Prepare the required materials: shovel or spade, knife or trowel, a small pail, plastic bags and labelling materials.
2. Make a map of the farm indicating the Sampling Area (SA). Divide the farm into specific sampling areas. Each sampling area should be more or less uniform in cropping history, past lime and fertilizer treatments, slope, degree of erosion, soil texture, color and should not be more than five (5) hectares.
3. In collecting spot soil samples from each identified sampling area, dig at least 10 pits and collect spot soil samples in each pit. The number of spot soil samples (marked X in the illustration) depends on the size of the land area. A spot soil sample is taken in the following manner:
a. Before digging the pit, clear the soil surface from stones, litter, and vegetation.
b. Using a spade or shovel, dig a pit to a depth of 30 centimeters (cm).
4. From one vertical side of the pit, take a slice of soil, two (2) cm thick, with a single downward thrust of the spade. Using a knife or a trowel, trim the slice of soil on both sides to a bar 10 cm wide. This bar of soil, which represents one spot soil sample, is then placed in a pail. Cover the pit and move to another spot.
If a subsoil sample is needed, take a bar of soil from the succeeding 30 to 60 cm depth and follow the previously mentioned steps. The subsoil sample should be placed in a separate container.
5. Prepare the Composite Soil Sample. After collecting all the spot soil samples from the entire sampling area, remove stones and leaves from the soil. Pulverize, mix thoroughly, and perform quartering.
The Quartering Method
Divide the collected soil sample into four quarters, remove the opposite quarters and retain the other opposite quarters. Mix well. Repeat the process four (4) times until you obtain one (1) kg of composite soil sample.
6. Place the soil sample in a clean plastic bag and label it properly indicating the following information: Name and address of the farm owner, farm location (include geographical coordinates, if possible), crops planted, date of soil sampling, and sampling area (e.g. 1 ha)
7. The composite soil sample is now ready for analysis using the Soil Test Kit (STK) or you can also send it to a Soil Testing Laboratory for a quantitative soil analysis.
** With permission from the DA-Bureau of Soils and Water Management, selected materials have been reproduced on this site to support information sharing on soil and water management.
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