Soil Sampling Technique
Soil testing service in India started in 1956 with the establishment of 24 laboratories. Proper management of the important nutrients of plants present in the soil is possible through soil testing. Soil testing is very important to manage various soil problems and use of fertilizers properly. Soil testing is especially beneficial for taking remunerative crop yields and planting orchards.
Main objectives of soil testing
- To identify the soil problems like acidity, salinity, alkalinity and pollution, and suggest remedial measures.
- To find out the fertile strength of the soil and recommend the amount of fertilizers accordingly.
- To assess the benefits of the use of fertilizers and help in future planning.
- To map the fertility of the soil and on the same basis to study the changes over time in the fertility of the soil in a particular area and to guide in the distribution of fertilizers.
Method of Sampling
Survey of the field
First of all, after surveying the field, divide it according to size, slope, color and crop. After this, mark 6-8 marks in each demarcated field part by walking erratically (Fig 1). The size of each farm should not exceed one acre. If the whole field is very uniform, then only one representative sample can be made from one hectare (2.5 acres).
Selection of tools
Use khurpi or tube auger for taking samples from top surface (0-6 to 8 inches) for taking deep samples or from wet soil and screw auger for sampling from relatively hard soils. Use a spade, shovel or an auger with a long rod to dig the pit.
Sampling depth
Take surface samples (0-15 to 20 cm) from 6-8 located marks for cereals, pulses, oilseeds, sugarcane, cotton, fodder, vegetables and seasonal flowers (Fig 2). For orchards or other trees take samples from depths of 0-15, 15-30, 30-60 and 60-90 cm. To take samples from the surface, a ‘V’ shaped pit of 15 cm is made with the help of a khurpa. A thick soil layer of about 2 cm from the edges is sliced.
Sample preparation
All the samples taken from a field should be kept in a clean cloth or polythene sheet, mix it very well, spread the entire quantity in uniform thickness and divide it into four equal parts by hand. Remove the two parts that are opposite to each other and divide the remaining two into four parts by mixing them again. Keep repeating this action till about half kg soil is left (Fig 3).
Sample labeling
In the end, about half a kilogram is left. Put the soil in a clean (new) bag of cloth, paper or polythene and write the farmer’s name, address, sample number on it. Write the same details on a separate paper and keep it inside the pouch as well. If the soil is a wet, dry it in the shade and keep it in a bag and send it to the laboratory within 2-3 days.
Other necessary information
Identification mark on the samples, depth of sampling, cropping system, quantity and timing of fertilizers used, irrigation facility, drainage and the name of the desired crop, for which crop the fertilizer recommendation are required.
Precautions
Sample should be true representative of the farm. Take separate samples from parts that seem different in terms of color, slope and fertility. The tools, bags, etc., used should be absolutely clean. Do not allow the samples to come in contact with fertilizers, medicines etc. At the time of taking the sample, remove the garbage, weeds, dung etc. lying on the surface in advance. Do not take samples around manure pits under trees and about 2 meters from field meadows.
Right time of soil test-
One month before sowing or transplanting the crop, get the soil test done before the use of manure and fertilizers. If needed, samples can also be taken from the standing crop and sent for testing so that nutritional improvement can be done in the standing crop. It must be ensured that samples may not be taken from recently fertilized / irrigated fields. A gap of 7-10 days is required under such situtions.
When to get the test done again?
For ordinary crops, soil test must be done once in a year or two. In case of poor quality crop, soil testing can be done for immediate solution in the middle. Before starting the cultivation, it is necessary to test the soil and irrigation water.
Can I do a soil test myself?
Yes, it can be done with soil testing kit (Dharti ka Doctor). But it can provide only limited information or can determine some soil parameters only. Furthermore, interpretation of test results is very important and a farmer cannot perform that alone without the subject matter expert.
Irrigation water testing is also necessary.
If the irrigation water is polluted or saline then irrespective of good fertilizers used, a good crop cannot be harvested. On the other hand fertile soil becomes alkaline or gets contaminated. Alkaline and saline soil can also be irrigated with good water to achieve the best results. The water from new irrigation source like tube well should be tested to avoid any major problem in future. Irrigation water should be sampled in a clean bottle after rinsing with same water many times. Label the bottle with date, address, name etc.
Strengths of soil testing laboratory
- Well trained lab staff and qualified scientists.
- Equipped with Hi-end equipments and advanced technology.
- In-time soil sample analysis and generation of report.
- Cost-effective service to farming community and other stake holders.