Soil Sampling And Its Importance

Maintaining of soil health is very important for sustainable and profitable agriculture. Soils are heterogeneous in nature. Soils need to be analyzed for various Physical, Chemical and biological property to maintain the fertility. The best method to study the soil is by soil sampling and nutrient analysis.

Soil test is a process by which elements (phosphorus, potassium, calcium, magnesium, sodium, sulfur, manganese, iron, copper and zinc) are chemically removed from the soil and measured for their “plant available” content within the sample. The quantity of available nutrients in the sample determines the amount of fertilizer need to be recommended for the ensuing crop. Soil test also measures soil pH, humic matter and exchangeable acidity.


  • Analysis indicates whether lime need to be applied and if so, what quantity needs to be applied?
  • Tells us the right quantity and quality of fertilizers or amendments that need to be applied.
  • Helps to avoid over application of fertilizers and save on cost.
  • Helps to know right time of fertilizer application.
  • Helps to maintain soil fertility for sustainable agriculture.
  • Helps to know suitability of soil for growing a particular type of crop.

Materials required:

  • Spade or auger (screw or tube or post hole type)
  • Khurpi
  • Core sampler
  • Sampling bags
  • Plastic tray or bucket

Factors to be considered while taking soil sample:

  • Size of area : 1 composite sample for every 2 ha
  • No of sub samples : 15 to 20 sub samples for every 2 ha
  • Depth of sampling :
    • Shallow rooted crops : 0-15cm (plough depth)
    • Deep rooted crops : 30 cm
    • Horticultural crops : Sample may be taken from different depths depending up on the root penetration.
Sl. No. Crop Soil sampling depth
Inches cm
1 Grasses and grasslands 2 5
2 Rice, finger millet, groundnut, pearl millet, small millets etc.(shallow rooted crops) 6 15
3 Cotton, sugarcane, banana, tapioca, vegetables etc. (deep rooted crops) 9 22
4 Perennial crops, plantations and orchard crops Three soil samples at 12, 24 and  36 inches Three soil samples at 30, 60 and 90 cm
  • Frequency of sampling : Once in 3 years for dry land crops Once after 3 crop harvests in irrigated areas.
  • Time of sampling : Ideal time is before onset of monsoon or Immediately after harvest.
  • Sampling in standing crop : Standing crops / Filed crops: Between rows Plantation/fruit crops: on the canopy circumference
  • Collect soil sample during fallow period or few months before starting any new landscaping.

Procedure /steps in soil sampling:

  • The field is divided into sampling areas so that each sample represents an area of not more than 2 ha. Each sample area should be uniform in soil type, slope, cropping pattern and past fertilizer management.
  • The sampling spots (about 15 or 20) are fixed at random in a zigzag pattern to represent the entire area taking care to avoid sampling near field bunds, wet places, tress roads, drainage ditches.
  • The surface is scrapped to remove litter, stones etc., and collect samples into a bucket from each spot up to the required depth by making a “V” shaped cut using a spade and soil is taken from both sides of the cut. A uniform quantity of sample from each of the sampling spots (10-20) is collected.
  • The sample is placed on a plastic sheet and mixed by discarding stones, roots etc. The required quantity of soil (half to one kg) is placed into a polyethylene bag by adapting quartering technique.
  • Quartering is done by dividing the thoroughly mixed sample into four equal parts. The two opposite quarters are discarded and the remaining two quarters are remixed and the process repeated until the desired sample size is obtained.
  • Label the bag with information like name of the farmer, location of the farm, survey number, previous crop grown, present crop, crop to be grown in the next season, date of collection, name of the sampler etc., and send to the laboratory for further processing and analysis.

Processing and Preparation of soil samples for analysis:

  • Assign the sample number and enter it in the laboratory soil sample register.
  • Air drying : The samples are air dried in the shade for 4-5 days in the laboratory.
  • Grinding and sieving : Air dried soil sample is powered by pounding with wooden pestle and mortar. Sieve the sample through 2 mm sieve and repeat the process of crushing and passing through the sieve till the whole soil sample is completed. Crushing of primary sand and gravel particle is to be avoided.
  • Mixing and Storage : The soil is mixed well and stored in suitable bottle with proper coding and labeling.
  • Analysis : By using standard method (required glassware’s, reagents, chemicals and instruments) for particular nutrient estimation.

Precautions to be taken while soil sampling:

  • Avoid collecting soil sample near bunds, near roads, near FYM/compost pits, below the trees, near building ,near nalas/streams/ponds/wet spots, irrigation canals and drainage lines and other unrepresentative spots.
  • Do not collect soil sample immediately after application of fertilizers, manures and amendments. There should be minimum 3 months gap after application of fertilizer manures and amendments.
  • If the soil sample has to be analyzed for micronutrients, avoid tools made of iron, copper and brass. Use only stainless steel, wooden, aluminum and plastic tools.
  • If soil sample is moist, dry it under shade before sending to laboratory and avoid drying near fertilizer/chemicals/pesticides godowns.
  • All sampling tools and storage bags should be perfectly clean to avoid contamination.
  • For micronutrients analysis like Cu, Fe, etc metals sieves should not be used. Plastic or Nylon sieves are preferred.

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