Agricultural Soil Sampling
Vcert is actively involved in soil sampling for their customers to take up soil for further testing, as this is an important part of organic base. A soil sampling done by the correct method can lead to full data for further sowing.
- Soil sampling, processing, and storage
- Soil sampling
- Principle
Soil testing is an essential component of soil resource management. Each sample collected must be a true representative of the area being sampled. The utility of the results obtained from the laboratory analysis depends on the sampling precision. Hence, the collection of a large number of samples is advisable so that a sample of the desired size can be obtained by sub-sampling. In general, sampling is done at the rate of one sample per two-hectare area. However, at least one sample should be collected for a maximum area of five hectares. For soil survey work, samples are collected from a soil profile representative of the soil in the surrounding area.
Materials required:
1. Spade or auger (screw or tube or post hole type)
2. Khurpi
3. Core sampler
4. Sampling bags
5. Plastic tray or bucket
Points to be considered
- Collect the soil sample during the fallow period.
- In the standing crop, collect samples between rows.
- Sampling at several locations in a zig-zag pattern ensures homogeneity.
- Fields that are similar in appearance, production, and past-management practices can be grouped into a single sampling unit.
- Collect separate samples from fields that differ in color, slope, drainage, and past management practices like liming, gypsum application, fertilization, cropping systems, etc.
- Avoid sampling in dead furrows, wet spots, areas near the main bund, trees, manure heaps, and irrigation channels.
- For shallow-rooted crops, collect samples up to 15 cm deep. For deep-rooted crops, collect samples up to 30 cm deep. For tree crops, collect profile samples.
- Always collect the soil sample in the presence of the farm owner, who knows the farm better.
Procedure
- Divide the field into different homogenous units based on visual observation and the farmer’s experience.
- Remove the surface litter at the sampling spot.
- Drive the auger to a plough depth of 15 cm and draw the soil sample.
- Collect at least 10 to 15 samples from each sampling unit and place them in a bucket or tray.
- If an auger is not available, make a ‘V’-shaped cut to a depth of 15 cm in the sampling spot using a spade.
- Remove thick slices of soil from top to bottom of the exposed face of the ‘V’-shaped cut and place in a clean container.
- Mix the samples thoroughly and remove foreign materials like roots, stones, pebbles and gravel.
- Reduce the bulk to about half to one kilogram by quartering or compartmentalization.
- 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. The process is repeated until the desired sample size is obtained.
- Compartmentalization is done by uniformly spreading the soil over a clean, hard surface and dividing it into smaller compartments by drawing lines along and across the length and breadth. From each compartment, a pinch of soil is collected. This process is repeated until the desired quantity of sample is obtained.
- Collect the sample in a clean cloth or polythene bag.
- Label the bag with information like the 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.
Collection of soil samples from a profile
- After the profile has been exposed, clean one face of the pit carefully with a spade and note the succession and depth of each horizon.
- Prick the surface with a knife or the edge of the spade to show up structure, color and compactness.
- Collect samples starting from the bottommost horizon first by holding a large basin at the bottom limit of the horizon while the soil above is loosened by a khurpi.
- Mix the sample, transfer it to a polythene or cloth bag and label it.
Processing and storage
- Assign the sample number and enter it in the laboratory soil sample register.
- Dry the sample collected from the field in the shade by spreading it on a clean sheet of paper after breaking the large lumps, if any.
- Spread the soil on a paper or polythene sheet on a hard surface and powder the sample by breaking the clods to their ultimate soil particles using a wooden mallet.
- Sieve the soil material through a 2 mm sieve.
- Repeat powdering and sieving until only materials of >2 mm (no soil or clod) are left on the sieve.
- Collect the material passing through the sieve and store it in a clean glass or plastic container or polythene bag with proper labeling for laboratory analysis.
- For the determination of organic matter, it is desirable to grind a representative subsample and sieve it through a 0.2 mm sieve.
- If the samples are meant for the analysis of micronutrients, the utmost care is needed in handling the sample to avoid contamination with iron, zinc and copper. Brass sieves should be avoided, and it is better to use stainless steel or polythene materials for the collection, processing, and storage of samples.
- Air-drying of soils must be avoided if the samples are to be analyzed for NO3-N and NH4-N as well as for bacterial count.
- Field moisture content must be estimated in an un-dried sample or preserved in a sealed polythene bag immediately after collection.
- Estimate the moisture content of the sample before every analysis to express the results on a dry weight basis.
S. 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, bananas, 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 |