Soil sampling a key for accurate soil testing

India is an agriculture based country where about 60% population earn livelihood from farming only. Crop yield is effected by several factor i.e., soil, climate, crop, crop management and among these soil is the most precious natural resources. To fulfil the basic need of ever growing population and continued decline in cultivable land, intensive cultivation has become essential.
Fertilizer is not only an indispensible input of modern agriculture but also a major contribution to increase crop production. Therefore over reliance on chemical fertilizer result not only in higher production but also several problems of environment i.e., decline in biodiversity, eutrophication, hypoxia, nitrate, pollution, heavy metal pollution, acid rains, emission of green house gases, etc. and human health i.e., methemoglobinemia, cancer, minamata disease,itai-itai disease etc.
To overcome these alarming problems there is urgent need for judicious use of chemical fertilizers which is possible through accurate fertilizer recommendation and soil testing, accurate soil sampling is only the way out. Authentic representative soil sample is essential for soil testing to save time and money, monitoring the changes in soil nutrient status and estimation of nutrient need for profitable crop production. Therefore to take accurate soil sample, a proper methodology with clear objective, time, depth and tools should be followed.
1.    Sampling tools should be selected according to soil condition i.e., tube auger, spade, khrupi, for soft and moist soil, screw auger for hard of dry soil and post hole bucket type auger for excessively wet areas.
2.    Ideal sampling tool should be able to take small and equal volume of soil, easy to use and clean, acceptable to dry, sandy, moist, and wet soil but also resistant to rust, bent and breakage.
3.    Sampling tool should be clean with non phosphate detergent and clean water to remove all visible particulate matter, residual soil, grease and soap residues etc. Finally tool should be rinsed with distilled water and if possible wipe the tool dry with towel paper or clean cloth.
4.    Sampling site should be cleaned properly by scraping the litter and plant parts from the soil surface.
5.    Sampling field should be traversed into homogenous units of uniform area based on degree of erosion, soil type, variation in slope, soil colour, soil texture, crop growth, cropping history, management practices and other factors affecting the nutrient status of the soil.
6.    Sampling should be avoided from unusual areas i.e., recently fertilized plots, manure piles, eroded knolls, low spots marshy tracts, area near bunds, channels, trees, wells, fences, roads, compost pits, and other non representative locations.  Sampling should be done separately if district area is large enough.
7.    Generally samples are collected with the help of khurpi and spade. Samples digging should be done in such a way that ‘V’ shape hole is made and cut out a uniformity thick 2.5cm slice of soil from bottom to top of the exposed surface.
8.    Random collection of soil sample from each unit at desired depth from 15-20 spots separately in a field is known as primary sample.
9.    Sample may be collected at any time within a year. Sampling should be done in autumn after the harvest of kharif crops or 2-4 weeks before crop planting. Sampling may be collected from the previous standing crop.
10.    Sampling frequency should also be considered i.e., sample each year for analysis of mobile nutrients and area where intensive cultivation is followed but for general purpose sample once in three year.
11.    Primary samples should be collected according to the size of the area for example for 2ha area of land 15numbers of samples is sufficient.
12.    Sampling depth should be decided according to soil condition and crop cultivation i.e. sample should be taken at 0-15 cm for shallow rooted agricultural crops and 0-15 and 15-30 cm for plantation crops/ annual crops.
13.    Primary samples of a uniform area / unit should be collected in a clean bucket and mixed thoroughly.
14.    Composite sample size should be reduced by quartering method to attain desired amount i.e. 250-500 gm.
15.    Samples should be air dried in shade by spreading on plastic sheet.
16.    Samples should be cleaned by discarding plant residues, gravels, coarse materials, stones and other debris if present.
17.    Samples should be processed by crushing large soil clods with the help of wooden roller.
18.    Entire quantity of soil samples after grinding should be passed through 2mm stainless steel sieve and discard the materials > 2mm size.
19.    Processed soil samples should be store in a clean cloth or polythene bag. Glass and porcelain jar should be used for long duration storage.
20.    Sample should be labelled properly with identification mark and other details i.e. name of the farmer, date of sampling, village, taluk and district. After keeping one label inside another label carrying similar details should be tied outside the bag.
21.    Separate information sheet should also be sent with details i.e. drainage irrigation, previous cropping history, fertilizers or manures used, sampling depth, number of spots sampled. Name of the crop should also be sent for which fertilizer recommendation sought.

Precautions:
•    Sampling should be done at the same time in each year.
•    Sample collected from unusual area should be kept separately with some identification mark.
•    Special care should be taken with the soil sample to avoid contamination with chemicals, fertilizers and manures.
•    Previously used bags for fertilizers and chemicals should not be used either for dying or storage of samples.
•    Excessive grinding of soil sample should be avoided.
•    Artificial heating to dry soil sample should also be avoided.

Therefore soil sampling with proper care and proper method reduces the cost of crop production resulting higher benefit. Because “as you sow so shall you reap” hence soil sampling is the back bone of soil testing.

Mr. Z. James Kikon
SMS (Soil Science)
KVK, Dimapur
ICAR, Nagaland Centre