Depletion of soil fertility in agriculture sector occurs due to continuous cultivation of different crops in a particular plot of land. Besides amount and kinds of fertilizer requirement for the same crop varies from soil to soil even field to field in the same field. It is therefore, for assessment of fertilizer status as well as with an aim to revival of fertility status in soil, it is necessary to test soil, which in turn, indicates the requirement of fertilizer for cultivation of different crops. It may be mentioned that soil testing process is the only means to acquire knowledge of amounts of soil nutrients available to plants. Under some circumstances, without the recommendation based upon a soil sample analysis data, a farmer may apply either excess or lower doses of fertilizer hampering production of crops. In order to help farmers towards economic and efficient use of fertilizer, better soil management practices, periodical soil testing of his cultivated area is an important tusk for the concerned farmer on his part. Soil test data also provides some related information regarding some of the soil characters. Soil analysis also indicates the pH value of a particular soil which otherwise indicates the requirement of lime in acidic soil.
In this context, collected soil sample, following correct procedure could provide almost assured soil test data which may subsequently be used as most vital tools in applying fertilizer and lime in a particular plot of crop land.
Generally most of the soil testing services do soil test to acquire knowledge on chemical properties of soil such as nitrogen, phosphorus, potassium, organic carbon in most of the soil testing laboratories. Along with other aspects soil analysis also determines the pH value of acidic character like Assam soils which are likely to need liming.
For the purpose of collection of soil sample different simple tools such as spade / khurpi / Sieve / marker / plastic sheet / cotton bag / sutli / information sheet / pen etc. are necessary. Soil sampling tools must be clean and it should be ensured that soil sample must not be contaminated at the time of mixing or packaging of soil samples. A small amount of fertilizer or other chemicals on tools or hands of the operator for instance can causes serious contamination of the soil sample.
Soil sample should be collected from represented area separately from different level or slope, water-logged area, soil with different colour and should be collected after crops are harvested. Collection of soil should not be taken out from the area recently fertilized or manured, or from below the tree, old bunds, marshy spots, compost piles etc.
At first instance some spots (10-15 numbers per 0.5 hectare of land) are to be identified within a specific character of soil to represent the particular soil. For collection of soil sample from each point, scraping away the soil surface with the help of a ‘kodali’ is advocated, so as to avoid all unwanted material such as leaf, stone or debris expected to mix with soil sample .
Further ,at each selected point, a ‘V’ shaped structure is recommended to dig out down to the plough depth (6 to 8 inch in case of shallow rooted crop) with the help of a khurpi and subsequently with scraping of soil layer of a thickness of uniform slice of about one inch thickness from both sides of the ‘V’ shaped structure.
Subsequently soil collected from different spots under a specific character of soil are to be cleaned using a sieve which will help to remove some unwanted matters, mostly broken portion of roots left after harvesting of previous crop .Thereafter some steps are to be followed such as placing collected soil mass in the plastic sheet, spreading the entire quantity in a circular manner and make four equal halves. The next step is to reject two opposite portions and collection of two opposite fragments and mixing it properly. Repetition of the process of rejection and collection is required till the quantity become around 500 grams for a specific soil sample. Sample should be dried up in shade (not in sunshine) before putting it into the cloth bag .
It may be mentioned that information sheet is a vital part of the procedure so as to get a very useful soil test data and should be well furnished with information such as, name and address of farmer with father’s name and village, date of collection of the sample, depth of soil, crop grown previously, crop to be grown and other related information. Also the sample should be properly labeled.
At the time of receipt of specific soil sample analysis report from the soil testing laboratory, it is necessary to tally the result sheet with that of the particular soil sample against which information are furnished in the information sheet. Hence it necessitates putting a specific code number in the Information sheet of a particular sample at the time of submission of soil sample to the soil testing laboratory.
In no case information sheet should be put inside the bag along with soil, instead the sheet should be tied conveniently outside, preferably around the neck of the bag. The information helps to select the correct kinds and amount of fertilizer and liming material which help maintaining soil more productive soil and increase soil production.
INTERVAL OF TESTING
For annual crop especially vegetables, soil sample should be analyzed before planting. In case of successive crops cultivation in a single season, no need to test before each planting. Soil samples analysis for a cultivated plot are generally recommended for every 2-3 years.
In Assam there are numbers of Soil Testing Laboratories under the Department of Agriculture, Assam Agricultural University and other organizations for analyzing soil samples so collected. Hence in this context communication in this regards may be initiated with the contact with the local agricultural authority regarding transmitting soil samples to be tested in soil testing laboratory.