SOIL TESTING - Introduction

 The farmers find it extremely difficult to know the proper type of fertilizer, which would match his soil. In using a fertilizer he must take into account the requirement of his crops and the characteristics of the soil.

            The basic objective of the soil-testing programme is to give farmers a service leading to better and more economic use of fertilizers and better soil management practices for increasing agricultural production. High crop yields cannot be obtained without applying sufficient fertilizers to overcome existing deficiencies. 

            Efficient use of fertilizers is a major factor in any programme designed to bring about an economic increase in agricultural production. The farmers involved in such a programme will have to use increasing quantities of fertilizers to achieve the desired yield levels. However the amounts and kinds of fertilizers required for the same crop vary from soil to soil, even field to field on the same soil. The use of fertilizers without first testing the soil is like taking medicine without first consulting a physician to find out what is needed. It is observed that the fertilizers increase yields and the farmers are aware of this. But are they applying right quantities of the right kind of fertilizers at the right time at the right place to ensure maximum profit? Without a fertilizer recommendation based upon a soil test, a farmer may be applying too much of a little needed plant food element and too little of another element which is actually the principal factor limiting plant growth. This not only means an uneconomical use of fertilizers, but in some cases crop yields actually may be reduced because of use of the wrong kinds or amounts, or improper use of fertilizers. 

            A fertilizers recommendation from a soil testing laboratory is based on carefully conducted soil analyses and the results of up-to-date agronomic research on the crop, and it therefore is most scientific information available for fertilizing that crop in that field.

             Each recommendation based on a soil test takes into account the values obtained by these accurate analysis, the research work so far conducted on the crop in the particular soil areas, and the management practices of the concerned farmer. The soil test with the resulting fertilizer recommendation is therefore the actual connecting link between agronomic research and its practical application to the farmers’ fields. However, soil testing is not an end in itself. It is a means to an end. A farmer who follows only the soil test recommendations is  not assured of a good crop. Good crop yields are the result of the application also of other good management practices, such as proper tillage, efficient water management, good seed, and adequate plant protection measures. Soil testing is essential and is the first step in obtaining high yields and maximum returns from the money invested in fertilizers. 

How to collect a soil sample
  1. Sample each field separately. However, where the areas within a field differ distinctly in crop growth, appearance of the soils, or in elevation, or are known to have been cropped or fertilized and manured differently, divided the filed and sample each area separately.
  2. Take a composite sample from each area. Scrape away surface litter, then take a small sample from the surface to plough depth from a number of spots in the field (10 to 15 per acre). Collect these samples in a clean bucket or some such wide container.
  3. Where crops have been planted in lines (rows), sample between the lines.
  4. Do not sample unusual area. Avoid areas recently fertilized, old bunds, marshy spots, near tress, compost piles, other non-representative locations.
  5. Take a uniform thick sample from the surface to plough depth. If a spade or a trowel is used, dig a v-shaped hole, then cut out a uniform thick slice of soil from bottom to op of the exposed soil face, collect the sample on the baled or in your hand and place it in the bucket.
  6. Pour the soil from the bucket on a piece of clean cloth or paper and mix thoroughly, discard, by quartering, all but 1 to 2 lbs. of soil. Quarterly may be done by mixing sample well, dividing it into four equal parts, then rejecting two opposite quarters, mixing the remaining two portions, again dividing into four parts and rejecting two opposite quarters, and so on. The sample should be dried in the shade for an hour or two before it goes into the cloth bag container.
  7. Each cloth bag should be large enough to hold a pound or two of soil, and should be properly marked to identify the sample.
  8. Fill out the soil sample information sheet for each sample. These forms may be sent separately to the laboratory or enclosed with the soil sample.
  9. Address the samples to the Soil Chemist, Soil Testing Laboratory, Goal Ghar, Port Blair.
  10. Keep a record of the areas sampled and a simple sketch map for reference when you get the soil test and fertilizers recommendation report from the soil testing laboratory.

 

  ROLE OF THE EXTENSION SERVICE IN SOIL TESTING 

The actual analysis of the sample and the making out of fertilizer recommendation is only part of the soil testing service. To a large measure, the efficiency of this service depends upon the care and effort put froth by extension workers and farmers in the collection and dispatch of samples to the laboratory. Its effectiveness also depends upon the proper follow-through of the fertilizer recommendations, including the establishment of result demonstrations on farmer’s fields to induce the farmers to follow the fertilizer recommendations. In this work the staff of the extension service play the most important role, since they are the people directly in contact with the farmers or this reason, the soil chemist in charge of the laboratory must give periodic and through training to the extension staff on these subjects.

COLLECTION OF SAMPLES 

             A useful soil testing service starts with the collection of representative soil samples. A fertilizer recommendation made after analyzing the soil can only as good as the sample on which it is based. Actually the one to ten grams of soil used for each chemical analysis should represent as accurately as possible the entire surface six inches of soil, weighing about 2 million pounds per acre. The importance of taking a representative composite sample is, therefore, self-evident. One field can be treated as a single sampling unit only if it is relatively uniform and does not exceed approximately five acres. Variations in slope, colour, texture, management, and cropping pattern should be taken into account and separate composite soil sample adequately representing the field, small portions of surface soil should be collected to depth of six inches from at least ten well-distributed spots in the field, mixed well, and about ½ kg of representative sample sent to laboratory. 

            Proper sampling tools are essential for collection of good soil samples. For a soft. Moist soil, the soil tube, phowda (spade), or khurpi (trowel) are usually quite satisfactory.

For harder soils, a screw type auger, or an adze might be more convenient. Post hole augers are convenient for sampling excessively wet areas like paddy fields. An extension worker whose duties include collection of soil samples should be supplied with at least a few of these tools, and also a plastic bucket. The phowda, khurpi and adze are very common implements available in most hardware shops and so there should be no difficulty in procuring these implements. 

            The farmers should be given help in filling out the soil sample information sheet with an ex-plantation of any items not understood. It should be remembered that the information sheet is very vital part of procedures that go to make a good soil test recommendation. This sheet must supply all of the background information that, in combination with the results of the analysis, makes possible an accurate fertilizer recommendation for a certain crop, for that particular field. Factors such as crop variety, slope of land, irrigation and drainage facilities, and pervious cropping seasons affect the amounts of fertilizer to be applied to particular crop. Any peculiarities noted in the soil or in the vigor or the crop would be very valuable information on the soil sample information sheet as a basis for making an adequate fertilizer recommendation. In the absence of this information, the soil chemist must base his recommendation upon the soil test values alone, and more often than not the farmer will receive an adequate fertilizer recommendation.