1.Introduction: In present days everybody is talking about the soil testing and soil health card distribution. But if we see the common farmers, they have a very little idea about the soil sampling, testing and its profitable practical benefits in their field. Some of them are also wish to test their soils, but they have so many questions in mind likes where to take samples, how to take samples, how much number of samples should collect for a particular area, what should be the depth of sampling, period/interval of soil testing, where the soil can be tested etc. So, for the successful soil testing programme, there are four important phase likes collection of soil samples, analysis of soil samples, interpretation and recommendation, and should be followed strictly.
- Collection of Soil Samples: Soil sampling is the most challengeable task, as a few grams of soil sample represents for a given area. Thus, the soil samples are required to be taken in such a manner that the collected sample should reflect the true fertility of soil for any targeted area. If the field is levelled and soil appears to be uniform, only one composite sample if taken properly could be enough for an area of 4-5 ha. Variation in slope, colour, texture, crop growth, unusual spots and management practice should be taken into account and separate sets of composite samples must be collected from each such area. Recently fertilized plots, bunds, channels, marshy tracts and area near trees, wells, cattle dung and compost piles or other non-representative locations must be avoided during the sampling.
2.1. Sampling Tools: The equipments like; spade/khurpi, auger (tube and screw type), plastic bucket, plastic bag, scale and water proof marker are required for soil sampling. For sampling in the soft and moist soil, the tube auger, spade or khurpi is quite satisfactory. A screw type auger is more convenient on hard/dry land.
2.2. Sampling Depth: The root growth of most of the field crops is confined to 10-20 cm depth and hence sampling upto 15-20cm is enough for the field crops. For most of the pasture crop, 10cm sampling depth is normally sufficient. However, soil samples from the areas growing deep rooted crops like sugarcane, cotton, plantation and horticultural crops are to be collected upto 80-100 cm depth.
2.3. Time of Sampling: Soil samples should be collected well before planting/sowing of the targeted crops, so that the soil can be tested in time. If one crop is cultivated in a year, then soil testing once in a three year is sufficient. But under intensive cultivation, say 2-3 crops in a year, then sampling should preferably be done every year prior to sowing of the first crop of the given cropping sequence.
2.4. Methods of Sampling: The greatest source of error in soil analysis is usually the soil sample itself. Consequently, soil samples should be taken in a zigzag manner (Fig. 1) to cover the entire field. At least 10-25 sub samples (cores) are taken randomly and mixed together to make a representative (composite) sample from a uniform field. First the sampling spot from where the sample is to be collected is cleaned with a spade. If a spade or khurpi is used for soil sampling, first a ‘V’ shaped cut is made up to the plough layer (0-15 cm) and then a uniform 1.5cm thick slice is taken out (Fig. 2). Collected soil samples are thoroughly mixed on a clean piece of cloth/polythene sheet/ thick paper and the bulk is reduced by the quartering so that about 500g of composite sample is retained and kept in a clean polythene bag. The sample bags should be clean and fixed properly so as to avoid any mix ups during processing.
Process of sample size reduction or quartering method: Sample should be divided into 4 parts by drawing a ‘+’ sign through it. Discard the soils from the opposite corners. Mix remaining soil, divide into 4 parts and again discard from corners (Fig. 3 and Fig. 4).
2.5. Sample Preparation: A sample is spread out on a plastic or a thick brown paper in the shade for drying, because the wet soil samples collected from the field cannot be stored as changes occur with time in storage condition. Sun drying is strictly prohibited and it is preferable to air dry soils at 20-25oC and 20-60% relative humidity (Jackson, 1958). Coarse concretions, stones and pieces of roots, leaves and other under-composed organic residues are taken away. Large lumps of moist soil are broken by hand. After air drying soil samples are crushed gently with a wooden mortar and pestle (Fig. 5), and sieved through a 2mm sieve (Fig.5). The material larger than 2 mm is discarded.
2.6. Sample Storage: Care should be taken to send the collected soil samples as soon as possible for analysis. However, until analyzed, processed samples should be stored in polythene bags or plastic containers properly tied and tagged with the sample label.
2.7. Relevant Information about the Sample: A tag should be attached with each sample includes: name of the farmer, address, date of sampling, sampling depth, previous crop(s) grown, etc. Any other relevant information such as intention of analysis, fertilization history, future crop/cropping plan, etc. should also be provided separately (Fig. 6). This supporting information helps for precise fertilizer recommendations. Further, the details, crop and yield history, along with the amount and types of fertilizers applied can also be employed to refine the fertilizer recommendation.
- Possible Benefits for Farmers:
- Alert about the deficiencies and toxic nutrients exist in their own field and get answers how to overcome.
- Identify the areas under problem soil (if any) which limits crop growth and gather knowledge for reclamation.
- Get an idea about fertilizer recommendation and develop their skill in the use of rational/efficient nutrient inputs.
- Practically observe the contribution in yield increase percent to the applied recommended nutrients.
Dr. Sanjay Kumar Ray
Subject Matter Specialist (Soil Science), ICAR Research Complex for NEH Region, Nagaland Centre,Jharnapani, Nagaland, email-dr.sanjaykumarray@yahoo.in
