Filed Testing & Sampling

Field identification of soil is one of the important steps in soil investigation. It includes a visual examination, dilatancy, toughness, dry strength, organic content, and shine test. Based on the size of soil particles soil can be gravel, sand, silt, or clay. 

How to sample fields: Soil tests can be no better than the sample. Therefore, proper collection of the soil sample is extremely important.

Divide the field into uniform areas: Each area should have the same soil color and texture, cropping history, and fertilizer, lime, and manure treatments. One sample should not represent more than 20 acres on level, uniform landscapes, or 5 acres on hilly or rolling land.

Sample Each Area : Within each area collect 15-30 subsamples (cores, borings, or spade slices) in a zig-zag pattern throughout the designated field area. The more variable the soil, the more subsamples should be combined per area sampled. Scrape off all surface residue from the subsample site. Sample to a depth of 6-8 inches (plow layer) for cultivated crops, or 3 inches for pasture or sod fields. Sample row crop fields between rows, except for ridge-till plantings. Where RIDGETILL is used, take the sample to a depth of 6-8 inches on the shoulder of the ridge, avoiding the starter fertilizer band. Also avoid sampling dead or back furrows, terraces, old fence rows, lime or fertilizer spill areas, headlands, eroded knolls, low spots, or small saline areas. Sample at least 300 feet away from gravel or crushed limestone roads because their dust changes soil pH.

Mix the subsamples: Mix the subsamples thoroughly in a clean plastic pail, and fill the sample box or bag to the fill line (1 pint). If the samples must be taken wet, they should be dried before being mixed and submitted to the Laboratory. Do not exceed a drying temperature of 97F, and do not use a microwave unless only the nitrate test is requested. 

Field moisture content must be estimated in un-dried sample or to be preserved in a sealed polythene bag immediately after collection. Estimate the moisture content of sample before every analysis to express the results on dry weight basis.