Another method is to take a common half-inch or two-inch carpenter's auger and bore into the soil with it. Pull it out frequently and put the soil which comes up with it into the jar until you have a sample a foot deep. If one boring twelve inches deep does not give sufficient soil make another boring or two close by and put all into the jar.
Take the sample, by whatever method obtained, weigh out ten or twenty ounces of the moist soil and dry it at a temperature just below 212 degrees. When it is thoroughly dry weigh again. The difference between the two weights will be the amount of water held by the sample. Now divide this by the weight of the dry sample and the result will be the per cent. of water held by the soil.
Several samples taken from different parts of the field will give an average for the field. Repeat this every week or oftener through the season and an approximate estimate of the water-holding capacity of the soil will be obtained and consequently an indication of the crops to which the soil is best adapted.
Example.
Weight of a soil sample, 20 ounces.
When dried this sample weighs 17¾ ounces.
20 - 17¾ = 2¼, the water held by the soil.
2.25 ÷ 17.75 = .12 plus.
This soil held a little over twelve per cent. of water. If this soil continues to give about the same result for successive tests during the growing season, the results would indicate a soil adapted to cotton, late truck or corn.