EXERCISE 13 



THE PHYSICAL ANALYSIS OF SOILS 





mn a > 







Statement. By physical analysis the constituents of a soil, such as vegetable matter, gravel, sand, 

 and clay, are determined and the properties of these materials observed. 



Object. To determine the physical constituents of the soil. 



Materials. Finely screened samples of soil collected in a previous exercise ; Mason fruit jars ; 

 lime; scales accurate to one- tenth gram. 



Directions, i . Weigh out one hundred grams of air-dry soil and heat it at the temperature of boiling 

 water for an hour. Reweigh and note the loss of water. Heat again for an hour and reweigh. If a loss in 

 weight is shown, repeat until the weight is constant. Compute the loss of moisture in per cent of the 

 original weight. Repeat for each soil to be tested, and tabulate the results. Correlate the loss due to 



heating the soils at this tem- 

 perature with the fineness and 

 structure of the soils as already 

 determined. 



2. Heat the same sample of 

 soil to a red heat until only a 

 reddish ash remains. As soon 

 as the sample is cool reweigh 

 and compute the loss. Classify 

 the soils with respect to their 

 loss from heating at this high 

 temperature. To what is the 

 loss of weight due? Which has 

 lost the greater amount of 

 weight, the soil or the subsoil? 



3. Weigh three empty quart 

 jars. Place a tablespoonful of 

 the soil which has been heated 



in one of the fruit jars and fill it half full of water. Seal the jar and shake thoroughly. Let it stand for 

 thirty minutes and shake it again for ten minutes. Let the soil settle for one minute, then pour off all 

 the water into the second jar. Let the water in the second jar stand for thirty minutes and pour the 

 water from it into the third jar. Evaporate the water in each jar. Note the size of the particles in 

 each of the jars. Compare them under the microscope. Determine the weight of dry material in each 

 jar. Considering the loss of organic matter as determined in 2, compute the percentage of organic 

 matter, sand, silt, and clay in each soil examined. On the basis of this comparison classify them as 

 clay soils, sandy soils, and loams. On the basis of the amount of organic matter contained in the soils, 

 classify them with respect to their productive power. Compare your results with the field notes made 

 when the samples were taken. 



Questions. How did the color of each soil sample compare with the amount of organic matter 

 contained in it? How did the water contained in the soil compare with the organic matter present? 

 How did the subsoil compare with the surface soil in amount of organic matter ? How did the subsoil 

 compare with the soil in the amount of clay it contained ? 



References. Waters, H. J. Essentials of Agriculture, pp. 58-66. Ginn and Company. Lyon, Fippin, 

 Buckman. Soils, their Properties and Management, pp. 83-108. The Macmillan Company. Burkett, C. W. 

 Soils, pp. 25-29, 35-36. Orange Judd Company. 



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a b c d e f g 



Fig. 17. The physical constituents of a loam soil 



a, gravel ; b, coarse sand ; c, medium sand ; d, fine sand ; e, very fine sand ; /, silt ; g, clay. 

 (Courtesy of the United States Department of Agriculture, Bureau of Soils.) 



