EXTEITSION COURSE IN SOILS. 15 



nitrate, a common source of nitrogen, is readily leached from the 

 soil. Very little loss occurs from the leaching of phosphorus com- 

 pounds. The amount of leaching also varies considerably with the 

 type of soil. Soluble materials are leached more readily from sandy 

 soils, for example, than from clays. Erosion is another cause of 

 much loss of fertility from soils. Leaching and erosion can both 

 be avoided to a large extent by keeping the soil covered with plant 

 growth. 



There are several ways and means by which plant-food materials 

 are replenished in the soil The removal by different agencies of 

 surface-soil materials subjects the subsurface to increased action 

 from the agencies of disintegration and decomposition which set 

 free plant food. Then the dissolving action of water in the soil is 

 constantly increasing the availability of the mineral nutrients. The 

 return of organic matter in the form of manures, straw, and plant 

 residues from crops and weeds is doubtless the best means at the 

 command of the average farmer for keeping up the productive- 

 ness of his soil. Various substances in the form of commercial ferti- 

 Hzers are now much used, the quantity and nature of these materials 

 depending upon the type of soil, the crops grown, and the judgment 

 of the user. 



EXERCISES, LESSON H. 



Materials needed. — Balance; porcelain dishes; sodium hydroxid; red and blue 

 litmus paper; muriatic acid; burnt Lime; covered fruit jar; glass tubing; one-holed 

 stoppers; rubber tubing; limestone; marble slab; some small boxes; sandy soil and 

 a few kernels of corn; sealing wax; large-mouthed pickle bottles; and eggs (to be 

 furnished by the class). 



Composition of plants. — Take a growing plant and weigh it. Record the weight. 

 Cut up and put pieces into a porcelain dish. Heat very gradually, causing the plant 

 to wilt and dry out, but do not apply enough heat to cause charring or burning. While 

 the drying is being done, hold a clean, dry glass plate over the containing dish. 

 Remove glass at times and note from its appearance what is being expelled from the 

 plant. After the plant is thoroughly dried, cool and weigh again. Record the 

 weight. What percentage of the total weight passed off as moisture? Now burn the 

 dried substance until only ash remains. Weigh again. Record the weight and 

 figure the percentage of ash. The ash contains the mineral materials taken from the 

 soil. The part consumed by burning represents what was formed from the carbon 

 dioxid of the air and the water and nitrogen from the soil. 



Formation of a salt. — Dissolve a piece of sodium hydroxid about the size of two 

 peas in a small quantity of water. Dip the tips of forefinger and thumb into the solu- 

 tion and rub together. Note the feeling, then wash finger and thumb. Put about 

 one-fourth teaspoonful of this solution into a separate dish (keeping remainder) and 

 add about 5 teaspoonfuls of water. Dip finger into this solution and touch to the 

 tongue. Note taste, then spit out. Put small piece of red litmus paper into this 

 weak solution. What happens? Sodium hydroxid is a base. After noting all its 

 properties, discard this weak solution. 



(a) Put about 10 teaspoonfuls of water into a dish. Add not over 5 drops of muriatic 

 acid and stir. Touch tip of finger to solution and taste, but do not swallow. After 



