16 MANUAL OF GENERAL AGRICULTURE. 



12. EFFECT OF HUMUS ON WATER HOLDING 

 CAPACITY OF SOILS. 



Materials: Three tin cans, dry well-rotted manure. 



Perforate the bottoms of three tin cans. Place a piece 

 of cheesecloth on the bottom of each and weigh, recording 

 the weights on the outside of each. Place in one 95 grams 

 of sand, and 5 grams of well-rotted manure ; into another 

 85 grams of sand and 15 grams well-rotted manure; into 

 the third 75 grams sand and 25 grams well-rotted manure. 

 Saturate each with water and weigh immediately. Write 

 results in each case as follows: 



Sand containing 5% organic matter retained % 

 moisture, etc. 



13. EFFECT OF MULCHES AND CULTIVATION ON 

 EVAPORATION FROM THE SOIL. 



Materials: As indicated in exercise. 



Secure three five-gallon oil cans and cut them in half 

 with a can opener. In case the upper half of any one can- 

 not be made water-tight another must be used. Place an 

 inch of gravel in each. Place in the corner of each a stu- 

 dent lamp chimney. 



Fill each can with soil to within two inches of the 

 top, slightly compacting the soil. Number the cans from 

 one to six. Cover the soil in number five with one inch of 

 sand. Cover number six with one inch of stable manure. 



Weigh each can and record its weight. Bury the 

 cans in an open place until the surfaces inside and out are 

 on the same level. Place them in a row according to num- 

 bers and about two feet apart. Pour into each chimney 

 a measured amount of water, allowing time for the soil to 

 absorb it. When the cans without a mulch show damp- 

 ness on top discontinue. Continue the experiment as fol- 

 lows: 



No. 1, check, let alone. 



No. 2, cultivate one inch deep once a week. 



No. 3, cultivate two inches deep once a week. 



No. 4, cultivate three inches deep once a week. 



No. 5, let alone. No. 6, let alone. 



