88 



SOILS AND FERTILIZERS 



Exercise VI. — Loss of water by transpiration. 



Materials. — Glazed gallon butter jar, oats seed, paraffined paper, 

 thistle tube, coarse sand and heavy balance. 



Procedure. — Fill a glazed jar with rich soil, first adjusting coarse 



sand and thistle tube as shown in 

 Fig. 19. Moisten soil with water, 

 but not too wet, and plant with oat 

 seed. When seedlings are one week 

 old, thin to suitable number. Then 

 cover surface of soil with paraffined 

 paper, allowing plants to protrude 

 through small holes cut for that pur- 

 pose. Paraffine the paper to side of 

 jar so that all losses of moisture by 

 evaporation may be prevented. 

 Bring soil up to optimum water con- 

 tent and weigh. You are now ready 

 to record losses by transpiration. 



Weigh jar each week, replacing 

 water lost through the thistle tube. 

 Record data and draw curves. By 

 changing the jar from sunshine to 

 shade, warm temperature to cold, 

 high humidity to low, etc., the fac- 

 tors influencing transpiration may 

 be studied. 



Jars with different crops, different soil or the same soil with differ- 

 ent fertilizers or different water treatments may be utilized if so 



desired. 



r 



Exercise VII. — Review problems. Chapters IV and VI. 



1. A soil weighs 100 lbs. per cubic foot when dry. The weight 

 of a cubic foot of water is 62.5 lbs. Calculate its apparent specific 

 gravity and weight per acre foot. Ans. 1 .6 and 4,356,000 lbs. 



2. This soil has an absolute specific gravity of 2.7. Calculate 

 its pore space. 



% pore space =100 



Fig. 19. — Glazed jar equipped 

 for observation of transpiration 

 of water from plants, (a) thistle 

 tube for watering, (6) plants, (c) 

 paraffined paper to prevent evap- 

 oration from the soil surface, (d) 

 soil, (e) gravel. 



T ap, sp. gr. x 10Q-I 

 Labs. sp. gr. 1 J 



Ans. 40.7+%. 



3. This soil contains 10 pounds of water a cubic foot. Calculate 

 percentage of water based on absolutely dry soil. On wet soil. 



Ans. 10% and 9.09%. 



