IOWA ACADEMY OP SCIENCE 
109 
the base of the soil tube at all times just 24 inches below the surface of the 
soil. It was found by previous experiments that the amount of water supplied 
to the soil was not a true measure of the amount evaporated. The amount of 
water in the soil varied greatly and without apparent cause. Tubes kept with 
the supply -of water constantly 24 inches below the .surface would vary in 
weight from week to week. The true measure of the evaporation was obtained 
by combining the loss or gain in weight of the tube of soil with the amount of 
water supplied. 
Five tubes of each soil were run. The necessity for so many duplicates is 
seen by examining the accompanying table. The duplicates do not keep close 
together, but the averages tell a very consistent story and it is felt that they 
can be relied upon. The tubes were prepared by placing 2 inches of gravel 
in the bottom, then filling to within 6 inches of the top with the same kind of 
soil in each. They were then run blank for several weeks and their behavior 
noted. The variation between tile different' tubes was very slight. The surface 
soil was then placed in the top of the tubes, the untreated soil in five tubes and 
the soil treated with 1.67 per cent of dry manure in the other five tubes. This 
gave the same subsoil to all the tubes, the difference lying in the surface 
6 inches. Mr. Humbert ran the series for about two months including the 
preliminary tests, and secured the results given in the third and fourth col- 
umns. On his departure I took charge of the experiment and secured the data 
for the last month. The results are given in c. c. 
EVAPORATION TEST. BEGUN JUNE 24, 190'7. 
This table shows that manure retarded evaporation to the extent of 10.2 c. c. 
during the first nineteen days, and 9 c. c. during the next month. Manure 
retards evaporation of water from the soil, but the effect is very slight. The 
amount of manure applied was equal to fifty-eight tons of average barnyard 
manure to each acre of soil. When the amount of water saved is calculated to 
inches it equals 1 inch in 505 days, if evaporation should go on at the summer 
rate all the time. Calculated in per cents it shows that this enormous appli- 
cation of manure, which is several times as much as the usual application of 
manure in field practice, prevented only 4.4 per cent of the evaporation of 
water from the soil. This is surprisingly small and evidently not capable of 
producing very profound effects on the growing' crop. 
To sum up the findings in regard to the physical effects of the manure on 
the soil, it has been shown that fresh stable manure decreases the volume 
