IOWA ACADEMY OP SCIENCE 
107 
larity as he states, but to retarded evaporation. It will oe noted that he 
claims this effect for the manure, after it is well incorporated with the soil. 
Storer^ says this: “Naturally enough, the power of the soil to hold water 
tends to retard evaporation from the soil.” He gives a table of S'chuebler 
showing that as the content of clay or vegetable mold increased, the amount of 
water evaporated from the soil decreased, and he adds, “It will be noticed that, 
in proportion as a soil absorbs more water by imbibition, so much the less 
water does it give off through evaporation.” 
Voelcher® cites the case of two soils, powdered and kept in a heated room 
until air-dried. One from a wheat field contained 6 per cent organic matter 
and retained 4.7 per cent of moisture. The other soil from a permanent pasture 
had 22 per cent of organic matter and held 22.35 per cent of moisture. 
These few references represent the sum of available knowledge of the 
physical effects of organic matter in the soil, but they do not give the specific 
information wanted. It should be kept in mind that though manure is organic 
matter, it is not, when first added to the soil, either vegetable mold or humus. 
A test was made of the effect of manure and peat on the water holding 
capacity of soils and the rapidity with which the water drained away. Soil 
tubes two inches in diameter and twelve inches high, with perforations in the 
bottom, were used; peat and manure were each added to the poor loess soil at 
the rate of 1.5 per cent. The per cents of water held at the different periods 
were as follows: 
EFFECT OF MANURE AND PEAT ON WATER HOLDING CAPACITY. 
Soil 
Saturated 
Saturated 
and set- 
tled 
Drained 
1 hr. 
20 hrs. 
44 hrs. 
3 da. 
j'5 da. 
Loess 
37.5 
54.2 
50.0 
50. 
49.2 
48.9 
48. 
Loess and manure 
37.2 
55.2 
53.7 
51.9 
50.8 
50.4 
49.5 
Loess and peat — 
57.6 
54.3 
51.8 
51.4 
50.8 
50.5 
49.6 
The same net weight of soil was put in each tube, but the soil containing 
the manure was a little more bulky; the fact that the latter was jolted down 
to the same level as the others, made it more compact and slightly reduced its 
water holding capacity at first. The tubes were allowed to set in the water 
three days and this settled them somewhat and lessened their water holding 
capacity as the figures show, but while they were in the water the manured 
tube settled less than the others, and its capacity was left 1 per cent greater. 
When they were allowed to drain, being kept covered to prevent evaporation, 
the manured tube lost its water more slowly than the check. The peat tube 
behaved nearly like the manured tube. These facts show that peat with 
respect to the retention of moisture affects the soil almost like the manure, 
and that they both helped to retain the water in the soil when it was near 
saturation. 
The two following experiments were worked in co-operation with E. E. Hum- 
bert, a senior student at the time. The soil used was old worn Marshall loam 
® “Agriculture.” Storer. Vol. 1, p. 110. 
^Journal Royal Agl. Society, Vol. 18, p. 347. 
