Mar. 3,1923 
Effectiveness of Mulches upon Soil Moisture 
733 
DEPTH OP MULCHING 
The depth of mulcting has just as much bearing upon the soil moisture 
as the mulch material. Experiments were carried out with straw and 
sawdust in galvanized tubes, 36 inches tall, all having the same diameter 
of 3.5 inches. The bottom of the tubes was perforated to allow free 
passage of water with the aid of the capillary action of sand. The 
depths tested were 1 inch, 2, 3, and 4 inches. Water measurements 
were taken on May 31 and were followed up at various intervals until 
June 28. 
Table V.—Loss of moisture during 60 days with different depths of mulches 
Depth. 
Sawdust. 
Straw. 
Inches . 
Cc. 
Cc. 
I 
309 
250 
2 
173 
162 
3 
no 
112 
4 
104 
IO9 
During the same period the unmulched or bare sand lost 531 cc. 
of water. This will serve to illustrate the point that the efficiency of a 
mulch increases with its depth. In both cases more water is saved 
when the depth is increased. Between sawdust and straw, when the 
depth is beyond 2 inches, there does not seem to be any material differ¬ 
ence in the amount of moisture lost, but with the 2-inch and especially 
the 1-inch mulches, straw is more efficient 
MULCH ACTIVITY UPON DIFFERENT SOIL CLASSES 
As the soil particles diminish in size, and therefore increase in surface, 
more water is brought to the surface. Soils that contain any appreciable 
amount of porous bodies, hydrates, or colloid matter have a larger 
water-holding capacity. Since the rate of evaporation is proportional 
to the moisture content and the extent of exposure of the soil particles, 
different classes of soil naturally will evaporate variable quantities of 
moisture. 
This subject in question is studied in connection with mulches. 
Duplicate samples of sand, loam, and clay were mulched with 
1 inch of hay. 
Table VI .—Loss of moisture during 55 days from different classes of soils under i-inch 
straw mulch 
Sand. 
Clay. 
Loam. 
Cc. 
Cc. 
Cc. 
73<5 
759 
846 
The same principle seems to govern the evaporation ratio of these 
three classes of soils. Sand, being much coarser than either clay or loam, 
lost the least quantity of water. Loam lost the most moisture because 
its physical structure is much finer and yet passage of water is not 
