ON DRY-FARMING INVESTIGATIONS IN THE UNITED STATES. 271 
so well adapted to a summer rainfall as to a winter precipitation, for the 
summer rains repeatedly pack the mulch, which necessitates frequent 
cultivation to keep the land in a receptive condition and to destroy 
the weeds which spring up after each rain. Summer tillage, however, 
affords some insurance against total loss of a crop during a dry season, 
which means disaster to the farmer with work-animals and cows to feed, 
and this element of insurance will doubtless always be a factor with 
the small farmer, even if summer tillage does not give the greatest 
returns. 
Owing to the frequent high winds in the Plains, the blowing of the 
mulch on summer-tilled land sometimes becomes a serious problem. 
It is highly important in fallowing the Plains to keep the surface of 
the soil in a rough condition; in other words, to maintain a clod-mulch 
on the fallow rather than a dust-mulch, a practice which is also 
advantageous in the absorption of rainfall. On lands subject to 
blowing, the practice of cultivating in strips is sometimes followed. 
The strips are laid out at right angles to the prevailing winds, and 
alternating strips are planted to grain or an intertilled crop. Jardine ® 
has recently emphasised the value of the lister in checking blowing in 
extreme cases. This implement opens a broad shallow furrow, 
throwing the dirt on both sides. Groups of two or three furrows each 
are listed at distances of from five to twenty rods across the field at 
right angles to the wind. The lister tends to form clods, while the 
disk harrow, except in moist ground, tends to pulverise the soil, and 
this must always be avoided in soils subject to blowing. 
Depth of Root System in relation to Storage of Soil Moisture. 
The great depth to which the roots of many of our cultivated 
plants extend has a very important bearing on the practicability of 
storing moisture in the soil. Burr’? has found that oats, spring 
wheat, barley, and corn growing on the loess soils of Hastern Nebraska 
use the water to a depth of 4 feet or more, while winter wheat 
feeds.to a depth of 6 or 7 feet. Excavations. made in winter- 
wheat plats in Utah showed the root system to extend to a depth of 
7 feet.** 
In a soil which can store 6 per cent. of ‘ growth water,’ there 
would be available in a section 6 feet in depth 600 tons of water 
per acre, or enough for the production of thirteen bushels of wheat 
in the central Great Plains. For a root penetration of 4 feet, this 
amount would be reduced approximately one-third. 
When the system of alternate cropping and fallowing is employed, 
water seldom moves below the zone occupied by the roots of the 
wheat plant. This has taken place, however, at the Dickinson experi- 
mental farm in western North Dakota. The water which moves below 
the feeding zone is practically lost to the plant, and remains undisturbed 
9 Jour. Am. Soc. Agron. 5, 213, 1913. 
10 Research Bulletin No. 5, Nebraska Experiment Station, 1914. 
1 Merrill, Bulletin 112, Utah Experiment Station, 1910. 
™ Briggs and Shantz, ‘Relative Water-requirement of Plants,’ Jour. Agri- 
cultural Rescarch, U.S. Department of Agriculture, 3, 1, 1914. 
