286 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1926 
for instance, that under heavy cropping, where little organic or min- 
eral matter is returned, loess soils need the addition of phosphoric 
acid and lime (6-63)—a deduction that might almost be made directly 
from an inspection of the analyses given above. In general, they say, 
whenever moisture relations are favorable loess is an exceedingly 
fertile soil. Since the Chinese loess often already carries a high lime 
percentage and the practice of manuring is universal, water supply 
becomes the vital factor. 
These theoretical conclusions seem to be borne out by the facts 
wherever observed in the field. During water-supply investigations 
Fig. 38 
along the foothill area west of the Peking-Hankow Railway in the 
Tingchow-Shuntehfu region I noticed that though the loess was 
porous enough to take up immense quantities of water® the fineness 
of its grain held the moisture by capillarity and prevented a rapid 
percolation of the ground water out from the walls into partially 
dug wells. (See Willis 12-250ff.) 
The fertility of the loess is due, then, in part to its physical con- 
dition (which, combined with a clay content comparatively low for 
such a fine texture, creates a porous soil both light to till and easily 
penetrated by water) and in part to its relatively fresh chemical con- 
6 Slichter notes that the pore Space in fine alluvial clays may amount to 40 or even 60 
per cent of the total volume. (U.S. G. 8. 19th Annual Report, Part II, 1899, quoted by 
Willis, 12—250),. 
