12 BULLETIN 6, U. S. DEPARTMENT OF AGRICULTURE. 
enough to reach the permanently moist soil beneath the dry surface 
layer, the young plants promptly die. It is safer, therefore, either 
to sow the seed with a drill or to broadcast it during a heavy rain, 
which will beat the seed into the ground and at the same time fur- 
nish sufiicient moisture to carry the young plants through the period 
of danger from drought. 
The turning under of heavy leguminous crops on these sandy soils 
restocks the land with humus and the humus decomposes to such a 
stage that a condition of partial or temporary alkalinity appears at 
times to have been reached, for good crops of even such nonacid 
plants as wheat and timothy are sometimes secured from these natu- 
rally acid lands after the treatment here described. 
BENEFICIAL EFFECTS OF SOIL ACIDITY. 
An actual beneficial effect from soil acidity is likely to be felt in 
another directicn hitherto insufficiently recognized, namely, the con- 
trcl of some of the fungous diseases of cultivated plants. Reference 
has already been made (p. 8) to the fact that the fungus causing 
the scab of the potato can not grow if the soil reaction is acid. 
Another example is furnished by the root-rot of the tobacco plant, 
caused by a fungus named Vhielavia basicola.. Briggs has shown 
that this disease is prevalent in tobacco plantations that have re- 
ceived excessive applications of lime or other alkaline fertilizers 
an] that it is readily controlled by the use of acid fertilizers. 
In Porto Rico the extension of the pineapple industry has been 
retarded by a disease known as chlcrosis, the principal external 
mark of which is the yellowing of the foliage and the consequent 
poor nutrition cf the plant. From investigations by Gile and by 
Loew it appears that the yellow color of the leaves and the accom- 
panying weakness of the plant are due to the lack of iron, and that 
where the soil contains an excess of lime the organic acids which are 
needed to dissclve the iron of the soil are themselves neutralized 
and the iron, although pieeens is not available for absorption by the 
pineapple roots. 
In the upbuilding of the agriculture of the arid Western States 
certain diseases of plants have appeared which are commonly called 
by plant physiologists cases of “ malnutrition.” The causes of these 
maladies are unknewn. The maladies themselves, however, are asso- 
ciated with pronounced alkalinity of the soil and they occur in 
plants that were native in humid regions where the soil varies from 
weak alkalinity to actual acidity. May it not be worth while for 
investigators to ascertain whether some of these mysterious * mal- 
nutrition ” difficulties can not be remedied by an acid treatment of 
the soil? 
a 
