21 
food coming into contact with the absorbing root surfaces of rice 
would be considerably less when planted in a soil thai had been 
thoroughly dried out. Later the mineral constituents would, of 
course, regain their former state of solubility, but just how much 
time would be required for the reestablishment of a permanent con- 
centration can not be definitely stated. It seem- certain, however, 
that a lowering of the availability of the mineral constituents would 
temporarily result from a thorough drying out of the soil. 
It is now the practice of the growers, both on the mainland and in 
Hawaii, to plow their rice lands some weeks before the flooding time, 
in the latter case immediately following each harvest, so as to permit 
as much aeration of the soil as possible. As would be expected the 
aeration prevents nitrification, so that by the time a new crop is 
planted nitrate has accumulated to a considerable extent. Upon 
resubmergence the nitrate thus formed becomes partially leached out 
of the soil and in part converted into poisonous nitrites. The nitri- 
fication therefore leads to a direct loss of nitrogen on the one hand 
and to the formation of a substance toxic to rice on the other. If, 
however, Hawaiian rice soils are not plowed or cultivated after the 
water is turned off and the previous crop harvested little or no 
nitrification sets in. The puddled state of the soil and its compacted 
condition effectively exclude air. It is only after cultivation and 
consequent aeration that active nitrification sets in. 
Unfortunately no experiments showing the practical effects on 
the growth of rice as produced by aeration against nonaeration have 
been conducted at this station. Such experiments, however, have 
been made in Mysore, the results of which are in complete harmony 
with the inferences drawn from the nitrogen transformations above 
referred to. As a result of experiments carried on through two 
years, Coleman and Ramaehandra Rao x found that a considerable 
gain in the yield of rice was obtained by leaving the land in the 
unplowed condition during the time between crops, the plowing for 
the new T crop being deferred until just before the new crop was 
planted. By growing a legume between rice crops all needed aera- 
tion can be brought about; while the nitrates formed during this 
period would be absorbed to a large extent by the legume, and in 
addition free nitrogen from the air would be added to the -oil 
through the growth of the Legume. Upon plowing under the Legume 
ammonification will set in, thus furnishing available nitrogen for the 
next rice crop. The nitrogen requirements of the rice would there- 
fore be met and other beneficial effects that arc believed to result 
from the rotation of crops would be secured. There i^ little ground 
1 LOC. 'il.. P. \K 
