15 
effects of green manuring is that it stimulates bacterial action. It 
is commonly believed that the presence of carbonate of lime is 
essential for nitrification, through the maintenance of neutral con- 
ditions, but it seems that when other conditions are suitable, active 
nitrification takes place in Hawaiian soils which contain unusually 
small amounts of lime. The results of our experiments indicate 
that the iron and alumina present may partially take the place of 
lime in maintaining the necessary neutral condition. On the other 
hand, experiments show that magnesium carbonate seems to be 
distinctly detrimental to nitrification, while the magnesia naturally 
present in the soils does not seem to interfere. While nitrate is 
probably the most available form of nitrogen, ammonia is also 
available for certain crops. 
AMMONIFICATION. 
Ammoriifi cation is more active in Hawaiian soils than nitrification, 
and investigations show that aeration is not as essential to this pro- 
cess as it is to nitrification. Aeration, however, also stimulates 
ammonification. During the several months, in which new lands 
are usually cultivated previous to planting, ammonification and 
nitrification are each stimulated to a considerable extent, but in 
many localities only very small amounts of nitrate are found. In 
such instances plants seem to absorb the nitrogen most largely in the 
form of ammonia. In the case of aquatic plants ammonia is prefer- 
able to nitrates. Soil heating stimulates the formation of ammonia, 
both as a direct result of the heat on the organic nitrogen and proba- 
bly indirectly, by increasing the activity of bacteria. It has also 
been found that the application of lime stimulates the formation of 
ammonia, and magnesium carbonate produces still greater stimula- 
tion. The effects of magnesium carbonate on ammonification are 
therefore the opposite of those on nitrification. 
All Hawaiian soils seem to be abundantly supplied with bacteria, 
and the wide distribution and vigorous growth of a great variety of 
leguminous plants indicate that the tubercle-forming organisms are 
abundantly distributed. In fact, nodules occur on the roots of 
many leguminous plants in the islands. Up to the present time 
very little use has been made of artificial inoculation, and it is of 
doubtful importance. 
SOIL, MANAGEMENT. 
TILLAGE. 
A part of the high cost of tillage in Hawaii is traceable to the un- 
usual properties of the soil. The clay when wet is extremely sticky 
and, even when the moisture content is low, it adheres tenaciously 
to the plow, thus materially increasing the draft. Frequent deep 
