14 
extent on the sugar lands with good effects, but in many instances 
negative results have been obtained by the pineapple growers. Where 
liming is to be practiced; coral sand is recommended. 
With the exception of phosphoric acid, all the mineral elements of 
plant food in Hawaiian soils are soluble in water to a considerable 
extent, and if suitable physical conditions be maintained, and the 
humus content kept up, the need for mineral fertilizers will be greatly 
reduced. The solubility of the mineral constituents can also be con- 
siderably increased by soil heating, which probably is a factor in the 
more vigorous growth of crops noticed where refuse had been burned. 
FERROUS IRON. 
Soluble ferrous iron is considered to be toxic to plants, but the 
amount of water soluble ferrous iron in Hawaiian soils is extremely 
small, except where there is insufficient aeration. Poor drainage and 
an excess of water in soils prevents the circulation of air, and such con- 
ditions are favorable for the formation of soluble ferrous iron. The 
injurious effects on crops attending heavy rains may be due to some 
extent to the formation of ferrous compounds. The high iron content 
of Hawaiian soils is composed in part of insoluble ferrous oxid, but 
the imperfections in analytical methods do not permit of its accurate 
determination. Consequently the percentages of ferrous iron are not 
given in the tables of analysis. 
BIOLOGICAL CONDITIONS. 
The availability of nitrogen in soils depends on the activity of bac- 
teria and fungi. There are many factors that influence their activity, 
one of the most important of which is the state of aeration. In general 
the aeration of Hawaiian soils is not sufficient for the best development 
of beneficial bacteria. Consequently the nitrogen does not become 
available fast enough for maximum growth of crops. 
NITRIFICATION. 
Nitrification in soils requires the free movement of air, and the 
more restricted the circulation of air the less actively are nitrates 
formed. This is strikingly illustrated by contrasting nitrification 
in the silty soils of Kula and the Parker ranch, where active nitrifi- 
cation takes place, with that of the heavy clay types common in 
other parts of the islands. In the rice soils nitrification is suspended 
and the clay soils frequently contain almost no nitrate. The inert- 
ness often observed in newly plowed sod lands is due in part to the 
lack of nitrification. It follows, then, that any treatment which in- 
creases soil aeration also stimulates nitrification. As pointed out 
above, aeration may be increased by increasing the humus content, 
and probably one of the most important reasons for the beneficial 
