8 
is no need for potash fertilizer. The decomposition of the lava frag- 
ments is greatly increased by the products arising from the decay of 
organic matter under the prevailing anaerobic conditions, with the 
result that potash is rendered soluble at a rate sufficient to supply the 
needs of rice, but the limited supply of potash present, together with 
the fact that large amounts of potash are taken up by rice, will sooner 
or later necessitate the use of potash-bearing fertilizer. 
FERTILIZER EXPERIMENTS. 
Some fertilizer experiments with rice have already been published 
by this station. 1 The results were such as to emphasize the need for 
a more systematic study of this question, and in view of the fact that 
the yields obtained by the rice growers throughout the islands are 
frequently unprofitable, a series of fertilizer tests were instituted on 
the rice trial grounds of the station in the spring of 1909. These ex- 
periments were continued on the same plats throughout seven con- 
secutive crops. In Hawaii little or no rotation of crops is practiced, 
and two crops of rice are grown on the same land each year. 
The soil on which these experiments were made had been previ- 
ously devoted to rice culture and was known to be quite uniform in 
productivity. After the plats had been laid out. however, an addi- 
tional crop, without fertilization, was grown for the purpose of 
determining more definitely their uniformity. The results showed 
the plats to be extremely uniform throughout, practically the same 
yield having been obtained from each. The plats were separated by 
low dikes so constructed as to prevent the lateral movement of fer- 
tilizers and irrigation was adjusted so as to insure a constant water 
supply of about 2 inches in depth above the surface of the soil. 
After harvesting the first crop the original plats were divided into 
two equal portions, which here are to be designated as series A and B. 
The former were fertilized previous to the time of transplanting the 
spring crop only, while the latter received the same applications in 
like quantities to both the spring and fall crops. Previous experience 
had suggested that nitrogen would prove to be the most needed ele- 
ment, and this was borne out by the results obtained later. The yields 
obtained, fertilizers applied, etc.. are recorded in the tables, using 
the following values in calculating the cost of fertilizers, profits, etc. : 
Ammonium sulphate, $80 per ton; superphosphate, $20 per ton: 
potassium sulphate, $55 per ton; paddy, $0,025 per pound. In calcu- 
lating the profit'or loss, the extra expense incurred from the increased 
labor attached to making the application of fertilizers, harvesting, 
and marketing the increased yields, etc., was not included. 
1 Hawaii Sta. ttpts. 1907 and 1908. 
