Jtdy*8» 3993 
Efficiency of Phosphatic Fertilizer 
173 
heads had turned yellow the plants were cut. This stage of maturity 
was reached in 36 to 48 days after the plumules had broken the ground* 
according to the season in which the plants were grown. Both green 
and oven-dried weights of the heads and stalks from each pot were 
obtained, but for the sake of conciseness only the oven-dried weights 
of the combined heads and straw are reported. The ratio of heads to 
straw appeared to be constant for plants of a given weight in any one 
experiment, irrespective of the source of phosphoric acid used. Where 
the larger quantities of available phosphates were used, the growth of 
the plants was fully equal to that made under good field conditions. 
Glazed earthenware pots were used in some of the tests, and tin pots 
that had been coated with tar paint were used in others. Each container 
had a capacity of 5 gallons, and both kinds of containers gave equally 
good results. During the day the pots were kept on trucks in a wire 
inclosure (5 meshes to the inch) and at night and during heavy rains 
they were run into a glasshouse. The order of the trucks was shifted 
daily and the order of the pots on each truck was changed every few 
days to insure uniform conditions of growth. 
As soon as an experiment was started the moisture content of each 
soil was made up to about 60 per cent of its maximum water-holding 
capacity, and was kept constant by weighing. When the plants attained 
considerable size the weights of the pots plus the soil were taken daily* 
and as the plants became larger, allowance was made for the added weights 
of the plants. Transpired water was replaced by rainwater containing 
only 17 parts per million of total solids. The plan of the experiment and 
the methods of comparison were such, however, that appreciable impur¬ 
ities should not have affected the accuracy of the result (6). 
The phosphates were thoroughly mixed with the first 4 inches of soil 
in the pots after the various applications had been made up to the same 
weight by the addition of silica sand. Whenever the phosphatic fertilizers 
were added to some of the pots in an experiment, the soil in all the other 
pots was stirred in a similar manner so that it might be in a uniform 
mechanical condition in all the pots at the time of planting. The sodium 
nitrate, ammonium sulphate, and potassium salts were added in solution* 
half of the total quantity being incorporated with the soil before planting 
was done, and the remainder when the plants were somewhat less than 
half-grown. Half the nitrogen was derived from sodium nitrate and half 
from ammonium sulphate, in order that the efficiencies of the insoluble 
phosphates might not be appreciably affected by the unassimilated acid 
and alkaline residues of the nitrogen salts. 
In the limed series sufficient lime (air-slaked lime containing some 
carbonate) was added to each pot to satisfy the lime requirement of the 
soil as determined by the Veitch method, the lime being thoroughly 
incorporated with the volume of soil in each pot three or four days 
before the phosphates were added. 
Analyses of the five different phosphates used in the experiments are 
given in Table I. 
