4 BULLETIN 1418, U. S. DEPARTMENT OF AGRICULTURE 
tons per acre. The superiority of the plots receiving acid phosphate 
was apparent from the first. They yielded at the rate of nearly 2 
tons per acre more than the check plots. The manured plots yielded 
approximately the same as the checks while the plots receiving sulphur 
fell appreciably below the checks. 
‘In May, 1921, another test was started, including one plot that 
received acid phosphate at the rate of 400 pounds per acre and another 
that received 400 pounds of gypsum per acre. After the application 
‘of fertilizers, four cuttings were made in 1921 and seven cuttings in 
1922. During this time the yield of alfalfa on the plot receiving acid 
phosphate was practically double that of the checks. Prior to the 
application of fertilizers, the plot to which the acid phosphate was 
ole had been the poorest in the series. The gypsum and check 
plots yielded approximately the same for the entire period. 
These preliminary tests indicate that yields of alfalfa may be profit- 
ably increased in the Yuma Valley by applications of acid phosphate. 
This is in line with the view expressed by Hilgard ? to the effect that 
many California soils are low in phosphoric acid. He states: ‘“‘The | 
forecast that for most California soils fertilization with phosphates 
is of exceptional importance has already been abundantly confirmed 
by cultural experience.”’ With the exception of stable manure, other 
fertilizers tried have given no appreciable response. In order to 
obtain more definite information as to the most profitable rate of 
application of acid phosphate, a more complete test was begun in 
1923 on 20 quarter-acre ane that were sown the previous fall. The 
fertilizers were applied April 27, 1923. With the exception of the 
plot receiving 250 pounds of acid phosphate on this date and an 
additional 250 pounds on October 10 and the manured plots which 
received manure at the rate of 12 tons per acre in three equal applica- 
tions of approximately 4 tons each on April 27, June 6, and Octobe re 
the plots have received no fertilizers since the first application. 
The 16 per cent acid phosphate was applied at three rates—250, 500, 
and 750 pounds per acre. The 44 per cent acid phosphate was 
apphed at the rate of 182 pounds per acre, which is equivalent 
in available phosphoric acid to 500 pounds of 16 per cent acid phos- 
phate. Inasmuch as sulphur has given remarkable increases in 
yields of alfalfa in parts of the West, applications were made to 
several plots to determine more definitely the results that might be 
expected from its use. 
The detailed and summarized results of this experiment are given 
in Table 2. 
Although there was an appreciable increase in growth the first 
year, the big increase in all cases came the second year (fig. 1), 
after which the yields declined rapidly. Results for 1925 have not 
been included, as they are not available for the entire year. Two 
light cuttings were obtained in the early spring and a third light 
cutting in the fall. During the intervening time the alfalfa was 
allowed to go to seed, and it is obvious that under such treatment 
the hay yields would not be representative. The effects of the acid 
phosphate, however, particularly the heavier applications, were 
still very apparent. Previous tests indicated that if the acid phos- 
phate had been applied earlier, about the latter part of February 
HILGARD, E. W. SOILS, p. 393. 1911. 
