70 BULLETIN 699, U. S. DEPARTMENT OF AGRICULTURE. 
and above the check plots) obtained from plots treated with the 
different types of phosphates up to the close of 1914. 
In reporting these results Brooks discarded the yields chee 
during the first two years of the experiment on the assumption that 
the difference in the natural fertility of the plots would be less 
strongly marked after two years of fertilization. It might be said, 
however, that if the same plan had been followed in the earlier 
experiment where equal money values of the various phosphates were 
applied the average results would have been even more favorable to 
the less soluble phosphates than reported. 
In comparing the crop yields in this later experiment each plot 
was compared with the check plots between which it lay and these 
checks were given a weight inversely proportional to their distance 
from the plot for which they served as a basis of comparison. 
The validity of such a method of comparison is based on the as- 
sumption that the variations in the fertility of a field are fairly 
regular. Other investigators consider that a comparison of the 
average yield of all check plots with each treatment is a much fairer 
basis on which to compute differences in fertilizer values. 
TABLE XXXIX.—Average increase per acre in corps produced on plots treated 
with different classes of phosphates (1899-1914). 
Corn, 3 Onions, 2 
years, 1899 Hay, 2 years, 1906, 1907. years, 1901 
-| °1913,1914. i 12S] 1902.” Coupee 
75 é s 
Fertilizer. 2] jp,’ 
: Seal 1908. 
j Grain. |Stover.| Hay. | Rowen.| Total. | Sound. lio 
ms 
Bush. | Lbs. Lbs. Lbs. Lbs. Bush. | Bush. Lbs. 
Natural mineral phosphates....) —1.06 | 318.87 | 398.30 |—131. 00 267.30 |—30.60 | 10.76 | 9,817.59 
Basic slag and bone meals....... 8.03 | 905.50 | 615. 55 97. 33 712. 88 | 143.60 |—19. 23 | 21,026. CO 
Dissolved phosphates...........- 9.96 | 651.11 | 753.33 | 350.67 | 1,104.00 | 1386.73 |—12. 56 i. 758. 60 
Soy beans, 1 Potatoes, 1 ~ 
Hun- ilae 1910. r,1910. | Oat and 
Oat hay,| garian Pnsilane a) Dame: alfalfa Se or 
Fertilizer. l year, | hay, ae ue eT hay, 1 ao 
1900. | Lyear, | Yoga’ Market- year, | {oi7? 
1900. Grain. | Straw anIC Total 1911. 
Natural mineral Lbs. Lbs. Lbs. Bush. Lbs. Bush. | Bush. Lbs. Lbs. 
phosphates. -..--.-- 231. 70 166. 70 |—1, 638. 70 0.77 | 290.56 }—10.70 | —8.30 80. 00 91. 70 
Basic slag and bone 
MOAI Se eis Se 1,324. 40 |—222.23 | 7,608.90 4.09 | 794.67] 16.40} 18.90 | 1,626.67 | 244.40 
Dissolved phos- 
phatessesseaee eee 1, 520.00 |—253.30 | 7,361.30 3.87 | 776.00 | 26.90] 29.50 | 1,560. 00 73. 30 
It will be seen by dividing the phosphates into classes and taking 
the average yield of each class, as Brooks has done in his summary, 
the soluble phosphate plots on the whole surpassed all the other 
phosphates. Next in order came the so-called available phosphates, 
consisting of raw bone, steamed bone, and basic slag, and finally 
ee 
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