N 
110 BULLETIN 699, U. S. DEPARTMENT OF AGRICULTURE. 
single year, it appears that their relative natural fertility varied 
greatly, yet check plot No. 23, which yielded 3 less bushels of corn — 
than check No. 12 in 1907, exceeded the yield of this latter plot in 
1908, by nearly 11 bushels. These same inconsistencies are noticeable 
throughout the table. The plot receiving a fair application of lime 
gave better yields than any of the phosphate treated plots, yet tt 
plots treated with basic slag, which is richer in lime than any of the 
other phosphates, gave poorer yields than either of the “ floats” plots 
and two out of three of the acid phosphate plots. While the raw 
rock phosphate plots produced on the whole better results than those 
treated with either of the other forms of phosphoric acid, the average 
yield of corn on these plots for the entire five-year period was only 
1 bushel greater than the average on all the check plots. 
In view of the fact that the applicat:ons of raw rock were entirely 
too light to prove effective and moreover were only from one-sixth 
to one-half as great as those of acid phosphate, no comparison be- 
tween the two forms of phosphoric acid would be justified even had 
the soil been responsive to phosphate treatment. Practically the 
only conclusion to be drawn from these results is that all forms of 
phosphoric acid were ineffective. 
Ellett and Hill? also published the results of four pot experiments 
with various phosphates on different but important Virginia soil 
types. The tests were made in the greenhouse and were similar in 
all respects. Twenty-five pounds of each soil type was taken for each 
pot, the fertilizer added, and the whole thoroughly mixed. The ~ 
moisture content was maintained in each pot throughout the experi- 
ment at about one-half the water holding capacity of each soil. The 
seed planted, the number of plants per pot, and the fertilizer treat- 
ments were the same for each series of pots. Every treatment was 
run in quadruplicate. The various soil types employed were as fol- 
lows: (1) A typical Coastal Plain sandy soil, low in phosphoric 
acid; (2). a Piedmont “ Red Lands” clay soil well supplied with phos- 
phoric acid and potash but low in nitrogen; (3) a Piedmont choco- 
late-colored clay loam suitable for general agriculture, with rather 
high contents of potash and phosphoric acid, but low in nitrogen; 
(4) a Piedmont gray sandy soil lower in its content of phosphoric 
acid and potash than the chocolate clay loam and very poor in 
nitrogen. 
The results of the pot experiments with these soils are given in : 
Table LX VI. 
1Va. Agr. Expt. Sta. (Blacksburg). Bul. No. 200, p. 24 (1912). 
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