IOWA ACADEMY OF SCIENCE 
115 
The first series to test the question was planted December 30, 1905. Pot 44 
was the check, pot 41 was treated with cattle manure at the rate of sixteen 
tons per acre, and pot 39 was supplied with mineral fertilizers in amount equal 
to the plant food found in the manure furnished to pot 41. On March 5, or 
sixty-five days after planting a picture was obtained of these pots and shown 
in Plate IV. 
MANURE vs. MINERAL FERTILIZERS. 
The same pots were photographed again May 3d, when the clover was 124 
days old, with the results as shown in Plate V. 
THE SAME POTS AT A LATER DATE. 
A study of these pictures is very interesting. The first picture shows that 
the manure helped the growth of the clover immensely, while there is very 
little benefit up to this time from the mineral fertilizers. The mineral fertil- 
izers had the advantage, too, of being soluble while the manure was largely 
insoluble. 
The second picture shows that the minerals have been helping the clover, 
and this pot is bidding fair to catch up with the manured pot. The check 
pot also has been growing much better than it did it first. It would seem that 
there was something in the manure that caused the soil to be a good medium 
for the growth of clover when it was quite young, but as the clover got older 
it was able to shift for itself and the mineral plant food helped it some. The 
stand varied so much in this series that it is difficult to make exact comparisons 
by means of the green weights, therefore they are not given. 
Complete description of a later series is given, fully establishing the fact 
that the manure helped the growth of the clover far beyond the help given 
by the soluble plant food, and proving that the mineral plant food theory is 
not a satisfactory explanation of the action of manure on this soil. 
A fresh sample of soil was secured from the field in October, 1906. The 
sample was pulverized and mixed as soon as it reached the laboratory and 
placed in closed cans to keep it as near to field condition as possible. Manure 
leachings, similar to that used in the last experiment described under the dis- 
cussion of the physical effect of the manure, were analyzed and found to con- 
tairf 1.005 per cent solid matter, .65 per cent ash, .02296 per cent nitrogen, .012 
per cent phosphoric acid and .05294 per cent potassium. 870 c. c. of the leach- 
ings, therefore, contained .2 g. of nitrogen. This amount of nitrogen was found 
by previous experiments to be sufficient for the clover. 870 c. c. of leachings 
contained .0456 g. of phosphorus and .46058 g. of potassium. The pots 208 and 
209 marked N. P. K. were given exactly the same amount of these three ele- 
ments of fertility. The nitrogen was furnished in 1.212 g. of sodium nitrate, 
the phosphorus was found in .5271 g. of disodium hydrogen pb-osphate and the 
potassium in 1.0255 g. of potassium sulfate. To ascertain wjbich one of these 
elements was responsible for the better growth of the clover, they were also 
applied separately as is shown by the table. For purposes ff comparison two 
other carriers of nitrogen were tried, namely dried blood and peptone. .2 g. 
of nitrogen was supplied to each pot. 870 c. c. of the manure leachings were 
divided by distillation into two approximately equal portions a distillate and a 
