106 
IOWA ACADEMY OP SCIENCE 
The data given in these tables show that when used alone, lime gave a slight 
benefit, but when used with manure, mineral fertilizers or green manure, there 
was an apparent disadvantage from its use. When all the pots are averaged, 
the limed pots are fourteen points below the unlimed ones. We are not justi- 
fied in concluding from this that lime injures the growth of clover. These few 
points are within the limits of error. However, we certainly are justified in 
deciding that lime does not help. 
The soil was tested for acidity as follows: water was percolated through 
the soil in a pot, 100 c. c. of this was secured and filtered,, boiled a few minutes 
to expel CO2 and tested with N-50 KOH and HNO3 using lacmoid as an indi- 
cator. The solution was found slightly alkaline. 
We conclude that this soil is not acid and the action of the manure in in- 
creasing the growth of the clover was not to correct acidity. 
THE PHYSICAL EFFECT OF THE MANURE. 
To what extent does the physical effect of the manure on the soil infiuence 
the growth of the crop? Agricultural writers often make the statement that 
manure puts the soil in better condition, or adds tilth to the soil, but definite 
information as to just what the physical action of the manure on the soil may 
be, is very scarce. Manure lightens the soil and makes it easier to cultivate, 
but what are the exact changes in the physical properties of the soil? How does 
the manure affect its specific gravity, its volume weight, its relation to heat, 
and above all, its relation to water. Then after these questions are answered 
there is the question of still greater importance, how do these changed physical 
conditions affect plant growth? Everybody has taken it for granted that there 
are changes and that they benefit plant growth, but just why and how it hap- 
pens, nobody has taken the trouble to ascertain. 
The following references contain practically everything of value which is 
published in English on this point. 
Aikman^ after discussing the plant food brought by the manure, says, “We 
must seek for perhaps the most valuable properties of manure in its indirect 
infiuences,” and these are enumerated as 1st, a source of humus; 2d, influence 
on texture of soil during fermentation; 3d, heat of soil by decomposition; 4th, 
carbonic acid given off in fermentation. 
Hilgard^ says this: “Unhumified organic matter lightens the soil, rendering 
it more previous to air and water, and in its progressive decay it gives off 
carbonic gas which is active in soil decomposition.” 
King® says: “One of the most important effects of stable manure when ap- 
plied to soils is its tendency to establish parting planes in the soil which 
favor both the formation and maintenance of strong granulation.” He also 
says: “When a soil is treated with farmyard manure which has become well 
incorporated with it, it has the effect of causing a stronger rise of the deeper 
soil moisture into the surface three feet, where it is most needed in the pro- 
duction of crops.”^ A table is given showing 1 per cent more moisture in the 
surface foot of the manured plot. But this may be due not to increased capil- 
^“Manures and Manuring” Aikman, p. 273. 
2“Soils” Hilgard, p. 135. 
3Year Book U. S. Dept. Agri. 1895, p. 168. 
^“Physics of Agriculture.” King. p. 172. 
