IOWA ACADEMY OF SCIENCE 
111 
EFFECT OP MANURE ON DROUTH LIMIT. 
Treatment 
Net weight 
soil g 
Per cent of moisture in the soil 
Pot 
Opti- 
mum 
First 
drouth 
Leaves 
dying 
h I’ves 
brown 
Dead 
n 
73 
4020.5 
20.9 
9.3 
8.7 
7.9 . 
7.5 
3985. 
20.7 
8.7 
8.2' 
7.4 
7.0 
Mcimii’e 
4003.7 
19.9 
10. 
9.5 
8.3 
8.0 
1. 
1.05 
.65 
.75 
It is seen that the manured pot had 1 per cent more moisture when drouth 
first overtook it, and .75 per cent more when the crop died. These figures are 
not taken to mean more than that the drouth limit is higher in soil that is 
manured than in untreated soil, hut as each experiment gave the same result, 
it is safe to claim that much. As the result of the work on the water holding 
capacity of soils, it was decided that manure enabled the soil to retain more 
water. It seems from the above data that a plant will wilt in a manured soil 
when there is more water in it than in an unmanured soil. In other words 
the extra water held by the manured soil is not all available to growing crops, 
and probably none of it. Manure can not help the growth of clover on account 
of its adding to the soil an increased ability to retain water, for it does not 
give this water up to crops. 
The above study of the physical action of manure on the soil is not con- 
sidered by any means to be exhaustive, but it was not thought necessary to 
carry it to completion because the soil in these experiments was kept in the 
best possible physical condition, and it was hard to see how any material as 
manure could benefit it to such an extent as to materially aid the crop, especi- 
ally as the effects of the manure on the soil were found to be so very slight. 
Besides, a simpler method of attack was found. 
The second way by which the problem of the physical effect of the manure 
was attacked was to study the action of a substance that gave the same physical 
effect without at the same time carrying plant food or other possible beneficial 
properties as does the manure. The above studies show that peat does fairly 
well in regard to duplicating the effects of the manure, and although peat 
carries some plant food, it is not in an available form. 
A series was run to test the effect of peat. Mineral fertilizers were added 
to the peat to make an artificial manure, giving both the physical effect and 
the plant food. The peat used lost 50 per cent on ignition. The series was 
planted February 24th. Pictures were* taken May 3d. Plate II, fig. 1, shows 
representative pots, both untreated and treated with peat. 
EFFECT OF PEAT. 
Pot 76 had mineral fertilizers added to it, and pot 80 had mineral fertilizers 
and peat added to it. There is no apparent benefit derived from the use of 
peat. 
Green weights were obtained June 1st. The series, with the treatment and 
the results are given in the following table. 
