IOWA ACADEMY OF SCIENCE 
103 
THE ACTION OP MANURE ON A CERTAIN IOWA SOIL. 
BY E. B. WATSON. 
The soil on which these studies were made was Southern Iowa loess from the 
experiment field in Decatur county, lowa^. It is a fine loess soil containing 
considerable clay with the silt, and enough organic matter in the surface to 
make it dark brown. This loess differs from that of both eastern and western 
Iowa in its color, which is grey rather than yellow. It is the prevailing type 
of soil in southern lowa.^ The field from which the sample was taken had 
been in cultivation thirty or forty years, and in that time had probably pro- 
duced no clover crops. The productiveness was quite low owing to continuous 
cropping with grain and poor cultural methods. 
On the experiment field located on this farm it was noted that manure in- 
creased the growth of all crops experimented with, but the results with clover 
were the most striking. In fact clover was almost a complete failure on the 
untreated plots, but it produced a very good stand and growth on the plots 
treated with manure. Laboratory work was undertaken to ascertain the 
reason that manure had this effect on the soil, and clover was chosen as the 
indicator because it responded so readily. 
A sample of soil was secured from the field in October, 1905. A short series 
of gallon pots were first run to find out if stable manure would benefit the 
growth of clover in the greenhouse in the same way that it did in the field. 
An application at the rate of sixteen tons per acre was chosen because it is 
double the usual application in field experiments, and it was desired to get as 
decided differences as possible by any treatment. The area of the surface of 
the soil in the pot is .23 sq. ft. and 76.8 grams per pot equals an application 
of sixteen tons per acre. The manure used was fresh cattle excrement con- 
taining no bedding. This contained 11.8 per cent of dry matter and .23 per 
cent of nitrogen. Average barnyard manure contains .5 per cent nitrogen, 
which would equal .384 g. per pot. To bring the amount of nitrogen in the 
application up to this standard, 167 g. of the manure were used. 
Plate I, fig. 1, shows two of the pots seventy-nine days after planting. 
Pot i is the check and it shows the poor stunted growth of the clover on 
the untreated soil. Pot 3 was treated with manure. The clover on this pot 
has made a fine normal growth, showing that the soil has been changed from 
a poor medium for clover growing to a very good one. This experiment gave 
the desired information, showing that the soil responded to the action of 
manure in the greenhouse as well as it did in the field. Results corresponding 
to the above were obtained in each of the series run in the subsequent work. 
The first and most evident conclusion in regard to the cause of the better 
growth of the clover is that the manure furnished plant food which the soil 
.^Bulletin 98. Iowa Exp. Sta. 
-Bulletin 82. Iowa Exp. Sta. 
