160 Proceedings of Indiana Academy of Science. 
THE RELATION OF NITROGEN, PHOSPHORUS AND ORGANIC 
MATTER TO CORN YIELD IN ELKHART COUNTY, INDIANA. 
R. H. CARR and LEROY HOFFMAN, Purdue University. 
The fertility of the soil is so closely related to the progress of a 
community that any considerable increase in the productiveness of the 
soil from any cause is reflected in greater community prosperity. It is 
therefore important to study the soil and its needs. 
INVOICE OF THE SOIL. 
Just as an invoice of the stock of goods in a store aids the merchant 
in estimating his resources, so an invoice of the plant food in the soil 
enables the farmer to get a rating of his possible crop yield and enables 
him to plan intelligently for future soil improvement. A supply of plant 
food does not necessarily insure a good crop yield, as there are present 
sometimes counteracting conditions. Examples of such are found in 
Samples 1, 10 and 51. But these are usually evident, and the data to 
be nreccnibed shows that crops are generally produced where there is 
present sufficient plant food. 
. 
RELEASE OF THE SOIL’S Foop SUPPLY. 
The soil is composed of small fragments of rock particles mixed with 
more or less organic matter in various stages of decay. Only a small 
part of the plant food in the rock particles is available at any time. 
It is thought that the food elements contained in these rock particles 
alone, are not liberated fast enough from year to year to produce a 
paying crop. This is not so, however, with that stored in organic mat- 
ter, especially the fresh organic matter, which not only releases its plant 
food rather rapidly, through bacterial action, but also aids materially 
in freeing that tied up in the rock particles of the soil. In view of this 
important part played by soil organic matter, it was thought best to 
classify all soils collected according to the amount of organic matter 
they contained. 
PLAN OF INVOICING. 
The samples of soil (total 57) from eleven soil types were collected 
late in September, 1917, in order to estimate more accurately the pos- 
