4,000 pounds of phosphorus
24,000 pounds of potassium
6,200 pounds of magnesium
23,400 pounds of calcium.

"These, remember, are the amounts per acre that would be added to
the soil by burning the eighty tons of clover on one-tenth of an
acre.

"Now compare these figures with the total amounts of the same
elements contained in the common corn belt prairie soil of Illinois,
which are as follows:

1,200 pounds of phosphorus
35,000 pounds of potassium
8,600 pounds of magnesium
5,400 pounds of calcium.

"From these figures you will see that the analysis of a single
sample of soil collected from a spot of ground that had sometimes
received such an addition as this would be positively worse than
worthless, because it would give false information, and that is much
worse than no information.

"The methods of chemical analysis have been developed to a high
degree of accuracy, and it is not a difficult matter to find a
chemist who can make a correct analysis of the sample placed in his
hands; but the chief difficulties lie, first, in securing samples of
soil that will truly represent the type or types of soil on the
farm; and, second, in the interpretation of the results of analysis