phosphorus was applied, the $29.52 worth of phosphorus produced
$98.02 increase in the value of the turnips, $37.45 in barley,
$48.93 in clover (and beans) and $45.99 in wheat.

The total value of the crops grown on the land not receiving
phosphorus during the thirty-six years was $432.43 an acre, while on
the phosphated land the crop values amounted to $662.82, an increase
of $230.39 from an investment of $29.52, the turnips being figured
at $1.40 a ton, barley at 50 cents a bushel, clover hay at $6 a ton,
beans at $1.25 a bushel, wheat at 70 cents a bushel, and phosphorus
at 12 cents a pound. As a general average at these conservative
prices, the investment of $3.28 an acre every four years paid back
$25.60 in the four crops.

In most states the legal rate of interest is 6 per cent but here is
an investment that paid the principal and 680 per cent interest
every four years. And these investigations show that the phosphorus
was used with profit for the production of markedly different crops,
including potatoes and turnips, barley and wheat, clover and beans.

But the soil at Rothamsted is no poorer in phosphorus than is the
average soil of the United States; and these results are given here
not only because they are the oldest and most trustworthy the world
affords, but because they are strictly applicable to the production
of common crops on vast areas of agricultural land in our own
country.

The Form of Phosphorus to Use

The unfertilized soil at the Rothamsted station contains, in