Iowa soils are not inexhaustible. A survey of the state recently completed by the Iowa Agricultural Experiment station and reported in this bulletin shows clearly that it is time now for Iowa farmers to give their best thought and effort to maintaining the fertility of their farms.

Hundreds of soil samples collected from the typical soil areas of the state and thoroughly analyzed show that sooner or later the production of maximum crops will he limited by the lack of some plant food element unless farming systems are changed to meet the situation. The phosphorus content of Iowa soils is not large and this element must be supplied to all the soil areas sooner or later. There is a marked tendency in many sections for Iowa soils to become acid and that must he corrected by lime applications. Even the supply of nitrogen and organic matter has its limitations also and demands more attention than commonly supposed.