Laboratory and greenhouse experiments were conducted to study the availability of fertilizer P in 20 samples of different soils representing 10 of the principal soil associations in Iowa.

Ryegrass plants recovered an average of approximately 50 percent of the added fertilizer P during a 385-day cropping period in the greenhouse. It appeared that continued cropping would have resulted in very little additional recovery of the added P. Differences in recovery of the added P from the different soils were relatively small, despite differences in rate of fertilizer addition or differences in soil pH, CaCO₃ content, level of available soil P, soil organic matter content, and soil texture.