This investigation included a 6-year study of the effects of irrigation, stand and fertility treatments on com yields on a clay loam soil near Ames, Iowa. The data obtained from 1956 to 1961 indicated that variations in yields were caused by all three variables. Significant yield differences caused by irrigation treatments were greatest in 1956, 1959 and 1960. The highest mean irrigated yields averaged over stand and fertility treatments usually correlated best with the irrigation treatment where the soil moisture was maintained at or above 60 percent of the available moisture content (AMC). The greatest yield response to irrigation occurred in 1956, primarily because of the very dry conditions throughout the entire growing season. In 1956, each inch of water increased yield by 2.7 bushels per acre up to the 60-percent AMC level. Beyond this point, maintaining soil moisture at 90 percent or greater of field capacity reduced yield per increment of added water.

There was not a significant response to irrigation in 1957, 1958 and 1961, primarily because of ample soil moisture storage and good rainfall distribution at critical periods during the growing season.