This bulletin is the report of the performance of corn hybrids tested at 24 locations in Iowa during the years 1955, 1956, 1957 and 1958. Summaries of 2-year, 3-year and 4-year periods are shown.

The presentation of this report does not imply approval or endorsement of the hybrids tested by any of the cooperating agencies.

The state was divided into 12 districts as shown on the Iowa map (fig. 1 ). Two test fields were planted within each district.

The name and address of each cooperator and the dates of planting and harvesting are shown in table A .

Any producer of hybrid corn seed was eligible to make entry in the 1958 test. Each producer was limited to a maximum of five entries in each district.

Seed for testing was obtained by representatives of the Iowa Crop Improvement Association by sampling at random from supplies of seed to be sold. Each sample was taken from several bags and often from supplies at more than one location.

Each hybrid was assigned a code number by which it was designated in the record books throughout the testing period. Thus, no person concerned with the test knew the identity of any entry.