Crops > Cost & Return > Yields

Iowa corn and soybean county yields

AgDM Newsletter
April 2009

The 2008 average corn and soybean yields for counties and districts in Iowa were released in early March 2009. This information is collected by the USDA National Ag Statistics Service Iowa Field Office each year through a County Agricultural Production Survey. The Ag Decision Maker website, we provides this data in Information Files A1-12 and A1-13, Historical Yields by County, which show county averages from 1999 through 2008. This information is helpful for seeing trends in yields over the past 10 years. Information File A1-14, Iowa Corn and Soybean Yields, also shows the 10-year average yield, and the year and yield results for the highest and lowest years for each county. This information is helpful in developing corn and soybean budgets, cash-flow projections, or other types of analysis for producers where the actual production history is not available. The crop yields are reported in bushels per harvested acre, some programs such as Average Crop Revenue Election (ACRE) use bushels per planted acre.

The USDA National Ag Statistics Service Iowa Field Office conducts the County Agricultural Production Survey each year to collect data that are then used to establish the county level yields as well as livestock inventory.  The address for the NASS website for Iowa is:

Each year, approximately 20,000 randomly selected operators in Iowa are interviewed using an eight page questionnaire.  The operator reports the whole farm’s acres, planted, harvested, yield and production for corn, soybeans, oat, wheat, and hay, storage capacity, cattle inventory, hog inventory, goat inventory, sheep inventory, and any other livestock.  They also are asked to report acres rented from someone else and cash rent paid for those acres.

The data for the sample of 20,000 are collected using several methods; mail, telephone interview, personal interview, or the operator can even report electronically. Data collection begins when corn and soybeans have reached 90 percent harvested in Iowa, typically around mid-November. Trained enumerators or census takers collect the data. The same enumerators are used to collect data for NASS year-round. Strict guidelines are followed by the Iowa office that match steps taken by other state Ag Statistics offices. This ensures comparable results on a national level.

Several steps are taken to check the reliability of the reports. The first step is a check for reasonableness, and any questionable results are double-checked with the operator. The results are then entered into a secure computer system checked again for extreme yields andoutliers in the data. At this point, the data are ready to be analyzed. NASS uses a system called Interactive Data Analysis System or IDAS. With this program, they can graphically look at all data that has been reported. It can be broken down by district and county at this point as well. During this phase, outliers are once again identified but by district and county. These are checked once more with the operator for reliability.

The data are then summarized by district and county indications (or point estimates) for acreage planted, harvested, yield, and livestock inventory. The summary indications are compared against “check data” from Farm Service Agency (FSA) and Risk Management Agency (RMA) at the county level. These finished estimates are reviewed by the NASS Ag Statistics Board in Washington, DC. This board reviews Iowa estimates as well as other states to check for consistency and once again for accuracy. After this final review, the yield reports are published and made available online.

Summary information is available on the Ag Decision Maker website. For other county estimates, including average livestock prices, crop reports, and farm numbers, visit the NASS website for Iowa at:


Ann M. Johanns, extension program specialist, 641-732-5574,