March 2020

The number of days suitable for fieldwork in Iowa is shrinking

The number of days available to complete tillage, planting, crop protection and harvesting is critical to maximizing corn and soybean yields in Iowa. Each year the Iowa Field Office of the National Agricultural Statistics Service (NASS) collects data on the number of suitable field days from local observers in each crop reporting district. The actual number of days available varies considerably from year-to-year, but the trend has been for a shrinking window of opportunity.

figure 1

Figure 1 shows the statewide average number of field days recorded each year from 1964 through 2019 for the period April 2 through June 17, when most tillage and planting operations are done. The number of days available varied from less than 20 in 1993 to 60 in 1977. In 2019, only 26 suitable field days were recorded, the fifth lowest number since 1964. Not surprisingly, the number of suitable field days is highly correlated (inversely) with the amount of rainfall received each year.

The straight line on the graph shows the trend in the number of field days over this period. The line has a downward slope, which means that the number has been decreasing over time. The trend line value has dropped from 48 days to 35 days since 1964, or almost one full day every 4 years. This means that the window for completing spring fieldwork in Iowa is shrinking significantly.

table 1

Some areas of the state have seen sharper downward trends than others. Table 1 shows the average annual decrease in the number of suitable field days for each of the nine crop reporting districts in Iowa.

Northwest Iowa has seen the sharpest decline in spring field days, followed closely by the North Central district, losing a full day in just over three years, on average. On the other hand, Southeast Iowa has shown a significantly slower rate of decline than other areas, losing one field day only every eight years.

figure 2

Figure 2 shows the number of suitable field days since 1964 for the period June 18 through September 9. Summer weather has been less variable than spring weather. One exceptional year was 1993, when only about half the normal number of suitable field days occurred. Many fields were flooded through most of the summer that year.

figure 3

Figure 3 shows the field days each year during the fall harvest season. Note that the two years with the fewest good days were 2018 and 2019. The number of good days has been declining in the summer and fall, as well, but at a slower rate than in the spring. Summer field days have been declining one day every 10 years, while fall days have been declining one day every 15 years.

More details about suitable field days can be found in AgDM File A3-25, Days Suitable for Fieldwork in Iowa.

Crop producers can adjust for fewer expected field days in several ways.

  1. Reduce the number of operations performed to cut down on the total hours of field time needed.
  2. Invest in larger machinery, which can cover more acres per day.
  3. Outsource some operations to a custom operator or input supplier.
  4. Improve the efficiency of field operations by using grain carts, seed tenders, auto-steer and other technologies that keep key machines running.
  5. Use multiple operators to increase the number of hours per day machinery can be utilized.
  6. Install artificial drainage to extend the days for which fieldwork can be completed.
  7. Diversify into crops that have different peak periods for field work.

AgDM File A3-28, Farm Machinery Selection, contains more information about estimating the number of field days needed each year, as well as a hand worksheet and electronic spreadsheet.

A new publication by Iowa State University researchers Gene Takle and William Gutowski provides extensive background information about how Iowa’s agriculture may have to adapt to future climate conditions, Iowa’s Agriculture Is Losing Its Goldilocks Climate.


William Edwards, retired economist. Questions?