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FEFO 10-06
April 5 , 2010


The National Agricultural Statistical Service (NASS) recently released 2009 county yield estimates for corn and soybeans. In this article, actual 2009 trend yields are compared to 2009 trend yields. For corn, most counties had actual yields above trend yields; however, there were several counties in northern Illinois that had yields below trend. For soybeans, 42 percent of the counties had yields above trend while the remainder has yields below trend yields. Also estimated are Group Risk Income Plan (GRIP) payments for 2009. Six counties will receive corn payments and one county will receive a soybean payment.

Comparison to Trend Yields

Actual 2009 yields were compared to 2009 trend yields to assess whether yields were above or below expectations. A trend yield represents an expectation of yield for the given year. If 2009 could be repeated ten times, the average of those ten yields would equal the 2009 trend yield. Actual yields above trend yields are above expectations. Yields below trend yields are below expectations.

table 1

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The 2009 trend yields were calculated by fitting a linear line through yields from 1972 to 2008 using ordinary least squares. The linear line fitted to the 1972 through 2008 data then was extended to 2009 to forecast 2009 trend yields. Figure 1 illustrates this process by showing corn yields for the state of Illinois. The solid line shows the line fit through the data from 1972 through 2008 while dots show actual state yields. The dashed portion shows the projection of the linear line to determine the 2009 trend yield. This process of estimating trend yields was repeated for each county in Illinois.

Two caveats about the above procedure. First, fitting a linear trend assumes that the yearly trend in per bushel increases have not changed between 1972 through 2009. Many believe that yields are increasing faster in recent years, particularly for corn. If yield are increasing at a faster rate, the linear trend may underestimate true expectations. Second, yield models that include weather variables explain much more of the yield variability (see ). Including weather observations in regression models could influence yield trends estimates; however, yield trend made without weather are unbiased.

Illinois Corn Yields

The state corn yields for 2009 was 174 bushels per acre, 9 bushels above the 2009 trend yield of 165 bushels. An above average yield seems remarkable given the late planting of corn due to a wet spring and delayed harvesting due to a wet fall. Countering poor spring and fall weather was a generally favorable growing season during the summer.

table 1

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Judging by bushels above trend, southern Illinois had a very good yielding year (see Figure 2). Thirteen counties had yields 20 bushels above trend yields. Ten of these counties were adjacent to one another in southern Illinois: Perry (35 bushels above trend), Franklin (32 bushels above trend), Saline (31 bushels above trend), Washington (31 bushels above trend), Williamson (31 bushels above trend), Edwards (28 bushels above trend), Hamilton (27 bushels above trend), Calhoun (23 bushels above trend), Jefferson (24 bushels above trend), Wabash (24 bushels above trend), Bond (23 bushels above trend), Massac (22 bushels above trend), and Wayne (21 bushels above trend) counties.

Not all areas in Illinois had actual yields above trend yields. Judging by yields below trend, DeKalb County had the poorest yields of any county. DeKalb County had an actual yield of 161 bushels, 14 bushels below trend yield. Other counties with yields below trend yields were Boone (12 bushels below trend), McHenry (11 bushels below trend), Edgar (10 bushels below tend), Kane (9 bushels below tend), Lee (7 bushels below trend), Stark (7 bushels below trend), Ogle (6 bushels below trend), Marshal (2 bushels below trend), Jo Daviess (2 bushels below trend), and Lake (1 bushels below trend) counties.

Actual and trend yields for all counties are shown in Appendix Table 1.

Soybean Yields

Illinois' state soybean yield was 46 bushels per acre, 1 bushel below the 2009 trend yield of 47 bushels per acre. From a trend yield perspective, soybeans had a worse yielding year than corn.

table 1

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Many counties had above average tend yields (see Figure 3). Forty-two counties, of 43 percent of the Illinois counties that had reported county yields, had yields above trend yields. Five counties had 2009 yields that were 5 bushels above trend. These included Ford (5 bushels above trend), Jackson (6 above trend), Pulaski (6 bushels above trend), Gallatin (7 bushels above trend), and Massac (9 bushels above trend) counties. Overall, actual yields above tend yields occurred in east-central Illinois, west-central Illinois, and southern Illinois.

Many counties had soybean yields below trend yields. Three areas of counties had yields 5 bushels below trend yields. Jo Daviess County in the northwest corner of Illinois had an actual yield of 46 bushels, 8 bushel below trend yield. A line in northwest Illinois also had yields five bushels below trend line. This line began in the northeast corner with Lee County, having a 2009 yield of 45 bushels, 4 bushels below trend line yield. Below Lee County then were Bureau (7 bushels below tend), Stark (8 bushels below trend), Knox (5 bushels below tend), Peoria (6 bushels below trend), and Fulton (5 bushels below trend) counties. In southern Illinois, a pocket of counties in the eastern part also had yields 5 bushels below trend. These included Jasper (9 bushels below trend), Clark County (8 bushels below trend), Crawford (76 bushels below trend), Fayette (6 bushels below trend), Clay County (5 bushels below trend), and Lawrence (5 bushels below trend) counties.

Actual and trend yields for all counties are shown in Appendix Table 2.

GRIP Payments

table 1

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Table 1 shows counties that are estimated to receive GRIP payments given that a 90% coverage level was selected. Note that actual yields for GRIP payment calculations differ from those typically reported by NASS. NASS typically reports yield per acre as the total production in a county divided by harvested acres. RMA calculate yield per acre as total production divided by planted acres. Since planted acres can never be less than harvested acres, yields used to calculate GRIP payments will be less than NASS yields.

Six counties are projected to receive GRIP payments for corn at a 90% coverage level (see Table 1): Boone ($71 per acre given a 100% protection level), DeKalb ($54), Jo Daviess ($6), Lee ($8), McHenry ($13), and Stark ($20) counties. These counties are located in the northern portion of the state. GRIP payments will vary depending on the protection level chosen. The maximum payment occurs at a 100% protection level. The lowest protection level is 60%. Insurance payments at the 60% coverage level will be 60% of the maximum payment.

Soybean GRIP payments are projected for only one county. At a 100% protection level, Jasper County is projected to have a $12 payment per acre.


Overall, corn yields were above trend yields over much of the state. Southern Illinois had an exceptional production year. Some northern Illinois counties had yields below trend yields. Most counties had 2009 soybean yields within 5 bushels of trend yields. Three counties had 2009 yields 5 bushels above trend. Fifteen counties had 2009 yields that were 5 bushels below trend. Six counties in the northern portion of Illinois will receive GRIP payments for corn. Jasper County will receive a soybean GRIP payment


Submitted by: Gary Schnitkey, Department of Agricultural and Consumer Economics, University of Illinois


table 1

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table 1

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Department of Agricultural and Consumer Economics    College of Agricultural, Consumer and Environmental Sciences
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