June 17, 2011

The 2011 production season has already proved challenging for much of the United States. So far we have seen a crippling drought across the southern Great Plains and incessant rains across the northern Plains and eastern Corn Belt leading to significant planting delays and major floods in the Mississippi and Missouri river basins.

Heavy rains this spring resulted in 90% of the Ohio corn crop being planted three to four weeks behind normal. Significant acreage in the Dakotas qualified for prevented planting. Across the southern Great Plains, record dryness extending back to last fall has virtually eliminated much of the winter wheat crop. To add insult to injury, heat and dry conditions are beginning to expand northward into Arkansas, Tennessee, Missouri, and Kentucky.

Here in the western Corn Belt, persistently cool conditions have developed across the Dakotas and Montana, with above normal moisture common from Montana southeast through the eastern two-thirds of Iowa. In addition the Missouri River is flooding due to excessive spring rains and winter snow accumulations. Flooding is expected to continue into at least late August.

For Nebraska, the average emergence date for the 2011 corn crop was May 20, according to the Nebraska Agricultural Statistics Service. This is about five days behind the five-year average.

For the past 30 days heat from the southern Plains and cold from the northern Plains have been battling it out over Nebraska. Generally, the southern third of the state has experienced above normal temperatures since May 20, while the northern third has fallen further behind normal with persistent below normal temperatures. See Table 1 for a complete list of the GDD accumulations for corn emerging on May 20.

Several columns in Table 1 provide insight as to where this crop stands and when it may mature if normal temperatures are realized from now to the end of the crop season. Under the GDD column, actual (act) accumulated GDD units and GDD units given normal (Norm) temperatures are listed. The “f +/-“ column calculates the percent of units ahead or behind normal when compared to the variety at full maturity. For this analysis all locations were assigned a 2569 GDD (110 day) variety .

The Cal/Day/Mature column lists the calendar day maturity that projects the day of the year the 2569 GDD variety will mature if normal temperatures are observed for the remainder of the growing season. Most producers in northern and western Nebraska typically grow varieties that can be 200-400 units less than the 2569 GDD units so be sure to consider the crop maturity you planted when reviewing this estimate.

It generally takes 23 GDD units to accumulate one day of crop growth. This is helpful in calculating where your crop stands in relation to the state average calculated by NASS. To determine how your crop relates to the state average, find the difference between actual GDD accumulations and normal GDD accumulations in Table 1 for the location nearest your farm. Divide the difference by 23.

For example, if the difference comes to -120, the crop is 5.2 days behind normal for the May 20 emergence date. Next, add the differential of this year’s crop compared to the five-year average. In this case it is five days. If you add together these two figures, you can estimate that your crop is about 10 days behind the five-year state average.

Al Dutcher
Extension State Climatologist