The continuing dry weather pattern in many areas of southern and western Minnesota, and adjoining areas of northern Iowa, has raised further concerns regarding 2013 corn and soybean yields. The very warm weather in recent weeks, along with the limited soil moisture in many areas, has lead to some deterioration in late season crop conditions. The fact that much of 2013 corn and soybean crop was planted later than normal, together with behind normal growing degree units (GDUs) until late August, led to behind-normal crop development when the very hot and dry conditions started. As a result, there will likely be more yield reduction in the affected areas in 2013, as compared to normal.

At the U of M Research and Outreach Center in Waseca, a total of 2.07 inches of rainfall was received in August 2013, which was the first month since January 2013, with below-normal monthly precipitation. Total precipitation for 2013 at Waseca through Aug. 31 was +6.63 inches, or about 25%, above normal. Stored soil moisture at the end of August at Waseca was at 6.5 inches in the top 5 feet of soil, which is slightly below normal.

By comparison, the U of M Research and Outreach Center in Lamberton, received only 11.67 inches of precipitation from May 1 to Aug. 31, compared to a normal level of 14.14 inches. However, Lamberton has received just 2.20 inches of rainfall in July and August, which is only 32% of normal precipitation. As of Sept. 1, there was only 2.48 inches of available soil moisture in the top 5 feet of soil at Lamberton, which is only slightly more than the drought year of 2012. Most of the available soil moisture was at the 3-5-foot soil depth. 

Of course rainfall amounts and timeliness of rainfall events have been quite variable across the region in 2013. Some localized areas of southern Minnesota, especially in southeastern Minnesota, have received more timely rainfalls during July and August than other portions of the region. Many areas of south-central, southwest, west-central and central Minnesota have received rainfall amounts similar to those listed at Lamberton, and are experiencing some level of drought conditions. Due to the variability of the rainfall events from farm-to-farm, and even from field-to-field, we are likely to see a wide variation in crop yields across the region in 2013, even in the same county or township.

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The very warm weather pattern across the region in late August and early July has reduced the crop maturity concerns for most of the Upper Midwest. Well-below-normal temperatures and accumulation of GDUs throughout most of June, July and early August, along with later-than-normal planting, left much of the 2013 corn and soybean crop behind normal development in mid-August. The total accumulated GDUs from May 1 to Sept. 6 at the U of M Research and Outreach Center at Waseca was at 2,160, which is only about 30 GDUs behind normal GDU accumulation. The GDU accumulation was approximately 130 GDUs behind normal on Aug. 20.

As of sept. 3, the National Ag Statistics Service listed 68% of Minnesota’s corn crop in the dough stage, compared to a five-year average of 98% in the dough stage by that date. Corn is considered safe from a killing frost once the corn reaches physiological maturity, which is when the corn kernel reaches the black layer stage, and this is still two to three weeks away in many cases. When the corn reaches back layer, it is still usually at a kernel moisture of 28-32%. Ideally corn should be at 15-16% kernel moisture for safe storage in a grain bin until next spring or summer. So even beyond the corn reaching maturity in the coming weeks, some nice weather conditions will be required to allow for natural drydown of the corn in the field, in order to avoid high corn drying costs this fall.