Crop and Weather Conditions
Weather plays a large role in planting and grain development, which, in turn, impacts final grain yield and quality. The principal weather factors include the amount of precipitation and the temperature just prior to and during the corn growing season. These weather factors interact with the corn variety and the soil fertility to power final grain yield and quality. Grain yield is a function of the number of plants per acre, the number of kernels per plant, and the weight of each kernel. Cold or wet weather at planting could reduce plant number, or hinder the plant growth, which may result in lower yields. At pollination time, higher than average temperatures or lack of rain typically reduces the number of kernels. Critical to the final grain quality is the weather conditions during the grain filling period in July and August. During this time, moderate rainfall and lower than average temperature, especially overnight temperature, promotes starch accumulation and increased yields. At the end of the growing season, drydown of the grain is dependent upon sunny, warm, days with low humidity. Conversely, early freezing before the grain has sufficiently dried leads to cracked, low quality grain.
During the 2011 corn growing season, planting and pollination were challenged by adverse weather conditions, which, in turn, impacted final grain yield and quality. Overall, the weather in 2011 involved poor conditions for pollination, which led to decreased kernel numbers per plant and lowered yields in all ECAs (See the “U.S. Corn Production, Usage and Outlook” section for information on yields.). However, the reduced amount of kernels available to be filled moderated the effects of the heat wave and drought in the Gulf and Pacific Northwest ECAs and led to grain with relatively high average test weights. The Gulf region produced the greatest yield, with some of the drought and heat tempered by the earlier rains. The Southern Rail region encountered weather conditions that resulted in the lowest yields, but the greatest protein concentrations and highest test weights. Conditions for field drying prior to harvest were generally favorable in all ECAs, as indicated by low average grain moisture contents.
The following discussion describes in more detail how precipitation and temperature impacted the 2011 corn planting season, and how the weather events affected pollination and the remainder of the growing season.
Just prior to, and during planting, the Ohio Valley and the Midwest (the Gulf and Pacific Northwest ECAs) experienced greater than average precipitation, with major flooding along the Ohio and Mississippi Rivers. In contrast, the Southern Rail ECA received below.
Also during this time, the upper Midwest experienced much cooler than normal temperatures. The combination of cool and wet weather delayed planting by an average of one week throughout the U.S. Typically, only 25% of the corn crop is planted after May 15, based on the 2006-2010 average as shown in the table below. However, in 2011, 37% of the corn remained to be planted. As a result, a higher proportion of the corn crop was planted later than what is considered optimum for yield. Delayed planting is generally associated with lower yields and often with poorer grain quality.
Just before pollination time, on July 11, 2011, there was a large windstorm which is estimated to have had straight line winds of up to 105 mph in a swath approximately 20 miles wide. This storm, called a derecho, affected six states, and travelled between central Iowa to Detroit, Michigan, a distance of 550 miles in the Gulf ECA. Afterwards, there was an unusual occurrence of the majority of these flattened plants lifting back up on their own after a few days. Areas impacted by these severe winds would potentially have lower yield and quality.
The major weather factor observed during the growing season was persistent, scorching heat in the central and eastern regions of the U.S. in July, primarily the Gulf and Southern Rail ECAs as shown in the map of July 2011 Divisional Ranks. The heat wave shattered long-standing daily and monthly temperature records, making it the fourth warmest July on recor nationally, according to scientists at NOAA’s National Climatic Data Center. The heat exacerbated drought conditions, resulting in the largest “exceptional” drought footprint in the 12-year history of the U.S. Drought Monitor. The heat wave came at the prime pollination time and impeded pollination and seed set.