Update on Crop and Soil Status Across the I-States – August 21, 2019

August 22, 2019 3:02 PM
Blog Post

Update on crop and soil status across the I-states – August 21, 2019

This year the FACTS project is providing a suite of regional scale maps to assist decision making. The data provided is based on APSIM model simulations which are driven by current and forecasted weather data, soil data, NASS planting date data and different corn hybrids and soybean varieties across the landscape. The maps were created from 30 field simulations per county. In this article we provide an update on weather, soil, and crop variables.

Precipitation: The May 1 to present precipitation accumulation is 2–6 inches above normal for most of the three I-states. This is largely the result of high rainfall amounts in May and limited rainfall in July. According to Weather Prediction Center, during next week (August 20 to 27) rain is expected across the area with higher precipitation to occur in southern Iowa.

Temperature: Growing degree day (GDD) accumulation from May 1 to present is about 50 to 150 GDD below normal in Iowa and about 50 to 150 GDD above normal in Illinois and Indiana. Since May 1, northern Iowa has accumulated 1800 GDD while southern Illinois more than 2500 GDD. For the next week, GDD accumulation is projected to be 20 GDD below normal for Iowa and 20 GDD above normal for Illinois and Indiana. Iowa’s 50% corn planting progress was about 2-3 weeks earlier than Illinois and Indiana. On the other hand, Illinois and Indiana are accumulating GDD faster, which suggests that the difference in crop maturity among states will be less than anticipated despite the 3-week difference in planting.

Map of inches of precipitation departure from normal from May 1 2019 to current dateMap of growing degree days departure from normal from May 1 2019 to current date

Soil moisture and rooting depth: Current soil moisture levels across the soil profile are within 75 to 115% of field capacity, which is considered ideal for plant growth and soil N mineralization. Crops are taking up water from the soil at a rate of about 0.20 inches/day. At present, model simulations indicate that both corn and soybean have roots at a 50 to 60-inch soil depth across much of the area.

Soil N mineralization and crop N uptake: On average for 60% of the region, soil N mineralization since May 1 is at or above normal. The exception is a transect from east central Iowa to southeast Indiana where soil N mineralization is below normal. However, at this period, soil N mineralization is of less importance for corn as corn plants have taken up most of their N needs and current N uptake is at about 1.5 pounds N/acre/day. In contrast to corn, soybeans are taking up 2-3 times more N than corn.  At the present soybean stage, N-fixation can provide up to 2.7 pounds N/acre/day. The current soil moisture is ideal to support high N fixation rates.    

Crop photosynthesis and grain accumulation: Currently corn photosynthesis, estimated as pounds C/acre/day, is 75 pounds C/acre/day while soybean photosynthesis is about half as much. According to USDA NASS, 29.4 million corn acres and 26.4 million soybean acres have been planted across the three I-states. Thus, the total amount of carbon that is fixed through photosynthesis across the area is about 3.2 billion pounds of C/day! Nearly all that C is being assimilated as in corn kernels and soybean seed. Across the area, model simulations for the next week indicate corn grain yield accumulation of 4.5 bu/acre/day.

Corn Net Photosynthetic RateSoybean Net Photosynthetic Rate

In conclusion, the temperature and radiation levels in September, which are currently unknown will determine the date of crop maturity, final yield levels, and expected rate of grain moisture dry down.

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Sotirios Archontoulis Associate Professor of Integrated Cropping Systems

Dr. Sotirios Archontoulis is an assistant professor of integrated cropping systems at the Department of Agronomy. His main research interests involve understanding complex Genotype by Management by Environment interactions and modeling various components of the soil-plant-atmosphere continuum. Dr...

Mark Licht Assistant Professor

Dr. Mark Licht is an assistant professor and extension cropping systems specialist with Iowa State University Extension and Outreach. His extension, research and teaching program is focused on how to holistically manage Iowa cropping systems to achieve productivity, profitability and en...