In-Season Corn and Soybean Forecast of Soil Water-Nitrogen and Yields for Central and Northwest Iowa: A Pilot Project

June 17, 2015
ICM News

By Sotirios Archontoulis, Mark Licht and Ranae Dietzel, Department of Agronomy

A team of Iowa State University Department of Agronomy faculty and staff specialists in crops, soils and climate have begun an innovative pilot project to provide an in-season crop and soil water-nitrogen status and an end-of-season yield forecast. The approach combines use of the Agricultural Production Systems sIMulator (APSIM) cropping systems model, the Weather Research and Forecast Model (WRF), and parallel in-field data collection to verify model predictions.

This pilot project focuses on two locations, two crops, and two planting dates (Table 1). In-field data collection is generated from replicated experimental plots at ISU Research Farms near Ames (central Iowa) and Sutherland (northwest Iowa) and are managed following standard practices for these regions to represent reality better. Data collection includes sensors for data logging of soil water, soil temperature, and groundwater; soil sampling for nitrate- and ammonium-nitrogen; plant sampling for leaf area index, biomass accumulation, nitrogen uptake; and crop staging. All the information on soil, crop, climate, and management is integrated into APSIM to perform the systems analysis and generate a forecast.

Information to date shows that corn and soybean growth is slightly below normal due to cooler conditions and that there were 21 rain events over the last 45 days (May 1 to June 15) at both locations. The frequent rain events have kept soil moisture at near-field capacity which is ideal for plant growth but, at the same time, the cloud cover reduced solar radiation needed for photosynthesis and lowered air temperatures as compared to historical years. The reduced temperatures have impacted soybean more than corn.

The soils have adequate water and nitrogen (nitrate- and ammonium-nitrogen) to sustain high crop growth over the forecasted period (Tables 2 and 3). In a scenario analysis for early planted corn in Ames, we found that an additional application of nitrogen has less than a 20% chance of increasing yield enough to pay for the additional nitrogen. Everything depends on how crop growth continues through the summer.

From current weather, crop and soil information, crop yields will be close to normal yields levels except for early planted soybean yields at the Sutherland location (Table 4). At Sutherland, air temperatures reached near-frost levels twice in May. Early planted crops lost growth and yield potential but there is still potential for high yields if weather conditions become more favorable. The simulated forecasts have high uncertainty early in the growing season and this is evident in the large differences between the 10% and 90% probabilities. The uncertainty in yield prediction will get lower as the growing season progresses.

These are the first results from the pilot project and should be interpreted as such. Cropping system forecasts are highly dependent on weather forecasts. Simulations and predictions will be updated frequently as new information on climate, soil, and crop information becomes available for model analysis. The forecast provided by this pilot project is valid at the time the forecast was completed (June 15, 2015). Additional forecasts will be made throughout the growing season to update the information provided in this ICM Newsletter article.

Table 1. Information on the eight cropping systems used in the pilot project.

Table 2. Current status of crop stage, soil water and soil nitrogen as of the June 15, 2015 forecast date.

Table 3. Predicted cumulative rainfall, water and nitrogen use, nitrogen mineralization and crop growth from June 15, 2015 to June 25, 2015 based on the forecasted weather.

Table 4. End-of season yield forecast using current crop management practices, current weather to June 15, 2015; forecasted weather to June 25, 2015; and historical weather (1980 to 2014) thereafter. Forecasted yields are attainable yields predicted by APSIM that account for water and nitrogen limitations to crop growth but do not account for pest limitations.

Click on each table to enlarge. The Soybean Field Guide and Corn Field Guide are available through the ISU Extension and Outreach Store.


Sotirios Archontoulis is an assistant professor of integrated cropping systems and can be reached at or 515-294-7413. Mark Licht is an extension cropping systems agronomist with responsibilities in corn and soybean management and production. He can be reached at or 515-294-0877. Ranae Dietzel is a post-doc research associate in integrated cropping systems and can be reached at


Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Integrated Crop Management News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on June 17, 2015. The information contained within may not be the most current and accurate depending on when it is accessed.


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...

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...