In-Season Corn and Soybean Yield Forecast in Iowa Using Apsim.

Forecasting crop yield at the end of the season is the ultimate goal of many scientists. Forecasting crop staging, expected growth, water and nitrogen use at regular intervals (every 7 to 14 days) over the growing season is even more important information for farmers so they can adapt their management. However this task is challenging and requires use of advanced modeling. In this study we present the results of the first in-season soil-crop-climate forecast that was implemented for corn and soybean in Iowa. We combined a climate model (WRF), which provided a 14-day weather forecast, with a cropping systems model (APSIM) that synthesized soil-crop-climate information and provided in-season predictions. The in-season predictions answer the following questions during growing season: (a) What is the crop and soil status at the time of the forecast date?; (b) How do the current weather and crop growth compare with historical years?; (c) What is the expected soil water and N status and crop needs over the next 14 days? and (d) What is the expected grain yield at the end of the season? Model predictions for eight cropping systems (2 crops: corn and soybean; 2 sites: central and northwest Iowa; and 2 planting date: early and late) were updated biweekly. The prediction accuracy of APSIM was verified from high resolution soil water, temperature, and nitrogen measurements as well as crop measurements including staging, leaf area index, biomass production, partitioning and tissue N concentration. Results as of August 25, 2015 showed good agreement between simulations and in-field measurements while the final assessment will be done at crop harvest. This pilot project revealed in mid-July that nitrogen availability determined the final corn yield level in central Iowa (which was expected to be above the average) and water availability determined the final corn yield level in northwestern Iowa.