GribStream
This simulation offers a practical way to predict corn (maize) development stages and evaluate growth stresses using detailed hourly weather data. It leverages precise weather inputs from NOAA's HRRR model, including temperature, solar radiation, wind speed, humidity, and soil moisture, to estimate corn crop growth realistically through advanced agrometeorological methods.
The simulation employs Photothermal Units (PTU), a metric that combines hourly temperatures above a base threshold (commonly 10°C for corn) with solar radiation (MJ/m² per hour). Unlike traditional Growing Degree Days (GDD), PTU incorporates both thermal and radiation conditions, providing a more accurate reflection of real-world crop growth. The raw PTU calculation is refined further by applying stress factors, simulating realistic conditions throughout the growing season.
Several key assumptions underpin this model. Hourly snapshot data for temperature and radiation are used, adjusted by an empirical scaling factor of 0.55 to align the predictions with typical corn development timelines observed historically in Iowa. Soil moisture stress calculations are based on a wilting point of 0.15 and a field capacity of 0.30, typical values for midwestern agricultural soils. Wind speeds measured at 10 meters are adjusted to approximate conditions at 2 meters height, ensuring accuracy in evapotranspiration (ET₀) calculations.
ET₀ is computed using the Penman-Monteith equation, offering hourly estimates of crop water demand, essential for predicting drought stress. A constant crop coefficient (Kc) of 1.05 represents typical water demand for corn throughout the season. The ET₀ stress threshold is set at 0.35 mm/hour, identifying periods when water stress could significantly limit growth.
Cold stress is assessed by comparing hourly temperatures to user-defined cold stress thresholds, helping highlight periods when chilling temperatures might negatively impact crop health and development. Radiation stress similarly identifies times of insufficient solar radiation, critical for understanding growth limitations during cloudy or overcast conditions.
The dashboard allows users to visually interpret key insights through clear, intuitive charts. Temperature data are presented alongside important thresholds, providing immediate visibility into potential cold stress events. Soil moisture is compared against the defined wilting point and field capacity, quickly indicating potential drought conditions. The ET₀ chart, accompanied by humidity data, highlights periods of elevated water stress clearly.
Additionally, the dashboard visualizes cumulative PTU over the growing season, allowing users to directly compare potential versus actual (stress-adjusted) crop growth. Final accumulated adjusted PTU values correspond to established corn growth stages, Emergence, Tasseling, Silking, Blister, Milk, Dough, Dent, and Maturity, providing an immediate understanding of expected crop progress.
This simulation provides farmers, agronomists, and researchers with a reliable, straightforward tool for predicting corn development. It helps inform decisions around planting, irrigation, and harvesting by accurately identifying stress conditions early, ultimately contributing to improved yields and better-informed agricultural management practices.
The charts below show the whole cycle from planting on May 1st to maturity the first days of September. Zoom in to better appreciate the correlations between weather variables, stressors and growth.