This simulation runs a daily FAO-style crop model that grows wheat, maize or soybean from sowing to harvest. Accumulated thermal time above each crop's base temperature drives the development stage (DVS) from 0 to 2, leaf area index builds the canopy, and absorbed photosynthetically active radiation is converted to biomass through radiation use efficiency. A simple soil water balance imposes drought stress on daily growth.
Pick a crop and adjust the sowing day of year, soil water capacity in millimetres, a temperature offset, and rain-fed versus irrigated water supply. Three views chart growth, daily weather, and stress factors. Such radiation-driven, thermal-time models underpin real agronomic decision tools used to forecast yield, schedule irrigation and assess climate impacts on cropping systems.
What does this simulation actually compute?
It steps a single crop through up to 250 days from your chosen sowing date, tracking development stage, leaf area index, shoot biomass and grain yield each day. The outputs shown are grain yield and biomass in tonnes per hectare, growing-season length and peak leaf area index.
How does thermal time drive development?
Each day adds growing degree-days equal to mean temperature minus the crop's base temperature (0C wheat, 8C maize, 6C soybean). These accumulate against a vegetative target, then a reproductive target, pushing the development stage from 0 through 1 (anthesis) to 2 (maturity), at which point the run ends.
What is radiation use efficiency and how is biomass formed?
Daily biomass gain equals absorbed PAR multiplied by the crop's radiation use efficiency (RUE) and the water stress factor. Absorbed PAR follows Beer's law, intercepting roughly 48 percent of incoming solar radiation according to leaf area index and an extinction coefficient. RUE ranges from about 1.0 g per MJ for soybean to 1.8 for maize.
Sowing day shifts the start of the season and so the weather the crop meets. Soil water capacity sets the size of the water store. The temperature offset warms or cools the whole climate by up to 5C, and the irrigation toggle keeps the soil topped up rather than relying on rainfall.
Grain accumulation begins at anthesis, when the development stage reaches 1. After that, a fixed fraction of each day's new biomass (the grain filling ratio, around 0.4 to 0.48 depending on crop) is partitioned into grain rather than leaves and stems.
A bucket-style soil water balance adds rainfall and any irrigation, then subtracts a radiation-driven evapotranspiration demand each day. When stored water falls below about a quarter of capacity, a stress factor below 1 scales down growth. The Stress view plots soil water, the stress factor and development stage together.
The model generates a deterministic 365-day temperate climate resembling Ukraine, with temperature following a sinusoid that peaks in summer, cloud-modulated solar radiation, and pseudo-random rainfall events. Because it is deterministic, the same settings always reproduce exactly the same season.
It captures the correct mechanisms and realistic parameter ranges used in operational crop models, so trends respond sensibly to temperature, water and crop choice. It is a simplified teaching model, though, omitting nitrogen, pests, soil layers and cultivar detail, so absolute yields should be read as indicative rather than field-precise.
During the vegetative phase leaf area index grows with thermal time towards a crop maximum (up to 6 for maize). After anthesis the canopy senesces, so leaf area declines, reducing light interception and shifting the plant's resources from canopy expansion to filling the grain.
Radiation-driven crop models inform yield forecasting, irrigation scheduling, sowing-date and variety selection, and climate-change impact studies. By exploring how warmer temperatures, drier soils or earlier sowing shift the harvest figures here, you can see the same trade-offs agronomists weigh when planning a season.