Every simulated day the plot runs through weather, light, water, soil chemistry, soil life and plant growth. Each plant is an individual with leaves, stems, fine roots, stored reserves and seeds, and its own nitrogen, phosphorus and potassium. The soil is a 40 × 40 grid of 25 cm cells, each with three layers.
- Weather: stochastic daily rain (wet/dry persistence, storm size), temperature and sunshine; reference evapotranspiration from the FAO-56 Penman–Monteith equation; slope and aspect change sunlight through the equivalent-latitude method. Climate presets use long-term normals for real places.
- Soil water: field capacity, wilting point, saturation and conductivity from sand, clay, organic matter and compaction (Saxton & Rawls 2006). Water percolates layer by layer, flows sideways downslope above slow layers, and seeps out at the foot of the slope.
- Runoff and erosion: SCS curve-number runoff adjusted for slope, wetness, plant cover, litter, frozen ground and sodium crusting; runoff is routed cell to cell, so vegetated patches, swales and basins soak up water running off bare ground. Soil detachment follows a MUSLE-style rule with a RUSLE slope factor, and sediment settles where water slows.
- Ground layout: raised beds add 25 cm of loose, compost-rich soil; paths are compacted and trampled; wood chips smother seedlings and tie up surface nitrogen as they rot; swales and berms change where water collects.
- Light: taller plants intercept first (Beer–Lambert extinction). Diffuse light falls straight down; direct sun is shifted toward the pole, so trees shade their poleward neighbours more in winter.
- Plants: C3 or C4 photosynthesis with temperature, CO₂, water and nutrient limits; maintenance and growth respiration; allocation shifts to roots when water or nutrients are short and to stems in shade; reserves, dormancy, flowering, seed banks, dispersal and clonal spread; regrowth from reserves after cutting.
- Minerals: potassium is tracked from soil to plant and back (leaching, release from clay, removal in harvests). Calcium, magnesium and sulfate follow liming, gypsum, weathering and leaching. Zinc, iron, manganese, copper, boron and molybdenum supply follows the soil test, shifted by each spot's pH, wetness and organic matter; every plant type has its own critical levels. Acid soil releases aluminium that stunts roots, salinity cuts water uptake and growth (Maas–Hoffman), and calcium shortage plus drought causes blossom-end rot in tomato and squash.
- Below ground: neighbours share water and nutrients in proportion to root length in each cell and layer. Mycorrhizal fungi extend phosphorus, zinc and nitrogen foraging at a carbon cost; each legume fixes nitrogen only with its own rhizobia (clover, alfalfa, soybean and bean groups differ in acid tolerance), and less when soil nitrate is high or molybdenum is short.
- Inoculants: named strains establish where their hosts and conditions suit them and fade elsewhere: Azospirillum boosts grass and cereal roots and fixes a little nitrogen; Bacillus, Trichoderma and Pseudomonas suppress root disease; Penicillium bilaiae frees bound phosphorus; mycorrhizal and rhizobial inoculants seed the partners plants need.
- Crops: maize, wheat, soybean, potato, bean, sunflower, tomato, squash and lettuce develop by thermal time through emergence, flowering, grain, tuber or fruit fill and maturity. Field markers stand for several plants at real planting density; hand-planted crops are harvested plant by plant. Harvests carry produce and its nutrients off the plot. Ploughing buries residue and breaks fungal networks; no-till leaves both in place.
- Pictures: the 3D view and the side view draw every plant from its simulated state: height, crown width, growth stage, flowers, grain, pods and fruit, autumn colour, dormancy, and yellowing from nutrient or water stress. Below ground, each soil layer is shaded by its moisture and humus, roots reach their simulated depth and spread, nodules appear on legumes that are fixing nitrogen, fungal threads on roots colonized by mycorrhizae, and earthworms where the soil suits them. The sun's angle and the shadows follow the latitude and season; snow buries short plants.
- Soil life: litter and roots decompose into fast and slow organic matter (CENTURY-style) driven by microbes, temperature, moisture and pH. Microbes mineralise or immobilise nitrogen; nitrification, denitrification and leaching follow soil water. Host-specific soil pathogens build up under their host plants. Earthworms pull litter underground, and roots, fungi and worms build soil aggregates that raise infiltration.
Main simplifications: plants are functional types or typical varieties rather than named cultivars; there is no plant water-potential model, fire, insects or pollinators; the plot edges are closed; micronutrients are availability indices rather than full budgets. Benchmarks: Lieth's Miami productivity model (1975), Fu's form of the Budyko curve, US tolerable soil-loss limits, Maas–Hoffman salt tolerance, and typical farm yields.