A reproducibly simulated agronomy field trial relating crop yield to
rainfall, fertiliser, soil pH and a management treatment. Used for the
regression, coefficient-plot, scatter-trend and interaction examples. The
data-generating process contains a genuine fertiliser-by-treatment
interaction: fertiliser raises yield far more under the enhanced treatment
than under standard, so interaction_plot(lm(yield ~ fertiliser * treatment + ..., crop_yield), "fertiliser", "treatment") shows real,
diverging slopes rather than noise. The main effects (rainfall, fertiliser,
soil pH and treatment) are retained.