Crop Growth Rate (CGR)

Field growth analysis means harvesting the same treatment twice: cut every plant inside a known ground area, oven-dry the material to constant weight, write down the mass. Between one harvest and the next, the useful figure isn't the final mass on its own — it's how much the canopy piled on per day over each square metre of ground. Raw mass misleads the moment sampled plots differ in size, or when rain pushed one harvest out by a few days and the intervals stopped matching. Almost every experimental season runs into one of those.

The arithmetic is CGR = (W₂ − W₁) ÷ (Δt × A). W₁ and W₂ hold the dry masses from the first and second sampling, in grams; Δt is the gap in days; A is the ground area that yielded the material, in square metres. Screen defaults — 120 g, 480 g, 21 days, 1.5 m² — give 11.429 g/(m²·day), or 114 kg of dry matter per hectare per day. Ground area sits in the denominator, not plant count: that separates CGR from relative growth rate, which divides by existing biomass and grades the plant rather than the field. Well-run maize and sugarcane clear 20 g/(m²·day) at peak; under 5 during grain fill, something held the crop back.

The figure averages the whole interval instead of describing harvest day. Straddle the end of vegetative growth and the start of grain fill and the true peak hides inside that average, which is why classical growth analysis keeps sampling intervals to 10 or 15 days. Mass has to be oven-dried at 65 °C to constant weight; fresh material inflates the answer four- or fivefold. Roots rarely go into the sample, and when they do the value jumps, so state what got harvested. The usual unit slip: entering area in hectares or square centimetres rather than square metres.