Crop growth rate (CGR) The rate of dry-matter accumulation per unit land area per unit time in crop stands. Units are g m-2 day. Crop growth rate is the gain in weight of a community of plants on a unit of land over a unit of time.
The relative growth rate (RGR) indicates the dry weight increase in plant matter over a time interval in relation to the initial weight. It is a commonly used parameter to measure crop plant growth over time.
Leaf area ratio (LAR) expresses the ratio between the leaf area (photosynthesizing tissue) and the total respiring plant tissues or total plant biomass. This measurement reflects the leafiness of a plant, but mean values are not precise.
The net assimilation rate (NAR) is the net gain of assimilate by the plant per unit of leaf area and time. Age of the plant can distort this reading as this measurement assumes that the relationship between plant weight and leaf area is linear—and, later growth phases may have the growth rate of leaf area exceed that of dry matter or vice versa.
Leaf area index (LAI) expresses the ratio of leaf surface area to the ground area occupied by the crop. This measurement is an attempt to optimize crop production strategies to maximize light interception by using leaf density and spatial arrangement to cover ground area and promote rapid leaf expansion. Indeed, in a crop canopy, bare ground (where leaves do not fill the canopy space) does not trap and convert light energy.
Leaf area duration (LAD) is a measurement that expresses the magnitude and persistence of leaf area (or leafiness) during the period of crop growth. In wheat this measurement has been shown to correlate highly with yield.