Vegetative crop growth model incorporating leaf area expansion and senescence, and applied to grass

Abstract. A crop growth model incorporating leaf area expansion and senescence is constructed. Leaf area is treated as an independent state variable with the incremental specific leaf area a function of the storage/structure ratio. The vegetative grass crop, which usually has three green leaves per tiller, is particularly considered; the above-ground dry matter is assumed to occupy four compartments: growing leaves, first fully expanded leaves, second fully expanded leaves, and senescing leaves. Each compartment is described by two state variables—structural weight and leaf area index. Newly synthesized structural material comprises leaf, sheath and stem in fixed proportions, although defoliation can alter these proportions in the standing crop. Photosynthesis and respiration are calculated in the usual way. Root growth, root: shoot partitioning, soil water and nutrients are assumed to be relatively unimportant for an established vegetative grass crop grown under favourable conditions. The model is used to simulate the time course of dry matter and leaf area development for crops that are exposed to a constant environment, a seasonally varying environment, and are defoliated.