Six model approaches of biomass allocation are described: (1) Descriptive allometry, proposing a predetermined ratio between the (relative) growth rates of the plant organs; (2) functional equilibrium, based on the ratio of shoot activity to root activity; (3) Transport and sink regulation, based on transport and utilization of carbon and nitrogen; (4) Physical analogue, proposing the plant to consist of a set of pools (sinks), each having a permeance and potential and each perceiving a common plant potential; (5) Potential demand functions of sinks and (6) Potential demand with priority functions of sinks, proposing, respectively, the biomass allocation to be determined by the potential growth rates or by potential growth rates and affinities (priorities) for substrate of the sinks (organs).
The general patterns of biomass allocation to each plant part are summarized and the applications of the different model approaches are discussed, with special reference to greenhouse crops.
It is concluded that the approach of potential demand and priority functions is most valuable for simulation under a large range of experimental conditions and for dry matter distribution between any plant part.
However, it requires extensive input data.
The approaches of descriptive allometry, the functional equilibrium or potential demand functions sometimes (under a more limited range of conditions) also give acceptable simulation results in a simpler way.
However, the simulation of biomass allocation is still one of the weakest features of crop growth models.