A dynamic model of maize 3D architecture: application to the parameterisation of the clumpiness of the canopy

A dynamic 3D maize canopy architecture model is proposed for radiative tran sfer computation required for canopy functioning or remote sensing applicat ions. It is based on a previous static model describing the 3D architecture of fully developed plants observed at the male anthesis stage. Laws of dev elopment and growth in dimension of the stem and the leaves are established based on experimental observations, in order to infer plant architecture a t any stage from that of fully developed plants. The leaf curvature and sha pe are assumed to be the same over the whole leaf duration, with the except ion when leaves are still within the top leafy cone at younger stages. The time is described by the number of visible leaves, which can easily be dedu ced from the cumulated growth degree days. The model requires only four inp ut variables: the sowing pattern (row distance, plant density), the final n umber of leaves produced, the maximum height at anthesis, and the cumulated leaf area for the fully developed plants. It was validated on independent data sets and provides globally good performances. The model is later used to parameterise the canopy gap fraction which is one of the main variables governing radiative transfer processes. The gap fraction P-o(theta) for the observation direction is classically described by an exponential function of the leaf area index, L: P-0(theta) = e-lambda(0) G(theta, theta(t))/cos theta . L where lambda(0) is the clumping parameter describing the non-random leaf ar rangement and G is the projection function that depends on the leaf inclina tion distribution function. The gap fraction model was adjusted over a time series of maize canopies simulated using our 3D dynamic canopy architectur e model. We showed that maize canopies have a marked clumped character, wit h an average clumping parameter of lambda(0) approximate to 0.8. However, r esults suggest that the clumping parameter depends on the developmental sta ge of the canopy, and, to a lesser degree, on the observation direction the ta. ((C) Inra/Elsevier, Paris.)