Studies of Energy and Gas Exchange within Crop Canopies (3) : Canopy structure of corn plants

[摘要] The canopy structure of crop communities plays an important role in both the diminish of radiation flux within the canopy and the photosynthesis of crop communities. In this paper the geometrical structure of a corn canopy was investigated as a preliminary to further study of the canopy structure and the photosynthesis relationships. The stand structure of the crop is well characterized by the distribution of the leaf. The orientation of a leaf is exactly determined by two parameters; the inclination angle of a leaf or a leaflet (foliage angle) and the azimuth angle of the normal on the upper surface. In 1966 and 1967, the vertical distribution of leaf area density, foliage angle and azimuth angle of corn plant canopies were determined with a silhouette method specially deviced for this purpose. Horizontal silhouettes of all leaves were projected on a graph by using values of the abscissas and the ordinates of the base (P1), top (P2) and tip (P3) of each leaf blade. The silhouette of each leaf was determined by eye-fitting the length of the leaf blade (1) through the three points (P1, P2 and P3) (see Fig. 1). The vertical distribution curves of the leaf area density in both years were characterized by the establishment of a peak with high density in the upper or middle layer of the canopy (see Fig. 3). Normalized height distribution curve were found to be approximated by the following formula (see Fig. 5). fLD=a+bz'+cz'2+dz'3 The constants (a, b, c and d) in the above formula showed clear change with the growth of the crop (see Table 1). The distribution function of the leaf area in relation to the foliage angle approached to approximately uniform distribution with growing the crop, agreeing well witht he results reported by Ross and Nilson (1966) (see Fig. 6). Though the distribution function of the leaf area in relation to azimuth angle was different from each other, the distribution in the layer with the highest leaf area density intended to be approximately uniform with respect to the azimuth (see Fig. 7).

[学科分类] 农业科学（综合）