Abstract
The influence of reduction of solar radiation by a concrete structure on the growth of komatsuna (Brassica campestris L. rapifera group) was studied. Five plots were laid out on the west side of the wall (5.3 m tall, and oriented 18° west of magnetic north). The distances of plots 1, 2, 3, 4 and 5 from the wall were 0, 1.5, 3.0, 4.5 and 6.0 m, respectively.
1. In control plot without shading, mean daily photon flux density, mean soil temperature and air temperature in early summer, 1989 (Exp. 1) were 29.1 mol•m-2, 21.2°C and 21.3°C, respectively, whereas in autumn, 1989 (Exp. 2), they were 21.6 mol•m-2 (74% compared with Exp. 1), 17.5°C (3.7°C lower) and 16.9°C (4.4°C lower), respectively.
2. In Exp. 1, the total photon flux density (TPFD) of the control during the growth period was 756.1 mol•m-2, those of plots 1, 2, 3 and 5 under shading were 60, 72, 76 and 97% compared with the control, respectively. The dry weight (DW) of the control plants 26 days after emergence was 1.97 g, those of plots 1, 2, 3, 4 and 5 were 53, 60, 79, 76 and 94% of the control, respectively. In Exp. 2, the TPFD and DW of control plants 25 days after emergence were 539.7 mol•m-2 and 0.77 g, respectively; the % reduction in DW of plants in the shade plots with respect to the control was similar to that in Exp. 1.
3. In both experiments, a linear relation (y = -0.08+1.06x; r = 0.92) existed between relative values of TPFD (x) and DW (y) about 2 weeks after emergence. Using this equation, we will be able to predict the degree of reduction of dry matter production of komatsuna under shaded conditions provided the reduction in solar radiation caused by the structure can be estimated.
4. The relationship between relative values of TPFD and top dry weight or leaf area was similar to that between TPFD and total dry weight. The influence of reduction of solar radiation on partioning ratio of dry matter and thickness of leaf was not statistically apparent.
