Abstract
In the paddy fields, plants in the outermost row next to the unplanted alley showed a general increase in yield and growth as compared with the center row. This penomenon has been referred to as 'border effect'. Main causes of border effect are considered to be advantageous environmental factors above the ground, such as higher solar energy, air circulation, etc. However, the magnitude of the border effects and the underground factors affecting the magnitude are not fully understood. This experiments addressed the above two questions. 'Sasanishiki', japonica type of rice, Oryza sativa L., was used as materials. The experiments were conducted at the Faculty experimental paddy field in the years 1979-1981. The plots included differences in levels of unplanted distances (0, 15, 30 and 47.5 cm), nitrogen fertilized (10 kg/10a) and unfertilized, and differences in levels of plant density (11.1, 22.2, 44.4, 88.9 and 177.8 hills per square meter). Results are summarized as follows: 1. The border plants in every treatment showed higher percentages of fertil tillers, shorter culms with the shortened internodes at lower positions, and greater rate of NAR, RGR and carbohydrate accumulation during early grain ripening stage. 2. The yield increase in plants in the outermost row was greater in plots with nitrogen supply in the alley and in plots with wider unplanted distances. The lowest yield response of border plants was observed in plots of narrow planting distances. This can be interpreted as due to availability of nitrogen from the space not occupied by other plants. 3. Among different densities of plant population, the magnitude of yield response in the border plants was the greatest in the highest density plots and least in the lowest density plots )249% and 45%, respectively, in the experiments of 1981). In conclusion, the underground conditions, particulary those affecting the nutritional supply have important contribution to the magnitude of yield increase in the outer-most plants. These underground factors must be taken into account along with aerial conditions in interpreting the phenomena of border effect.
