Abstract
The number of strut bamboos is determined by the planting density in “Toramame” cultivation. Usually strut bamboos are set up and taken away manually, which accounts for nearly 75% of the total labor (35hours/10 a). The planting density has been based on the experience of the farmer. We investigated the correlation of seed yield with planting density, the number of hills per unit area and that of plants per hill. The optimum number of plants per hill from 1 to 6 plants per hill examined was 4 either when the number of hills was 2300 or 1800 hills/10 a. The yield in 1500 hills/10 a (35% lower than the conventional density) was 11% lower than the conventional yield, but the yield in 1800 hills/10 a (20% lower than the conventional density) was decreased less than 5% on the average. The yield reduction due to fewer hills was greater in the fields with lower yields. In addition, the yield was lower and the rate of yield reduction due to fewer hills was higher in the field with a lower level of autoclaving extractable nitrogen in the soil. Considering the costs in 2012, the profits with 1800 hills coincided with those with 2300 hills when the yield reduction rate was approximately 5% in the high yield field (400 kg/10 a), 7% in the average yield (300 kg/10 a), and 10% in the low yield (200 kg/10 a). The yield reduction rates in 1800 hills compared to 2300 hills in 7 out of 9 fields with higher than average yield was less than 5%. The profits of 1800 hills in those 7 fields were equal to or higher than those with 2300 hills. Thus, we considered that the planting density of 1800 hills/10 a brought 20% reduction in the labor hours related to the strut bamboos without loss of benefits.
