INFLUENCE OF PLANTING DENSITY ON ROOT-GROWTH AND YIELD IN POTATO

The influence of planting density on root growth and its relationship to leaf and tuber growth were investigated with two maincrop varieties in the potato. Three levels of planting density were examined; 23810, 47620 and 95240 hills ha(-1). The root length (RL) was investigated to a depth of 1 m at 90 days after emergence (DAE). The root length density (RLD) to a depth of 30 cm was also investigated at 30 DAE. The leaf area and tuber dry weight were measured at several stages. Total RL to a depth of Im at 90 DAE in the sparse, intermediate and dense plots was 12.5, 15.9 and 24.1 km m(-2) in Norin 1 and 6.4, 7.0 and 10.4 km m(-2) in Konafubuki, respectively. These differences were mainly due to those in RL at a depth of 0-30 cm. RL below a depth of 30 cm did not increase in Norin 1, or decreased in Konafubuki in the dense plot. The similar differences were also seen in RLD at 30 DAE. Total RL at 90 DAE showed significant positive correlations with leaf area index (LAI, r=0.929**) and tuber growth rate (GR, r=0.913**) at the late stage. These results confirmed the importance of longer RL to maintain larger LAI and tuber GR at the late stage. They also suggested that poorer deep roots at the dense plot might cause severe drought in dry soil conditions.