The objective of this study is to determine the optimum planting density in napier-grass (Pennisetum purpureum Schumach) among two dwarf varieties introduced from Thailand and two normal ones under three levels of density. Dwarf varieties showed lower plant height and mean tiller weight, and higher leaf area index (LAI) and leaf blade percentage. Crop growth rate was positively correlated with LAI, and net assimilation rate and canopy extinction coefficient (K) were negatively correlated with LAI in the second year, including all dwarf and normal varieties, while K tended to be lower in the dwarf varieties. With the increase in the planting density, dry matter yield tended to increase, the difference between the normal varieties and early-heading dwarf variety was reduced, and the over wintering ability in all varieties was decreased. It was concluded that late-heading dwarf and normal varieties should be planted at the medium density by a desirable combination of productivity and considerable over wintering ability.
