Abstract: Studies on the influence of proportion and amount of N, P and K on grouth of Oriental arborvitae (_{Platycladus orientalis} (Linn) Franco) seedling (1+0) were made.Seeds were sown on seedbed in nursery. Calcium Superphosphate was used as ground fertilizer and N and K as additional fertilizers after emergence of the seedlings. The time of absorbing N and P by the seedlings was traced by radioactive isotopes ¹⁵N and ³²P.The results are: (1) the 1-year old seedling reacted readily with N-fertihzer. Growth of the seedling was significantly increased. The most satisfactory result occurred when N was applied with P. (2) In effect P was only next to N and was necessary to obtain the maximum quantity of up to standard seedlings to achieve the best monetary result. (3) The optimal quantities of fertilizers to be applied was N 150-200kg/ha and P₂O₅ 100-200kg/ha for production of 2.10million qualified seedlings per hectare. The best proportions for N and P on moist loess soil in our experiment were 3—2 to 2—1. N+P=300—400kg. (4) N and P could be absorbed by the seedlings before lateral roots appeared. (5) Application of fertilizers would increase by 81.3%—99.7% of seedling production and economic benefit respectively over comparison.

Key words: Platycladus orientalis (Linn) Franco seedling, Application of fertilizers in nursery ground, The best proportions of N and P, The optimal quantities of fertilizers to be applied, Equation of yield response surface.