Highlights: Increasing exponential fertilization rates in the nursery increased seedling biomass, N content, and N concentration for Chinese pine seedlings; Second year seedling survival illustrated a curvilinear response to seedling fertilization rates rather than a linear one; Considering both nursery responses to fertilization and field performance after two years yielded a recommended nitrogen supply rate of 80 mg N seedling–1.
Optimum fertilization levels are often determined solely from nursery growth responses. However, it is the performance of the seedling on the outplanting site that is the most important. For Pinus species seedlings, little information is known about the field performance of plants cultured with different nutrient rates, especially with exponential fertilization. In this study, Chinese pine (Pinus tabulaeformis Carr.) seedlings grown in 187 ml containers were fertilized exponentially in 6 treatments ranging from 10 to 120 mg N seedling–1 for 25 weeks before outplanting. Dry mass and N content were measured at planting. Survival and field growth were monitored for two growing seasons. In the nursery, our data showed no difference in dry mass among the 40, 80, 100, and 120 mg N seedling–1 fertilizer treatments; collectively, these treatments were significantly greater than at 10 and 20 mg N seedling–1 treatments. Seedling N content was greatest for the 100 and 120 mg N seedling–1 rates. These data suggested that nursery optimum N fertilization rate was no less than 100 mg N seedling–1. Outplanting height and root-collar diameter growth characteristics were not significantly different after two years, whereas maximum mean survival was best for seedlings nursery-fertilized at 80 mg N seedling–1. In consideration of both nursery and field performance metrics, our data suggest that exponentially fertilizing Chinese pine seedlings at 80 mg N seedling–1 maximizes both nursery biomass accumulation and outplanting survival.