Combined pre-hardening and fall fertilization facilitates N storage and field performance of Pinus tabulaeformis seedlings

Exponential fertilization during the pre-hardening stage and fall fertilization during the hardening stage have each been used independently to nutrient load seedlings. However, nursery and field responses of seedlings to the combination of exponential fertilization and fall fertilization have received little attention. Chinese pine (Pinus tabulaeformis Car.) container seedlings were exponentially fertilized with accumulated totals of 40, 80 or 120 mg N per seedling during pre-hardening, and fall-fertilized with 0, 12, 24 or 48 mg N per seedling, and were subsequently outplanted and followed for two growing seasons. Interactions of exponential and fall fertilization had significant effects on plant N content in the nursery and first-year height after outplanting. Fall fertilization promoted additional nutrient loading during hardening for the 40-80 mg N per seedling pre-hardening regimes. The highest exponential fertilization rate enhanced N concentration in foliage and roots compared to the other two rates. Maximum diameter was observed in the lowest exponential fertilization rate at the second year after outplanting. Fall fertilization enhanced foliar N concentration. Supplemental 12 and 24 mg N per seedling during fall were more effective in increasing height increment at the second year after outplanting. Our results indicate that pre-hardening fertilization is a useful tool to nutrient load Chinese pine in the nursery and facilitate outplanting performance in the field. In combination, fall fertilization has potential to further augment this response, although further research is needed to precisely match rates of pre-hardening and fall fertilization to optimize seedling performance