ENVIRONMENTAL CONDITIONS AND FERTILIZATION EFFECT ON Pinus engelmannii Carr. HARDENING IN NURSERY

Abstract

The hardening stage in the nursery acclimatizes seedlings for the harsh conditions at the planting site. This study evaluated morphological and physiological characteristics on Pinus engelmannii Carr. during the hardening stage at the nursery, at four shading conditions (greenhouse, outdoor, outdoor shade-cloth, and shade-cloth combination) and an additional fertilization treatment (outdoor condition fertilized at 50 ppm of N, P and K); onfield performance was also evaluated. After two months of hardening, seedlings exposed to outdoor conditions and outdoor plus fertilization showed the largest increments (P ≤ 0.05) in root (38 %) and total dry biomass (32 %), root volume (30 %), and shoot/root ratio. Root collar diameter and above-ground biomass were least sensitive since they showed increases of 18 and 6 %, respectively. The highest increments on nutrient concentration in leaves occurred when seedlings grew outdoors and were fertilized or grew under greenhouse conditions. Nitrogen concentration was 30 % higher in the outdoor plus fertilization condition compared to the outdoor without fertilization condition; phosphorus concentration was 57 % and 43 % higher, while potassium concentration was 42 and 58 % higher in the same treatments. Root growth potential was higher in the outdoor condition with 67 % in number, 53 % in length, and 35 % in dry biomass of new roots, compared to the greenhouse condition. After 120 d of being transplanted to the field, the hardening treatments showed no effect on seedling growth, except on the relative growth rate of root collar diameter (P ≤ 0.05). The best morphological and physiological seedlings characteristics were achieved when seedlings were hardened under outdoor conditions for two months.