Nitrogen levels, top pruning, and lifting date affect nursery development and early field performance of loblolly pine seedlings
Loblolly pine seedling nursery development and 3-year field performance were contrasted between two nitrogen (N) application regimes and comparable top pruning regimes. Other initial soil nutritional elements were comparable, but high N seedlings received 150 lb/acre N (as NH4NO3) and low N seedlings received half this amount. Seedlings were either not top pruned, top pruned in August, or top pruned in August and September. The seedlings were outplanted during 12 equally spaced planting periods from mid-October to mid-March. The high N nursery seedlings were taller and had larger root-collar diameters as compared to the low N seedlings, but the latter survived and grew better after outplanting. Survival was 100 percent for the low N seedlings regardless of pruning treatment but did not reach acceptable levels for the high N seedlings until late December. The low N seedlings were consistently taller after three growing seasons and, depending on planting period, had consistently larger diameter at breast height (early planting periods) or had comparable diameter at breast height (later planting periods) compared to high N seedlings.