Growth and Soil Nutrient Responses to Stocking Rate and Nitrogen Source for Mid-Rotation Loblolly Pine in West-Central Arkansas

ABSTRACT

Fertilization is needed to replace nutrients removed from pine straw plantations, but tree response to fertilization could be influenced by stocking rate. Our objective was to determine effects of three N fertilizer sources on loblolly pine (Pinus taeda L.) growth and pine straw yield as a function of stocking rate (trees ha-1, TPH) at about midrotation (12-14 years post-planting). Commercial mineral fertilizer (CF), poultry litter (PL, 5.4 Mg ha-1), and pelletized poultry litter (PPL, 4.6 Mg ha-1) were applied once in April 2006 at 0 (control) and 200 kg ha-1 of N at plantation stocking rates of 2300, 1200, and 970 TPH near Booneville, AR. Basal area (range 32.6 to 42.8 m2 ha-1) was very high and did not respond to fertilization, and pine straw yield also did not consistently increase with fertilization compared to the control. Concentrations of pine straw N and foliar N increased with fertilization, especially with CF compared to litter. Topsoil NO3 --N and NH4 +-N were greater for CF than PL and PPL 3 mo after fertilization, but responses ≥ 9 mo after application did not differ from the control. While the plantations were able to acquire N, overstocking seemed to constrain N utilization for increased BA or foliage production. Thinning should improve tree growth and pine straw yield responses to fertilizer applied at mid-rotation.