Nitrogen and phosphorus fertilization effects on Venezuelan montane forest trunk growth and litterfall

In a montane rain forest in Venezuela plots were fertilized with N, with P or with N + P for 4.5 yr. N was applied at 225 kg.ha.yr^-1 and P at 75 kg.ha^-1.yr^-1 for the first 2 yr, and subsequently N was applied at 150 kg.ha^-1.yr^-1 and P at 50 kg.ha^-1yr^-1. Rates of trunk growth in N and P fertlized plots were roughly double those in control plots (1.4 vs 0.6 mm/yr). Total litterfall averaged 4.3 Mg.ha^-1.^-1y in the control plots. In the fourth year after fertilization litterfall was significantly higher in plots fertilized with N + P (1.50 g.m^-2.d^-1) than in control plots (1.00 g.m^-2.d^-1). Litterfall in control plots fell by 9% per year, that in P-fertilized plots fell by 5% per year, and litterfall in N and in N + P fertilized plots remained approximately constant. Nitrogen concentrations in litterfall were unaffected by fertilization with N or with P. Phosphorus concentrations were significantly increased by P fertilization. N was therefore more limiting than P. -from Authors