Figure 1

Vegetation (a), Lixisol soil (b), and layout of the full factorial N-P-K experiment (c) in the Budongo Forest Reserve, Uganda. The 32 experimental plots consist of eight randomly assigned treatments: Control, N, P, K, NP, NK, PK, and NPK with four replicates each. Nitrogen (125 kg N ha⁻¹ year⁻¹) was added as urea ((NH₂)₂CO), P (50 kg P ha⁻¹ year⁻¹) as triple superphosphate (Ca(H₂PO₄)₂), and K (50 kg K ha⁻¹ year⁻¹) as muriate of potash (KCl) similar to an earlier experiment in Panama¹⁰. Plots are 40 m × 40 m in size and are at least 40 m apart, accessed using a walking trail (black dashed-line).