Nutrient fluxes in rainfall, throughfall and stemflow in tree-based land use systems and spontaneous tree vegetation of central Amazonia

The quantification of nutrient fluxes is an important step in the developme nt of sustainable land use systems, especially on low-fertility soils of th e humid tropics. Nutrient concentrations in rainfall (RF), throughfall (TF) and stemflow (SF) were measured for ten rainfall events in a polyculture ( multi-strata agroforestry system) composed of five tree crops, three tree c rop monocultures, spontaneous tree fallow and two rainforest tree species i n central Amazonia and nutrient fluxes were calculated for a 1 year period. Nutrient inputs in wet deposition during 1 year were 5.5 kg ha(-1) of tota l N, of which 42% were in the organic form, 0.07 kg ha(-1) of total P, of w hich 71% were in the organic form, 2.6 kg ha(-1) of K, 0.8 ka ha(-1) of Ca and 0.3 kg ha(-1) of Mg. The nutrient concentrations in TF and SF were infl uenced by tree species, land use system, nutrient status of the trees and s ize of the rain events. The rainforest species had high N but low P concent rations in their TF and SR The highest P concentrations were measured in SF of annatto (Bixa orellana), which was 115 times richer in total P and 400 times richer in phosphate-P than RF for small rain events. Higher fertilize r application increased the concentrations of P and Mg in TF and SF. On the plot level, the nutrient fluxes in TF and SF were greatest in the systems with the highest plant density and crown cover (fallows and palm monocultur es). On the species level, strong increases of the nutrient fluxes in TF an d SF were observed close to the stem of certain trees compared with the plo t average (more than 10 fold for P, K and Mg under peach palm Bactris gasip aes). In the polycultures and the fallow, the recycling of N, P, Ca and Mg in TF and SF was about 5-10% of the total recycling including Litterfall, b ut was 50-53% for K (77% in the peach palm monocultures). Throughfall and S F are most relevant for K cycling and by influencing small-scale patterns o f nutrient inputs into the soil. Stemflow is especially important in vegeta tion with high stem density, such as certain fallows and in systems dominat ed by palms. These results can help to devise measurement programs for nutr ient cycling in tree-dominated land use systems and spontaneous vegetation in the humid tropics. Possible effects of concentrated nutrient solutions o n microbial processes in soil and litter merit further investigation. (C) 2 001 Elsevier Science B.V. All rights reserved.