Effect of five tree crops and a cover crop in multi-strata agroforestry attwo fertilization levels on soil fertility and soil solution chemistry in central Amazonia

The spatio-temporal patterns of soil fertility and soil solution chemistry in a multi-strata agroforestry system with perennial crops were analysed as indicators for the effects of crop species and management measures on soil conditions under permanent agriculture in central Amazonia. The study was carried out in a plantation with locally important tree crop species and a leguminous cover crop at two fertilization levels on a xanthic Ferralsol. S oil fertility to 2 m soil depth was evaluated 3.5 years after the establish ment of the plantation, and soil solution chemistry at 10, 60 and 200 cm so il depth was monitored over 2 years. Several soil fertility characteristics exhibited spatial patterns within the multi-strata plots which reflected t he differing properties of the plant species and their management, includin g the fertilizer input. Significant differences between species could be de tected to 150 cm depth, and between fertilization treatments to 200 cm dept h. Favourable effects on nutrient availability in the soil were found for a nnatto (Bixa orellana) (P, K) and cupuacu (Theobroma grandiflorum) (Ca, Mg) in comparison with peach palm (Bactris gasipaes) and Brazil nut (Bertholle tia excelsa). Nutrient concentrations of the soil solution showed pronounce d fluctuations in the topsoil, corresponding to fertilizer applications. La rge nutrient concentrations in the soil solution were accompanied by increa sed concentrations of aluminium and low pH values, caused by exchange react ions between fertilizer and sorbed acidity and reinforced by the acidifying effect of nitrification. The soil solution under the leguminous cover crop Pueraria phaseoloides had relatively large N concentrations during periods when those under the tree crops were small, and this could partly explain why no yield responses to N fertilization were observed at this site.