Development of the soil macrofauna community under silvopastoral and agrosilvicultural systems in Amazonia

Abstract

In the Brazilian Amazon region, millions of hectares of forest land have been converted into cattle pastures and then been abandoned. Agroforestry is a potential option for the transformation of in parts degraded lands into productive agricultural systems. The re-establishment of a diversified soil macrofauna can help in the process of recuperation of the often compacted soil structure of the pastures. The soil macrofauna community was studied during the rainy season in four different agroforestry systems near Manaus in Central Amazonia: 1. a high-input silvopastoral system (ASPh), 2. a low-input silvopastoral system (ASPI), 3. a palm based system with four tree crop species (AS1) and 4. a high-diversity tree crop system with ten tree crop species (AS2), plus a spontaneous fallow for comparison. The sampling method recommended by the Tropical Soil Biology and Fertility Programme was used. The highest diversity of fauna groups was observed in the ASPh and ASPI where trees were associated with the leguminous cover crop, Desrnodiurn ovalifoliurn. The cover crop exerted a favorable effect on the soil fauna presumably by maintaining the soil moist and shaded and providing litter as a substrate. Of the 15 soil fauna groups that were found in all systems, four were absent from AS1. Within the AS2 system a significantly greater density of the soil fauna was observed under peach palm (Bactris gasipaes) and cupuaçu (Theobroma grandiflorum) (3107 and 524 ind.m-2, respectively) than under the other three tree species. The soil under peach palm and cupuaçu also tended to have a higher number of soil fauna groups. In AS1, the soil under peach palm had a higher fauna density than the soil under cupuaçu, probably caused by the abundant residues of the heart of palm harvest on the soil. The earthworm biomass was particularly high in AS1. Under cupuaçu approximately 7 times more earthworms were found in AS1 (17.9) than in AS2 (2.4). The study of the macrofauna community, including both the litter layer and the superficial soil layers, allows to identify the plant species/management combinations which favour the increase of the diversity of the invertebrates.