VERTICAL DISTRIBUTION AND SPATIAL PATTERN OF FINE ROOT DENSITY IN COFFEE – BASED AGROFORESTRY SYSTEMS UNDER ORGANIC AND CONVENTIONAL INPUTS

Abstract

This research shows results on spatial changes of fine roots (d < 2.0 mm) in two Coffea arabica- shade tree associations: coffee shaded by a) Abarema idiopoda (timber and nitrogen fixing tree), and b) Terminalia amazonia (timber tree). These associations were submitted to organic and conventional inputs. In order to identify fine root vertical distribution and using soil cores, coffee and shade tree fine roots were quantified to 50 cm depth. A geostatistical approach was used to quantify the scale of spatial heterogeneity (aggregation patterns) of coffee and shade- tree fine root length density (RLD, cm cm-3; 0- 20 cm soil depth). Results about vertical distribution demonstrated that in all the associations the coffee fine roots were concentrated in the upper 20 cm of soil. The significant amount of coffee fine roots in the litter layer demonstrated the importance of including this layer for a real estimation of coffee fine roots in shaded coffee systems. The shade tree fine roots showed marked differences in their vertical distribution and affected the fine root density of coffee plants between 0- 50 cm soil depth; being more abundant when coffee is planted with T. amazonia. The scale of spatial heterogeneity (aggregation patterns) for coffee RLD was longer in the organic plot than in the conventional plot for all of the coffee- tree associations. In the coffee- T. amazonia association, the semivariogram of the coffee RLD under conventional management showed a spatial correlation at a relative short scale (3.5 m); however, in the organic plot, the semivariogram did not show spatial heterogeneity and exhibited a random pattern of coffee RLD at the scale examined. It is concluded that the type of management affects the pattern of spatial aggregation (spatial heterogeneity scale) of C. arabica fine roots. Implying that the ability of coffee roots for the water and nutrient intake change spatially, either vertically or horizontally, depending on the accompanying shade- tree. According to the occupation of the fine roots within the layers of the soil to the depth studied, T. amazonia seems to be the timber species recommended for the establishment of a coffee-based agroforestry system.