Agroforestry system effects on soil characteristics of the Sarapiquı́ region of Costa Rica

Abstract

Agroforestry systems have been considered sustainable land-use alternatives for the humid tropics because they may imitate characteristics of natural ecosystems – notably those that have beneficial effects on soil properties. The objective of this study was to compare the effects of agroforestry systems on selected soil properties of Haplic Acrisols and Dystic Fluvisols, in the Atlantic Region of Costa Rica, approximately five years after their establishment. The agroforestry systems were established on unmanaged pastures near the La Selva Biological Station in 1989 and 1990. The original forest had been removed on most of these areas at least 25 years earlier. Tree components of the agroforestry systems were the tropical hardwoods Vochysia ferruginea (Botarrama), V. guatemalensis (Chancho), Stryphnodendron microstachyum (Vainello) and Hieronyma alchorneoides (Pilón). The soil properties studied included physical (soil bulk density; 0–10 cm), chemical [pH, exchangeable bases, extractable P, soil organic C (SOC) and total soil N; 0–50 cm] and biological parameters (mineralizable C and N and microbial biomass C and N; 0–15 cm). Soils were sampled in August 1995. Lower exchangeable bases and soil pH were noted in agroforestry treatments as compared to pastures. Extractable P was higher in the surface 25 cm of agroforestry plots. Total soil N, soil organic C and soil C : N ratios were not influenced by agroforestry systems. Higher mineralizable C levels were observed in pasture surface soils, but no differences in mineralizable N in soils under pasture and agroforestry systems were observed. Soil microbial biomass C and N and specific respiratory activity were not significantly different in pastures and agroforestry systems. Agroforestry systems did not appear to improve soils in this study compared to pasture.