Water balance and soil loss under long fallow agriculture in the Venezuelan Andes

In the paramo ecological belt of the Venezuelan Andes, a long fallow agricu ltural system is used to produce potatoes and cereals. Total rainfall, surf ace runoff, soil moisture, drainage, and soil loss were measured in this sy stem during two consecutive years on 10 plots cropped with potatoes and on two successional plots with fallow periods of 1 and 15 years. Total rainfal l (1129 mm on average) is characterized by many low-intensity events. The l ow rainfall intensity and high soil infiltration capacity partly explain th e very low runoff (only 1.7% of the rainfall) and the low rates of soil los s (0.58 t/ha/y) on the cultivated plots. The main water outputs were by eva potranspiration (61%) and drainage (37%). The greatest runoff and soil loss es were observed at the beginning of the fallow period when the ground cove r was scarce; however, after a few months of fallow, both processes decreas ed below the rates measured on the cultivated plots. Because soil loss was not significant on all study plots, it is suggested that traditional fallow agriculture does not have a negative environmental impact at a local scale .