A comparison of productivities and energy values between slash and burn agriculture and secondary succession in the upper Rio Negro region of the Amazon Basin

An analysis of the energy inputs and outputs for conuco agriculture (i.e., shifting cultivation) and a comparison of productivity between conuco crops and successional vegetation was undertaken near the town of San Carlos de Rio Negro in southern Venezuela. The main crop, yuca (Manihot esculenta, Crantz), yielded (m.t. = metric tonnes) 4.31 m.t. ha^-1 wet weight in year one; production declined to 2.81 m.t. ha^-1 in the second year. The infertile soils of the region are the major cause of these low yields. Although relatively unproductive, conuco agriculture is much more energy efficient than mechanized agriculture. The ratio of energy output, in the form of processed food, to energy input in the form of human labor, averaged 13.9:1 over two cropping periods. Slightly more energy was devoted to field activities than to processing activities. The conuco crops were more productive than the adjacent succession site vegetation (532 vs. 109 g m^-2 dry weight) during the first year after cutting and burning; but in the second year the successional vegetation was more than twice as productive as the conuco crops (1446 vs. 529 g m^-2 dry weight). This difference in second year production was attributable to greater resource allocation to leaves and longer leaf retention time for the successional vegetation.