Improved Fallows in Eastern Zambia

Abstract

In Zambia, the production of the main staple crop, maize (Zea mays L.), has fallen steadily over the past few years due to the removal of fertilizer subsidies, the collapse of agricultural credit programs and the occurrence of periodic droughts. In 1992, the International Centre for Research in Agroforestry (ICRAF) and the Zambian Ministry of Agriculture, Food and Fisheries initiated on-farm research in eastern Zambia, a hilly region with an average rainfall of 960 mm, to develop soil fertility systems that are easily accessible to smallholder farmers. Together with a number of national and international partners, they have developed systems with Sesbania sesban (L.) Merr., Tephrosia vogelii Hook. f., Gliricidia sepium (Jacq.) Walp. and pigeon pea (Cajanus cajan [L.] Millsp.) where maize yields following 2-year improved fallows approach those of fully fertilized fields. The fallow species are either planted in a nursery (Sesbania and Gliricidia) or directly in the field after the beginning of the rains. In the first year, they can be intercropped with maize or sunflower (Helianthus annuus L.). They are weeded during the first year and a fire-break is constructed around them. At the end of the second year, the trees are cut and the field is replanted to maize or, occasionally, to cotton (Gossypium hirsutum L.), groundnuts (Arachis hypogaea L.) or sunflower. The principal product removed from the improved fallow system is the main crop but others include firewood and building materials, tree seeds and at times Tephrosia leaves for use as a pesticide. After 2-year Sesbania, average maize yields are 3000 to 5000 kg ha−1, and after 2-year Tephrosia or pigeon-pea fallows, they are 2000 to 3000 kg ha−1, in comparison with 3000 to 5000 kg ha−1 for fully fertilized, and less than 1000 kg ha−1 for unfertilized, continuously cropped maize. These yields decrease over time and, typically after 2–3 years of maize cultivation, another improved fallow needs to be planted. Over a 5-year period (2 years fallow and 3 years cultivation), improved fallows require 11% less labour than unfertilized maize and 32% less labour than fertilized maize. Overall returns per hectare are highest for fertilized maize and lowest for unfertilized maize. However, returns to labour are highest for improved fallows and lowest for unfertilized maize. The main problems include insects (Mesoplatys beetles on Sesbania, termites), grazing by livestock (pigeon pea), the additional labour required for establishing a fallow (especially Sesbania) and the long period required before benefits accrue. An estimated 20 000 farmers have planted improved fallows. A regional network of farmers, non-governmental organizations, research organizations and government extension personnel promotes the system. It utilizes farmer participatory methods and attempts to ensure the availability of a wide range of options for farmers as regards species, planting methods and period of fallow.