Conservation farming strategies in East and Southern Africa: Yields and rain water productivity from on-farm action research

Improved agricultural productivity using conservation farming (CF) systems based on non-inversion tillage methods, have predominantly originated from farming systems in sub-humid to humid regions where water is not a key limiting factor for crop growth. This paper presents evidence of increased yields and improved water productivity using conservation farming in semi-arid and dry sub-humid locations in Ethiopia, Kenya, Tanzania and Zambia. Results are based on on-farm farmer and research managed experiments during the period 1999-2003. Grain yield of maize (Zea mays L.) and tef (Eragrostis Tef (Zucc)) from conventional (inversion) tillage are compared with CF with and without fertilizer. Rain water productivity (WPrain) is assessed for the locations, treatments and seasons. Results indicate significantly higher yields (p < 0.05) for CF+ fertilizer treatments over conventional treatments in most locations, increasing from 1.2 to 2 t ha(-1) with 20-120% for maize. For tef in Ethiopian locations, the yield gains nearly doubled from 0.5-0.7 to 1.1 t ha(-1) for best bet CF+ fertilizer. WPrain improved for CF+ fertilizer treatments with WP gains of 4500-6500 m(3) rainwater per t maize grain yield in the lower yield range from 0 to 2.5 t ha(-1). This is explained by the large current unproductive water losses in the on-farm water balance. There was a tendency of improved WPrain in drier locations, which can be explained by the water harvesting effect obtained in the CF treatments. The experiences from East and Southern Africa presented in this paper indicate that for smallholder farmers in savannah agro-ecosystems, conservation farming first and foremost constitutes a water harvesting strategy. It is thus a non-inversion tillage strategy for in situ moisture conservation, rather than solely aimed at minimum tillage with mulch cover. Challenges for the future adoption of CF in sub-Saharan Africa include how to improve farmer awareness of CF benefits, and how to efficiently incorporate green manure/cover crops and manage weeds. (C) 2008 Elsevier B.V. All rights reserved.