Where is the limit? lessons learned from long-term conservation agriculture research in Zimuto Communal Area, Zimbabwe

Smallholder farming in Zimbabwe is increasingly affected by dwindling maize (Zea mays L.) yields due to declining soil fertility and the negative effects of climate variability and change. A long-term on-farm study was established between 2004 and 2013 at the Zimuto Communal Area near Masvingo, Southern Zimbabwe to test the feasibility and viability of conservation agriculture (CA) systems under the circumstances of low fertility and erratic rainfall. CA seeding systems based on animal traction excelled and significantly increased maize productivity by up to 235% (1761 kg ha(-1)) and legume productivity by 173% (265 kg ha(-1)) as compared to the conventional control treatment. Soil quality indicators such as infiltration and soil carbon improved 64-96% and 29-97 %, respectively, over time. However, a direct link between increased infiltration and grain yield could not be established. Increased plant population, because of greater precision and moisture conservation during direct seeding as well as an improved response to fertilizer application due to gradually increasing soil carbon could be the reasons why yields on CA systems outyielded the conventional control. CA systems were more economically viable than planting crops under the normal conventional practice with mouldboard ploughs and removal of crop residues. Farmers generally rated important crop characteristics of maize planted under CA as high but weed control was rated as low, due to the lack of an appropriate herbicide under the prevailing environment. The results of this study show that CA is a potential option even in areas of climate risk and low soil fertility. However, the adoption of CA was low amongst members of the rural farming community due to the perceived risk of crop failure, lack of appropriate and accessible inputs and markets for farm produce, and lack of appropriate information and knowledge about alternative agricultural methods. This highlights the need for better resource and input availability as well as more vibrant and efficient extension services. Successful CA promotion requires that the systems are adapted to farmers' circumstances. However, CA cannot expand where farmers depend on remittances, are donor dependent, and where crop production in general is doubtful. Land uses such as extensive livestock production or game ranching may be better and more profitable alternatives for farmers in these situations.