Productivity and profitability of maize plus groundnut rotations compared with continuous maize on smallholder farms in Zimbabwe

Experiments to assess the yield and economic performance of a maize-groundn ut rotation compared with continuous maize (both when inorganic fertilizer was applied to maize and when not), were conducted under management by smal lholder farmers in Zimbabwe over six years. The experiment was planted on-s tation near Harare and at six smallholder sites in northeast Zimbabwe, pred ominantly on sandy soils. Fertilizer rates and practices were those used by farmers, as described in surveys. On-farm grain yields from continuous mai ze without fertilizer were generally in the range 0.5-0.8 t ha(-1) over fiv e years. Maize yield responses to inorganic fertilizer on smallholder farms were highly variable, but moderate (up to 29 kg grain per kg N) with adequ ate rainfall. With no inorganic fertilizer applied to maize, the on-station groundnut crop (producing 0.260-0.355 t ha(-1) shelled grain) almost doubl ed the grain yield of the following maize crop (in 1995-96), increasing out put from 2.46 t ha(-1) to 4.61 t ha(-1) Where inorganic fertilizer was appl ied to maize, the rotation produced even more additional maize grain (an in crease of 2.93 t ha(-1)). Up to 0.50 t ha(-1) extra grain was obtained in t he second year of maize following groundnut (1996-97). With inorganic ferti lizer, groundnut improved the grain yield of following maize crops at only two of five on-farm sites. Without fertilizer, the groundnut rotation incre ased maize grain yields at five on-farm sites by an average of only 0.28 t ha(-1) For the on-station groundnut and two subsequent years with maize, di scounted net benefits (DNBs) over cash costs (seed and fertilizer) were gre ater for the rotation than for continuous maize, irrespective of whether or not inorganic fertilizer was applied. When labour costs were added, contin uous maize plus fertilizer showed better returns than did the rotation, whi le the returns for the rotation and continuous maize without fertilizer wer e almost the same. On-farm the rotation was far less profitable. At only tw o sites, DNBs over cash costs were higher for the rotation whereas DNBs ove r all costs (including labour valued at a local casual-worker wage) were al ways negative or close to zero. At three sites, it was far more profitable to grow continuous maize, especially with fertilizer. These findings of low groundnut yield, marginal to zero profitability, and high labour cost of g roundnut-maize rotations, support and explain the general trend by smallhol der farmers to reduce groundnut area in Zimbabwe.