Maize-sesame intercropping in Southeast Tanzania : Farmers' practices and perceptions, and intercrop performance

Keywords: Intercropping,farm household objectives, marginal factor returns, cost-benefit analysis, inter-seeding time, Land Equivalent Ratio, maize, sesame, niche differentiation, spatial arrangement.InSoutheast Tanzania, the major food crop maize is often inter-seeded with the cash crop sesame using an additive design. Farmers consider maize an essential crop for securing their basic food requirements, whereas sesame is added to generate cash. In this research, farmers' motives for adopting maize-sesame intercropping systems were studied. Concurrently, experiments were conducted to evaluate the performance of the maize-sesame intercropping systems and to explore options for improvement.A household survey revealed that in the study area arable cropping is the main occupation, responsible for 75% of the mean annual household income. Cashew, maize and sesame were found to be the most important crops contributing to the household income. About 90% of the farmers intercropped maize and sesame to diversify their cash income. All farmers consider maize the more important crop, as it should secure the basic food requirements of the household. The risk of crop failure associated to growing sesame in pure stand is an important reason for adding sesame to maize. Growing the intercrop also puts less demand to labour and fertile land, both of which are limited in supply. Furthermore, maize and sesame are regarded as good companion crops, which additionally contribute to restoration of soil fertility and weed suppression.Simultaneous sowing of maize and sesame caused reductions in maize grain yield, of on average 27%. These reductions decreased with delayed inter-seeding times. Conversely, delayed seeding led to significant reductions in sesame yield, caused by a direct effect of sowing time and an increased competitiveness of maize. Based on a long-term averagemaize :sesame price ratio of 1:3.5, simultaneous sowing turned out to be the option with the highest gross financial returns. At the same time, the study demonstrated that there are associated risks with simultaneous sowing such as seedling mortality of sesame due to water logging and severe reductions in maize grain yield (up to 60%). Farmers generally introduce sesame about two weeks after maize, to reduce those risks. This study showed however that the recently developed improved sesame varieties are not very well suited for late introduction, due to their poor competitiveness. As sesame is mainly grown in intercrop, future breeding efforts should not only consider characteristics as yield, seed colour and seed oil content, but should also take into account characteristics as competitive ability and growth duration, that determine the suitability of sesame in intercropping systems.Density experiments revealed that maize was more competitive than sesame, but more importantly the experiments also demonstrated that maize and sesame are partially complementary in resource acquisition. Niche differentiation forms the basis for a yield advantage in intercropping. This observation confirms the notion of farmers that maize and sesame are good companion crops. At both the relatively high fertile site and the poorly fertile site, P/N ratios of shoot tissue of maize and sesame were high (between 1/1.5 and 1/6.4), indicating that nitrogen was a major limiting factor in the study area. At the low soil fertility site (Mkumba), both maize and sesame in pure stand responded significantly to N and NP-fertilization. At this site, the application of nitrogen fertilizer resulted in 2.5 and 3.6 fold increases in pure stand yield of maize and sesame, respectively. In intercrop, N fertilization increased the dominant position of maize in the intercrop. Consequently, only maize profited from N fertilization, as for sesame the advantage of additional N was counterbalanced by the presence of a more competitive maize crop. Nitrogen recovery was highest in the intercrop. The results question the general fertilizer recommendations, which advice to supply N and P in nearly equal amounts.Studies on spatial arrangement showed that, both in pure stand and intercrop, sesame seed yield was independent of sowing method (row or broadcast). In the intercrop, grain yield of maize was affected by the method of sowing sesame. When broadcast sown, sesame caused reductions in maize grain yield ranging from 53 to 69%. These reductions were only 19 to 55% with row sowing. Two to three maize plants per station were found optimal in pure stand as well as in intercrop. This last result indicates that farmers' practice of growing two-three plants per station is superior to the institutional recommendation of growing one plant per stationThe results of this study clearly indicate that recommendations for intercropping should be based on intercropping research and cannot simply be extrapolated from results obtained with pure stands of the respective component crops. Efforts for breeding improved varieties should also consider the use of the crops in intercropping. Furthermore, a proper analysis of experimental results requires a thorough understanding of farmers' objectives and production constraints. At the same time, an inventory of farmers' objectives and production constraints without exploring the options for improvement seem ineffective. For these reasons it was recommended that future projects should put emphasis on participatory research in teams of social scientists, technical scientists and farmers in the process of co-innovation to improve the well being of farmers and rural households.