Assessing intensification options of common bean cultivation to improve food security on smallholder farms in the Northern Highlands of Tanzania
Complementarities of common bean (Phaseolus vulgaris L.) with non-legume food crops and their significances to the agricultural systems are underexploited. Based on the description of this study, eight options were assessed for the sustainable intensification of common bean cultivation (through manipulations of intercropping and rotation) against the monocultures of maize (Zea mays L.), and the improved and local varieties of common bean in the northern highlands of Tanzania. The factors assessed were the cropping seasons/years (S) (2015 to 2017), agro-ecological zones (A) above sea level (lower 843 m, middle 1051 m, upper 1743 m), cropping systems (C) (sole, intercrop, rotation), and bean varieties (V) (improved Lyamungu 90 and local Mkanamna) and their interactions. Results indicated that S, A, C, and S×A, S×C, S×A×C were significant and bean grain yields increased in intercrops ranging from 1.5 to 2.9 t ha-1 with land equivalent ratio (LER) of 1.58. Intercropping over five cropping seasons indicated that with S×V grain yields increased from 0.2 to 3.5 t ha-1 in bean and from 2.3 to 2.6 t ha-1 in maize with LERs of 1.48 and 1.55. In rotations, higher bean grain yields were attributed to S (3.3 t ha-1 ), C (3.4 t ha-1 ), and V (2.7 t ha-1 ) and for maize were in C (2.9 t ha-1 ) and S (2.6 t ha-1 ). In conclusion, out of eight assessed options, this study found two main useful options for improving food security on smallholder farms in the northern highlands of Tanzania. The options were continuous cultivation of the improved and/or local varieties of common bean in intercrops with the maize throughout two rainy seasons of the year (long and short). Another option was cultivation of the improved and/or local varieties of common bean intercropped with maize in the long rainy season and rotating of these intercrops with the maize cultivated in the short rainy seasons. Importantly, the improved bean variety Lyamungu 90 was heavier in weight, using the same number of seeds, than the local bean variety Mkanamna, which provided additional factors to be considered to improve income where weight is the acceptable standard in the market.