Effect of Mucuna fallow on weed dry matter and composition in succeeding maize

Weeding requires a major proportion of labour in farming of smallholders in Africa. Any technology that can effectively reduce the weeding requirement increases the productivity of the household. Studies were conducted on farmers' fields in the Sunyani District (2 degrees 8' to 2 degrees 31'W latitude, 7 degrees 7' to 7 degrees 36'N longitude), located in the Forest-Savannah Transitional Zone of Ghana in 1999 and 2000 to assess the impact of two different slash-and-mulch Mucuna fallow systems on weed dry matter (DM), weed density and frequency in succeeding maize compared with the prevailing slash-and-burn natural fallow system. Late maturing Mucuna pruriens (L.) DC var. utilis (Wright) Burck reduced weed DM by 58% in 1999 and 68% in 2000. The system with the local early maturing Mucuna variety did not reduce weed DM significantly. On the whole, 58 weed species from 27 families were identified. The most dominant species were Chromolaena odorata (L.) R.M. King & Robinson, Centrosenta pubescens Beath., Euphorbia heterophylla Linn. and Mucuna spp. volunteer seedlings. The M. pruriens system reduced eight persistent weeds (frequency of occurence > 20%) both in frequency and average density compared with the short season natural fallow treatment. In contrast, only two persistent weed species were affected in the same way by the system with the local Mucuna variety, while six persistent weeds increased in frequency of occurence and seedling density. Poaceae species were negatively affected by the Mucuna systems. While in the natural fallow treatment Poaceae comprised 27.8% of all species identified, their proportions were reduced to 23.1% and 21.7% after fallow with the local Mucuna variety and M. pruriens, respectively. The greater weed suppressing effect of M. pruriens is considered to be a result of its longer life span than the early maturing local variety.