Summary

Most field crop production by smallholder farmers in Zimbabwe’s semi-arid region is extractive ie there is limited fertilizer application and poor conservation of soil and moisture. But soil nutrients and water are yield-limiting factors. AS a solution, Conservation Agriculture (CA) is being promoted in these regions. CA can improve and sustain crop productivity while preserving and enhancing the resource base and environment in agro-ecosystems (FAO, 2012). It is characterised by three linked principles such as minimum or zero tillage, permanent or semi-permanent soil cover and integration of legumes. This study was determining the benefits of integrating legumes under CA in cereal crop production systems in semi-arid region by intercropping them with Sorghum bicolor at staggered planting dates.

To achieve this broad objective, the following aspects were measured: sorghum yield (biomass and grain yield), land equivalent ratio (LER) and nitrogen benefits. Two experiments were established.  

Experiment 1: Researcher-managed trial
This involved four sorghum-legume intercrop experiments as follows: Sorghum + cow peas (Vigna unguiculata) cv. CBC3, Sorghum + groundnuts (Arachis hypogeae) cv. Natal Common, Sorghum + velvet beans (Mucuna pruiens var. utilis) and Sorghum + sunnhemp (Colarata juncea) var. ‘Tropic Sun’.

Experiment 2: Farmer-managed trials
This farmer-managed field trial was done over two years. A network of 26 sorghum farmers were chosen based their location. They intercropped sorghum with cow peas as shown below.

For each sorghum-legume species polyculture, a 2x5 split plot factorial treatment structure in a randomized complete block design was used. Tillage method was the main plot factor while planting patterns were  sub-plot factors.