Long-Term Yield Sustainability and Financial Returns From Grain Legume–maize Intercrops on a Sandy Soil in Subhumid North Central Zimbabwe

Abstract

To measure the yield and financial returns from five grain legume-maize intercrop combinations over 12 years of cropping, a field experiment was conducted on a loamy sand soil in the subhumid unimodal rainfall environment of Domboshava in north-central Zimbabwe. Inputs and management followed smallholder practice, including partial grazing of crop residues and a zero mineral fertilizer treatment. The intercropped legumes grew moderately well most years. Cowpea averaged the highest grain yield (0.244 t ha −1 ) and haulm yield (1.54 t ha −1 ) over the 12 years, followed by pigeonpea and sugar bean. Intercropped pigeonpea yield was the least variable of the legumes over the years. Maize grain yield was highly variable across years with or without fertilizer and was reduced in years of low (533 mm) and high (1313 mm) rainfall. The pigeonpea-maize intercrop grown without fertilizer produced 0.11 t ha −1 (6.25 %) more maize grain yield per year than sole crop maize, in addition to pigeonpea grain and haulms. Intercropped cowpea (which yielded more than double the above-ground non-grain biomass of pigeonpea) had less effect on maize grain yield. There was no trend to greater benefits from the legumes on maize yield after more years of intercropping. Net present values of annual margins accumulated over the 12 years for sole maize with fertilizer (US$1719 ha −1 ) and without fertilizer (US$935 ha −1 ) were higher than the fertilized and unfertilized intercropping options (US$1017 and US$745 ha −1 ). Pigeonpea or cowpeaunfertilized maize generated more financial returns than the other intercrops, but the low yields and high labour costs for the legumes made the intercrops financially unattractive. We conclude that regularly intercropped pigeonpea or cowpea can to a small extent help to maintain maize yield when maize is grown without mineral fertilizer on sandy soils in sub humid zones of Zimbabwe, and simultaneously provide some nutritious food, but that financial considerations will encourage smallholder farmers to persist with growing low input sole crop maize.

Yield response of maize (Zea mays L.) to conservation agriculture cropping system in Southern Africa

“…Ngwira et al (2012b) reported similar results from Malawi in maize-legume intercropping systems with minimum tillage as well as Rusinamhodzi et al (2012) in central Mozambique. Our results support earlier findings of Sakala (1994) who reported a yield penalty of only 10% when intercropping with pigeonpea, although yield penalties can also be much larger especially when the timing between main crop and intercrop is not well synchronized (Shumba et al, 1990;Waddington et al, 2007).…”

Environmental impacts and constraints associated with the production of major food crops in Sub-Saharan Africa and South Asia

“…These include improved soil and water conservation methods (e.g., Fowler and Rockström 2001;Hobbs et al 2008;Erenstein et al 2012), integrated nutrient management (e.g., Vanlauwe et al 2010;Timsina et al 2010Timsina et al , 2011, the retention and use of biodiversity on crop fields (Mapfumo et al 2005;Snapp et al 2010) and the improved management of farm fields with different nutrient status (e.g., Giller et al 2006;Tittonell et al 2008). Across Sub-Saharan Africa, many of the more-traditional maize systems maintain productivity while reducing abiotic and biotic environmental impacts by intercropping or rotating leguminous trees and shrubs, and annual legumes with maize (Snapp et al 1998(Snapp et al , 2010Waddington et al 2007;Ajayi et al 2011;Pretty et al 2011), or by incorporating legume weed residues into croplands (Mapfumo et al 2005). The expansion of such practices should be encouraged.…”

Conservation agriculture in Southern Africa: Advances in knowledge

“…Intercropping maize and legumes is another way to achieve food security and cash income for smallholder farmers, and abundant literature from Southern Africa supports this observation 81,102,[130][131][132][133] . Although intercropping with legumes is associated with many benefits, including improving soil structure and fertility and the potential to increase farm income through selling legume grain, the potential of legumes within farming systems of Southern Africa is currently limited by a plethora of constraints.…”