Ecology of maize-cowpea intercropping on biological nitrogen fixation, productivity and grain mineral composition along soil fertility gradients in Zimbabwe.

Abstract

Recurrent droughts, infertile soils, lack of adequate machinery and other inputs are jeopardizing crop production in the smallholder farming sector of Sub Saharan Africa. Diversification and intensification of farming systems through inclusion of cowpea as an intercrop with staple cereal crops represents a key technology in the drive towards sustainable development of agriculture in SSA. Integration of cowpea into maize based cropping systems as an intercrop improves productivity especially in poor soils through N2-fixation. A two season field experiment was carried out in Goromonzi District, Mashonaland East province (17°51′22″S, 31°22′48″E) to (1) determine the level of grain mineral accumulation in maize and cowpeas grown as intercrops or sole crops at different soil fertility levels. (2) To determine N2-fixation of two cowpea varieties planted as sole crops or intercrops across soil fertility gradients; (3) To determine the land equivalent ratio (LER) of maize-cowpea intercrops, maize sole crop and cowpea sole crops. Treatments were laid out in a 2 × 8 split plot arrangement in a RCBD, with field types at two levels and cropping systems at eight levels. Soil analysis results did not conform to farmers’ perceptions on field types. There were no differences (p>0.05) between home fields and out fields. Soils had 0.75% Soil Organic Carbon, 7.57% clay content and pH was 4.4 in home fields and 4.2 in outfields. Significant differences (p<0.05) were observed on nodules and N2-fixation, where highest nodule number of 6.92 was recorded in landrace – N treatment. N2-fixation ranged from 22kg Nha-1 to 102 kg Nha-1 , where landrace + N fixed 102 kg Nha-1 and intercropped improved cowpea + N fixed 22 kg Nha-1 . No differences (p>0.05) were observed on the effect of intercropping on maize and cowpea grain mineral content. Significant differences were observed on maize and cowpea yield, where sole maize + N and improved cowpea + N produced more grain yields. Intercropping was productive as LER was greater than one in both field types. N2-fixation was higher in monocrops especially when N was supplied to a landrace variety. Intercropping increased productivity especially in outfields, which farmers perceived to be poor. Landrace cowpea was adopted to intercropping than improved cowpea.