Abstract
Poor soil fertility is a major challenge to crop production in the communal farming areas of Zimbabwe. Intercropping legumes and cereals is a common soil fertility management technology among the farmers. A 3-year field experiment was conducted to evaluate cowpea–sorghum relay intercropping advantages in response to different cattle manure application rates. A 3 × 4 factorial experiment laid in a completely randomized block design (CRBD) with three replicates was conducted. The treatments were three cropping systems (sorghum sole, cowpea sole, and cowpea–sorghum intercrop) and four cattle manure application rates (0, 50, 75, and 100%). Crop growth rate (CGR), grain yield, harvest index (HI), relative competitive ability of each crop, and land equivalent ratio (LER) were measured. Analysis of variance and non-linear regression analyses were done to determine the yield benefits of cowpea–sorghum intercrop and estimate the relative competitive ability, respectively. Application of >75% cattle manure in a cowpea–sorghum intercrop enhanced the sorghum grain yield (75%) and HI (125%) of unmanured cowpea–sorghum plots. Cowpeas had higher CGR (159.6, 166.7 and 149.5 g m−2 day−1 at 7, 21, and 35 days after planting, respectively) at >75% cattle manure application rates on both intercrop and sole cropping than sorghum but with lower grain yield (1.4 t ha−1). Intraspecific competitive stress in sorghum was reduced at a high (>75%) quantity of manure applied. The effects of the intraspecific competition in cowpea were stronger (0.693) on grain yield than biomass at >75% manure application rates. The LER was >1 in all the treatments and was highest (2.73) under the cowpea–sorghum relay intercrop without cattle manure. Cattle manure application at 75% in a cowpea–sorghum intercrop enhanced the grain yield in sorghum and vegetative growth in cowpeas. It is therefore recommended to use the >75% cattle manure application rate in the intercrop if one wants higher grain in sorghum and high biomass in cowpeas possibly for fodder. Further studies are recommended to quantify the rate of increase in available N under the cowpea–sorghum relay intercrop with >75% cattle manure application rates.
Highlights
A majority (>70%) of Zimbabwe’s 14.5 million people live in the communal areas and more than three-quarters of these communal areas are characterized by low and unreliable rainfall and inherently low soil fertility (Anderson and D’Souza, 2014)
The soil was low in total C, N, P, and Ca which were consistent with the lower [8.0 cmol(+)kg−1] cation exchange capacity (CEC) compared to the cattle manure
The grain yield and harvest index (HI) of sorghum were increased by 100% cattle manure inclusion but were reduced in cowpea
Summary
A majority (>70%) of Zimbabwe’s 14.5 million people live in the communal areas and more than three-quarters of these communal areas are characterized by low and unreliable rainfall and inherently low soil fertility (Anderson and D’Souza, 2014). Crop productivity is still low due to poor soil fertility management among these communal farmers. The low crop productivity has been exacerbated by the changing climate in Zimbabwe; the rainfall is becoming more and more unreliable and unpredictable, the difficulties in the planning cropping schedules among the farmers (Parwada et al, 2020). There is a need for sustainable crop production methods because many of the communal farmers are poor and cannot afford to purchase offfarm inputs. Numerous sustainable crop production methods are available for the farmers; e.g., good agricultural practices like crop rotation, mixed cropping, and intercropping can offer many advantages to these resource-poor farmers
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