Effect of hand-hoe based conservation agriculture on soil fertility and maize yield in selected smallholder areas in Zimbabwe

Conservation agriculture (CA) based on hand-hoe prepared planting basins is being widely promoted in southern Africa, targeting resource-constrained farmers with limited access to draft power. This study was conducted across 15 districts covering four agro-ecological zones in Zimbabwe where paired CA and conventional animal drawn tillage (CADT) plots had been established on 450 farms as part of CA promotion. The aim of the study was to assess the effect of CA on soil pH, organic C, total P and maize (Zea mays L.) grain yield compared with CADT, and also to evaluate the yield benefits of mulching and crop rotation in CA with or without mineral fertilizer use. It was hypothesized that CA improved the pH, organic C, total P of the soils (Arenosols) and grain yield compared with CADT and that mulching and crop rotation in CA increased maize grain yield. A total of 1014 soil samples (0–0.2 m depth) were taken at the end of the 2009/10 cropping season and analyzed for pH, organic C and total P. Grain yield was determined in 2009/10 and 2010/11 from 0.01 ha net plots. There was no significant difference in average soil pH, total P and organic C between CA and CADT plots and therefore the hypothesis that CA improves these soil properties was rejected. Average concentration for organic C for both CA and CADT plots was less than 10 g kg−1, a minimum threshold for well managed soils. When combined with mineral fertilizer: mulching, crop rotation, and mulching + crop rotation in CA increased maize grain yield by 20–33%, 7–9% and 58–69%, respectively. With no mineral fertilizer application, mulching, crop rotation, and mulching + crop rotation depressed maize grain yield by 48%, 28% and 36%, respectively. Therefore the hypothesis that mulching and crop rotation increase maize grain yield was accepted when mineral fertilizer was added and rejected when the fertilizer was not added. It was concluded that the yield benefits of CA can only be realized when mineral fertilizer is also applied. All the three CA principles in combination with mineral fertilizer results in highest yield benefits compared with one or two principles as currently done by most smallholder farmers in Zimbabwe. Access to mineral fertilizer is an important factor in the targeting of CA promotion in smallholder areas of Zimbabwe and similar socio-ecological zones in sub-Saharan Africa

Grain Yield Responses of Selected Crop Varieties at Two Pairs of Temperature Analogue Sites in Sub-humid and Semi-arid Areas of Zimbabwe

Climate analogues, based on 30 years meteorological data, were identified in smallholder areas of Zimbabwe. The sites were Kadoma (722 mm annual mean rainfall; 21.8 °C annual mean temperature) which was the higher temperature analogue site for Mazowe (842 mm annual mean rainfall; 18.2 °C annual mean temperature) for wetter areas, and Chiredzi (541 mm annual mean rainfall; 21.3 °C annual mean temperature) which was the higher temperature analogue site for Matobo (567 mm annual mean rainfall: 18.4 °C annual mean temperature) for drier areas. At each site and for each crop, three varieties were laid out in a randomized complete block design with three replications. The trials were conducted for two seasons (2011/2012 and 2012/2013). Maize and groundnut yields were higher at the cooler and wet sites and decreased significantly at the warmer and dry sites. In case of sorghum and cowpea, yields at the hotter site remained high implying that these crops are more tolerant to warmer temperatures predicted for 2050. At the drier sites, yields for all crops were significantly lower at the hotter site implying that crop production in the 2050s climate of the cooler site will be more difficult. The hypothesis that with increasing surface temperatures in a climate change scenario short duration genotypes can perform better compared with long duration was not confirmed

Grain yield of selected crops at four climate analogue locations in Zimbabwe

Predicted warmer climates are likely to negatively affect production systems and expose smallholder farmers in sub-Saharan Africa, whose adaptive capacity is limited mainly due to poverty, to food insecurity. We studied the performance of selected varieties representing short, medium and long duration growth periods of four crops (maize (Zea mays L.), sorghum (Sorghum bicolor L.), groundnut (Arachis hypogaea L.) and cowpea (Vigna unguiculata L.) at two pairs (wet and dry) of 2050s climate analogue sites. Climate analogues, based on 30 years metereological data, were identified in smallholder areas of Zimbabwe. The sites were Kadoma (722 mm annual mean rainfall; 21.8oC annual mean temperature) which was the higher-temperature analogue site for Mazowe (842 mm annual mean rainfall; 18.2oC annual mean temperature) for wetter areas, and Chiredzi (541 mm annual mean rainfall; 21.3oC annual mean temperature) which was the higher-temperature analogue site for Matobo (567 mm annual mean rainfall: 18.4oC annual mean temperature) for drier areas. First season (2011/12) results showed that for the wetter pair, maize and groundnut grain yields were significantly higher at the cooler site (Mazowe). Sorghum yields were not significantly different between the sites and there was no grain yield for cowpea at the cooler site due to a fungal disease. Varietal yield differences were only significantly higher (P<0.05) at the cooler site for groundnut where the short duration variety had the highest yield (3809 kg/ha) and the medium duration variety the lowest yield (1420 kg/ha), compared with 140-355 kg/ha at the hotter site where growth was poor for all varieties. For the drier sites, maize, sorghum and cowpea grain yields were higher at the cooler site (Matobo) compared with the hotter sites (Chiredzi) but varietal differences were not significant. Results for the second season (2012/13) will be presented

Weed growth and labor demand under hand-hoe based reduced tillage in smallholder farmers’ fields in Zimbabwe

Conservation agriculture based on hand hoe dug planting basins has been widely promoted for the last decade or two in the smallholder farming sector of southern Africa targeting resource constrained households without access to draft power. In Zimbabwe planting basins are used by about one hundred thousand households but on small plots (<0.5 ha) although most are unable to adopt soil surface mulching and crop rotation due to competing uses for crop residues as livestock feed and poorly developed markets for other crops, respectively. We report on the effects of reduced tillage based on hand-hoe dug planting basins (PB) on weed growth (20 farms), and labor demand and returns to investment (50 farms) compared with animal-drawn mouldboard plough based conventional tillage (CONV) in maize (Zea mays L.) fields, across selected districts located in contrasting agro-ecological zones in Zimbabwe. Weed growth was assessed through a survey conducted at the end of the 2009/10 and 2010/11 cropping seasons. Labor demand and returns to investment were measured on 50 farms across five districts using direct observations during the 2011/12 cropping season. The survey showed that farmers on average weeded their PB plots 2.7 times per season compared to 1.7–1.9 times in CONV plots (P < 0.001), and timing was often delayed in the former. Reduced tillage plots had 17% (P < 0.001) more weed ground cover and 9% (P < 0.05) more weed dry matter compared with CONV plots in the 2009/10 season, and differences in 2010/11 were not significant. Weed growth was highest in semi-arid areas (natural regions III and IV) compared with wetter sub-humid areas (natural region II) and arid areas (natural region V). Farmers planted their PB plots 12–23 days earlier, weeding frequency was 42.1–58.9% higher in PB plots, compared with CONV. Labor demand was more than double under PB (84.7 man days ha−1, weeding 48.1 man days ha−1) compared to CONV (38.6 man days ha−1). However, returns to investment were 42.7% higher under PB (U$1.77) compared with CONV (U$1.24). Weed growth and labor demand remained high under PB tillage even after several years, interventions such as the use of alternative weed control methods need to be introduced to farmers to reduce labor demand and consequently increase its adoption both in terms of number of farmers and cultivated area in southern Africa

Effect of Conservation Agriculture on Maize Yield in the Semi-Arid Areas of Zimbabwe

Globally, a range of agronomic factors have been reported to have an impact on the performance of conservation agriculture (CA) and often determine its performance in relation to conventional agriculture (CONV). To assess this performance in Zimbabwe, 48 CA experiments were conducted by the International Crops Research Institute for the Semi-Arid Tropics in the semi-arid areas of southern Zimbabwe from 2004 to 2010, to calculate the weighted mean difference (WMD) through meta-analytical methods. The two CA practices, planting basins (Basins) and ripper tillage (Ripper), were compared with CONV. It was hypothesised that CA results improved yield compared with CONV and that the effect of CA practices on yield is affected by soil type, rainfall amount and distribution and selected management practices, which included rates of inorganic fertilisers and manures and mulching. Basins were superior to CONV in 59% of the experiments and the overall effect was significant (p < 0.001). The effect of Ripper was non-significant. The hypothesis that CA practices result in improved maize grain yield over CONV was accepted for Basins. The WMD for experiments conducted on sandy soils was 0.365 t ha−1 for Basins and 0.184 t ha−1 for Ripper, and in both cases was significant (p < 0.05). For clay soils, only the WMD for Basins was significant. A higher rainfall regime (500–830 mm) resulted in a lower WMD for Basins (0.095 t ha−1) and Ripper (0.105 t ha−1) compared with 0.151 t ha−1 for Basins and 0.110 t ha−1 for Ripper under lower rainfall (320–500 mm). The overall effect of Basins under the higher rainfall regime was not significant. There was better yield performance for Basins when the rainfall was well distributed; the reverse was noted for the Ripper. The application of 10–30 kg ha−1 of N (micro-dose range) resulted in a higher WMD for Basins than zero N application. Without N application, the WMD of Basins was not significant. For zero manure application in Basins, the WMD was 0.043 t ha−1 compared with 0.159 t ha−1 when manure was applied. The application of mulch depressed the WMD in Basins by 44% and Ripper by 89%. The hypothesis that yield performance under CA is influenced by soil type, rainfall amount and distribution, inorganic fertiliser and manure application was accepted

Effect of hand-hoe based conservation agriculture on soil fertility and maize yield in selected smallholder areas in Zimbabwe

Conservation agriculture (CA) based on hand-hoe prepared planting basins is being widely promoted in southern Africa, targeting resource-constrained farmers with limited access to draft power. This study was conducted across 15 districts covering four agro-ecological zones in Zimbabwe where paired CA and conventional animal drawn tillage (CADT) plots had been established on 450 farms as part of CA promotion. The aim of the study was to assess the effect of CA on soil pH, organic C, total P and maize (Zea mays L.) grain yield compared with CADT, and also to evaluate the yield benefits of mulching and crop rotation in CA with or without mineral fertilizer use. It was hypothesized that CA improved the pH, organic C, total P of the soils (Arenosols) and grain yield compared with CADT and that mulching and crop rotation in CA increased maize grain yield. A total of 1014 soil samples (0–0.2 m depth) were taken at the end of the 2009/10 cropping season and analyzed for pH, organic C and total P. Grain yield was determined in 2009/10 and 2010/11 from 0.01 ha net plots. There was no significant difference in average soil pH, total P and organic C between CA and CADT plots and therefore the hypothesis that CA improves these soil properties was rejected. Average concentration for organic C for both CA and CADT plots was less than 10 g kg−1, a minimum threshold for well managed soils. When combined with mineral fertilizer: mulching, crop rotation, and mulching + crop rotation in CA increased maize grain yield by 20–33%, 7–9% and 58–69%, respectively. With no mineral fertilizer application, mulching, crop rotation, and mulching + crop rotation depressed maize grain yield by 48%, 28% and 36%, respectively. Therefore the hypothesis that mulching and crop rotation increase maize grain yield was accepted when mineral fertilizer was added and rejected when the fertilizer was not added. It was concluded that the yield benefits of CA can only be realized when mineral fertilizer is also applied. All the three CA principles in combination with mineral fertilizer results in highest yield benefits compared with one or two principles as currently done by most smallholder farmers in Zimbabwe. Access to mineral fertilizer is an important factor in the targeting of CA promotion in smallholder areas of Zimbabwe and similar socio-ecological zones in sub-Saharan Africa