The yield stability of intercropping systems is important in developing cropping systems that produce economic yields over a wide range of environments. Field studies were conducted during the 1997/98 and 1998/99 growing seasons at three locations in the forest and forest–savannah transition zones of Ghana to determine yield, land use efficiency and yield stability of cassava (Manihot esculenta), maize (Zea mays), soya bean (Glycine max) and cowpea (Vigna unguiculata) intercrop systems. The cropping systems consisted of a factorial combination of two cassava varieties: ‘Gblemoduade’ (an improved, highly branched variety) and ‘Ankra’ (a local variety with fewer branches) and three spatial arrangements. Cowpea rows were planted in the minor season into cassava as a successive crop to maize and soya bean after their harvest in the major season. Intercropping significantly reduced grain or tuber yield of maize, cassava ‘Gblemoduade’ and cassava ‘Ankra’ by 23–70%, 16–49% and 24–64%, respectively. Maize yield decreased with increased number of soya bean rows. ‘Gblemoduade’ outyielded ‘Ankra’ by more than 100% under both intercrop and sole crop. The yield of soya bean increased with increased number of soya bean rows, but did not differ in response to the cassava variety. However, cowpea yield was higher when intercropped with ‘Ankra’ than with ‘Gblemoduade’. The intercrops had higher land use ratios (LER=1·27–2·83) and were more stable than the sole crops. Intercrops involving ‘Ankra’ had higher LER (2·14–2·18) than systems with ‘Gblemoduade’ (LER=1·83–1·99), but their yield stabilities were similar.

Innovation platforms (IPs) are a way of organizing multistakeholder interactions, marshalling ideas, people and resources to address challenges and opportunities embedded in complex settings. The approach has its roots in theories of complexity, the concept of innovation systems and practices of participatory action research. IPs have been widely adopted across Africa and beyond in recent years as a "must have" tool in a range of "for development" modes of agricultural research. Our experiences with establishing and facilitating nine IPs in local settings in west and central Africa contribute to understanding factors that impact on their effectiveness. The nine IPs were variously focused on developing dairy, crop and/or meat value chains by strengthening mixed crop-livestock production systems or seed systems. Using case study methods, we identified variables that contribute to explaining the performance of these IPs in relation to six domains of change in the agricultural system and the sustainability of changes. Thematic analysis was guided by a conceptual framework which grouped variables into four categories (context, structure, conduct, and process) that interact to influence IP performance. Stronger market connections and value chains were generated through some of these IPs but the most prevalent changes overall were in farm productivity and technical knowledge of producers. The structures evolved in some IPs, akin to those of producer collectives, suggested they were filling an institutional gap locally. The effect of the IPs on deeper level institutions that influence agricultural systems and food security was modest, constraining prospects for the IPs to generate impact at scale. Impacts from the IPs on research and development organisations were uncommon but had transformative significance. Our conceptual framework did not offer optimal guidance to understanding how the many variables that contributed to performance of these IPs combined and sequenced, but the pattern of interactions was consistent with increased social capital being the prime mediator for change. Achieving greater prospects for transformational

The study evaluated staking options to address the problem of deforestation for sustainable yam production in the Forest and Forest-Savannah Transition zones of Ghana. A split-plot design with three yam varieties (Dente, Water Yam and TDR95/19177 line) and three staking options (No staking, Vertical staking and Trellis with 50% and 30% number of vertical stakes for 2012 and 2013 respectively) as main plots and subplots respectively were used. Results revealed a significant (P < 0.05) interaction between yam variety and staking options on yam tuber yields in both locations and years. While water yam had similar tuber yields under all staking options, Dente and TDR95/19177 under no staking had significant yield reductions ranging from 37 to 65% compared to the other staking options. The observed yield reduction under no staking of Dente and TDR95/19177 could be attributed to higher incidence of yam mosaic virus leading to significantly lower fresh leaf biomass production. Reducing the number of stakes in trellis to as low as 30% of the vertical/optimum staking option did not result in a significant reduction in tuber yields for TDR95/19177 and Water yam. The economic analysis revealed that it is more profitable to produce water yam and TDR95/19177 under no staking and trellis (50% and 30% number of optimum staking) respectively in both locations. The results suggest trellis/minimum staking can be used to minimize the use of stakes, yam mosaic virus disease infection and for sustainable yam production in the face of climate change.

findings that, when available, soil N is the main source of N for soybean growth rather than N fixation (Her-Plant population of soybean [Glycine max (L.) Merr.] may influridge and Brockwell, 1988). Thus, growing soybean can ence the residual N contribution to a cropping system and yield beneresult in a net depletion of soil N (Zapata et al., 1987). fits to following cereals. Field studies were conducted from 1994 to 1996 on a N-depleted Sharpsburg silty clay loam soil at Mead, NE High amounts of N are removed by harvested soybean to: (i) determine soybean yield at different plant populations; (ii) seeds (144 and 169 kg N ha Ϫ1 , Clement et al., 1992; investigate residual N, chlorophyll-N-yield relations, and yield bene-150-200 kg N ha Ϫ1 , Varvel and Peterson, 1992). This fits from these different soybean populations to a following maize 12678. Work supported in part by the Canadian Int. Dev. Agency (CIDA).

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Modelling and multiple linear regression were used to explore the reason for low maize yield in the Atebubu-Amantin and West Mamprusi Districts of Ghana, West Africa. The study evaluated maize yields on twenty farms against measures of soil fertility, agronomic attributes and soil water availability. Correlations between yield, soil fertility, rain, crop density, and weed biomass, were low, and no single factor could explain the low yields. A 50-year virtual experiment was then set up using the Agricultural Production Systems Simulator (APSIM) to explore the interactions between climate, crop management (sowing date and nitrogen fertilization) and rooting depth on grain yield and nitrate (NO3-N) dynamics. The analysis showed that a lack of optimal sowing dates that synchronize radiation, rainfall events and nitrogen (N) management with critical growth stages explained the low farm yields.

Two field experiments were conducted at Ellembelle and Jomoro districts in the Western region of Ghana where rubber cultivation is a predominant farming activity. The objective of the study was to assess the effect of rubber and plantain intercropping systems on selected soil properties. The experiment was arranged in a randomized complete block design (RCBD) with 3 replications. The treatments were the sole crop rubber (R), sole crop plantain (P) and three intercrop systems comprising an additive series of plantain: one row of plantain to one row of rubber (PR), two rows of plantain to one row of rubber (PPR) and three rows of plantain to one row of rubber (PPPR). Generally, agroforestry systems improved the soil hydraulic properties considerably, with the highest cumulative infiltration rates of 5.16 and 8.68 cm/min observed under the PPPR systems at the Ellembelle and Jomoro sites, respectively. Microbial biomass C (Cmic), N (Nmic) and P (Pmic) was significantly improved (P < 0.05) under the agroforestry than the monocrop systems. The Cmic, Nmic and Pmic values were highest under the PPPR system at both Ellembelle (Cmic, = 139.9 mg/kg; Nmic = 36.26 mg/kg and Pmic = 87.6 mg/kg) and Jomoro (Cmic = 78.7 mg/kg; Nmic = 80.3 mg/kg and Pmic = 3.45 mg/kg) sites.

An on-station study at Fumesua and Ejura in Ghana with two yam varieties (Pona and Dente), seedbed option (ridge and mound) and NPK fertilizer rates (0, 45-45-60, 60-60-60 and 60-60-80 kg ha-1 N-P 2 0 5-K 2 0) revealed significant (p < 0.05) increases in soil carbon and phosphorus with fertilizer application to yam. Fertilized yam had acceptable culinary qualities. Another study on staking options using a promising non-staked yam line TDR95/19177 showed that non-staked yam resulted in a high (32.5%) yield reduction, suggesting the need for further plant breeding work. On-farm studies showed significant (P  0.05) interaction between fertilizer rate and seedbed preparation method on continuously cropped lands, with mechanised and manual ridging having significantly (p < 0.05) higher yam plant population (5,503-7,483 plants ha-1) than farmers' mounding (4,219-4,579 plants ha-1), and a greater yield response to fertilizer. Benefit Cost Ratio (BCR) was highest (2.7:1) when 45-45-60 kg ha-1 N-P 2 0 5-K 2 0 was applied to yam on ridges. On newly cleared fields, yam planted on ridges with trellis/minimum staking gave highest tuber yields and BCR of 3.8:1. Mechanised ridging for yam seedbed preparation fertilizer application and the significant reduction in the use of stakes will reduce drudgery and the contribution of yam production to deforestation and climate change.