In Kenya, seed potato quality is often a major yield constraint in potato production as smallholder farmers use farm-saved seed without proper management of seed-borne pests and diseases. Farm-saved seed is therefore often highly degenerated. We carried out on-farm research to assess whether farmer-managed positive seed selection could improve yield. Positive selection gave an average yield increase in farmer-managed trials of 34%, corresponding to a 284-€ increase in profit per hectare at an additional production cost of only 6€/ha. Positive selection can be an important alternative and complementary technology to regular seed replacement, especially in the context of imperfect rural economies characterized by high risks of production and insecure markets. It does not require cash investments and is thus accessible for all potato producers. It can also be applied where access to highquality seed is not guaranteed. The technology is also suitable for landraces and not recognized cultivars that cannot be multiplied formally. Finally, the technology fits seamlessly within the seed systems of Sub-Saharan Africa, which are dominated by self-supply and neighbour supply of seed potatoes.

By identifying the success factors of a programme on positive seed potato selection, this article analyses the role of research in agricultural innovation. The positive seed selection programme developed an approach to improve the quality of seed potatoes by ware potato growers, complementary to specialized seed production systems now widely promoted in sub-Saharan Africa. With more weight being placed on innovation rather than on research outcome, the role of research has been widened and research has assumed responsibility for developing and piloting effective training through partnership with extension. Researchers effectively contributed to innovation because they were given and took the liberty of pursuing a ‘bright idea’. The case discussed in this article points out that innovation can emerge from old technology within existing institutional environments, and can be surprisingly simple as long as researchers have room to manoeuvre and opportunity to engage in partnerships with practitioners.

Crop growth models are required to be extensively evaluated against actual data from field grown plants in order to have confidence in their prediction of crop productivity under various management options or a future changed climate. We evaluated the ability of the APSIM-potato model to predict production, phenology, and N-uptake of potato (Solanum tuberosum L.) under Tasmanian conditions. On-farm monitoring plots were established in north-west Tasmania within four different well-managed potato fields grown during the 2012/13 cropping season. Detailed soil and crop data sets measured in the on-farm plots planted with two potato cultivars, 'Russet Burbank' and 'Moonlight' were used to parameterise and evaluate the model. The model realistically reproduced the observed tuber yield with high precision (a mean N-RMSE of 15.4% and modelling efficiency of 1.0 for both cultivars). Measured mean dry matter (TDM) tuber yield was 17 t ha -1 for 'Russet Burbank' with a simulated yield of 20 t ha -1 . For 'Moonlight' simulated TDM yield was 16.0 t ha -1 compared to measured yield of 15.1 t ha -1 . The simulation results provide insight on the model performance under Tasmanian conditions. The results suggest that the model has potential to be used for purposes such as simulating productivity under various management options and climate change impact studies. Additional experiments are however required to improve cultivar specific input parameters such as phenology, leaf area and leaf duration and other functions that needs further refinement to improve model ability to simulate plant organs beside the tuber.

Limited availability and access to quality seed is a major challenge faced by the Kenyan potato subsector. Smallholder farmers cultivate the bulk of potato mainly planting seed from informal sources without any quality assurance which contributes to low yields. In recent years, private sector businesses have engaged in certified seed potato production with positive impact on the volumes available, relying on minitubers to multiply in the field over three to four generations. Rooted apical cuttings (RACs) provide a productive alternative starter material that can further boost the Kenyan seed systems. Stokman Rozen Kenya Ltd (SRK) is a private sector business that has embraced this technology in 2017. Also, small‐scale nurseries have recently started the commercial production of cuttings. They both sell RACs mainly to seed growers for further bulking, but ware potato farmers can also produce quality seed on‐farm for their own use from RACs when applying good agricultural practices. This paper examines the initial experiences of both SRK and small‐scale nurseries in the production and marketing of RACs as well as their performance during subsequent field multiplications. Producing and selling RACs offers a profitable business opportunity, especially when productivity and sales increase. Compared to other rapid multiplication technologies, RACs also allow to significantly increase the volumes of early generation seed produced. Key recommendations are to create awareness and to develop adequate marketing strategies to promote their uptake, and to ensure RACs are adequately multiplied into commercial seed to improve its availability to smallholder farmers in Kenya.

A study on contract farming among 137 randomly selected potato farmers in the Bomet and Molo districts was done to evaluate its impact on potato production and productivity using cross-sectional data. Descriptive and inferential statistics on farmers' socio-economic, institutional and geographical aspects were used. Stochastic frontier model analysis was used to evaluate farmers' attributes that affect their production efficiency under contract farming. Contract farming enhanced potato productivity and incomes while also becoming an incentive for farmers to supply a niche market and it increased their demand for farm inputs. Due to the lack of a sound organized market for potatoes, there was inefficiency in potato production which caused a decline in inputs demanded. To overcome these problems farmers formed an organized production and marketing system under a contractual arrangement with the buyers. This led to increased demand for quality inputs and enhanced access to credit. In response to the challenges in contract farming, a tri-partied system of farmers, service providers and processors was constituted for arbitration. Contract farming in the districts has shown that farmers could produce sufficient quantities of high quality potatoes that fetch premium price if they are organized to do so. However, rules on contracts have to be agreed on and followed by all participating players. Contract farming involved extra costs but the accrued benefits were higher due to improved productivity, efficiency and the premium price paid under the contract. There was also a reduction in processing losses due to delivery of quality tubers (losses due to rotting, browning and peeling were reduced by 0.78%, 0.3% and 0.75%, respectively) compared with the pre-project period. Attributes of respondents such as being the head of the household, highest level of training received, large family size and contract farming participation significantly enhanced production efficiency while credit access and age of respondent had significant negative effects on production efficiency.