Potato Crop Nitrogen Status Assessment to Improve N Fertilization Management and Efficiency: Past–Present–Future

Improving nitrogen use efficiency is important for the potato crop, because of its relatively low ability to take up available soil mineral nitrogen (N). Splitting of N fertilizer application is a suitable approach to better match N need and supply. In-season crop N monitoring methods are therefore required to support such strategies. This paper deals with the state of the art and potential development of characteristics, use and implementation of well known and more recent methods aimed to assess in-season potato Crop Nitrogen Status (CNS). A short overview of this concept is given for the potato crop. The most important and available methods for CNS assessment are evaluated for their accuracy, precision, sensitivity, sensibility and feasibility. These are: the petiole sap nitrate concentration test; the leaf chlorophyll concentration measurement using a hand-held chlorophyll meter; the measurement of crop light reflectance through a hand-held radiometer using passive sensors. More recent methods still under investigation based on near, ground-based, air-borne or space-borne remote sensing are discussed for their scientific and practical interest in the near future. The current and potential use and implementation of these methods into decision support systems for potato N fertilization management aimed at improving the potato crop nitrogen use efficiency are analysed by: comparing relative and raw data; establishing threshold values of CNS; and combining or integrating the CNS values into models dedicated to N recommendation or to crop growth simulation.     

Sweet Potato Weevil Damage,Production Constraints,and Variety Preferences in Western Tanzania: Farmers’ Perception

Sweet potato weevils (Cylas spp.) are among the most important constraints to sweet potato (Ipomoea batatas [L.] Lam.) production in most agro-ecological zones of Tanzania. Integration of farmers’ perception on sweet potato weevil damage, production constraints, and variety preferences is crucial in developing sweet potato varieties with farmer-preferred traits and weevil resistance. The aim of this study was to identify farmers’ perceptions on sweet potato weevil damage, production constraints, postharvest storage options, and criteria used to select and grow the best sweet potato varieties in western Tanzania. Surveys were conducted in four selected districts of western Tanzania (Nzega, Sikonge, Kigoma rural, and Kasulu) known for sweet potato production. Data were collected using a structured questionnaire, focus group discussions (FGDs), and transect walk involving 122 sweet potato farmers. Weevil damage was reported by 84% of the respondents to be the overriding constraint to sweet potato production. Sweet potato diseases and drought were the next production constraints, reported by 57% and 54% of the respondents, respectively. Farmers’ preferred agronomic traits of sweet potato included high yield (25% of respondents), drought tolerance (24%), and disease and pest resistance (21%). Farmers’ preferred sweet potato culinary traits in the study areas were high dry matter content (reported by 21% of the respondents), followed by reduced cooking time, taste and fiber content (each reported by 19% of the respondents). The above-mentioned production constraints and farmers’ preferred traits are useful selection criteria for improving sweet potato with respect to weevil resistance and enhanced storage-root yield and quality.     

Benchmarking Food Crop Markets in Southern Africa: The Case of Potatoes and Potato Products 1961–2010

Pressures and opportunities in food systems across Southern Africa have generated renewed interest in potatoes both as a food crop and a source of income in recent years. With populations growing at over 2.0 %/year in several countries and urban consumers often eager to diversify their diets, new markets are also opening up. Given these trends, growers, traders and governments are seeking out new ways to capitalize on these developments. This paper examines the evolution of growth rates in potato production, utilization and trade in Southern Africa over nearly the last half century using FAO annual secondary data. After highlighting the different roles that potatoes have played in crop diversification across the sub-region, the paper identifies some key issues for future research as well as some opportunities for industry both large and small.     

Farmers’ Management Practices and Grain Yield of Rice in Response to Different Water Environments in Kamping Puoy Irrigation Rehabilitation Area in Northwest Cambodia

Abstract

The farmers’ management practices and grain yield were examined in the consecutive 4 cropping seasons from wet season rice (WSR) in 2008 to dry season rice (DSR) in 2010 across upstream, midstream and downstream fields, along two secondary drainage canals (located either upstream or downstream side along the main canal) in the Kamping Puoy Irrigation Rehabilitation area (KPIR). In WSR, standing water depth was much deeper in downstream fields where medium and late maturing varieties were planted from May than in upstream fields where early and early medium maturing varieties were planted later (mostly in July and August). In DSR there was less difference in water conditions between upstream and downstream fields and variation in planting and harvesting time was small. As the area percentage of fields where DSR was introduced increased from 2008 (54%) to 2010 (100%), planting time in WSR was later (e.g., from May to July) with declining proportion of dry seeding method and mid-season tillage. Grain yield was low in DSR, particularly in 2010 (287 and 247 g m-² in 2009 and 2010 on average, respectively), due to insufficient weed control and small amount of fertilizer, and the yield was lowest in fields which practiced DSR for the first time. Grain yield in WSR (286 and 291 g m-² in 2008 and 2009 respectively) increased by transplanting, use of high yielding Raing Chey variety, and application of a larger amount of N chemical fertilizer. These findings indicated that the agriculture extension support to farmers, particularly in DSR, is a key important factor for rice yield improvement in KPIR.