Effets de l'effeuillage et de l'écimage sur les rendements en feuilles et en racines du manioc et de la patate douce

Réunion: Symposium triennal sur les plantes-racines de la Société internationale pour les plantes-racines tropicales - Direction Afrique, 8-12 sept. 1980, Ibadan, NGDans IDL-471

An overview of cassava in Africa

Cassava is one of the most important staple food crops in Africa. It is a major source of energy for over 200 million people in the continent. The ten countries in the world whose food energy comes mostly from cassava are all in Africa. More cassava is now being produced in Africa than in South America where the crop originated. Apart from the production of tuberous roots, millions of tons of cassava leaves are harvested and used as a vegetable which provides protein, vitamins and minerals. The crop's production is among the most stable of the world's major food crops. It is adapted to the diverse African farming systems, can grow on a wide range of soils, is an efficient producer of calories and its capability for protein production is higher than commonly realised. Despite the numerous advantages that cassava offers, there were limited research and development activities on the crop in Africa until comparatively recently. This is because the crop was for long and erroneously considered to be of inferior status because it is oflow value. There is also a perceived inverse relationship between cassava consumption and standard ofliving. Most African governments have been importing large quantities of grain, mainly to satisfy politically active urban populations. This discourages farmers in rural areas from producing cassava, which is generally well adapted to local environmental conditions. Concerted national, regional and international efforts are now being made to overcome the numerous constraints that limit cassava production in Africa. There are several serious challenges facing cassava researchers in Africa today; key among these are the need to address the problems of low yield, pests, diseases and weeds. There is also a need for studies on intercropping, cassava farming systems, post-harvest technology and cyanogenesis, and for training cassava researchers and those engaged in technology transfer. Moreover, varieties are required that are adapted to lowland conditions, to a range of growing seasons and with mealy cooking quality and drought tolerance. The effectiveness with which these challenges are met will largely determine whether the need for food security in the continent is realised.Key Words: Manihot esculenta, food security, adaptation, post-harvest, pests, diseases, weeds, intercropping  Le manioc est une des cultures vivrières les plus importantes en Afrique. C'est une source majeure d'énergie pour plus de 200 millions d'habitants sur le continent. Les dix pays du monde, dont l'énergie alimentaire provient essentiellement du manioc, se trouvent en Afrique. Celle-ci produit aujourd 'hui plus de manioc que Amérique du Sud. Independamment de la production de tubercules, des millions de tonnes de feuilles de manioc sont récoltées et utilisées comme égume pour un apport en proteines, vitamines et sels minéraux. La production est une des plus stables parmi celles des cultures vivrières mondiales. Le manioc est adapté à la diversité des systèmes de culture africains, peut pousser dans une grande variété de sols, s'avère un efficace producteur de calories et son aptitude à fournir des protéines est plus grande qu'on ne le pense. Malgré les nombreux avantages qu'offre le manioc, les activités de recherche et développement sur cette culture en Afrique ont été réduites, et cela jusqu'à une date relativement récente. C'est parce que cette culture fut considérée pendant longtemps, et de façon erronée, comme de statut inférieur, car peu couteuse. La consommation du manioc est également perçue comme étant en relation inverse avec le niveau de vie. La plupart des gouvernements africains importent de grandes quantités de grains, principalement pour satisfaire politiquement les populations actives des villes, ce qui décourage les agriculteurs en zones rurales de produire du manioc, genéralement bien adapté àl'environnement local. Des efforts concertés, à 1' échelle nationale, régionale et internationale, sont actuellement entrepris pour surmonter les contraintes nombreuses qui limitent la production du manioc en Afrique. Les chercheurs qui travaillent aujourd 'hui sur le manioc en Afrique sont confrontés à plusieurs défis sérieux. Parmi ceux-ci, la nécessité de se saisir du problème des bas endements et de celui des ravageurs, maladies et mauvaises herbes. Il y a également un besoin de recherche sur les cultures associées, les systèmes de culture, les technologies post-récolte et la cyanogénèse; ainsi qu'un besoin de formation des chercheurs et des personnels qui sont impliqués dans les transferts de technologies. De plus, il y a une demande pour des variétés adaptées aux conditions des basses-terres, a la diversité des conditions saisonnières de la culture, aux qualités de la famine pour les préparations culinaires et à la tolérance à la sécheresse. La sécurité alimentaire, sur le continent, dépend largement de 1'efficacité avec laquelle ces défis seront relevés.Mots Clés: Manihot e.sculenta, sécurité alimentaire, adaptation, post-récolte, ravageurs, maladies, mauvaisesherbes, cultures intercalaire

Effects of leaf harvests and detopping on the yield of leaves and roots of cassava and sweet potato

Meeting: Root Crops Symposium, 1st, 8-12 Sept. 1980, Ibadan, NGIn IDL-271

Competition in a rice - cowpea intercrop as affected by nitrogen fertilizer and plant population Competição em uma cultura consorciada de arroz-guandu em função do fertilizante nitrogenado e da densidade populacional de plantas

The increased productivity or yield advantage provided by intercropping is attributed to a better use of resources by crops grown in mixtures, as compared to the same species grown in sole stands. In an intercropping system with upland rice and cowpea, the intra and inter-competition was quantified, as affected by plant population density and rate of nitrogen. Reductions in number of panicles per rice plant and number of grains per panicle were obtained with high density in both sole and mixture rice populations. Increasing nitrogen rate did not affect yield and yield components in both populations, but number and weight of pods per plant of cowpea in sole stands increased. Land equivalent ratios exceeding unity were obtained, indicating an improved resource use by the crop mixture. Relative crowding coefficient and aggressivity indices showed cowpea to be the dominant crop, with rice being dominated. Nitrogen utilization efficiency was high with intercrops, but was generally poor in stands of high population density.<br>O aumento em produtividade devido a plantios consorciados é atribuído ao melhor uso dos recursos presentes pelas plantas em desenvolvimento conjunto, em comparação às mesmas espécies crescendo em dosséis separados. Em um sistema consorciado de arroz e guandu quantificou-se as inter- e intra competições em relação à densidade populacional e taxa de aplicação de nitrogênio. Reduções significativas do número de panículas por planta de arroz e número de grãos por panícula foram observados para alta densidade, tanto para culturas solteira de arroz como em populações mistas. O aumento das doses de nitrogênio não afetou a produção e os componentes de produção em ambos os sistemas, ao passo que o número e peso de vagens por planta do guandu aumentaram em culturas solteiras. Foram obtidas razões de área equivalente maiores que a unidade, mostrando melhoria no uso da terra nas culturas mistas. O coeficiente relativo de superpopulação e os índices de agressividade mostraram que o guandu é dominante e o arroz dominado. A eficiência do uso de nitrogênio foi alta nas culturas consorciadas, mas em geral baixa para populações de alta densidade