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Chapter 6 Agronomy and Cropping Systems Dietrich Leihner Research, Extension and Training Division, Sustainable Development Department, FAO, Via delle Terme di Caracalla, 00100 Rome, Italy Introduction Cassava is often grown under low-input/low- output production systems, particularly when it is grown as a food crop. Planting material is easily obtained from the plant stems available from the farmers’ own or neighbouring fields. Although the crop is affected by a number of arthropod pests, diseases and by weed competi- tion, it generally requires little attention once established. Nevertheless, attention to a few simple aspects of agronomic management can result in a doubling or tripling of output at low cost. In this chapter principles of good agro- nomic management are described, dealing with the preparation and handling of planting material, soil preparation, planting techniques, weed control, intercropping techniques and soil conservation systems. Planting Material Production and Handling Rapid multiplication and selection Propagation of cassava through true seed is feasible, but no commercially viable seed propa- gation system is yet available. Cassava contin- ues to be propagated vegetatively through stem cuttings or stakes (as they should be called). The number of commercial stakes obtained from a single mother plant in a year ranges from three to 30, depending upon growth habit, climate and soil conditions. This is considerably less than the propagation rate that can be achieved with other commercial crops that are propa- gated through true seed. Thus the development of improved cassava production technology should include more effective propagation schemes. A system using small two-node cuttings from which a number of successively growing shoots are obtained, rooted in boiled water and planted in the field was devised by Cock et al . (1976). This system produces 12,000–24,000 commercial stakes after 1 year. A much more productive method was devised later (Cock, 1985) using cassava leaves excised with their axillary buds, transferred to a mist chamber for sprouting and root formation of the propagules, which are transferred to a peat pot and 2–3 weeks later, to the field. Although this system is more labour intensive, 100,000–300,000 commercial stakes can be produced in about 18 months. Stems must be transported with care to prevent bruising and peeling. Stakes should be cut at a right angle without placing stems on a base to prevent breaking or splitting that provides entry points for pathogens and insect pests. A stake should be at least 20 cm long and have a minimum of 4–5 nodes with viable buds to ensure crop establishment. Stems should be sufficiently lignified to ensure that stakes do not ©CAB International 2002. Cassava: Biology, Production and Utilization (eds R.J. Hillocks, J.M. Thresh and A.C. Bellotti) 91
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dry out too fast after planting, but overlignified tissue should be avoided. Stakes have the right degree of maturity when their pith diameter measures approximately half the total stake diameter.
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