Ekanayake, Kasele and Kapinga. 1999. Cassava based cropping systems and G x E analyses
Chapter 10 Implications of G x E Interactions of Cassava under Different Cropping Systems Indira J. Ekanayake, Idumbo N. Kasele and Regina Kapinga 10.1. Introduction 10.2. G x Cropping system considerations 10.3. Stability in Intercropping 10.4. Analytical approaches to G x E in Intercropping 10.5. Conclusion References
10.1. Introduction The production of cassava for commercial and subsistence purposes is increasing rapidly in sub-Saharan Africa (Nweke, 1996). This increase is marked in some African countries. For example. during the 1974.1996 period, Nigeria achieved a substantial increase in cassava production, from a yearly mean of 10.3 t fresh roots (from 1974 to 1976) to 31.3 t (from 1994 to 1996), with a comparable mean rate of increase in production (10 .1% per year) (FAO, 1998). In contrast, rate of increase in world cassava production during this period was much lowl1r (2.5% per year). Irrespective of expansion in the area of cassava production, evidence is Jackbtg to support an increase in cassava sole cropping vis-a-vis intercropping. Simultaneous cultivation of two or more crops on the same piece of land or mixed cropping or intercropping is a widespread and time immemorial agricultural practice in the humid and the sub-humid tropics. In traditional cassava growing areas of Sub-Saharan Africa, mUltiple crops are produced in a single field by most farmer, and for cassava mixed cropping is the usual practice (Nweke, 1996). Results from the Collaborative Study of Cassava in Africa (COSCA) show that farmers grow an average of6 to 7 crops, with a range of 1 to 15 crops (Nweke et al., 1996; Spencer and Kaindaneh, 1997). Less than 25% of the surveyed fields were planted to a single crop such as cassava (Nweke et at, 1996). Rice, yam and cassava were the crops grown most often as sole crops in the COSCA-sampled countries. The diversity of intercropping systems for cassava is well described across many of the agroecological zones where it is a dominant crop (Dorosh, 1988; Elemo et al., 1990; Mutsaers et aI. , 1993; Okigbo, 1994; Nweke, 1996; Nweke et at, 1994 and 1996). Despite attempts by extension workers to bring about the adoption of the sole cropping, the practice of intercropping has persisted because of its adaptability to ecological, socio-economical, and socia-cultural conditions of the tropics (Steiner, 1982; Zandstra, 1979; Porto et aI., 1979). In recent years, IITA has focused on improving cropping systems as well as introducing improved cassava genotypes into lowland dry and moist savanna. These are non-traditional cassava growing areas with good potential owing to its ability to withstand stressful environments (i.e., drought and low soil fertility) and to its high yield potential. A large bulk of cassava production is in the forest zones. Savannas are dominated by cereals and legumes and are characterized by low rainfall, poor soil fertility, and a diversity of traditional cropping systems. Urgent priority in this approach is to relate growth patterns of cassava to measurable physiological and morphological traits, which can be incorporated in the selection
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