Competitive relationships in potato/maize intercropping : involvement of root system architecture

Abstract

Potato/maize intercropping is practised in many tropical countries because it offers several benefits for sustainability. However, the practical use of this system is often limited by a relatively low maize or potato yields. This thesis analyses the competitive relationships in potato/maize intercropping with a focus on the root system architecture (RSA) and below-ground competition. Field experiments were conducted in South Kivu, eastern of D.R.Congo to quantify the effects of interspecific competition (IC) on the yields of the two species. These were followed by greenhouse and virtual experiments designed to separate above- and belowground competition in order to improve our understanding of these competitions. The results obtained in field conditions suggest that the density of maize should be equal or lower than that of potato to improve the relative yield in intercropping comparatively to sole crops. A strip crop has an advantage comparatively to simple row alternating because of the better light interception by the crops in the canopy. Simultaneous sowing of the two partners can be beneficial compared to a delayed maize sowing. The greenhouse's results show an asymmetric development of potato and maize in ntercropping. Canopy was dominated by potato during the first 45 days after planting and by maize thereafter in simultaneously sowing. Maize does not seem to tolerate early competition for light, as illustrated by the dramatic effect of a delay in maize germination or sowing on RSA and maize grain yield. This response reflects the fraction of incident radiation intercepted by potato at early stage and possibly some level of IC for belowground resources due to the contrasting temporal patterns of root growth and soil exploration of the two species. The superiority of the potato RSA at early stage would result from its rapid, synchronized growth and its horizontal to oblique growth habit, in presence of a maize root system that is only progressively established and has a rather vertical growth behaviour. For potato, the number of stolons and of adventitious roots per stolon were increased under shoot IC, probably as a consequence of a reduction of the soil temperature and an increase of soil moisture. Finally, the distribution of potato roots and potato tuber yield were not affected by the full IC.Doctorat en sciences agronomiques et ingénierie biologique (AGRO 3)--UCL, 200