Annual Report 2006/07 - ETH - North-South Centre North-South ...

Research fellowValéry Kouamé Hgaza KouasiSupervisorE. Frossard, ETH ZurichCollaboratorLucien Diby, CSRS, Côte d’Ivoire /Jan Jansa, ETH ZurichDurationDecember 2005 – December 2008Research Fellow Partnership Programme (RFPP)Understanding yam (Dioscorea spp.)response to fertiliser applicationWe hypothesise that the variability of yam (Dioscorea spp.)responses to fertiliser application could be related to an inefficientuptake of nutrients derived from the fertiliser due to alimited root density. Field experiments were conducted inCentral Côte d’Ivoire in 2006 with the aim of describing rootgrowth. Dioscorea alata cv TDa 95/00010 was used as a plantmodel and grown in a savannah site with and without fertiliserinput. Root growth was assessed by measuring RootLength Density (RLD) and Root Mass Density (RMD) at 0 – 15cm (H1) and at 15 – 30 cm (H2) on the hill and at the top15 cm of the soil profile in the interrow (H3) at 76, 104, 130,166 and 190 days after planting (DAP).Results obtained showed that at H1, RLD increased steadilywith time and reached a plateau at 166 DAP. At H2, RLD andRMD reached a peak at the tuber initiation (104 DAP) andthen decreased until the end of the plant growth. In theinterrow (H3), RLD increased sharply during the tuber growthbetween 104 – 166 DAP. At H1 and H3, the RMD increasedsharply, reached a peak during the tuber bulking (166 DAP)and then decreased. This result suggests a successive growthof adventitious roots and tuber roots during the plantgrowth that was confirmed by visual observations. The top15 cm of the soil profile in the hill and in the interrow was themost important zone of root growth. Roots in the interrowprobably came from the tuber. RMD and RLD were low indepth (H2). RMD and RLD measurements were completed byA student gathering data with a porometer, measuring the degree of opening ofstomata located on the surface of yam leaves, to assess how leaf cutting (sourcesuppression) or the restriction of tuber growth (sink limitation) could affect thegas exchange between the leaf and the atmosphere.horizontal and vertical root maps to give better descriptionof root growth in the yam crop.Unfertilised plants produced more roots than fertilised onesin H1. These data show that plant root distribution is affectedby the addition of fertiliser and therefore do not supportour hypothesis.55