Growth and Distribution of Roots of Dioscorea Alata L. Do Not Respond to Mineral Fertiliser Application

Abstract

Water yam (Dioscorea alata) is a staple crop for many of the poorest in the tropics. Yam tuber response to fertiliser application has been reported to be erratic. We hypothesised that this variable response could be due to the development of a suboptimal root system that would not allow the plant to capture the nutrients added with the fertiliser. To verify this hypothesis we studied during two seasons (2006 and 2007) in Central Côte d'Ivoire, the growth of yam root system in relation to plant growth as affected by fertiliser input, using sequential root coring. In addition, we assessed the horizontal and vertical distribution of yam roots using the wall profile method in the same site. Three root types (seminal, adventitious and tubercular roots) were identified. Roots grew within the mound until 100 days after planting (DAP) and afterwards, extended radially in the soil outside of the mound remaining in the first soil horizon (15 cm depth). Maximum root extension was observed at 160 DAP. Root length density and root mass density were higher at higher soil temperature whereas the average root diameter decreased at higher soil temperature. Specific root length did not change with soil temperature. Root growth parameters were not affected by fertiliser application. Roots were mostly distributed in clumps. As tuber yield formation was independent from root growth we conclude that the root system of this cultivar did not limit tuber productivity. Other factors have to be considered to explain the variable response of yam to mineral fertiliser additions.

Root distribution patterns of white yam (Dioscorea rotundataPoir.): a field study

“…The maximum RLD of 0.26 cm cm (3 observed in D. rotundata was smaller than the maximum RLD of 11.3 and 1.5 cm cm (3 , reported for potatoes (Ahmadi et al 2011) and cassava (Lose et al 2003), respectively. The root spatial distribution pattern observed in this study showed that D. rotundata is also a shallow-rooting species, similar to D. esculenta (Melteras et al 2008), D. alata (Hgaza et al 2011), cassava (Lose et al 2003) and potatoes Groenwold 1986, Ahmadi et al 2011).…”

“…No roots were observed below a depth of 15 cm at a distance of 50 cm from the crown (i.e. outside the mound) by Hgaza et al (2011). While shoot and tuber production were significantly increased by mineral fertilizer application, these authors did not observe any significant effect of the applied fertilizer on root growth and distribution.…”

“…O'Sullivan (2008) showed that the roots of D. alata (water yam) could grow horizontally as far as 5 m from the crown of the plant and could penetrate as deep as 40 cm. Recently, Hgaza et al (2011) showed that D. alata planted in 50-cm high mounds had a low root length density (RLD) and a low root mass density (RMD) when compared with other crops. No roots were observed below a depth of 15 cm at a distance of 50 cm from the crown (i.e.…”

Nitrogen Use by Yam as Affected by Mineral Fertilizer Application

“…batatas ; 25%] (Hartemink et al, 2000) but lower than in potato ( Solanum tuberosum L.; 61%) (Darwish et al, 2006). This result suggests that although D. alata has been described as a shallow‐rooting species with low root density and heterogeneous distribution (Hgaza et al, 2011), it can capture the applied N efficiently.…”

“…The amplitude of this “priming effect” in this low‐N soil must nevertheless be emphasized. If we assume that most of the N taken up by the plant is derived from the mound and from the surrounding surface soil that was explored by roots as observed by Hgaza et al (2011), and if we consider that the total N content of the foraged horizon is 0.7 g N kg −1 soil (Table 1) with an apparent density of 1.3 Mg m −3 , then the uptake of 205 kg N ha −1 would represent about one‐seventh of the total soil N. These low soil total N contents have already been reported in this region of West Africa (e.g., Nacro et al, 1996, 2004), and our results suggest that the rate of mineralization of soil organic matter can be very high. These results suggest that intensive yam cultivation in this region should always be accompanied by a proper scheme of organic matter management, without which soil organic matter depletion would occur rapidly.…”