Tropentag, September 18 - 20, 2019 in Kassel "Filling gaps and removing traps for sustainable resources development"

Nitrogen Fixation in White Yam (Dioscorea rotundata) Using Naturally Abundant ¹⁵N

¹Tokyo University of Agriculture, International Agricultural Development, Japan
²International Institute of Tropical Agriculture (IITA), Yam Breeding, Nigeria
³International Institute of Tropical Agriculture (IITA), Grain Legume, Nigeria

Abstract

White yam (Dioscorea rotundata), a tuber crop cultivated and utilised as a staple food in West Africa, plays an important role in the daily diet of millions of people in the region. However, in spite of the growing local demand for white yam, little progress has been made in increasing supply by optimising fertilisation methods to improve yield. Several experiments conducted throughout the region to determine the optimal quantity of nitrogen fertiliser needed for the crop arrived at contradictory conclusions, suggesting the need to take a different approach to elucidate the nitrogen absorption mechanism and to apply it to cultivation. Here we report on the nitrogen absorption mechanism in white yam with a special focus on its nitrogen fixation ability using naturally abundant ¹⁵N (δ¹⁵N).
A field experiment was conducted at the International Institute of Tropical Agriculture in Ibadan, Nigeria using six white yam accessions with squash (Cucurbita moschat) plants as a reference. Experimental plots with three replicates for each accession were prepared without the application of fertiliser in a randomised block design. The percentage of plant N derived from atmospheric N₂ (%Ndfa) was calculated based on δ¹⁵N values.
A wide range of variation was observed in %Ndfa values among the six white yam accessions. The highest value was accession DrDRS074 (45.5%) and the lowest was DrDRS042 (-4.7%). Moreover, the %Ndfa of accession DrDRS074 (45.5%) was statistically significant than that of DrDRS058 (7.2%) and DrDRS042 (-4.7%). The results obtained in this study suggest the ability of white yam to fix atmospheric nitrogen; however, intra-specific variation must be also considered. To ascertain the nitrogen fixation ability of different white yam varieties, further research on the presence of symbiotic bacteria as well as the effect of nitrogen fixation on plant growth should be conducted.

Keywords: δ¹⁵N, low soil fertility, nitrogen fixation, white yam

Contact Address: Kanako Takada, Tokyo University of Agriculture, International Agricultural Development, 1-1-1 Sakuragaoka, 156-8502 Setagaya-ku, Japan, e-mail: 46317402nodai.ac.jp