The influence of arbuscular mycorrhizae fungus, mulch and fertiliser application on the yield of yams in an agroforestry system in southwestern Nigeria

Abstract

The effects of chemical fertiliser and arbuscular mycorrhizae (AM) inoculation, and mulching on tuber yield of breeder selected cultivars and unselected landraces of Dioscorea rotundata Poir, and Dioscorea alata was studied in an agroforestry (Tungya) system. The field trials were conducted in three growing seasons (1996, 1997 and 1998) in the derived savanna zone of southwestern Nigeria. Gliricidia sepium trees served as live stakes for yams and source of mulch. The treatments comprised of AM inoculated (Glomus mosseae), non-inoculated, NK fertiliser application, no-fertiliser applications and AM + fertiliser application. Mulching as a treatment factor was added in the third year. The results obtained in the first cropping year showed that both inorganic fertiliser and mycorrhizae applications improved tuber yield for the two selected yam species, with the response to fertiliser application being stronger. The unselected landraces did not respond to mycorrhizal and fertiliser application. In the second year, significant variations (P≤0.05) in tuber yields of all the cultivars were observed but all the three interventions increased yield relative to the control treatment. The third year experiments showed that unselected landrace yields were improved by a combination of mycorrhizal inoculation and fertiliser application and by mycorrhizal inoculation alone but fertiliser application alone had no effect even on selected cultivars. In landrace 1, TDr93-2, and TDr93-31 yields were reduced by fertiliser application. The selected cultivars also responded to AM and fertiliser combined with AM applications. Contrary to expectations, mulching with Gliricidia sepium leaves in the agroforestry system had a detrimental effect on yam tuber yields. However, improved cultivar TDr93-2 had positive yield gains with application of mulch combined with AM inoculation.