Abstract

Yellow yam (Dioscorea cayenensis) is one of the major varieties of yam produced in Midwestern Nigeria mainly by traditional farmers. Most of these traditional farmers employ zero tillage system and mulching after planting. But, is this the best practice for optimising yield? This paper examines the effect of tillage systems and mulching on soil microclimatic conditions, growth and yield of yellow yam. To generate the needed data, the physiological approach was employed. An experimental farm that measured 35 x 47 m was established at Agbor, Delta State, Nigeria, for two planting seasons 1997/98 and 1998/99. The microclimatic parameters monitored include air and soil temperatures and relative humidity while the physiological parameters measured were emergence, growth rate, leaf area accumulation and yield. Time series, multiple correlations, chi-square, ANOVA, least square range test and stepwise regression analysis were the statistical tools employed in analysing the data. The results showed that soil moisture at 0-15 cm depth was significantly higher in zero tillage (40 g/g), followed by ridge (30 g/g) and mound (24 g/g) but the reverse was the case with soil temperature where mound tillage (34.2°C) had the highest temperature followed by ridge (31.4°C) and zero (29.5°C). Mulching also significantly influenced the soil microclimatic condition. While soil moisture enhanced yam emergence, soil temperatures favoured the growth, leaf area accumulation and yield. Mound tillage significantly gave the highest yam tuber yield (12.0 t/ha^-1), followed by ridge (8.8 t/ha^-1) and zero (5.0 t/ha^-1). Partially mulched treatment significantly produced the highest yam tubers (10.3 t/ha^-1), followed by the unmulched (8.1 t/ha^-1) and mulched (7.4 t/ha^-1) treatments. The best practice recommended for the production of ware yams is mound tillage that is partially mulched. This recommended practice yielded more than the local practice by 44.6%.

Key words: Tillage systems, yellow yam, Midwestern Nigeria, soil microclimate, mulching, yam yield.