Effect of tillage on soil properties and yam yield on an Alfisol in southwestern Nigeria

There is scarcity of research information on tillage methods most suitable for yam (Dioscorea rotundata) cultivation on Alfisols in Africa. Four tillage methods were compared as to their effects on soil physical and chemical properties, leaf nutrient concentration, and yield of yam. Tillage methods compared during 2 years on an Oxic Tropuldalf at Owo in the forest–savanna transition zone of Nigeria were zero tillage (herbicide-based), manual clearing (a form of zero tillage), manual mounding and manual ridging. Mounding and ridging resulted in higher leaf N, P, K, Ca and Mg, tuber length and girth compared with zero tillage and manual clearing. Zero tillage had significantly higher concentrations of organic C, N, P, K, and Mg for surface soil (0–20 cm). Mounding and ridging increased mean tuber weight during both years by 35% compared with planting on untilled soils. Soil bulk density was negatively correlated with tuber length, leaf nutrient concentration and yield. Zero tillage and manual clearing could not be substituted for manual mounding or ridging on these soils, because there was significant loss in yield of yam. Yam requires tillage for optimum productivity.