The data on tillage systems are needed to identify appropriate tillage methods for managing the fragile
soils of the humid tropics to ensure sustained productivity. Hence, five tillage methods were compared as to
their effect on soil physical and chemical properties, leaf nutrient concentration, growth and yield of sweet
potato (Ipomoea batatas (L.). Tillage methods compared during 3 years on an Oxic Tropuldalf at Owo in the
forest-savanna transition zone of southwest Nigeria were manual clearing (MC), manual mounding (MM),
manual ridging (MR), row tillage (RT) and conventional tillage (CT). These were replicated three times in a
randomized complete block design. Tilled plots (manual mounding), (manual ridging), (row tillage) and
(conventional tillage) resulted in higher soil N, P, K and Ca and leaf N, P, K, Ca and Mg concentrations,
growth and yield of sweet potato compared with untilled (manual clearing) plot. The growth and yield were
in increasing order; manual clearing, row tillage, manual mounding, manual ridging and conventional tillage.
This was consistent with the decreasing order of bulk density and increasing order of porosity. Bulk density
and total porosity were negatively and positively correlated with yield, respectively. Compared with manual
clearing, manual mounding, manual ridging, row tillage and conventional tillage increased tuber weight by 64,
66, 45 and 92%, respectively. The highest yield was obtained with conventional tillage with the lowest soil
bulk density and highest porosity. It is concluded that sweet potato can be grown successfully on well tiled
soils of marginal fertility
