Effect of Tillage Systems and Tithonia diversifolia Mulch on Soil Physical and Chemical Properties, Growth and Cocoyam Yield in a Tropical Alfisol

Field experiments were carried out during 2012 and 2013 cropping seasons on an Alfisol (Oxic Tropuldalf) at Owo in the forest–savanna transition zone of southwest Nigeria to evaluate the effect of different tillage systems (zero tillage (ZT), ploughing plus harrowing (P+H) and ploughing plus harrowing twice (P+2H), and with or without Tithonia diversifolia mulch (TM) on soil properties, growth and yield of cocoyam. The experiment was laid out in a randomized complete block design in a factorial combination of six treatments that were replicated three times. Among the tillage systems, zero tillage had the highest soil moisture content (12.3%), lowest soil temperature (31.8°C) and lower soil bulk density (1.36 Mg m-3) and higher total porosity (48.7%) that was similar to P+H. ZT also produced the best values of soil chemical properties, growth and yield of cocoyam compared with P+H and P+2H. P+2H had the highest soil bulk density (1.56 Mg m-3) and temperature (34.6ºC) and lowest soil moisture (9.6%) and total porosity (41.1%) and also produced the least soil chemical properties and hence poor growth and yield compared with ZT and P+H. ZT increased cocoyam corm yield by 15 and 33% over the P+H and P+2H respectively. The corresponding increases in cormel yield were 12 and 28%, respectively. Application of 7.5 t ha-1 tithonia mulch in combination with tillage system significantly reduced soil bulk density and temperature, increased soil moisture content and total porosity, soil organic matter, N, P, K, Ca and Mg, growth and cocoyam yield than their sole tillage systems. Among the tillage – tithonia mulch combinations, the most satisfactorily corm yield (9.1 t ha-1) and cormel yield (13.3 t ha-1) was produced by zero tillage plus tithonia mulch (ZT+TM) while the lowest corm yield (7.2 t ha-1) and cormel yield (11.1 t ha-1) was produced by ploughing plus harrowing twice plus tithonia mulch (P+2H+TM).