Effects of Tractor Wheel Passes-induced Compaction and Organic Amendments on Soil Properties and Yield of Cowpea (Vigna unguiculata L. Warp) in an Alfisol of the Rainforest Zone of Nigeria

A field experiment was conducted to examine the effects of tractor wheel passes and organic amendment on soil physico-chemical properties and yield of cowpea (Vigna unguiculata L.) in an Alfisol of the rainforest zone of Nigeria. Varying degrees of penetration resistances were imposed on the seed bed via multiple tractorised wheel passes (4, 8 and 12) and the ploughed and harrowed only seed bed were imposed using Messy Ferguson tractor. Treatments which were laid out using split-plot design, consisted of 3 x 4 factorial combinations of tractor wheel passes and organic manure application and replicated 3 times on field plots of 60 x 12 m. The multiple tractor wheel passes increased soil strength (penetration resistance) and affected growth and seed yield of cowpea. The results show high soil strength was obtained within the plough layer and the active portion of crop root zone (10 - 30 cm) while there was increasing trends in values of soil strength from planting to crop maturity especially at depth (30 – 50 cm soil depth). Shoot biomass, pod and seed weight were lower for 8 and 12 tractor wheel passes compared with ploughed and harrowed seedbed and plots treated to 4 wheel passes. Application of organic manures ameliorated compaction effects on soil properties and enhanced growth and yield of cowpea. Organic amendment of the variously tractorized seedbed decreased bulk density thus alleviated the consequences of compaction especially within the plow layer on root development, growth and yield characters of cowpea. Close relationships among soil moisture status (content), mechanical impedance and cowpea seed yield characters obtained indicate strong interactions among soil moisture status, mechanical impedance and cowpea performance.