STRENGTH AND PHYSICOCHEMICAL CHARACTERISTICS OF SOIL PLANTED WITH COWPEA (Vigna unguiculata) UNDER DIFFERENT TILLAGE SYSTEMS IN AKURE, NIGERIA

Abstract

Tillage operations have a major influence on the strength and physicochemical characteristics of soils, roots growth, biomass and grain yield of tropical crops. Field experiment was conducted on sandy clay loam soil of Akure in the south west of Nigeria to determine the influence of different tillage systems on soil bulk density, total porosity (PT), hydraulic properties, penetration resistance, soil organic carbon, water holding capacity, moisture content and growth characteristics of cowpea. There were three soil treatments plots A, B and C each of area 5 x 11.2 m2; The plot A was zero-tillage treatment (ZT) using paraquat herbicide, plot B was Minimum tillage (MT) using light implement (cutlass and hoe) while the plot C was under conventional tillage system (CT) using tractor mounted disc plough. The soil tillage treatments were replicated four times in a randomized complete block design totalling 12 plots. Higher organic content (OC) of the soil with a value of 5.52 (± 0.98) was recorded in conventional tillage treatment plots. Zero-tillage treatment plots progressively increased in bulk density between 1.59g cm−3 to 1.91 gcm−3 from the 0-30 cm soil depth. The plots under conventional tillage had the highest total porosity of 44.15(±3.41)% which allow root growth and development of cowpea in the soil layer between 0 – 30 cm.Highest moisture content of 15.98 % was obtained within the 0 – 10 cm soil layer in plots under zero tillage during the 5 weeks after planting (5WAP).The zero tillage plots had the highest hydraulic conductivity of 5.36 x 10-4 cms-1, while hydraulic conductivity of plots under minimum tillage and conventional tillage are 9.15 x 10-4 cms-1 and 9.50 x 10-4 cms-1,respectively. At the 5 week after planting, soil penetration resistance ranged from 710 kPa under zero tillage to 680 kPa under minimum tillage and 340 kPa under disc ploughed treatment plots (conventional tillage). Disc ploughed plots which produced the lowest soil penetration resistance gave the best cowpea (Vignaunguiculata)yield, an indication of the need for soil pulverization to enhance crop growth and yield.The results show that tillage treatments affect moisture retention, especially mostly between 20 – 30 cm soil layers and thus the ease of cowpea roots penetrating into the soil for improved growth and yield. The highest grain yield of cowpea with mean value of 0.64(±0.03) tonha-1 was obtained in plots under convectional tillage treatment. However, the mean grain yield of 0.52(±0.03) tonha-1 was recorded in plots under minimum tillage while the zero tillage treatment plots had a mean yield value of0.41(±0.02) tonha-1. Finding from the research showed that the yield and yield components of cowpea were raised in the plots under convectional tillage system comparatively with other tillage systems