SOIL STRENGTH, HYDRAULIC FUNCTION, GROWTH AND YIELD PARAMETERS OF CASSAVA (Manihotesculentacrantz) UNDER DIFFERENT TILLAGE SYSTEMS

Abstract

The aim of this study was to investigate the effects of different tillage operations on penetration resistance, the hydraulic properties and yield of cassava (Manihot esculentaI crantz) on a sandy clay loam soil of southwestern Nigeria. A replicated randomized complete block design with treatments consisting of secondary tillage (ST), primary tillage (PT) and no-tillage (NT) operations was established at the Teaching and Research Farm of the Department of Agricultural Engineering, Federal University of Technology, Akure, Nigeria. Field experiments were conducted during 2012/2013 and 2013/2014 seasons. Disease free stems of the cassava were planted at a spacing of 1 m by 1 m. The soil bulk density, cone index of penetrometer resistance, unsaturated hydraulic conductivity and moisture retention characteristics were determined for each of the treatments. The cone penetration resistance was determined at the depths of 7.5, 15, 22.5, 30, 37.5 and 45 cm, while suction relationship was determined on the surface (0 – 15 cm) soil at the suction of – 2 cm. All the tillage operations were significantly different in their effects on soil penetration resistance. Prediction of soil penetration resistance (kPa) using Pedotransfer models were obtained from the combination of bulk density (BD), moisture content (MC) and hydraulic conductivity (K). The pedotransfer models, which were developed using some soil physical properties, were statistically significant p = 0.001. Models predicting the yield of cassava for the two cropping seasons were developed using some important soil parameters such as organic matter content, nitrogen and bulk density. The results indicated zero/no tillage has the highest penetration resistance compared to other tillage methods. Primary tillage produced the plant having the highest height, leaf count and leaf area, while zero/no tillage produced the plant with the highest stem diameter and leaf area index. PT produced the highest yield of cassava (25.25 tons/ha) followed by zero/ no tillage (19.33 tons/ha) and the least was in ST (17.17 tons/ha) during the 2012/2013 season. In the second year (2013/2014 cropping season), zero/no tillage (NT) produced the lowest mean yield of cassava (10.58 tons/ha) followed by secondary tillage (ST) (14.5 tons/ha). The yields were significantly different from primary tillage (PT) (21.42 tons/ha). The R square value for cassava yield at harvest for both seasons indicates a close agreement between the measured and observed value of cassava yield for the experiments. Response surface methodology (RSM) was successfully applied using Minitab version 17.1.0 to identify the optimum levels of five important parameters for cassava yield production. The optimal values of OMC, N, PR, MC and K were found to be 1.49 %, 0.28 %, 1446.9 kPa, and 10.67 % and 3.53 cmh-1, respectively, to achieve a maximum of 46.06 tons per hectare of cassava yield in 2012/2013 cropping season, while the best operating conditions to obtaining a maximum value of 42.97 tons per hectare of cassava yield in the 2013/2014 season are 1.47 %, 0.08 %, 2357.12 kPa, 10.06 % and 2.77 cmh-1 for OMC, N, PR, MC and K, respectively.