Development and Performance Evaluation of Instrumented Subsoilers in Breaking Soil Hard-Pan

Abstract

Four instrumented subsoilers were developed for alleviation of compaction on agricultural land.  Draughts and soil disturbance of the subsoilers were measured during operation at the outdoor soil bin. Straight shank subsoiler (SSS), semi-parabolic subsoiler (SPS), parabolic ‘C’ shank subsoiler (CSS) and winged subsoiler (WSB) were designed and constructed for use by the tool carrier in loosening soil hard pan. Soil cone penetrometer (CP40II, 333 mm³, 60^o cone tip angle) and electronic moisture meter were used to take readings at various locations and depths on the soil bin before and after subsoiling. Soil samples were taken to laboratory for analysis for physico-chemical properties. Each of the shanks was hitched to the tool bar of the carrier. A 100 kN calibrated load cell was connected to the tool carrier via the drawbar of a 31.6 kW (MF 415) Massey Fergusson tractor. The load cell was connected to the data logger via instrumentation amplifier. Laptop computer system was connected to the data logger to download the draught data for each shank which was operated at four levels of depth - 20, 30, 40 and 50 cm. Profilometer of dimension 80 by 75 cm height and width respectively was used to measure the area of soil disturbance by each subsoiler. Data collected were analyzed to establish relevant relationships between subsoiler draughts and tillage parameters in the form of correlation, regression models and graphs. Results showed that the best subsoiler in terms of draught reduction was parabolic C-shank subsoiler (CSS) with 4.581 kN, followed by semi-parabolic subsoiler (SPS) with draught of 4.905 kN at depth of 40 cm. At this working depth the SSS, WSB and SSS37 had draughts of 6.874, 7.003 and 7.385 kN respectively. Thus WSB had the highest power requirement followed by straight shank subsoiler at 37⁰ rake angle (SSS37), both had 34.09 and 31.20 kW at 50 cm depth respectively. Thus at 20 cm depth of operation WSB and SSS37 subsoilers had 13.95 and 14.29 kW respectively. CSS had the lowest power requirement followed by SPS with 5.55 and 7.76 kW respectively. Straight shank subsoiler at 37⁰ rake angle, SSS37 showed the highest soil loosening ability at all the depths followed by WSB, SPS, SSS and CSS respectively. Thus, at 50 cm highest working depth SSS had 0.0451 m² followed by SPS with 0.0487 m², while CSS, WSB and SSS37 had 0.0403, 0.0683 and 0.1061 m² respectively. Regression equations were established for the draught of each subsoiler. They all had R² of more than 99 %. Draught of subsoilers had high positive correlation with depth, cone index (CI) and bulk density (BD), and negative correlation with soil moisture (MC) and porosity (PR).