DEVELOPMENT OF INSTRUMENTED SUBSOILERS AND EFFECT OF COMPACTION ON GROWTH AND YIELD OF SOYBEAN

Abstract

Increasing demand for food, feed and fibre due to rising world population has caused agricultural mechanization to be on the increase. This has consequently increased soil compaction of arable terrains as a result of the deployment of agricultural machinery to the field, thereby hindering crops growth and yield. The research was aimed at developing and evaluating the performance of instrumented subsoilers in alleviating soil compaction, and to study growth and yield response of soybean to different levels of tractor-induced soil compaction. The work was carried out at the Department of Agricultural and Environmental Engineering, Federal University of Technology, Akure (FUTA), Nigeria (7o15’00’’N and 5o11’42’’E) and the Department of Agronomy, Cross River University of Technology (CRUTECH), Obubra, Nigeria (08o20’00’’E and 6o05’00’’N). Four instrumented subsoilers were developed. Their draughts were measured at the outdoor soil bin, located at the Science and Technology Education Post Basic (STEP-B) Research Farm (FUTA). Profilometer was developed and calibrated to measure the area of soil disturbance by each subsoiler. Straight shank subsoiler (SSS), semi-parabolic subsoiler (SPS), parabolic ‘C’ shank subsoiler (CSS) and winged subsoiler (WSB) were adapted in loosening soil hard pan. Soil cone penetrometer 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 physico-chemical properties analysis. Each of the shanks was hitched to the tool bar of the carrier. A 10-tonne calibrated load cell was connected to the tool carrier via the drawbar of a 31.6 kW 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, operated at four levels of depth - 20, 30, 40 and 50 cm. Effect of soil compaction on growth and yield of soybean (var TGX-14482E) was carried out in 2011 and 2012 cropping seasons at the Research Farm of Agronomy Department, CRUTECH, Obubra Campus and STEP-B Research Farm, FUTA respectively. The soil types on both sites were sandy loam and sandy clay respectively. Similar activities were carried out on both sites; area of land, 945 m2 was cleared, ploughed and harrowed. A 50 kW and 55 kW tractors were used to induce compaction on the sites at CRUTECH and FUTA respectively. Four treatments, replicated 3 times were imposed on the land. The treatments were PLH = ploughed, harrowed and zero pass of tractor traffic (control), PHC10 = ploughed, harrowed and 10 passes of tractor traffic, PHC20 = Ploughed, harrowed and 20 passes of tractor traffic, and PHC30 = Ploughed, harrowed and 30 passes of tractor traffic. Treatments and replications were laid in a Randomized Complete Block Design (RCBD). Each plot had an area of 25 m2 separated from each other by 3 m for manoeuvering of the tractor. Soil cone penetrometer and electronic moisture meter were used in taking readings at three levels of depth (0-15, 16-30, 31-45 cm) one week before treatment (1WBT), just after treatment (JAT), 6 and 12 weeks after planting (WAP). Soybean (var TGX-1448-2E) was planted on each of the 12 plots. Data on growth parameters and yield of soybean were obtained. Correlation, regression and ANOVA analysis of data was carried out using SPSS 21 and MS Excel 2010 to establish relevant relationships between subsoiler draughts and tillage parameters; and relationship between cone index, soil parameters, growth and yield of soybean. Results showed that the best subsoiler in terms of draught reduction was parabolic C-shank subsoiler (CSS) with 4,581.02 N followed by semi-parabolic subsoiler (SPS) with draught of 4.91 kN at depth of 40 cm. SSS, WSB and SSS at 370 rake angle (SSS37) had draughts of 6.87, 7.00 and 7.39 kN respectively. SSS37 showed the highest soil loosening ability at all depths followed by WSB, SPS, SSS and CSS respectively. Thus, at 50 cm highest working depth CSS had 0.0403 m2, SSS had 0.0451 m2, SPS had 0.0487 m2, while WSB and SSS37 had 0.0683 and 0.1061 m2 respectively. Draught of subsoilers increases with increasing depth of operation, cone index and bulk density, and decreases with increasing soil moisture and porosity. Hard pans of 2.0 MPa and above were observed at different locations on STEP-B Research Farm of FUTA at depths of 25 to 50 cm. Increasing cone index reduces growth and yield parameters of soybean. Regression equation (90.1% accuracy) was established for the prediction of yield of soybean. Tractor traffic was found to affect negatively the cone index of a soybean-cultivated land.