EFITA/WCCA 2005 25-28 July 2005, Vila Real, Portugal 2005 EFITA/WCCA JOINT CONGRESS ON IT IN AGRICULTURE Draft and Fuel Requirements in Tillage Operations: Modelling for Optimizing Tractor-Implement Systems João M. Serrano a , José O. Peça a , Fernando Santos b a Engineering Department, University of Évora, 7000 ÉVORA - PORTUGAL; jmrs@uevora.pt b Engineering Department, University of Trás-os-Montes e Alto Douro, 5000 VILA REAL -PORTUGAL __________________________________________________________________________________________________________ Abstract A three years research project was developed to study tractor-implement dynamics in tillage operations. This paper reports the results of field tests performed under real working conditions, using more than twenty tractors (four-wheel-drive) and trailed disc harrows combinations, in different soils conditions. The data show the existence of a linear relationship between the drawbar pull per unit of implement width, and the fuel consumption per hectare. The results put in evidence the benefits of the “gear up, throttle down” approach. Key words: Fuel consumption per hectare, draft, disc harrows. _____________________________________________________________________________________ 1 Introduction Soil working operations in traditional farming systems involving the use of the tractor are among the operations which incur the highest levels of energy costs. The sustainability of such systems requires the strictly-controlled management of resources leading to the significant reduction of crop-production costs deriving from savings in fuel consumption. The overall energy efficiency is the ratio of the energy transferred from the tractor to operate the implement, to the energy equivalent of the fuel consumption required to perform the operation. The overall energy efficiency is dependent on a range of performance factors namely, engine, power transmission and the interaction of tyres with the soil. This last factor implies the definitive influence of the soil as a major factor on the overall energy efficiency. This is the reason behind different authors (Bowers, 1985; Riethmuller, 1989; Smith, 1993), being cautious concerning the domain of application of their results. The Tractor Performance Monitor (TPM) is increasingly being supplied as standard tractor electronic equipment, or factory-fitted option, and they provide information to assist tractor drivers and farm managers. TPM are also an excellent base to perform experiments in real working conditions gathering data that can be used to validate the real importance of the different variables present in the dynamics of tractor-soil-agricultural implement (Peça et al, 1998). A program of experiments using a 59kW TPM equipped agricultural tractor, pulling two different trailed disc harrows has been accomplished (Serrano, 2002; Serrano et al, 2003). Tests performed in different soil conditions and at several paired relations of tractor weight/implement width enabled to establish relations between fuel consumption per hectare (C ha ) and soil/implement resistance per unit of implement width (ℑ). Figure 1 shows one of such relations valid for dry, undisturbed loam soils and two engine settings: rated speed and 80% of the rated speed, selecting in both cases the highest gear in the transmission at which the work could be performed with the required quality (tilth, buried stubble), within accepted comfort and safety for the operator, and without engine overcharge (no significant decrease in engine speed). 831