Due to the worrying observations about climate change and biodiversity reduction, attention is paid to assess the environmental impact of human activities, such like agricultural ones. Tools like "Life cycle assessment" have been developed to determine very precisely the environmental impact of agricultural products and activities. This paper presents a method to assess the energy performance of tractors used for spreading tasks. Long term monitoring equipments were installed on tractors in five agricultural equipment cooperatives in France. Each of them has to carry on spreading works that could differ in kind of sludge, but also in machine characteristics. Data were collected for more than a year representing 2000h of agricultural works and about 1000h of spreading works. The work is analysed through the comprehensive "tank unit", divided into four phases: filling up the tank of organic matter, transporting to field, spreading, and transport empty back. Then, average mission profiles are deduced from recorded data. It allows delivering a variety of indicators for spreading work. These indicators are then used in LCA to compare different spreading scenarios and study work organisation. The machine efficiency is also analysed. For sewage sludge, the significant impact of transport is shown on both duration and fuel consumption. Because the distance between the field and the storage area is longer, more than 75% of the total fuel used for a tank unit is dedicated to the transport phases. Finally, improved management scenarios for organic spreading are proposed. But the operator driving style clearly affects both work and fuel efficiency during spreading works.