Repeated soil application of organic waste amendments reduces draught force and fuel consumption for soil tillage

Soil application of organic waste products (OWP) can maintain or increase soil organic carbon (SOC) content, which in turn could lead to increased porosity and potentially to reduced energy use for soil tillage. Only a few studies have addressed the effect of SOC content on draught force for soil tillage, and this still needs to be addressed for fields that receive diverse types of organic waste of urban, agricultural and agro-industrial origin. The objective of this study was to determine the effect of changes in SOC induced by repeated soil application of OWP on draught force for soil tillage and tractor fuel consumption. Draught force was measured for tillage with conventional spring tillage tines, as well as bulk density, soil texture and SOC content in the CRUCIAL field experiment, Denmark in which diverse types of OWP had been applied annually for 11 years. The OWP included household waste compost, sewage sludge and cattle manure. The results showed that repeated waste application increased the SOC content from 1.4% SOC for the control NPK treatment to up to 3.5% SOC for the compost applied at an accelerated rate. Bulk density was also changed by OWP additions and strongly correlated with SOC. Specific draught for soil tillage was significantly explained by SOC, clay content, bulk density and soil cohesion, and could be expressed as a linear function of SOC and clay content explaining 67% of the variance. However, no evidence was found that the composition of SOC accumulated for different organic wastes influenced the specific draught. Overall, the decrease in draught force could lead to a decrease in tractor fuel consumption for soil tillage of up to 25% for compost applied at an accelerated rate and up to 14% for compost applied at a normal rate. This reduced fuel consumption could have a significant impact if taken into account in environmental assessments of organic waste recycling.