The role of clay, organic carbon and long-term management on mouldboard plough draught measured on the Broadbalk wheat experiment at Rothamsted

Despite a high energy requirement, the mouldboard plough remains the dominant tillage tool in northwest Europe. The aim of this work was to evaluate the relative influences of soil texture (clay content), soil organic carbon (SOC) and long-term management on soil-specific draught (S), where S is the force per cross-sectional area of worked soil. Measurements were made during autumn 2000 on the then 157-year-old Broadbalk wheat experiment at Rothamsted, UK, where clay contents vary from 19 to 39% and the different cropping history, mineral and organic fertilizer treatments lead to SOC values of 0.7-3.2%. Minimum SOC values increased with increasing clay and were associated with zero or low mineral N inputs, while higher SOC values (> 2%) were associated with long-term applications of farmyard manure (FYM), despite these being on the lighter (< 24% clay) soils. S values ranged between 52 and 142 kPa, with higher values co-located in areas with high clay contents. Contour maps were generated to illustrate the spatial variability of S and show similarity to those for clay. Where FYM had been added, S was 66 kPa compared with 74 kPa where only mineral or no fertilizer was applied on soils of the same texture. Increasing applications of mineral N resulted in relatively small increases in SOC but up to 12% reduction in S.