Tillage effects on barley residue cover during fallow in semiarid Aragon

Maintenance of crop residues on the soil surface is considered the most effective method to control wind erosion. In semiarid Aragon (NE Spain), where the risk of wind erosion can be high, the adoption of conservation tillage systems has been encouraged as a fallow management alternative. However, little information concerning the dynamics of residue cover during fallow is available for this area. We report here results on the evolution of barley residues during two fallow periods under conventional tillage (CT), reduced tillage (RT) and no-tillage (NT). The three tillage treatments were compared under both continuous cropping (CC) and cereal–fallow (CF) rotation. The CC system involves a summer fallow period of 5–6 months and the CF rotation a long-fallow of 17–18 months. Effects of specific tillage operations on soil cover are also presented and discussed in relation to wind erosion control during the long-fallow period. Average dry mass of barley residues at harvest was 1395 and 729 kg ha-1 in the first and second year of the study, respectively. In general, crop residues at harvest were not significantly affected by tillage or cropping system. Primary tillage operations had the major influence on residue incorporation with reduction percentages of residue cover of 90–100% in CT (mouldboard ploughing) and 50–70% in RT (chiselling). During the two long-fallow periods, large clods (4–10 cm diameter) produced by mouldboard ploughing did not fully compensate for the complete burial of residues and the soil surface was insufficiently protected against wind erosion (soil covers <3% and random roughness ~4%). The most critical period corresponded to that elapsed between primary and secondary tillage operations. The lack of residue-disturbing operations in NT makes this practice the best strategy for fallow management. After 17–18 months of fallow, the NT plots still conserved a surface residue cover of 10–15%. Similarly, standing residues, representing between 20 and 50% of the total residue mass, were also present on the no-tilled surface during the first 11–12 months of fallow. In general, RT plots maintained a soil erodibility condition similar to that of NT due to the combined effect of soil cover by clods and residues retained after tillage (5–15%) and the roughness created by clods (6–13%).