Overall assessment of soil quality on humid sandy loams: Effects of location, rotation and tillage

Conservation tillage and diversified crop rotations have been suggested as appropriate alternative soil management systems to sustain soil quality. The purpose of this study was to quantify the effect of implementing three crop rotations (R2-R4) on soil structural changes and the "productivity function" of soil. R2 is a winter-dominated crop rotation (winter wheat was the main crop) with straw residues incorporated. R3 is a mix of winter and spring crops with straw residues removed. R4 is the same mix of crops as in R3, but with straw residues incorporated. Three tillage systems were used for each rotation: mouldboard ploughing to a depth of 20 cm (MP); harrowing to a depth of 8-10 cm (H); and direct drilling (D) at two experimental sites with a sandy loam soil and different water budgets in Denmark. The Muencheberg soil quality rating (M-SQR) method and simpler soil quality indices (i.e. visual evaluation of soil structure (VESS), overall visual structure (OVS) and overall soil structure (OSS)) were employed to differentiate the effects of these alternative management practices on soil structural quality and relative crop yield (RY). A Pearson correlation was also employed to find the correlation between the soil quality indices and relative crop yield. Relevant soil properties for calculating the soil quality indices were measured or obtained from previous publications. Crop rotation affected the soil structure and RY. The winter-dominated crop rotation (R2) resulted in the poorest soil structural quality and produced the lowest RY compared to the mixed rotations (R3 and R4). Tillage systems clearly influenced the soil quality and RY. The MP resulted in the best soil structural quality, and consequently the highest RY compared with both the reduced tillage treatments. Significant correlations were found in most cases between soil quality indices (including M-SQR) and RY. This highlights the influence of soil quality (as measured by the selected indicators) - and soil structure in particular - on crop yield potential.