Reduced tillage effects on physical properties of silt loam soils growing root crops

In the scope of the increasing concern for soil conservation, reduced tillage (RT) agriculture is growing more important in today's agriculture in Western Europe. However, crop rotations often include beets and potatoes, crops that are generally assumed to be less suitable under RT agriculture because they result in a high disturbance of the soil at the formation of the ridges and at harvest. Therefore, the short- and long-term effect of RT agriculture on bulk density (BD), water retention curve (WRC) aggregate stability and field-saturated hydraulic conductivity of silt loam soils with crop rotations including root crops was evaluated. Ten fields at seven locations representing the important RT types, applied for a different number of years, and eight fields under conventional tillage (CT) agriculture with similar soil type and crop rotation were selected. At each location, BD of the 5-10 cm layer was mostly lower in the RT fields (1.42 +/- 0.05 Mg m(-3) laverage with standard deviation]) compared to the CT fields (1.44 +/- 0.09 Mg m(-3)) and the water content at saturation was mostly higher (0.394 0.027 M3 M-3 and 0.382 +/- 0.021 m(3) m(-3) for RT and CT fields, respectively). No differences in BD (1.53 +/- 0.03 Mg m(-3)) or WRC could be found in the 25-30 cm soil layer when comparing the RT with the CT fields. The stability index of the 0-10 cm layer measured by dry and wet sieving [De Leenheer, L., De Boodt, M., 1959. Determination of aggregate stability by the change in mean weight diameter. Mededelingen van landbouwhogeschool en de opzoekingstations van de statat te Gent 24,290-300] was 40% higher under RT than CT agriculture. The mean weight diameter (MWD) [Le Bissonnais, Y., 1996. Aggregate stability and assessment of soil crustability and erodibility: 1. Theory and methodology. Eur. J. Soil Sci. 47, 425-437] was significantly higher even after short-term RT compared to CT agriculture. The MWD after a heavy shower, a slow wetting of the soil and stirring the soil after prewetting was 19%, 38% and 34% higher for RT than CT fields, respectively. The field-saturated hydraulic conductivity tended to be higher under RT compared to the CT fields. Despite the high disturbance of the soil every 2 or 3 years of crop rotations including sugar beets or potatoes, RT agriculture had a positive effect on the investigated physical soil properties. (c) 2008 Elsevier B.V. All rights reserved.