R. Gracia

Tillage effects on soil surface conditions and dust emission by wind erosion in semiarid Aragón (NE Spain)

Wind erosion is one of the most serious soil degradation problems in many agricultural regions of the world. Due to particular soil and climate conditions and inappropriate agricultural practices, Central Aragon (NE Spain) is a semiarid region prone to land degradation by wind erosion. However, actual wind erosion data are not yet available. We report here results from a wind erosion study conducted during the summer 1995 within a single dryland field located in Central Aragon. Two consecutive field experiments investigated the effects of chisel ploughing (reduced tillage) and mouldboard ploughing (conventional tillage) on soil surface conditions and vertical dust flux. Micrometeorological data and suspended sediment samples were collected in the month following each tillage operation. Likewise, soil surface properties affecting wind erosion were determined immediately after tillage. Values of vertical dust flux varied from 0.52 to 5.03 μg m−2 s−1 (for a range of wind shear velocity of 0.46–0.56 m s−1) during the first experimental period (after chisel ploughing) and from 1.45 to 11.66 μg m−2 s−1 (for shear velocities between 0.37 and 0.72 m s−1) in the second experiment (mouldboard ploughing). The wind-erodible fraction of soil surface (aggregates<0.84 mm diameter) was 41% and 50% after chiseling and mouldboard ploughing, respectively. The percentage of soil cover with crop residues and clods was 15% after chiseling and only 4% after mouldboard ploughing. The frontal area of this nonerodible material and soil roughness was reduced four times after mouldboard ploughing. Although direct comparisons of tillage effects are still necessary, these first results suggest that reduced tillage, with chiseling as primary tillage, could be considered as a viable alternative for wind erosion control during the fallow period in semiarid Aragon. This study indicates, likewise, the need to consider the temporal and spatial variability of soil properties affecting wind erosion in agricultural soils.

Effects of reduced tillage on soil surface properties affecting wind erosion in semiarid fallow lands of Central Aragon

Abstract In Central Aragon (NE Spain), where strong and dry winds are frequent all year round, fallow lands are susceptible to wind erosion due to insufficient crop residues on the surface and loose, finely divided soils by multiple tillage operations. Effects of conventional tillage (CT — mouldboard ploughing followed by a compacting roller) and reduced tillage (RT — chisel ploughing) on soil surface properties affecting wind erosion were studied during three experimental campaigns in a dryland field of Central Aragon. RT provided higher soil protection than CT through a lower wind erodible fraction of soil surface (on average, 10% less) and a significantly higher percentage of soil cover with crop residues and clods (30% higher). Random roughness was also higher after RT than after CT (15 vs. 4%). These results indicate that RT can be an effective soil management practice for wind erosion prevention during the fallow period in semiarid Aragon. The study shows, likewise, that significant changes in soil aggregate size distribution associated with wind erosion processes may occur in short periods of time. Thus, temporal variability of soil surface properties, including crust and clods stability, needs to be considered in wind erosion research in agricultural soils.

Long-term effect of no-tillage on soil organic matter fractions in rainfed Aragon (NE Spain) .

This paper assesses the long-term effect of no-tillage (NT) on soil organic carbon (OC) content and its distribution among different organic matter fractions in rainfed agrosystems of Aragon (NE Spain). Adjacent fields of NT, conventional tillage (CT) and natural soils (NAT) were compared in three different cereal production areas. In the soil surface, the higher OC content found in the NAT soils was due to the particulate organic matter. In the case of agricultural soils, in general, the fractions responsible for the OC increase under NT were the fine particulate organic matter and the mineral-associated organic matter occluded within stable microaggregates.