Crop diversification to reduce wind erosion hazard in a semiarid blown-sand area of Hungary

The soils of flat alluvial fans mantled by blow sand (Humic Arenosols) usually present unfavourable properties for agriculture: low organic matter and soil moisture content, low levels of aggregation, low clay content to absorb nutrients and high exposure to wind erosion. In dry periods when the protective effect of vegetation is reduced, sand storms detach and carry away large amounts of organic particles. The soil profile of the Hungarian study area shows buried humic horizons which indicate intensive reworking by wind action in historical times. Given the limited choice of crops which can be cultivated in the region, an asparagus field was selected for experimentation. Asparagus rows are aligned in the direction of the prevailing wind. The plastic foil cover of asparagus ridges intensifies wind erosion through a wind channel effect. Two different crop diversifications were introduced to assess possible improvements in ecosystem services including wind erosion control: plots with asparagus monocropping (M as control) alternated with pea (D1) and oat intercropping (D2) between asparagus ridges. The flux of eolian transport captured by sediment traps in a 1-metre high and 100-metre wide cross section, measured and analyzed for composition at four heights: on the ground surface, at 30 cm, 200 cm and 400 cm heights. Meteorological records were evaluated for starting velocities of sand movement estimated from wind tunnel experiments. For the region  critical starting wind velocity at 10 cm height was established at c. 6 m s^-1. Large-scale irrigation to allow surface crusting is not feasible because of the lowering of the groundwater table. Cover crops were found to reduce soil erosion by wind in two ways: through providing vegetation cover in the periods critical for sand storms (early spring and late summer) and through enriching the soil with organic matter by way of green manuring, which is also beneficial for soil fertility. There were significant differences between treatments. The pea and oat crops well utilized the moisture derived from occasional thunderstorms and in the second year provided a continuous vegetation cover. There was minimal concurrence between the main crop (root zone at 0-150 cm) and the cover crops introduced (root zone at 0-20 cm). Although no significant rise in total nitrogen contents of the soil could be achieved (explained by the extremely low clay content and aggregate formation capacity), organic matter contents grew due to the biomass added to the soil in form of crop residues. (Although their decomposition rate is low due to the dry environment.) Dust amounts captured at 200 cm above 105.39 kg y^-1, at 400 cm above the ground surface amounted to 26.75 kg y^-1, while sand saltated along the surface at 0-15 cm reached an average 2130 kg y^-1. In sediment traps near the surface saltated sand had a median diameter of 174 µm, at +15 cm 134 µm, at +200 cm 118 µm and grain size substantially reduced to 42 µm (coarse silt) at +400 cm.