Nitrogen losses in vineyards under different types of soil groundcover. A field runoff simulator approach in central Spain

The soils of Mediterranean vineyards are usually managed with continuous tillage, resulting in bare soil,low infiltration and high soil erosion rates. Soil nutrients, such as nitrogen, could be lost dissolved in therunoff, causing a decrease in soil fertility on such degraded soils and producing eutrophicationdownstream. The influences of groundcover on the soil erosion processes and sediment yields inMediterranean vineyards have been widely addressed. However, the runoff process itself, excluding theeffect of raindrop impacts, has barely been studied. Thus, afield runoff simulator was built to assessrunoff and nutrient losses under different soil management strategies in Central Spain. In the winter ofthe 2012–2013, four vineyards were selected, and two types of groundcover were established to comparewith conventional tillage (T): spontaneous vegetation (CS) and seeded Brachypodium distachyon (CB). In2014 and 2015, 72 runoff simulations were performed to assess the influence of the two different types ofgroundcover on the dissolved mineral nitrogen losses in runoff. The results showed that spontaneousvegetation cover was the most effective management choice to reduce runoff and nitrogen loss byproducing 3 times less runoff than conventional tillage and 6 times less nitrate loss. Conventional tillageresulted in higher mineral nitrogen loss because it produced more runoff and higher runoff nitrateconcentrations. The vegetation cover had a strong influence on runoff and nitrogen losses, while the slopeangle and rock fragment cover showed a negligible impact.