Appraising trapping efficiency of vegetative barriers in agricultural landscapes: Strategy based on a probabilistic approach based on a review of available information

Vegetative barriers have proven their effectiveness in controlling water erosion and enhancing other ecosystem services in agricultural areas. This characteristic has led to the conservation and promotion of vegetative barriers as landscape elements by the Common Agricultural Policy and other policy initiatives. Numerous reviews have dealt with the trapping efficiency of vegetated barriers, although they usually focus on studies from humid climates where their implantation and survival are more favourable. However, vegetated barriers are also an attractive alternative in arid and semi-arid climates. They limit competition for water and nutrients with crops to a reduced area compared to other best management practices, such as cover crops. This study presents a review of trapping efficiency of sediment, runoff, and nutrients (P and N) by vegetative barriers in regions of humid and arid, and semi-arid, climates, and a strategy based on sediment trapping efficiency probability, which in turn is based on the results obtained from our review. Different types of independent variables were grouped and identified for the review: related to the vegetative barrier dimension (buffer width, slope of the plot, and buffer area ratio), and related to the experimental conditions (type of vegetation in the buffer, soil protection of the non-buffered area, type of climate, type of experimental measurement and origin of rainfall). An exploratory analysis evaluated the significance of the experimental variables, which identified the need to focus on experiments under natural rainfall since those carried out with simulated rainfall presented statistically significant differences. In general, average trapping efficiencies for runoff and sediment were 40.1 and 62.6 %, respectively. For nutrients, values of trapping efficiencies had an average of 44.9 % for phosphorus and 38.4 % for nitrogen. Runoff and sediment trapping efficiency in arid and semi-arid regions tended to be higher than in humid regions. Regarding dimensional variables, a positive trend was observed in the runoff and sediment trapping efficiency with the width of the vegetative barrier, with a large variability across all the width range. Finally, based on the results of our review, we developed a probabilistic model for sediment trapping efficiency as a normalised cumulative probability distribution function for the two climatic regions separately. Also, we developed it as a function of the width of the vegetative barrier for each climatic region, to facilitate decision-making. This model shows that in 92 % of the cases, a vegetative barrier will reduce erosion in humid climates, while this trapping efficiency will be 100 % in semi-arid and arid conditions. This analysis showed that vegetative barriers are an alternative to other best management practices, e.g. cover crops, when there are operational or agronomic impediments to their implementation, having a high success rate in reducing erosion in any agricultural area.