## 2 Edge-of-Field Technologies
### Vegetated Buffer Strips  
As opposed to CWs and RWs, which are waterlogged systems, VBSs do not hold water over the soil surface. These systems are naturally occurring or implemented between the edge of an agricultural field or catchment and running surface waters such as rivers and streams in order to intercept and reduce the load of nutrients downstream as well as to increase the bank stability and prevent erosion [126; 127; 128]. Thus, they may contain native or planted vegetation consisting of species of forest plants and/or grass [129]. Vegetated buffer strips are normally used to reduce the nutrient load from agricultural surface and subsurface runoff in catchments lacking a tile drainage system. The retention of P from agricultural runoff mainly occurs through entrapment of PP in the soil matrix or by the vegetation, where larger particles are more easily retained than fine clay particles [126; 130]. This retention mechanism is benefited in these systems due to infiltration of the runoff into the soil and enhanced hydraulic roughness of the vegetation, which decrease the water flow velocity and particles transport, and subsequently favor deposition [127; 128]. The retention of DRP is mediated by plant uptake in the root zone during the growing season and sorption to reactive sites in the soil profile, and is thus influenced by the level of runoff infiltration as well [128; 129]. However, VBSs tend to decrease the retention of P in the long-term or even become a source of dissolved reactive and organic P due to saturation of sorption sites and/or release of P from senescing plants [127; 128; 130; 131]. Therefore, the soil geochemical characteristics (e.g., P sorption capacity) and vegetation composition and density markedly affect the retention efficiency of dissolved P. Despite that, the higher retention efficiency of PP than that of DRP commonly results in higher ratios of dissolved P to total P at outflows than at inflows [132]. A suggested management method to prolong the retention of dissolved P may involve periodic harvesting of vegetation to enhance plant uptake and prevent release from mineralization [131], presumably before the end of the growing season. The studies dealing with agricultural surface and subsurface runoff demonstrated that VBSs generally work as P sinks, especially for PP. [PERSON] and [PERSON] [133], for example, tested the ability of VBSs to mitigate the loss of PP from agricultural areas owing to soil erosion, and found that these systems reduced by 20% and 36% the PP losses in comparison to sites with no VBS. Nevertheless, it is normally observed a large variability in P retention between systems [126; 127; 134]. Part of the variability can be attributed to the incoming P concentration and to the ratio of the system area to the catchment area [134]. Moreover, the width of VBSs has been widely discussed in relation to P retention. It has been commonly found that wider systems enhance P retention [126; 127; 128; 130], especially on steeper slopes [131]. However, widening a VBS consequently reduces the land area for agriculture. Therefore, attempts to estimate the optimal width for acceptable P retention under specific catchment characteristics (e.g., slope, soil clay content and drainage pattern) are highly desired [128]. In tile-drained agricultural catchments, however, the P load may bypass the plant root zone and soil profile, and be directly discharged to downstream surface waters, thus skipping the P retention mechanisms [127; 128; 129]. [PERSON] and [PERSON] [129] indicated the limitation of VBSs in this situation when compared to the treatment of groundwater. The discharge of concentrated P load from tile drains into VBSs may, on the other hand, overload the P retention mechanisms and consequently decrease the P retention efficiency [126]. As a result, VBSs are rarely used to treat agricultural drainage discharge. Therefore, the literature addressing the treatment of agricultural drainage discharge by VBSs is rather limited. [PERSON] et al.