The fallowing of land in arable rotations has been a traditional practice across Europe for much of its agrarian history. Rotating crops and leaving land uncropped has a range of agronomic benefits including weed control, disease prevention and improved soil fertility for future cropping (IEEP, 2008). Due to agricultural intensification, however, traditional set-aside has decreased. Set-aside was re-introduced in 1988 as a voluntary and in 1992 as an obligatory supply control mechanism within EU agricultural regulations. While the primary aim of the policy was to control the supply of agricultural production, a
wider role for set-aside in relation to environmental protection was recognised in the 2003 CAP reform. The ESS affected by set-aside, tackled in this literature review, are:
• habitat provision and connection • water purification
• soil fertility
• erosion control/prevention
• climate regulation (via carbon capture and storage in plants and soils) • production of raw materials (biomass for energy and biofuels) • aesthetic information
The effects of set-aside on ESS depend on a variety of factors (IEEP 2008; Vannini et al. 2008):
1) whether set-aside is rotational i.e. it forms part of a crop rotation and moves around a holding over time or whether it is non-rotational and remains in one place. For non-rotational set-aside the duration of the set-aside (short term, long term or permanent) is important.
2) whether set-aside remains bare or has a vegetation cover. Differences in environmental impact also arise from different vegetation covers, which can be for example natural regeneration, stubble or sown vegetation. The type of vegetation sown also makes a difference (e.g. legumes vs. oil seeds). 3) the way in which set-aside is managed e.g. if herbicides are used to control weeds or if vegetation is
cut.
4) site-specific conditions (like area and steepness of slopes) and more generally the environmental and climatic conditions of the areas in which set-aside lands are located, including the kind of vegetation surround the fallow land.
5) the history of use and management of the area.
Clear benefits arise from naturally regenerated set-aside for breeding and feeding farmland birds. Where set-aside land is allowed to naturally regenerate, a patchy habitat containing many broad-leaved plants develops and this has been shown to provide good breeding and feeding habitat for many birds. Crop stubbles and weed seeds benefit wintering birds. The other major form of management for set-aside involves sowing it with a grass mixture. The resulting dense grassland is not ideal for the foraging of small birds, but is attractive to a variety of small mammals. Non-rotational set-aside generally develops a greater abundance of invertebrates than other in-field arable habitats, but access for birds may be constrained by the density of the vegetation (van Buskirk and Willi 2004; Silcock and Lovegrove 2007; Hodge et al. 2006; Vannini et al. 2008). For a more detailed analysis of the consequences of fallow set- aside for biodiversity see Hodge et al. (2006) and a meta-analysis of 127 published studies from van Buskirk and Willi (2004) quoted therein.
The main benefit set-aside brings to water quality is in the reduction of inputs, such as fertilisers or pesticides, to farmland and consequently reduced pollution from pesticides and fertilisers (Silcock and Lovegrove 2007; Kersebaum et al. 2003). Apart from this very simple fact, the effect of set-aside on water quality via leaching is again dependent on the factors mentioned above. Not surprisingly, Froment et al. (1999) found that uncovered, bare fallow and natural regeneration appear to increase leaching risk of nitrate as there is no root zone that can keep soil mineral nitrate. Keeping an adequate soil cover is hence a key factor for retaining the beneficial effects of set-aside in this respect (Tonitto et al. 2006). Sown crops can reduce leachable nitrate. This is especially true for so-called catch crops. Laurent and Ruelland (2011) analysed the capacity of Lopsided oat (Avena strigosa) to reduce nitrate loads. Lopsided oat is recognised in conservation agriculture for its rapid growth, its efficiency in limiting weeds and the fact it can be destroyed by rolling after freezing, i.e. it does not require herbicides. The authors found the efficiency of the crop to be high as it can reduce the nitrate load from 20% to 70%. However, the capacity
to reduce nitrate loads depends on the type of crop or mix of crops adopted for the soil cover (Vannini et al. 2008). The effects of set-aside on the ecosystem service water purification have been analysed in chapter 3.
As pointed out above, set-aside was traditionally used to improve soil fertility. The positive impacts were associated with introducing certain plants as green cover to improve soil structure and improve soil organic matter (Oréade-Brèche 2002) (see also crop rotation/diversification above). Crop yields have been found to be higher following set-aside than after another crop (Silcock and Lovegrove 2007). Set-aside, however, does not only play a role in improving soil fertility but also in erosion control. Van Rompaey et al. (2001) show that there is lowering of the average soil erosion rate of the remaining arable fields when set-aside is introduced. This is due to the fact that farmers tend to take the steepest fields out of production. Apart from the choice of fields taken out of production, soil protection depends largely on management and more precisely the presence and type of green cover (Vannini et al. 2008). The greatest erosion benefits are provided by non-rotational grass cover (Oréade-Brèche 2002). Bare soil is considered to have the highest negative effect on soil erosion (e.g. Bonan 2002).
Some studies also attest to the fact that set-aside has a positive effect in terms of climate change adaptation. Non-rotational set-aside, for example, is considered capable of helping species to adapt to climate change by providing connectivity of habitats within fragmented landscapes, i.e. green infrastructure, aiding species dispersal between isolated remnants of habitats (Silcock and Lovegrove 2007; IEEP 2008).
In terms of climate change mitigation set-aside plays a role in soil carbon sequestration i.e. the removal of atmospheric CO2 by plants and the storage of fixed carbon as soil organic matter, which is increased by the conversion from conventional agriculture to land uses with high carbon inputs and low levels of disturbance, such as permanent set-aside (IEEP 2008).
Set-aside is currently also used for the production of non-food crops such as biofuels, biomass for energy production, pharmaceuticals and industrial lubricants (IEEP 2008). Silcock and Lovegrove (2007) found that nearly 6 million ha of set-aside in Europe is used for growing non-food crops and the majority of EU countries are increasing their use of set-aside for non-food crops. Thereby, the vast majority of industrial crops grown on set-aside are energy crops, in particular oilseed rape used for biodiesel and, to a lesser extent, short rotation coppice (SRC) and miscanthus (Silcock and Lovegrove 2007). However, Don et al. (2011) argue that, in the light of the high future demand for energy crops in Europe, second- generation crops such as SRC or miscanthus should be increased as they emit 40% to >99% less N2O than conventional annual crops. This is a result of lower fertiliser requirements as well as a higher N-use efficiency, due to effective N-recycling (Don et al. 2011).
While at least second-generation crops are low input crops both in terms of fertilisers/pesticides and fossil- fuel-powered field operations (Silcock and Lovegrove 2007), they can have greater water requirements than the crops they are replacing (Berndes 2002). In practice, this means that drier regions are likely to be much less suitable for biomass production than wetter regions (Silcock and Lovegrove 2007). Another concern associated with biomass crops is their possibly adverse landscape impact. This relates to their height and unfamiliar appearance, but also landscape diversity may be reduced by producing extensive monocultures of energy crops (Robertson et al. 2008).
While Silcock and Lovegrove (2007) state that short rotation coppice are at least more beneficial for wildlife than the arable crops which are replaced, other authors show that in general the cultivation of energy crops is causing the loss of species (see for example Groom et al. 2007, Kovács-Hostyánszki et al. 2011).
In terms of cultural services, set-aside can be seen as introducing diversity into arable landscape and improving its amenity value. It can also introduce colour into landscape, for example through flowers (e.g. poppies) and butterflies in species-rich field margins or naturally regenerating wildflower grassland (Silcock and Lovegrove 2007). Yet, some citizens may feel that uncropped areas make the landscape look untidy and unattractive or disturb the more uniform appearance of the surrounding land. Overall, across Europe, the impact of set-aside on the landscape, concerning its aesthetic value, was assessed to be neutral (Oréade-Brèche 2002).
Comparing the relative merits of rotational and non-rotational set-aside as well as differences in cover crops is not straightforward and much depends on the environmental objectives being pursued (Baldock and Beaufoy, 1992).