1. Introduction
Water excess and shortage (drought) are becoming more frequent phenomena
that challenge the development of agriculture and crop production in
Nordic countries. Indeed, water excess has been traditionally the main
cause for crop failure in Nordic agriculture, and waterlogging causes
substantial yield losses in this region (Bertholdsson, 2013; Wiréhn,
2018; Sundgren et al., 2018). In addition, drought in early
summer, related to low snow
conditions and early summer heatwaves occurring at crop water-sensitive
stages, is a recurring phenomenon in the Nordic region. Lack of water
causes substantial (10 - 20 %) irreversible yield losses of crops
(Peltonen-Sainio et al., 2021), which undermine food production. For
example, the 2018 summer drought in the Nordic region has reduced cereal
yield by 40 - 50 % (Bakke et al., 2020; Beillouin et al., 2020;
Statistiska-Meddelanden, 2018). These challenges are amplified by the
uncertainty and the expected long-term effect caused by climate change’s
impact on hydrological variables like precipitation, temperature, and
soil moisture (Vautard et al., 2013; Putnam and Broecker, 2017;
Ruosteenoja et al., 2017) as well as seasonal changes. The projected
increase in precipitation in Northern Europe is mainly concentrated in
winter and autumn, while precipitation is predicted to decrease in
spring and summer (Chan et al.,
2020; Rummukainen et al., 2004). Furthermore, global climate model
projections show that the long-term mean soil moisture will decline in
spring in northern Europe (Ruosteenoja et al., 2017), which can
negatively affect agricultural crop production here.
To tackle the water excess and summer drought challenges, drainage,
irrigation and crop choices are often promoted as ideal solutions.
Nevertheless, the effective implementation of such solutions is open to
debate both from technical and regulatory perspectives. To handle wet
periods, drainage is required in most agricultural fields in the Nordic
region to handle waterlogging (Jacks, 2019; Järvenpää and Savolainen,
2015). Additionally, supplemental irrigation is often required during
drought conditions, but the existing field setting is yet not well
equipped for irrigation. Nevertheless, implementing a supplemental
irrigation strategy is quite challenging if the field is far from
natural lakes or streams, which is often the case in lowland regions.
Groundwater has also been suggested as a potential solution to provide
irrigation potential. However, long-term dependence on groundwater for
irrigation may have considerable adverse effects on environmental
conditions, which need special consideration. This calls for further
research on the issue. Controlled drainage, whereby drainage water
release or retention from the field is regulated, can be used as a
potential solution to limit summer drought damage and reduce nutrient
loading to surface water.
In Europe, diffuse nutrient pollution (e.g., around 90 % of phosphorous
and about 70 % of nitrogen) from agriculture, mainly due to poorly
managed subsurface drainage systems, is a primary concern for the
ecological health of European river basins (Grizzetti et al., 2021). At
the same time, fertilizer use is expensive but considered necessary to
achieve good crop yields. Taking advantage of nutrients available in
drainage waters may provide an avenue to the reduction of fertilizer use
on the fields and, at the same time, reduce the nutrient pollution of
surface, sub-surface and coastal waters.
Circular Economy (CE) is a mindset that intends to move away from the
end-of-pipe systems and linear approaches towards restorative and
regenerative business models by intention and design (MacArthur, 2013).
In the European Union (EU), the Nordic region is no exception to this
trend where political actions have received much attention in the past
years to accelerate the transition towards a circular economy
(Rodríguez-Antón et al., 2021, Hosseinian et al., 2021). The Finnish
Roadmap to circular economy from 2016, for instance, highlights
sustainable food systems as one of the four focus areas and stresses the
need for utilizing recycled fertilizers (Hosseinian et al., 2021).
Changing the management of drainage waters from linear to circular
systems and thus taking advantage of the embedded fertilizers in the
drainage water for fertigation purposes (fertilizing with irrigation
water) may promote technological loops that reduce waste, enhance reuse
and result in stable crop yields in light of climate change.
The reuse and improved use of drainage water for fertigation
through improved drainage control
could be an essential strategy to reduce yield losses during summer
drought and nutrient loading to surface water. We present a simple,
flexible, and eco-friendly approach to reusing drainage water for
fertigation through improved drainage control and promoting a circular
economy in challenging Nordic conditions. This also joins the European
Union (EU)’s effort to accelerate the transition towards the circular
economy to achieve the Sustainable Development Goals (SDGs).