Improving water resilience with more perennially based agriculture

Abstract

Land conversion from natural to managed ecosystems, while necessary for food production, continues to occur at high rates with significant water impacts. Further, increased rainfall variability exposes agricultural systems to impacts from flood and drought events. In many regions, water limitations are overcome through technological approaches such as irrigation and tile drainage, which may not be sustainable in the long term. A more sustainable approach to combat episodes of floods and droughts is to increase soil water storage and the overall green water efficiency of agroecosystems. Agricultural practices that promote “continuous living cover,” such as perennial grasses, agroforestry and cover crops, can improve water management relative to annual crop systems. Such practices ensure living roots in agricultural systems throughout the year and offer an approach to agroecosystem design that mimics ecological dynamics of native perennial vegetation. We review how these practices have been shown to improve elements of the water balance in a range of environments, with an emphasis on increased soil hydrologic function. A specific focus on the agriculturally intensive state of Iowa provides insight into how land use centered on agroecological principles affords greater water resilience, for individual farms as well as for broader community and ecosystem health.

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Improving water resilience with more perennially
based agriculture
Andrea D. Basche & Oliver F. Edelson
To cite this article: Andrea D. Basche & Oliver F. Edelson (2017) Improving water resilience with
more perennially based agriculture, Agroecology and Sustainable Food Systems, 41:7, 799-824
To link to this article: http://dx.doi.org/10.1080/21683565.2017.1330795
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2017 Andrea D. Basche and Oliver F. Edelson
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Improving water resilience with more perennially based
agriculture
Andrea D. Basche
a
and Oliver F. Edelson
a,b
a
Union of Concerned Scientists, Washington, DC, USA;
b
Environmental Studies Program, Dartmouth
College, Hanover, NH, USA
ABSTRACT
Land conversion from natural to managed ecosystems, while
necessary for food production, continues to occur at high rates
with significant water impacts. Further, increased rainfall varia-
bility exposes agricultural systems to impacts from flood and
drought events. In many regions, water limitations are over-
come through technological approaches such as irrigation and
tile drainage, which may not be sustainable in the long term. A
more sustainable approach to combat episodes of floods and
droughts is to increase soil water storage and the overall green
water efficiency of agroecosystems. Agricultural practices that
promote “continuous living cover,”such as perennial grasses,
agroforestry and cover crops, can improve water management
relative to annual crop systems. Such practices ensure living
roots in agricultural systems throughout the year and offer an
approach to agroecosystem design that mimics ecological
dynamics of native perennial vegetation. We review how
these practices have been shown to improve elements of the
water balance in a range of environments, with an emphasis
on increased soil hydrologic function. A specific focus on the
agriculturally intensive state of Iowa provides insight into how
land use centered on agroecological principles affords greater
water resilience, for individual farms as well as for broader
community and ecosystem health.
KEYWORDS
Agroforestry; climate
variability; continuous living
cover; cover crops; perennial
crops
Introduction
Environmental characteristics, particularly temperature, rainfall and sunlight,
are the predominant factors that determine photosynthetic rate and plant
growth, which ultimately comprise the foundation of agricultural science
(Gliessman 2015). The field of agronomy, for example, evaluates how culti-
vation can occur in regions most optimal for growth and development of
specific crops, given the climate and soil characteristics of different environ-
ments (Hay and Porter 2006). However, increased rainfall variability from a
warming atmosphere is measured in the recent record and is projected to
CONTACT Andrea D. Basche abasche@ucsusa.org Union of Concerned Scientists, 1825 K St. NW,
Washington, DC 20006-1232, USA.
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/wjsa.
Part of the special issue “Agroecology: building an ecological knowledge-base for food system sustainability.”
AGROECOLOGY AND SUSTAINABLE FOOD SYSTEMS
2017, VOL. 41, NO. 7, 799–824
https://doi.org/10.1080/21683565.2017.1330795
Published with license by Taylor & Francis © 2017 Andrea D. Basche and Oliver F. Edelson
This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives
License (http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial re-use, distribution, and reproduction
in any medium, provided the original work is properly cited, and is not altered, transformed, or built upon in any way.

intensify into the future, and this threatens the productivity and resilience of
agroecosystems (IPCC 2013; Pryor et al. 2014).
Further, centuries of agricultural development have led to highly mechan-
ized and specialized farming operations, including two practices that drama-
tically alter the water cycle—irrigation and tile drainage. Water added to
agricultural systems through irrigation systems can occur from either surface
waters or groundwater. In the United States, irrigated agriculture is concen-
trated in the West (USDA 2013) and globally, it is estimated to comprise
approximately 21% of cultivated lands (FAO 2014). Subsurface tile drainage
allows for the rapid removal of water during periods of excess precipitation
that could lead to saturated soil conditions unsuitable for crop cultivation
(Strock et al. 2010). In the United States, subsurface tile drainage is predo-
minantly located in the northern tier of the Midwestern states, as subsurface
drains are installed on approximately 40–50% of agriculture land in Iowa,
Indiana, Illinois, and Ohio (USDA-NASS 2014a).
Unfortunately, these alterations of the water balance to optimize agricul-
tural production have come at the cost of sustainable water management in
many regions. The irrigation of agricultural crops is depleting groundwater
in arid and semi-arid areas (Scanlon et al. 2012). In more humid regions,
technologies have enabled cropland expansion into grasslands and wetlands,
reducing the ecological flood mitigation capacity of these agroecosystems
(Lark, Salmon, and Gibbs 2015; Wright and Wemberly 2013). Although the
addition of drainage systems in wetter and/or poorly-drained environments
benefits crop productivity, such systems can increase water and pollutant
flows (David, Drinkwater, and McIsaac 2010).
More recently, agricultural water management approaches have been
developed to evaluate how these technological investments in boosting crop
productivity can be balanced with soil and water sustainability. A promising
and widely researched effort is the advancement of precision irrigation
techniques, which utilize spatial (i.e., GIS, GPS) technologies to maximize
irrigation efficiency through site-specific analysis and application (Sadler
et al. 2005). Additional research efforts have focused on how best to use
controlled drainage structures that allow current drainage systems to adjust
the water table in a way that limits excess water flow during high precipita-
tion periods (Strock et al. 2010). Controlled drainage benefits are beginning
to be quantified and are demonstrating capacity to buffer water and pollutant
flow (Williams, King, and Fausey 2015).
While advances such as precision irrigation and controlled drainage offer
improvements in agricultural water management, the previously mentioned
concerns—groundwater depletion from irrigation as well as increased water
and pollutant flow from tile drainage—indicate that the efficacy of techno-
logical approaches is limited. Consequently, there is developing interest in
applying water dynamics observed in natural ecosystems to improve
800 A. D. BASCHE AND O. F. EDELSON

managed agricultural landscapes. More complex agroecological systems that
mimic natural environments may be one approach to reduce consumptive
water use, while also mitigating the impacts of increased rainfall variability
due to climate change on agricultural production (DeLonge and Basche 2017;
Morris and Bucini 2016; Pryor et al. 2014; Vandermeer 1995). This review
will address several aspects of the water cycle—with a focus on soil water
storage through improved soil hydrology—that might be maximized for
agriculture using lessons from ecological and agricultural research. A closer
look at an intensively managed agricultural region, the state of Iowa in the
Midwestern United States’“Corn Belt,”demonstrates how land conversion
from a perennially-based ecosystem to an annually-based agroecosystem
created negative hydrological impacts, particularly flooding, and how a
greater focus on agroecological processes offers an insight into improving
water resilience in the region.
Regional water impacts of agricultural land conversion
The major native biomes of the contiguous United States (Figure 1) include
temperate and tropical grasslands and savannahs, Mediterranean and tempe-
rate forests and woodlands, as well as deserts and dry shrublands. Because
water is a major limiting factor of plant growth (Hay and Porter 2006), the
predominant biomes in various regions reflect regional rainfall and climate
Figure 1. Major ecoregions of the contiguous United States include forest, grassland, desert and
shrubland environments. Source: The Nature Conservancy (http://maps.tnc.org). Data from Olson
and Dinerstein (2002); Bailey, R. (1995); Wilken (1986).
AGROECOLOGY AND SUSTAINABLE FOOD SYSTEMS 801

regimes (Stephenson 1990). More humid regions support grasslands and
forests, while arid regions feature shrublands (Figure 2). These biomes con-
sist of perennially-based vegetation ranging from deciduous and coniferous
trees, to tall and short prairie grasses, and finally to bush-type shrubland
plants as annual rainfall diminishes. Annual evapotranspiration varies in
these different environments and can range from greater than 1200 mm in
tropical and swamp environments, 400–700 mm in forest environments,
400–650 mm in grasslands, and less than 300 mm in shrublands
(Rockstrom et al. 1999). It follows that a crop such as maize, which demands
from 500–800 mm per growing season, is cultivated in regions previously
occupied by forest and grasslands. It also follows that tropically-adapted
crops, such as bananas and sugarcane, are cultivated in warmer and more
humid biomes, given that their average water requirements range from 1200
to 2200 mm annually. Wheat and other small grain crops having water
requirements in the 450–650 mm range are frequently cultivated in semi-
arid regions (FAO 1986).
While land conversion of natural to agricultural ecosystems is necessary
for food production, it continues to occur at high rates, both globally and in
the United States, and this land conversion often leads to profound impacts
on water. The Millennium Ecosystem Assessment calculated that 0.8% of
forests and other native environments were converted to agricultural use
Figure 2. Aridity index (calculated from temperature and rainfall values) for the contiguous
United States. Data from the CGIAR-CSI Global-Aridity and Global-PET Database (Zomer et al.
2008).
802 A. D. BASCHE AND O. F. EDELSON

annually for the last several decades (Vorosmarty, Leveque, and Revenga
2005). More recent estimates of land conversion, particularly in the
Midwestern and Plains regions of the United States, suggest that policies
supporting grain-based biofuel have led to dramatic land conversion, includ-
ing up to 5% annual conversion to cropland from grasslands and wetlands,
with highest rates in locations proximal to ethanol refineries (Lark, Salmon,
and Gibbs 2015; Wright et al. 2017; Wright and Wemberly 2013). Rost et al.
(2008) estimate that croplands consume between 85 and 92% of global green
water (water that is stored temporally in the soil) when averaged in rainfed
and irrigated systems, with the remaining portion consumed by natural,
unmanaged ecosystems. Additionally, given the combined effect of land
cover on water use through transpiration and of plant communities on
preventing runoff, it is estimated that land conversion for general agricultural
purposes reduced global evapotranspiration by 2.8% and increased discharge
by 5%, from 1970 to 2000 (Rost et al. 2008).
Further underscoring the impact of land conversion and water impacts, an
increasing body of research highlights how declining soil structure from
agricultural practices has contributed to the reduction of water infiltration
and soil water storage capacity (O’Connell et al. 2007; Wheater and Evans
2009). Raymond et al. (2008) analyzed water discharge data from 106 United
States Geological Survey (USGS) locations with long-term data (dating back to
at least 1966) across the Mississippi River Basin, finding that the amount of
land used for general agricultural production in a watershed basin greatly
affected the amount of water discharge. In fact, they noted an inflection
point where watersheds that had greater than approximately 60% of land in
agriculture resulted in exponential increases in discharge that were not
accounted for after normalizing data for precipitation trends (Raymond et al.
2008). Therefore, they concluded that modifications in water storage capacity
from land use have profoundly changed the relationship between precipitation
and discharge (Raymond et al. 2008). To maintain the integrity of ecosystem
services in a variety of environments, ecologists now suggest that there is a
need to limit land conversion for agricultural uses, as sustainable boundaries
for water use are already being approached (Rockstrom et al. 2009).
Benefits of continuous living cover for water cycle management
“Continuous living cover”(Anderson 2005; Jordan and Warner 2008;
Asborjsen et al. 2014) is an approach to match the function of perennial
vegetation in agroecosystems. While managed agricultural systems cannot
directly mimic undisturbed systems, practices that offer continuous living
cover, notably maintaining canopy cover and roots in the soil throughout the
year, present an opportunity to reproduce and/or apply ecological principles
in an agronomic setting. There are numerous practices that could be
AGROECOLOGY AND SUSTAINABLE FOOD SYSTEMS 803

categorized as continuous living cover, including cover crops, perennial
grasses (for bioenergy, grain, or forage), and agroforestry.
Agricultural systems with primarily annual crops are more susceptible to
direct water losses through increased soil evaporation, surface runoff, and
leaching, than perennially-based agriculture. However, due to longer canopy
duration, perennial systems may also increase transpiration which, depend-
ing upon location and practices utilized, may offset some of the water savings
from reduced soil evaporation and runoff or drainage. It is important to
recognize that the increased water use of perennially-based systems may
create crop water availability challenges, particularly in more arid regions
and during periods of limited rainfall, such as extended drought or even flash
drought-type conditions. Research demonstrates, though, that the principles
of continuous living cover can increase soil water storage, through increased
carbon sequestration and improved soil hydrologic function (e.g., enhanced
aggregation, increased infiltration rate or hydraulic conductivity, greater
porosity), where a variety of inter-related soil water properties contribute
to enhanced soil structure (Table 1). Given these soil benefits and the
associated water risks in more arid regions, there is a need for additional
research to select perennial crops and/or cover crops that take into account a
cropping systems water use approach. This could include breeding efforts
that emphasize drought escape or resistance techniques, such as increased
rooting depth or rapid phenological development, to optimize both vegeta-
tive and reproductive plant growth so that yield components are not sacri-
ficed (Connor, Loomis, and Cassman 2011). Overall, most studies indicate
net positive water balance outcomes when the agroecological systems are
compared to annual cropping systems, with many researchers recognizing
the climate resilience opportunities afforded by such approaches.
Cover crops
There is growing interest in protecting and regenerating soil during periods
when it would otherwise be bare—practices that achieve this objective, such
as cover crop or green manure incorporation, can also improve agricultural
resilience to climate change (Kaye and Quemada 2017). Cover crops can
contribute to system resilience to rainfall variability through several mechan-
isms, including improved soil hydrologic function through aggregation
(which increases soil stability and ultimately water storage capacity), greater
infiltration rates, and reduced runoff (Blanco-Canqui et al. 2015). Further,
cover crops can offer reductions in soil evaporation and increases to water
storage, resulting in additional water available for cash crops, even during
drought conditions (Basche et al. 2016a)(Figure 3).
Across different climatic conditions and soil types in the United States,
there is a great deal of evidence demonstrating how cover crops can improve
804 A. D. BASCHE AND O. F. EDELSON

Table 1. Overview of water balance impacts from continuous living cover practices.
Water balance component
Location
Soil water
storage or
content
Soil
hydrologic
function
b
ET
Drainage
or runoff WUE Reference
Perennial
grass
Wisconsin ⇑⇑⇓Brye et al. (2000)
Iowa ⇓⇑⇓Daigh et al. (2014b)
Iowa ⇓Hernandez-Santana et al.
(2013)
Upper
Midwest
⇑VanLoocke et al. (2012)
a
Southern
Great
Plains
⇑⇓⇑Chen et al. (2016)
a
Northern
India
⇑Verma and Sharma (2007)
Northeast
India
⇑⇑ Ghosh et al. (2009)
Iowa ⇑Rachman et al. (2004)
Cover crop Iowa ⇑⇑⇑ Basche et al. (2016a)
a
,
(2016b)
Kansas ⇑Blanco-Canqui et al. (2011),
(2013)
California ⇑Gulick et al. (1994)
California ⇑Folorunso et al. (1992)
Illinois ⇑Villamil et al. (2006)
Iowa,
Indiana
⇑Daigh et al. (2014a)
Maryland ⇑Steele, Coale, and Hill (2012)
Northwest
India
⇑⇑ Sharma et al. (2010)
Northern
India
⇑⇑ Walia, Walia, and Dhaliwal
(2010)
Northwest
India
⇑Singh, Jalota, and Singh
(2007)
Southwest
Nigeria
⇑Lal, Wilson, and Okigbo
(1978)
Agroforestry Ethiopia ⇑⇑ Ketema and Yimer (2014)
Loess
Plateau
China
⇑Wang et al. (2015)
Kenya ⇑Kiepe (1995)
Iowa ⇑Bharati et al. (2002)
Missouri ⇓⇑⇑⇓ Anderson et al. (2009), Seobi
et al. (2005), Udawaata and
Anderson (2008)
Table 1. A selection of published studies analyzing continuous living cover practices and the direction of change for
various components of the water balance (ET = evapotranspiration, WUE = water use efficiency), relative to annual
cropping systems. Most studies reporting evapotranspiration values did not separate transpiration from soil
evaporation but indicated that increases were likely a result of greater plant transpiration.
a
Modeling studies.
b
Includes several different hydrologic properties including the following (definitions from Hillel 1998; Nimmo
2004):
Aggregation: Assemblages of organic matter that are bound to mineral particles in the soil matrix.
Aggregate stability: measure of vulnerability to externally imposed destructive forces.
Bulk density: A ratio of the mass of solids to the mass of total soil volume (solids and pores together).
Hydraulic conductivity: Ability of a conducting medium to transmit water.
Infiltration rate: The rate of downward flow of water into the soil, determining how much water will runoff
and how much will enter the root zone.
Porosity: index of the relative pore space of the soil, which can be broken down further specific to aggregate
porosity or pore size (macroporosity or microporosity).
Soil strength: The capacity of a soil body to withstand forces without experiencing rupture, fragmentation or
flow.
AGROECOLOGY AND SUSTAINABLE FOOD SYSTEMS 805

the overall water balance of agroecosystems. In the semi-arid Great Plains,
for example, a multi-year experiment found that wheat cover crop systems
(including vetch, pea, clover and triticale cover crop species) significantly
improved water-stable aggregates compared with wheat fallow or continuous
wheat systems (Blanco-Canqui et al. 2013) in a silt loam soil. At another
location in Blanco-Canqui et al. 2011 also found that wheat-sorghum rota-
tions including cover crops increased the mean weight diameters of soil
aggregates by 80% in the surface soil and improved water infiltration rates
up to three times more than in fields that did not include cover crops. There
is also evidence of cover crops improving water dynamics in California
vineyard environments. Folorunso et al. (1992) found improved soil strength
and water intake (by up to 100%) after 5 years of mixed cover crop use in
orchard and tomato system environments. Gulick et al. (1994) similarly
found that just one to two years of cover crop use in sandy loam environ-
ments of California increased infiltration rates by more than 140%.
Cover crops produce similar effects in more humid environments.
Experiments in Illinois and Iowa measured increases in plant available water
when cover crops were included in maize-soybean crop rotations (Basche
et al. 2016b; Villamil et al. 2006). During the drought of 2012, Daigh et al.
Figure 3. Simulated data based on the modeling experiment of Basche et al. (2016a) for the
drought year of 2012 in Iowa, United States. This represents how in an idealized simulation, the
various components of the water balance change and by what magnitude with the inclusion of a
winter rye cover crop in a corn-soybean crop rotation. Even with cover crop transpiration of
approximately 50 mm in the spring, water savings from reduced soil evaporation translates to
greater soil water and approximately 22 mm more water available for cash crop transpiration. In
this year of the simulation, there was no calculated water lost via drainage or runoff from either
system due to low rainfall. Total soil water represents the annual sum of daily values of moisture
content multiplied by the depth of the soil profile simulated (1.8 m).
806 A. D. BASCHE AND O. F. EDELSON

(2014a) found that rotations involving winter rye cover and maize-soybean led
to greater available water in Iowa and no negative impacts in Indiana, relative
to a control with no cover crop. At multiple experimental locations in
Maryland with continuous maize systems, incorporating cover crops improved
several soil physical properties, including water infiltration and aggregate
stability (Steele, Coale, and Hill 2012).
Similar results are documented outside the United States, particularly in
regions where water management is critical due to monsoon climatic condi-
tions. In the north-western region of India where maize–wheat systems are
susceptible to water stress after the rainy season concludes, Sharma et al.
(2010) found that green manure crops, such as sunn hemp, increased both
soil moisture and water infiltration, and ultimately led to greater crop
productivity compared to the no cover crop control. Similarly, for intensive
rice–wheat cropping in the same region of India, Singh, Jalota, and Singh
(2007) found that green manure crops increased soil aggregation and infil-
tration while decreasing bulk density on a loamy sand soil. Relatedly, after
23 years of repeated legume green manure use in a loamy sand in a rice–
wheat system, Walia, Walia, and Dhaliwal (2010) reported higher moisture
contents and faster infiltration rates compared to fertilizer only treatments of
the same nutrient content. Further, in the tropical climate and degraded,
sloping soils of southwestern Nigeria, Lal, Wilson, and Okigbo (1978) found
significant improvements (up to a 300% increase) in infiltration rates when
grass and legume species were grown ahead of annual crops, such as maize,
cowpea, pigeon pea, soybean, and cassava.
Agroforestry
Agroforestry systems are also proposed as a climate adaptation and water resi-
lience strategy, because they can also directly influence water balance by reducing
runoffanddosoindirectlybyimprovingsoilhydrologythroughincreased
porosity and infiltration (Altieri and Nicholls 2017;Schoenbergeretal.2012).
In general, the water balance of these tree and crop systems is more complex than
crop only systems, necessitating management of the ideal mix of inter-species
water demands. While tree species may have greater water use through transpira-
tion relative to grasslands (Huber, Iroumé, and Bathurst 2008), agroforestry and
intercropped systems are known to promote hydraulic lift of water from deeper
layers of the soil profile (Asbjornsen et al. 2011; Bayala and Wallace 2015).
Therefore, a mix of more deeply rooted trees interspersed with crops offers
diverse resource allocation of soil water during periods of variable rainfall
(Bayala and Wallace 2015). Further, tree belts have been found to capture
significant amounts of rainfall runoff from sloped landscapes (Ellis et al. 2006).
Research on the water relations of agroforestry systems compared with
annual crop systems supports the overall benefits of these more diverse
AGROECOLOGY AND SUSTAINABLE FOOD SYSTEMS 807

agroecosystems. Ketema and Yimer (2014) compared a no-till maize only
system to an agroforestry-based mixed crop system with livestock in Ethiopia
and found several positive water indicators, including increased soil porosity,
reduced bulk density, increased infiltration and greater soil moisture content.
Notably, in the agroforestry system there was an improvement in infiltration
rates over time, with infiltration rates greater after 15 years than at 5 years
(Ketema and Yimer 2014). Wang et al. (2015) similarly reported a consistent
improvement in infiltration rate when comparing an alley cropping wheat–
walnut system to a wheat monoculture over 11 years in the Loess Plateau of
China. An experiment in Kenya found infiltration rates four times greater in
hedgerows of Cassia siamea compared to the maize-cowpea sections of the
field (Kiepe 1995). Agroforestry riparian buffers at an experiment in the
Midwestern United States (Iowa) increased infiltration rates by up to 500%
relative to a maize-soybean only treatment (Bharati et al. 2002).
Extensive research has been conducted at a long-term agroforestry research
site in northeast Missouri in the Midwestern United States. The annual crop
treatment at this site is a maize-soybean rotation (established in 1991), and the
agroforestry treatment is a mixed grass-legume species hedgerows and mixed
oak species agroforestry buffers (established in 1997). Udawatta and Anderson
(2008) measured 2–2.6 times more macropores in the grass and agroforestry
buffer regions than in the maize-soybean treatment. Seobi et al. (2005) reported
significant increases in total porosity, hydraulic conductivity and water storage
in the grass and agroforestry buffers compared to the maize-soybean treatment.
While larger (but not statistically significant) infiltration rates were recorded in
the agroforestry and grass buffer regions, Anderson et al. (2009) also measured
lower soil water content in the agroforestry buffer during the cash crop growing
season, which they attributed to higher transpiration levels. However, they also
found that after rainfall events later in the summer, soil water recharge was
greater in the agroforestry buffers than the maize-soybean treatment. Overall,
soil measurements from this long-term research site demonstrate the complex-
ity of water dynamics in agroforestry systems, but that overall, soil hydrologic
function is improved relative to annual crop systems.
Perennial grasses
Research also notes the opportunity for perennial grasses, with their deep
roots and high water use efficiency, to improve climate resilience
(Asbjornsen et al. 2014). As is the case with cover crops and agroforestry,
there is a need to balance water use among cash crops in mixed annual-
perennial systems. Yet numerous experiments in a variety of environments
have repeatedly demonstrated the ability of perennial grasses to improve
hydrology in a way that might negate any transpiration losses. Verma and
Sharma (2007) reported an approximately 10% increase in aggregate porosity
808 A. D. BASCHE AND O. F. EDELSON

after several years when perennial grass management was compared to a
rice–wheat system in northern India. In northeast India, perennial forage
grass regenerated a topographic landscape, compared to continuous annual
crop cultivation, resulting in 20% more soil water, 63% faster infiltration
rates, and 40% greater hydraulic conductivity (Ghosh et al. 2009). In one
experiment in Iowa, switchgrass hedgerows were found to have six times
larger hydraulic conductivity, a greater number of macropores, and higher
soil water retention compared to a conventionally tilled continuous maize
treatment (Rachman et al. 2004).
Further experimental research from the Midwestern United States com-
paring perennial grasses to annual cropping systems underscores the
ability of perennial grasses to reduce water losses from runoff and drai-
nage. Brye et al. (2000) monitored multiple aspects of the water balance
over three crop growing seasons and found that the prairie ecosystem had
on average 65–75%lesswaterlosttodrainageascomparedtoamaize-
only crop system. The researchers also noted that the prairie ecosystem
had higher soil water content and water storage relative to the maize
system (Brye et al. 2000). Daigh et al. (2014b) similarly found that a
mixed prairie and winter rye cover crop system reduced cumulative drai-
nage by 37–46% compared to maize and soybean systems, due to greater
evapotranspiration and lower stored soil water. Intercropping perennial
grass strips in maize-soybean crop rotations reduced runoff by 37% in
Iowa (Hernandez-Santana et al. 2013).
Modeling studies from the Midwestern United States provide additional
insight into the overall water use efficiency of perennially-based systems.
VanLoocke et al. (2012) found greater net biome productivity (carbon diox-
ide converted to dry matter by evapotranspiration) in miscanthus and
switchgrass over maize in an experiment with the Agro-IBIS land surface
ecosystem and ecosystem process model. This is a unique metric that assesses
the tradeoff between carbon and water and provides an overall indicator of
productivity per water use. Chen et al. (2016) compared annual cotton
production in the Southern High Plains to several different species of per-
ennial grass bioenergy crops using the Soil and Water Assessment Tool
(SWAT). They found that, in general, the perennial grasses decreased runoff,
increased soil water content during many months of the year, and improved
water use efficiency overall. Agroecosystem models are helpful tools in
considering tradeoffs associated with water use and productivity, and as
these experiments demonstrate, there is added benefit of continuous living
cover from a productivity and water perspective.
While we have identified perennial grass opportunities predominantly
around forage and bioenergy crops, there is ongoing research with perennial
grain crops that might offer significant opportunity to replace land currently
under annual crop production (Baker 2017; Glover et al. 2010). Crop
AGROECOLOGY AND SUSTAINABLE FOOD SYSTEMS 809

breeding efforts are complex because of the many numbers of genes that
control the perennial habit, yet they hold tremendous promise as many staple
grain crops have perennial relatives (Curwen-McAdams and Jones 2017). A
shift toward more perennial grains, given the current predominance of
annual grain crops, will require significant financial investments in research
and development, and such efforts have recently received a boost on the
industry front to support such an expansion (General Mills 2017). Further,
research suggests that farmers are cognizant of the multiple opportunities
that perennial grains offer for diverse markets, soil regeneration and water
quality, particularly on marginal lands, indicating willingness to utilize such
new crop technologies (Adebiyi et al. 2016; Mattia, Lovell, and Davis 2016).
Conservation agriculture and agroecological practices that promote
continuous living cover
There is much emphasis in the scientific literature around “conservation
agriculture,”and as generally defined, it includes three principles:
1. Reduced tillage and/or zero tillage agriculture
2. Permanent soil cover through practices that retain crop residues
3. Crop rotations
Many researchers suggest that the principles, which may be achieved
through this variety of practices, offer climate resilience and the ability to
improve water outcomes in agroecosystems (Delgado et al. 2011; Palm et al.
2014) in a similar manner as has been described for the practices associated
with continuous living cover. However, the primary emphasis of this review
was to highlight opportunities around more complex agricultural practices
that maintain living roots in the soil and describe how ecological principles
in agroecosystems can benefit water outcomes, ultimately creating more
resilience to climate change.
Greenwater efficiency through altered management adds up globally
Although approximately 70% of all freshwater (blue water) use goes to
irrigated agriculture (Vorosmarty, Leveque, and Revenga 2005), it is further
estimated that 90% of rainfed and 48% of irrigated agricultural water use
comes from water stored temporarily in the soil (green water) (Mekonnen
and Hoekstra 2011). Thus, many researchers contend that managing green
water deserves greater research attention as an approach for reducing agri-
culture’s water and land use conversion footprint (Raza et al. 2012; Sposito
2013; Stewart and Peterson 2015). Two global modeling studies underscore
the importance of these greenwater management approaches. Rost et al.
810 A. D. BASCHE AND O. F. EDELSON

(2009) estimated how on-farm management changes that recover 25% of
current evaporative and runoff water losses could result in up to 19% yield
improvements, while current irrigation practices only lead to an approximately
17% yield improvement (Rost et al. 2009). More recently, Jägermeyr et al. (2016)
used a similar approach but combined multiple water use efficiency approaches,
including rainwater harvesting and soil moisture conservation, and estimated
that these strategies had the potential to reduce water-related yield gaps by 62%.
As the numerous studies outlined in Table 1 indicate, improved greenwater
efficiency is possible through a variety of continuous living cover practices. If
scaled up on a global level, as the water and land use estimates in Rost et al.
(2009) and Jägermeyr et al. (2016) studies conclude, they could offer significant
environmental and water sustainability gains. Biophysically-based models that
represent biogeochemical processes on a global scale, as well as agroecosystem
models utilized on a more detailed regional scale, are important tools in asses-
sing how complex agricultural management influences multiple aspects of
sustainability and are necessary to move forward agronomic and ecological
research on green water use efficiency.
Landscape level impacts of perennially based or annually based land
use: insights from Iowa
Land use change and climate change in the Midwestern United States
The temperate climate of the Midwestern United States, as well as its fertile
soils derived from native prairie grasses, makes the region ideally suited for
agricultural production (Aldrich, Scott, and Leng 1975)(Figure 4a). Since the
mid-twentieth century, Iowa’s agricultural landscape has undergone a pro-
found intensification. First, the overall acreage in crop production increased
by 22%, from approximately 20 million acres in 1940 to 24.5 million in 2012
(USDA-NASS 2014b). Further, in 1940, perennial crops and crops that grow
over winter (such as alfalfa, hay, barley and oats) comprised approximately
45% of harvested acres. After World War II, though, commodity-based
monocultures began to dominate this landscape, as the agricultural sector
emphasized increasing output while minimizing both on-farm expenditures
and food prices (Gliessman 2015). As a result, by 2012, the same perennial
and winter-growing crops represented approximately 7% of harvested acres,
while maize and soybean production represented approximately 56% and
38% of harvested acres, respectively (USDA-NASS 2014a,Figures 4b and 5).
This landscape simplification is occurring simultaneously to shifts in climate.
Scientists observe changes in seasonal rainfall and temperature that are
increasing the frequency of flood events in the Midwestern U.S.
(Mallakpour and Villarini 2015). Researchers also note that the additional
basin wetness resulting from increased precipitation, and anthropogenic
AGROECOLOGY AND SUSTAINABLE FOOD SYSTEMS 811

Figure 4a. Historic vegetation for the state of Iowa demonstrating that the predominant land
cover was prairie grass and forest in the mid-1800s. Vegetation map created by Anderson (1996)
using original public land survey data from 1832 to 1859 and digitized to create a vegetation
layer for GIS analysis. Water attributes from the USGS National Hydrography Dataset.
Figure 4b. More recent vegetation for the state of Iowa, demonstrating the predominance of corn
and soybean crops across the landscape, which currently represent approximately 94% of har-
vested acres in the state. Red circles represent select major urban areas that have been affected by
flood events over the last several decades. Data from the USDA-NASS 2015 Cropland Data Layer
(USDA-NASS 2016) and water attributes from the USGS National Hydrography Dataset.
812 A. D. BASCHE AND O. F. EDELSON

impacts (i.e., urbanization and agriculture) become a precondition for
increased flood potential (Slater and Villarini 2016).
Sixty-eight percent of Iowa’s land area is harvested for agriculture (ISU
Extension 2017), so the large shifts in the state’s cropping patterns over the
last seventy years have resulted in additional impacts to the landscape’s
hydrology. From a water cycle perspective, the loss of crops growing over
winter creates the likelihood that plant transpiration could decrease and
water losses from agricultural lands could increase due to greater runoff. In
fact, strong evidence from Iowa watersheds demonstrates precisely how these
projected water changes have come to fruition. Zhang and Schilling (2006)
analyzed streamflow rates at river stations in the Mississippi River basin,
including several in Iowa, over the period from 1940 to 2000 and concluded
that the conversion of perennial vegetation to annual row crops and related
agricultural activities, such as tillage, has affected the basin-scale hydrology of
the Mississippi River, leading to increased baseflow and streamflow (Zhang
and Schilling 2006).
A simple analysis of two stream gauge locations near urban centers in Iowa
demonstrates a statistically significant upward trend in stream flow with time
(Figures 6a and 6b). Further, in the past 30 years, the monthly stream flow was
2.6–3.7 times more likely to be two standard deviations above the long-term mean
than during the earlier recorded period, even as the region experienced two severe
Figure 5. The change in crops planted across the state of Iowa from 1940–2012. Closed symbols
represent summer annual crops, while open symbols represent perennial crops or crops that
grow over winter. Alfalfa, barley, hay, and oats represented 45% of harvested acreage in 1940
and 7% in 2012. Source: (USDA-NASS 2014b).
AGROECOLOGY AND SUSTAINABLE FOOD SYSTEMS 813

droughts. The more extensive analyses of Zhang and Schilling (2006)arrivedat
similar conclusions. The relationship of land use and hydrology in agricultural
regions suggests that more rainfall variability with climate change may only
intensify stream flow and subsequent impacts, assuming continuation of the
same annual crop-based land use patterns. While limited research directly links
soil function to drought effects in the same way that the research on flood events
does,thesimilarmechanismsthatpromotewaterstorageforheavierrainfalloffer
resilience for lesser periods of rainfall. To this point, experts in Iowa identified that
the 2012 drought led to a decline in soil structure, which made it more difficult for
water retention to occur, exacerbating negative impacts (Al-Kaisi et al. 2013). It has
also been demonstrated that drought effects during the Dust Bowl of the 1930s
Figure 6a. The monthly stream flow (monthly rates divided by drainage area) near Ames, Iowa
since the early 1930s. The red arrows note the droughts of 1988 and 2012, while the blue arrows
note the flood events of 1993 and 2008. There was a statistically significant increase in stream
flow over time, with a slope of 0.21 mm month
−1
. Dashed lines represent +2 and +3 standard
deviations above the mean monthly stream flow. Source: USGS National Water Information
Systems (2017).
Figure 6b. The monthly stream flow (monthly rates divided by drainage area) near Cedar Rapids,
Iowa since the early 1930s. The red arrows note the droughts of 1988 and 2012, while the blue
arrows note the flood events of 1993 and 2008. There was a statistically significant increase in
stream flow over time, with a slope of 0.21 mm month
−1
. Dashed lines represent +2 and +3
standard deviations above the mean monthly stream flow. Source: USGS National Water
Information Systems (2017).
814 A. D. BASCHE AND O. F. EDELSON

were in large part driven by land use change, including soil degradation and the
loss of vegetative plant cover on the landscape (Cook, Miller, and Seager 2009),
further demonstrating the feedbacks between climate, agricultural management
and negative outcomes in extreme events.
Perennially based agriculture and conservation practices improve water
resilience
Research already demonstrates that a more perennially-based agricultural
system can reduce the negative consequences of flooding events. Schilling
et al. (2014) used the SWAT model for a large Iowa watershed to analyze
shifts in downstream flood risks. Their analysis assumed a baseline scenario
of current land use where 76% of the watershed was planted with maize and
soybean, as well as four hypothetical land use changes, including a 100% shift
to perennial crops (Schilling et al. 2014). While their predictions demon-
strated that shifting all cropland to perennials offered the greatest reduction
in flooding frequency (by 50–100%), implementing extended crop rotations
(that included alfalfa), and/or increasing perennial crop plantings in the
more vulnerable regions of the watershed also reduced the frequency of
downstream flood events by 25–35% (Schilling et al. 2014).
The potential for farmlands to reduce the intensity of flood and drought
events through increased water storage capacity is an important point sub-
stantiated by disaster reports. For example, the Iowa Flood Disaster Report
(IFDR), written by a recovery team after the 1993 severe floods, cited the
success of conservation measures, including reduced tillage, in preventing an
additional six million acres from flooding (IFDR 1994). It was noted that
conservation measures also played a role in reducing urban flood impact and
damages to the state’s infrastructure (IFDR 1994). A report prepared by the
Rebuild Iowa Office, a temporary state agency created by the government
following 2008 flooding, concluded that industrial agricultural practices
caused a dramatic reduction in the ability of Iowa’s land to absorb and
hold back water due to a decrease in soil organic material (AETF 2008).
This report notes how public policy and expenditures should internalize
flood mitigation priorities to encourage practices that foster greater hydro-
logical resilience (AETF 2008).
Flood and drought impacts beyond the farm
Increased precipitation variability not only adversely affects farmers who must
cope with flood and droughts on a more frequent basis but also downstream
urban citizens who experience negative impacts related to infrastructure and
public health. For example, as Iowa endured a major drought in 1988, many
municipal water supplies were reduced to dangerously low levels (Kunkel and
AGROECOLOGY AND SUSTAINABLE FOOD SYSTEMS 815

Angel 1989), while low water levels on the Mississippi River led to a 50%
reduction in barge traffic (Changnon, Kunkel, and Changnon 2007). During
the 1993 floods, a failed levee flooded the water treatment plant in Des Moines,
causing the city to go without drinking water for 19 days (Parrett, Melcher, and
James 1993). In 2008, severe flooding caused multi-billion dollar damages to
downtown Cedar Rapids (Morelli 2016).
Another side effect of increased rainfall variability is nutrient runoff and
water quality issues, which is a critical issue in the state of Iowa and as far
downstream as the Gulf of Mexico (Diaz and Rosenberg 2008; Potter 2011;
Raymond et al. 2008; Schilling 2005). Over 700 of Iowa’s waterways are
impaired because their water quality does not meet the waterway’s intended
use (i.e., consumption or recreation) (IDNR 2015). Pollution from non-point
sources, especially agricultural lands, is estimated to contribute approxi-
mately 92% of the total nitrogen and 80% of the total phosphorus that
enter Iowa’s streams annually (Iowa NRS 2012).
Further, the well-researched social phenomenon known as environmental
racism documents the disproportionate impacts of water-related events on
communities of color and those with lower socioeconomic coping capacity
(Umokoro, 2015). With declining water quality resulting from pollution and
increased extreme weather events, water costs rise. A report found that water
bill increases grew at a rate much faster than inflation, due to climate events
and increased vulnerability (Feinstein et al. 2017). These price increases
disproportionately affect resource–scarce populations, as they are forced to
spend a greater portion of their disposable income on a basic need. More
generally, a recent review found that low-income communities are more
vulnerable to flood risks because of their limited housing opportunities and
lack of information about, and access to, disaster mitigation and recovery
assistance programs (Rufat et al. 2015).
Conclusion
Modern agricultural systems have overcome productivity limitations due to
excessive or insufficient water through approaches such as tile drainage and
irrigation infrastructure, respectively. While such approaches have been
successful and many efforts are working toward improving their sustainabil-
ity, there are limits to these approaches. There is much to learn from the
ecology of natural systems adapted to climatic and environmental limits. One
way to mimic the function of perennial and native vegetation patterns in
agroecosystems is through practices featuring continuous living cover. Unlike
exclusively annual systems, there are practices—such as cover crops, agrofor-
estry, and various perennial forage, grain or bioenergy crops—that ensure
canopy cover and living roots in agricultural systems throughout the year.
These practices have been shown repeatedly, and in a range of environments,
816 A. D. BASCHE AND O. F. EDELSON

to enhance multiple elements of agricultural water balance, including
improved soil hydrology. Amid projections for a changing climate with
increased rainfall variability, reducing agricultural water risks is more critical
than ever, and the increasing recurrence of water-related extreme events
underscores the susceptibility of the current system. The historical shift in
Iowa’s agricultural landscape highlights how cropping patterns have played a
role in increased flood and drought frequency and severity, which adversely
impact on-farm water resilience as well as public health and infrastructure
downstream. Increased use of perennials or continuous living cover practices
that mimic the function of perennial plant communities could significantly
improve the ability of agricultural land to enhance resilience and buffer
negative impacts of climate change and increased rainfall variability.
Funding
The authors would like to recognize the Union of Concerned Scientists Kendall Fellowship
Program, TomKat Foundation and The Grantham Foundation for the Protection of the
Environment, for funding that supported the lead author while writing this article. Support
for Oliver F. Edelson came from Dartmouth College’s Porter family fund for sustainability in
the curriculum and the Richard and Jane Pearl Family Fund for Environmental Studies.
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