Published August 19, 2016
Review & Analysis—Soil & Water Management & Conservation
Growing Dedicated Energy Crops on
Marginal Lands and Ecosystem Services
Humberto Blanco-Canqui*
Dep. of Agronomy and Horticulture
Univ. of Nebraska-Lincoln
261 Plant Science Hall
Lincoln, NE 68583
Marginal lands are candidates for growing dedicated energy crops such
as perennial warm-season grasses (WSGs) and short-rotation woody crops
(SRWCs), but actual field data on ecosystem services have not been widely
discussed. This review (i) discusses potential marginal lands studied for energy
crop production, (ii) considers the impacts of energy crops on ecosystem services, and (iii) underlines research needs. Some marginal or degraded lands
studied for energy crops include highly erodible, flood-prone, compacted,
saline, acid, contaminated, or sandy soils, reclaimed minesoils, urban marginal sites, and abandoned or degraded croplands. Field data are few but
indicate that ecosystem services vary with the type of marginal land, management (i.e., fertilizer or amendment rates), and perennial species. Biomass
yields can vary between 1 and 14 Mg ha−1 yr−1 under WSGs and between
0.5 and 9.5 Mg ha−1 yr−1 under SRWCs. Growing energy crops on marginal lands can reduce water and wind erosion, sequester soil C between 0.25
and 4 Mg C ha−1 yr−1, restore contaminated or compacted soils, and improve
biodiversity. Fertilization or addition of organic amendments increases biomass yield and C sequestration on marginal lands. Future research on energy
crops on marginal lands should evaluate (i) all ecosystem services, (ii) sitespecific management strategies, (iii) species tolerant to adverse climatic, soil,
and environmental conditions, and (vi) economic viability, among others.
Overall, dedicated bioenergy crops can provide biofuel feedstocks and other ecosystem services, but more experimental data are needed to reduce the
uncertainty regarding the performance of energy crops under different types
of marginal or degraded lands.
Abbreviations: CRP, Conservation Reserve Program; SRWCs, short-rotation woody crops;
WSGs, perennial warm-season grasses.
M
arginal lands are candidates for growing dedicated bioenergy crops,
such as perennial WSGs and SRWCs, to reduce competition for land
between energy and food production. Marginal lands can be defined
as soils that have physical and chemical problems or are uncultivated or adversely
affected by climatic conditions. The potential of marginal lands for growing WSGs
and SRWCs as biofuel has received increased attention in recent years. Several
questions remain, however, about which and how to grow dedicated energy crops
on marginal lands, how dedicated energy crops will perform on different types of
marginal lands, and whether these sites can produce abundant biomass while maintaining or improving ecosystem services.
Many have used models to address the above questions and estimate the global
and regional potential of marginal lands for cellulosic biomass production. These
modeling studies have suggested that marginal lands offer a large potential for producing dedicated bioenergy crops while sequestering soil C, reducing net greenhouse gas emissions, and improving water quality (Davis et al., 2010; Gelfand et
Core Ideas
•Dedicated bioenergy crops can
enhance ecosystem services in
marginal lands.
•Ecosystem services vary with the type
of marginal land.
•More field data are needed about
the performance of energy crops on
marginal lands.
Soil Science Society of America Journal
Soil Sci. Soc. Am. J. 80:845–858
doi:10.2136/sssaj2016.03.0080
Open Access.
Received 20 Mar. 2016.
Accepted 29 Apr. 2016.
*Corresponding author ([email protected]).
© Soil Science Society of America. This is an open access article distributed under the CC BY-NC-ND
license (http://creativecommons.org/licenses/by-nc-nd/4.0/)
al., 2011; Lee et al., 2012; Bandaru et al., 2013; Feng et al., 2015;
Qin et al., 2015). However, few studies have synthesized field
data to discuss the biomass yields and soil and environmental
benefits from growing dedicated energy crops on different types
of marginal lands. Thus, discussions based on field data are needed to better understand the real potential of marginal lands. A
synthesis of field data can also be useful for future modeling studies and projections of the potential of marginal lands for growing
dedicated energy crops while enhancing ecosystem services.
The objectives of this review were to: (i) review and synthesize published studies on dedicated bioenergy crops (WSGs and
SRWCs) grown on different types of marginal lands; (ii) review
the impacts of dedicated bioenergy crops on ecosystem services
including biomass production, soil C sequestration, soil erosion,
soil properties, and biodiversity; and (iii) underline research needs
to better understand energy crop production on marginal lands.
Potential Marginal Lands
for Growing Energy Crops
A literature review indicated that some marginal lands studied as potential sites for cellulosic biomass production for biofuel
occur on highly erodible, flood-prone, compacted or highly susceptible to compaction, saline, acid, contaminated, sandy soils,
reclaimed mine sites, urban marginal lands, and abandoned or
degraded croplands (Fig. 1). Each of the selected marginal lands
is discussed below with regard to its potential for the production of WSG and
SRWC biomass and the delivery of ecosystem services. Studies assessing SRWCs
on marginal lands are very few. Thus, the
discussion is mostly focused on WSGs.
production on CRP lands can be low and variable, depending
primarily on climatic conditions (Mulkey et al., 2006). The addition of inorganic fertilizer or organic amendments is required
to increase biomass production on erodible lands (Mulkey et al.,
2006). Also, biomass yield may decline with time due to annual
harvests (Venuto and Daniel, 2010).
Growing WSGs on former CRP erodible lands can sequester soil C, although field data are limited. The potential of CRP
lands to sequester soil C depends on management. For example,
switchgrass can accumulate as much as 4 Mg ha−1 yr−1 of C in
the soil on CRP lands if cattle manure is added (Lee et al., 2007).
Without intensive management, erodible sites could only sequester about £1 Mg ha−1 yr−1 of C in the soil (Gebhart et al.,
1994; Follett, 2001; Mi et al., 2014). After 3 yr, Old World bluestem (Bothriochloa spp.) and a mixture of native grasses grown
on highly erodible sites (i.e., CRP lands) in Oklahoma increased
soil organic matter from 2.3 to 2.6% at the 0- to 100-cm depth
(Venuto and Daniel, 2010).
Findings from the few CRP studies suggest that intensive
management of erodible lands can produce significant amounts
of biomass and sequester soil C if N fertilizer or animal manure
is applied. Thus, a potential strategy can be to intensively manage
erodible lands by planting perennial WSGs and harvesting once
or twice per year (³10-cm cutting height) with the addition of
optimum amounts of manure or fertilizers. Erodible sites with
Highly Erodible Lands
Experimental data on growing dedicated energy crops on highly erodible lands
are limited. Some data are available for
WSGs grown on Conservation Reserve
Program (CRP) lands. In the United
States, much of the erodible land is under
the CRP, which was established under
the Food Security Act of 1985 to convert
highly erodible lands to perennial grasses or
trees. It has been projected that up to 50%
of CRP lands could be used for cellulosic
biomass production for biofuel (Perlack et
al., 2005; Venuto and Daniel, 2010).
Studies in South Dakota, North
Dakota, Kansas, and Oklahoma have suggested that growing perennial WSGs (e.g.,
switchgrass [Panicum virgatum L.]) on former CRP lands can produce between 2 and
6 Mg ha−1 of biomass with the addition of
inorganic fertilizers and animal manure
(Mulkey et al., 2006; Table 1). Biomass
846
Fig. 1. Potential marginal lands that have been recently studied to assess their potential for
cellulosic biomass production and provision of soil ecosystem services.
Soil Science Society of America Journal
Table 1. Biomass yield of short-rotation woody crops grown as biofuel on some marginal lands.
Type of marginal
land
Sandy soil
Location
Energy crop
Poland
black locust
Time after
planting
yr
3
poplar (Populus nigra × P.
Maximowiczii Henry cv. Max-5)
willow (Salix viminalis)
Coarse-loamy soil
of poor quality
Wadena County, Minnesota
Reclaimed minesoil
4 sites in
Brandenburg,
Germany
7 willow hybrids
3
Fertilization or
amendment
no amendment
L + F + M†
no amendment
L+F+M
no amendment
L+F+M
none
2 native willow accessions
Welzow I
Jänschwalde
black locust
poplar (Populus spp.)
willow (Salix spp.)
black locust
Biomass
produced
Reference
Mg ha−1 yr−1
1.1 ± 0.4
Stolarski et al.
(2014)
3.6 ± 1.1
5.9 ± 1.8
8.8 ± 1.7
4.5 ± 1.7
9.3 ± 3.2
2.47–5.33‡
0.23 and.61‡
14
none
9.5
3.0
3.6
Zamora et al.
(2014)
Grünewald et
al. (2009)
3, 9
200–410–280
6.9–7.6, 7.4
kg ha−1 N–P–K
poplar
2.6–4.0
willow
1.0–2.9,0.5
Welzow II
black locust
4
120–100–80
3.2
kg ha−1 N–P–K
poplar
–
willow
–
Sedlitz
black locust
4
none
3.1
poplar
–
willow
–
† L, lignin; F, mineral fertilization; M, mycorrhiza inoculation. Results for single amendments are available in Stolarski et al. (2014).
‡ Original values have been divided by three to represent annual yield. Original values = 7.42–16 and 0.69–1.83 Mg ha−1.
low initial levels of soil C could be potential C sinks if WSGs are
successfully established.
Reclaimed Minesoils
Reclaimed minesoils can also be potential lands for biofuel
feedstock production (Fig. 2). Minesoils are considered marginal
because they are often rocky and gravelly, with low soil organic
matter concentrations and adverse soil physical and chemical
characteristics. Surface mining drastically changes soil profile
characteristics. Also, coal mining often creates environmental
concerns (e.g., water pollution). In the United States, about
4.4 million ha of mine land can be reclaimed and made available
for biofuel feedstock production (Lemus and Lal, 2005).
Most of the minesoils are reclaimed to cool-season grasses.
These grasses are generally shorter, produce less biomass, use
more water and nutrients, and could thus provide fewer ecosystem services (i.e., wildlife habitat) than WSGs (Blanco-Canqui
et al., 2004; Werling et al., 2014). Establishing perennial WSGs
such as switchgrass on reclaimed minesoils is an option to produce cellulosic biomass with the addition of amendments such as
mulch, lime, flue-gas desulfurization products, animal manure,
and compost. Marra et al. (2013) suggested that to be economically viable, switchgrass biomass yield on reclaimed minesoils
should be at least 5 Mg ha−1. Growing perennial deep-rooted
WSGs on reclaimed minesoils can help to rebuild some of the
soil profile characteristics while producing biomass for biofuel.
There are, however, management challenges with growing perennial WSGs on reclaimed minesoils due to their adverse soil
physical and chemical properties. On two reclaimed minesoils
www.soils.org/publications/sssaj
in southern West Virginia, biomass production differed due
to differences in the reclamation material (Marra et al., 2013).
Averaged across cultivars and years, switchgrass annual biomass
yield was 5.76 Mg ha−1 at a site where the surface material consisted of “topsoil and treated municipal sludge”; but it was only
0.803 Mg ha−1 at another site where the reclaimed surface material consisted of “crushed, unweathered sandstone.” Yields at
both reclaimed sites were, however, lower than on prime agricultural lands (12 Mg ha−1). Amendments are needed to significantly increase switchgrass yields on reclaimed minesoils.
Plant species will vary in their performance on reclaimed
lands. On a reclaimed site in the Appalachians, switchgrass, sericea lespedeza (Lespedeza cuneata L.), reed canarygrass (Phalaris
arundinacea L.), tall fescue (Festuca arundinacea Schreb.), and
crownvetch (Coronilla varia L.) had the lowest nutrient requirements and were most tolerant to drought and moisture conditions out of 16 forage grass and legume species in monocultures
and mixes after a decade of establishment (Evanylo et al., 2005).
Short-rotation woody crops can also be grown on reclaimed
minesoils. In Germany, with additions of mineral fertilizer and
compost, black locust (Robinia pseudoacacia L.) yielded more
than poplar (Populus spp.) or willow (Salix viminalis L.) for
different rotation periods (3-, 6-, and 9-yr rotations) on two reclaimed mine sites (Grünewald et al., 2009).
Reclaimed minesoils have a high potential to sequester soil
C, particularly in the first 20 or 25 yr following reclamation.
They can sequester soil organic C from 0.3 to 1.85 Mg C ha−1
yr−1 under pastures and from 0.2 to 1.64 Mg C ha−1 yr−1 under
forest management in the upper 30 cm of the soil profile (Ussiri
847
Fig. 2. Perennial warm-season grasses (top) and miscanthus (bottom)
growing in reclaimed minesoils in West Virginia (photo by Dr. Jeffrey
Skousen, West Virginia University).
and Lal, 2005). These rates of C sequestration can be increased if
perennial WSGs or SRWCs are planted on these reclaimed lands.
For example, planting SRWCs on reclaimed minesoils could sequester as much as 4 Mg ha−1 yr−1 of soil C in the upper 30 cm
of the soil (Matos et al., 2012). Because reclaimed minesoils are
low in initial soil organic C concentration, they can more rapidly accumulate soil C compared with prime agricultural lands,
which often have higher levels of organic C. The level of soil disturbance, soil profile characteristics after reclamation, initial soil
C level, and management (e.g., application of amendments) will
dictate biomass yields and the rate of soil organic C sequestration
in reclaimed soils.
Flood-Prone Soils
Flood-prone soils are also potential candidates for growing
WSGs (Fig. 3, top). Because WSGs do not have to be planted
every year, they can withstand occasional flooding once established. Biomass production on floodplains, however, can be
lower than on prime agricultural lands. For example, in a study
in the southeastern United States, Alamo switchgrass yielded
higher on well-drained upland soils (17.7 Mg ha−1) than floodplain soils (8.5 Mg ha−1) under different N fertilization rates
(0, 67, 134, and 201 kg N ha−1; Mooney et al., 2009). The same
study found that the maximum switchgrass yields occurred at
67 kg N ha−1 on the well-drained soil and at about 160 kg N
ha−1 on the poorly drained floodplain, suggesting that mar848
Fig. 3. Switchgrass growing on a flood-prone section of a field (top)
and a wind-erosion-prone soil (bottom) in a semiarid region in
the central Great Plains (photo by Humberto Blanco after 3 yr of
switchgrass establishment).
ginal lands can require higher rates of N fertilizer than prime
farmlands to produce the same amount of biomass. On some
flood-prone soils, perennial WSGs can yield as much biomass
as corn (Zea mays L.). On a flood-prone soil in eastern Kansas,
switchgrass biomass yield (10.89 Mg ha−1) did not statistically
differ from corn biomass yield (8.46 Mg ha−1), but miscanthus
(Miscanthus ´ giganteus) yielded more biomass than corn by
5.3 Mg ha−1 after 5 yr of management (Evers et al., 2013).
The drainage class will influence the energy crop performance.
Floodplain soils severely limited by poor drainage (Mooney et
al., 2009) can yield less biomass than moderately drained floodprone soils (Evers et al., 2013).
The ability of WSGs to improve soil properties on floodprone soils can also be variable. In eastern Kansas, switchgrass,
big bluestem (Andropogon gerardii Vitman), and miscanthus
grown on a flood-prone site reduced the wind erosion potential
but did not increase soil organic C stocks compared with row
crops such as continuous corn and grain sorghum [Sorghum
bicolor (L.) Moench.] after 4 and 5 yr of management (Evers et
al., 2013). The soils under perennial WSGs had 8 to 16% lower
wind erodible fractions and three to four and a half times higher
geometric mean diameters of dry aggregates than soils under annual row crops, indicating that dedicated energy crops reduced
the soil’s susceptibility to wind erosion. In fertile flood-prone
soils with high initial soil C levels, perennial WSGs can protect
Soil Science Society of America Journal
the soil from erosion but may not rapidly increase the soil C pool
compared with row crops.
Selection of ecotypes is important for managing WSGs
on flood-prone soils. Two ecotypes of switchgrass are available: upland (hexaploid or octoploid) and lowland (tetraploid;
Barney et al., 2009). The upland ecotypes can grow on drier
soils, while lowland ecotypes can grow on wetter or flood-prone
soils. Lowland ecotypes are less susceptible to waterlogged conditions but can be more susceptible to water stress and drought
than upland ecotypes (Barney et al., 2009). Thus, depending on
the ecotype, switchgrass is one of the few WSG species that can
grow relatively well under both moisture stress (dry) and flooded
(wet) conditions. Perennial WSGs have the ability to grow on
flood-prone soils due to their unique root characteristics. The
presence of aerenchyma cells in the stems and roots of some perennial grasses can allow them to grow in waterlogged soils by enhancing the internal transfer of O2 from shoots to roots (Krizek
et al., 2003). Because of such unique characteristics, WSGs can
also be planted around wetlands as buffers to produce cellulosic
biomass while reducing the sedimentation and pollution of wetlands and enhancing wildlife habitat.
Compacted or Compaction-Prone Soils
Some native perennial WSG species can grow in compacted
soils or compaction-prone soils because they have stiff stems and
deep roots that can penetrate layers and alleviate compaction in
deeper soil layers as growth time increases. Eastern gamagrass
(Tripsacum dactyloides L.) is one of the species that is more tolerant to compacted conditions than other WSGs. It can grow under compacted conditions that otherwise inhibit the growth of
row crops. Soils susceptible to compaction, such as fine-textured
soils, can benefit from perennial grasses. Well-established eastern
gamagrass roots can penetrate compact claypan soils (>40% clay
content) to deep layers while producing a significant amount of
biomass (Clark et al., 2003). Warm-season prairie grasses have
coarser root systems than cool-season grasses and can better
withstand compaction risks. Eastern gamagrass can penetrate
soil layers with a bulk density as high as 1.7 g cm−3 and a penetration resistance as high as 5.4 MPa in the root zone (Clark et al.,
2003; Krizek et al., 2003). Penetration resistance values >3 MPa
can drastically reduce root growth and yields of row crops, but
WSGs such as eastern gamagrass can withstand higher levels of
compaction than row crops. It is important to note, however,
that eastern gamagrass biomass yield on highly productive soils
is about 20 Mg ha−1, but it can be lower on compacted soils
(Krizek et al., 2003).
While the mechanisms by which roots can grow in compacted layers are complex, the main factors are related to the root
characteristics (Clark et al., 2003). Grasses with thicker roots can
better resist and adapt to mechanical impedance than thinner
roots. Additionally, Clark et al. (1998) found that the increased
presence of aerenchyma and the fibrous sheath of perennial roots
may enable roots to transfer O2 and penetrate compacted layers.
The ability of some grasses, including eastern gamagrass, to grow
www.soils.org/publications/sssaj
in compacted layers suggests that they can survive under limited
O2 and water availability. The deep roots can create biopores and
allow water, heat, and air flow through the soil. In dry and compact soils, perennial grass roots may penetrate deep in the profile
to obtain water and nutrients, while in wet and compact soils,
they can adapt to saturated conditions due to aerenchyma cells
and other root characteristics (Krizek et al., 2003).
Growing perennial grasses, compared with row crops, can
also reduce a soil’s susceptibility to compaction by reducing the
bulk density (Blanco-Canqui et al., 2014). An increase in soil
organic C, soil aggregation, and macroporosity may result in
reduced bulk density with time after establishment. Perennial
grasses may reduce the soil bulk density by about 10% compared
with row crops (Kucharik et al., 2003). This reduction in bulk
density can increase the soil’s ability to absorb and conduct water. Deep-rooted perennial grasses can also alleviate compaction
in deeper depths in the long term (>5 yr).
Sloping Soils
Perennial WSGs have been used as conservation buffers on
sloping croplands (with >5% slope) to reduce runoff and sediment loss and improve water quality (Fig. 4). Thus, establishing
WSGs for bioenergy in sloping fields is a potential opportunity.
A few studies have investigated the benefits of WSGs for improving soil erosion and soil properties on sloping croplands. On a
steep soil with slopes ranging from 8 to 16% in southeastern
Iowa, 6-yr-old switchgrass hedges reduced runoff by 52% and
sediment loss by 53% compared with steep slopes without grass
hedges under no-till continuous corn (Gilley et al., 2000). On a
10% slope in Iowa, switchgrass barriers increased water infiltration, saturated hydraulic conductivity, macropore volume, and
soil organic C concentration compared with the adjacent no-till
corn rows (Rachman et al,. 2004). In eastern Nebraska, switchgrass barriers increased soil organic C and total soil N (BlancoCanqui et al., 2014). The same study reported that switchgrass
barriers improved soil structural properties such as wet aggregate
Fig. 4. Switchgrass hedges after 15 yr of establishment on a sloping
corn field to control water erosion in eastern Nebraska (photo by
Humberto Blanco).
849
stability and porosity in the 0- to 60-cm depth compared with
no-till row crops. Improved soil structural properties could explain the reduced soil erosion observed in fields with switchgrass
buffers (Gilley et al., 2000).
Research data on biomass yield from WSGs grown on sloping fields are few. In Tennessee, biomass yield of switchgrass
grown on a moderately to somewhat poorly drained eroded sloping upland did not differ from the biomass yield of switchgrass
grown on a moderately to well-drained level upland position
(Boyer et al., 2013). The same study found that switchgrass biomass yield increased with N fertilization up to 134 kg N ha−1
(7.38, 15.11, 17.95, and 17.12 Mg ha−1 at 0, 67, 134, and
200 kg N ha−1, respectively), suggesting that the application
of 134 kg N ha−1 was the optimum amount of fertilization to
maximize biomass yield on the sloping position. In a 2-yr study
in South Dakota, the annual biomass yield ranged from 3.7 to
5.6 Mg ha−1 for switchgrass and 2.7 to 4.2 Mg ha−1 for big bluestem, but biomass yields of switchgrass and big bluestem at the
backslope position were 4 and 14% lower than at the footslope
position (Lee et al., 2009). The same study found that the application of animal manure increased the biomass yield by about
30% regardless of topographic position.
A few studies have suggested that planting switchgrass and
other WSGs for bioenergy on sloping marginal lands not only
provides cellulosic biomass but also improves ecosystem services
such as reducing water erosion and improving soil and water
quality, soil C sequestration, and biodiversity (Gilley et al., 2000;
Rachman et al., 2004; Blanco-Canqui et al., 2014). Growing
deep-rooted WSGs in fields with steep slopes can anchor and
stabilize the soil while improving soil properties at deeper depths
in the profile. Studies have also indicated that the addition of
fertilizers or organic amendments is needed to increase biomass
yields on sloping fields.
Acidic and Saline Soils
Some WSGs can grow in acid soils with pH as low as 3.5.
In Maryland, the eastern gamagrass cultivar Pete produced
5.289 Mg ha−1 of biomass across 3 yr in an acid soil with pH
between 4.3 and 4.4 (Krizek et al., 2003). In the southern Great
Plains, both Kanlow and Blackwell switchgrass had similar tolerance to acid soils (pH 3.9–5.0; Hopkins and Taliaferro, 1997).
The application of amendments to acid soils can increase biomass production. For example, coal-combustion byproducts can
be an effective amendment to manage and reclaim acid minesoils. In Ohio, the addition of flue gas desulfurization product at
280 Mg ha−1 to a minesoil increased the pH from 3.1 to about
7 in the upper 20 cm of soil and allowed the growth of grass–
legume mixtures in the reclaimed minesoil (Chen et al., 2013).
Some saline soils (pH <8.5, electrical conductivity [EC]
>4 dS m−1) can also support the production of cellulosic feedstocks for biofuel. While highly saline soils reduce seedling
emergence and biomass production, moderately saline soils can
support the growth of WSGs. One of the main causes of soil salinization is evaporation, which leaves salts on the soil surface.
850
Growing WSGs can provide permanent soil cover and develop
deep roots to use water, thereby reducing evaporation rates and
the capillary rise of salts. In the northern Great Plains, Schmer et
al. (2012) evaluated big bluestem, Indiangrass [Sorghastrum nutans (L.) Nash], prairie cordgrass (Spartina pectinate Link), and
switchgrass at EC values of 0, 4, 8, 12, 16, and 20 dS m−1 and reported that big bluestem had the highest germination rates under
increased salinity levels. Similarly, Anderson et al. (2015) found
that switchgrass produced more biomass than prairie cordgrass
populations under moderately saline (5 dS m−1) irrigation water,
but differences with highly saline water (10 dS m−1) were not significant. Perennial WSGs can be moderately tolerant to salinity,
depending on the species and cultivar. In general, perennial grasses
can perform well under EC values below 10 dS m−1 and soil pH
below 8.5. In North China, Zhuo et al. (2015), in a greenhouse
pot experiment of switchgrass cultivars (Cave-in-Rock, Blackwell,
and Sunburst), reported that tolerance to salts varied among the
cultivars and were in this order: Cave-in-Rock > Blackwell >
Sunburst. All cultivars performed well at £2 g NaCl kg−1, but
yields decreased at higher salt concentrations.
Contaminated Soils
Perennial WSGs can grow on moderately contaminated
soils. Restoring contaminated soils with conventional techniques
using physical, thermal, and chemical treatments as well as excavation, transport, and landfills can be costly. As a result, growing
WSGs as biofuel feedstock can be a cost-effective and ecological strategy for in situ reclamation of partly contaminated soils.
Recent reviews have indicated that miscanthus is a potential grass
species for both producing biomass and removing trace elements
(i.e., metals), petroleum hydrocarbons, and other contaminants
through phytoremediation processes (Nsanganwimana et al.,
2014; Pidlisnyuk et al., 2014). Perennial grasses can be tolerant
to metal phytotoxicity. Entry et al. (1999) reported that switchgrass, bahiagrass (Paspalum notatum Flueggé), and Johnsongrass
[Sorghum halepense (L.) Pers.] inoculated with mycorrhizal
fungi accumulated significant amounts of 137Ce and 90Sr from
the soil without a reduction in biomass production, suggesting
that these grass species can be used to reclaim soils contaminated
with radionuclides. At former mining sites with the presence of
Pb and Zn in southeastern Kansas, northeastern Oklahoma, and
southwestern Missouri, the growth of big bluestem and switchgrass between mined and unmined sites did not differ (Levy et
al., 1999).
Warm-season grasses can reduce the transport of pollutants from contaminated sites by various mechanisms: (i) deeprooted WSGs can sequester pollutants, reduce leaching of
metals, and keep pollutants from reaching food crops; (ii) harvesting of WSG biomass can remove some of the contaminants
from the soil; and (iii) WSGs can reduce the transport of pollutants by accumulating soil organic matter in the long term.
The increased soil organic matter filters and degrades organic
contaminants in the soils relative to row crops. Pidlisnyuk et
al. (2014) discussed that miscanthus (Miscanthus saccharifloSoil Science Society of America Journal
rus M.) can contribute to the reclamation of contaminated
land through five phytoremediation processes: immobilization, stabilization, extraction, volatilization, and degradation.
Trace elements or heavy metals (e.g., Cd, Zn, Pb, As, Se, and
Cu) can be phytoremediated through stabilization, while organic contaminants can be phytoremediated through degradation. Growing perennials in contaminated soil may also improve belowground biodiversity and faunal abundance and increase the numbers of earthworms, arthropods, and microbes
(Chauvat et al., 2014). Warm-season grasses on contaminated
soils not only produce biomass but can also restore soil and environmental quality. While high concentrations of heavy metals may adversely affect plant growth and biomass conversion
processes, low levels of metal contamination have small or no
adverse effects on WSG performance.
Sandy Soils
Precipitation or irrigation water can be an important factor for the successful establishment and growth of energy crops
in sandy soils due to the low water holding capacity of these
soils. Sandy soils in water-limited regions can produce lower
biomass yields than those in regions with abundant precipitation. For example, on low-productive sandy soils in southeastern England, the biomass yield of switchgrass with N fertilization was <4 Mg ha−1 due to the limited precipitation during
the study years (Shield et al., 2012). However, on a sandy loam
in a Mediterranean climate in central Italy, Di Nasso et al.
(2015) found that Alamo switchgrass yield under high precipitation and appropriate N fertilization was much higher than
the 4 Mg ha−1 reported by Shield et al. (2012), suggesting that
sandy soils may not be considered marginal in regions with
abundant precipitation.
The performance of WSG species can vary with soil textural classes. In regions with low precipitation, switchgrass
yield can be higher on fine-textured soils than coarse-textured
soils due to the higher water holding capacity of soils with a
high clay content. Sandy soils will require more frequent irrigation or rainfall events than clayey soils to produce a similar
amount of biomass. Evers and Parsons (2003) estimated that,
on sandy soils, rainfall should occur every 10 d for optimum
switchgrass establishment. Achieving a good soil–seed contact
through appropriate packing of the soil can be critical for facilitating water and nutrient uptake for the establishment of
WSGs on sandy soils. In a 2-yr study on a fine sandy loam in
Massachusetts, Sadeghpour et al. (2015) suggested that the use
of a cultipacker can be an alternative to the use of a roller to
improve switchgrass seed–soil contact and biomass production on sandy loam soils. With abundant water inputs, WSG
biomass yield on coarse-textured soils can be similar to that on
fine-textured soils (Di Nasso et al., 2015).
Drought-Prone Soils
Switchgrass is one of the WSG species that has been tested
under different drought stress conditions. Studies have shown
www.soils.org/publications/sssaj
that biomass yields can be reduced in years with below-average precipitation under rainfed conditions. In western North
Dakota, Berdahl et al. (2005) reported that Sunburst switchgrass
biomass yield was 3.20 Mg ha−1 in a drought year and 12.48 Mg
ha−1 in a year with above-average precipitation. They concluded
that biomass yields among switchgrass cultivars can fluctuate
significantly due to the differences in precipitation and plantavailable water. Severe droughts particularly can have a negative
effect on switchgrass biomass production (Barney et al., 2009).
Full irrigation can be required to maintain biomass yields in water-limited environments. Vamvuka et al. (2010) reported that
switchgrass biomass yields decreased as irrigation rates decreased.
In central Texas, Stroup et al. (2003) tested two lowland, Alamo
and Kanlow, and two upland, Blackwell and Caddo, cultivars of
switchgrass for their response to water deficit and reported that
Alamo appeared to be the best cultivar for biomass production
under drought and non-drought conditions in the study region.
Switchgrass is often considered a candidate for drought-prone
marginal lands owing to its relative resistance to drought. These
few studies suggest, however, that severe droughts or frequent
dry years can reduce switchgrass biomass yield.
Urban Marginal Soils
Marginal lands in urban areas such as vacant lots are also
being considered as potential sites for cellulosic biomass production for biofuel (Saha and Eckelman, 2015). Growing perennial
WSGs or SRWCs on urban marginal lands could contribute to
energy production while improving urban aesthetics, environmental quality, and economic development. It can be a strategy
to better manage vacant lots or areas while generating potential
ecosystem services. However, urban soils are often highly disturbed systems through mixing and burial during construction,
demolition activities, and landfilling. As a result, urban soils can
be shallow and compacted, with low organic matter and high
clay content. Some urban sites can be partially contaminated or
located near contaminated areas, which can require site-specific
management strategies.
Recent estimates indicate that urban marginal lands can
produce significant amounts of biomass as biofuel feedstock.
For example, in Boston, MA, Saha and Eckelman (2015), using
ArcGIS, estimated that about 2660 ha of urban marginal land
including vacant lots and underutilized areas can be suitable for
the production of short-rotation poplar. In Pittsburgh, Zhao et
al. (2014) found that urban marginal lots with a size above 0.2 ha
with low levels of concentrations of heavy metals such as Al, Fe,
Zn, Ni, Pb, As, Cd, Cr, and Se in the soil can be safely used for
biofuel biomass production.
Brownfields in former industrial or commercial sites
are also being considered for biofuel feedstock production.
Perennial grasses have been used for phytoremediation of
brownfield sites, but growing perennials for biofuel at these
sites has not been documented. The few emerging studies
suggest that the biomass production potential of brownfields
should be considered on a site-by-site basis. In northeastern
851
England, Lord (2015) studied brownfield sites to grow willow,
miscanthus, reed canarygrass, and switchgrass amended with
green-waste compost and found that reed canarygrass yielded
from 4 to 7 Mg ha−1, which was greater than willow or miscanthus yields, suggesting that, in some brownfields, cool-season
grasses may yield more than WSGs. Smith et al. (2013) compared the quality of switchgrass biomass with that of soybean
[Glycine max (L.) Merr.], canola (Brassica napus L. var. napus),
and sunflower (Helianthus annuus L.) on a brownfield site and
cropland in Michigan and found that brownfields can produce
suitable biomass similar to agricultural lands. Overall, urban
marginal sites have the potential to produce biofuel feedstock
under proper management (i.e., fertilization and irrigation).
Abandoned or Degraded Croplands
A number of the marginal lands discussed above (i.e., CRP
lands, compaction-prone soils, flood-prone soils, and acid or saline soils) are degraded or abandoned croplands. The degraded
croplands are defined as areas of low productivity relative to
prime croplands. Some degraded lands are found within the existing productive croplands. Most existing croplands have some
low-yielding areas, which often exhibit physical and chemical
problems such as compaction, susceptibility to flooding, erosion,
and acidity or salinity, among others. These partially degraded
areas are often classified as marginally productive croplands and,
in addition to the abandoned croplands, could be suitable for
growing perennial WSGs or SRWCs under proper management.
The inclusion of patches of perennials in degraded portions
of existing croplands would create a multifunctional mosaic of
perennial crops and food crops, contributing to the overall agricultural landscape diversification. Growing WSGs or SRWCs
on degraded or marginal spots in a field can contribute not only
to biofuel feedstock production but also to enhanced ecosystem
services including improved wildlife habitat and diversity, soil C
sequestration, and soil and water quality. Expansion of croplands
in recent decades has significantly reduced ecosystem services.
Thus, returning portions (marginally productive areas) of these
lands to perennial vegetation, which is similar to the original
condition, can enhance both soil services and resilience of the
agricultural systems.
This potential strategy must be considered during a time
when enhancing productivity and resilience of agroecosystems is
increasingly important. Recently, Brandes et al. (2016) proposed
a framework to evaluate the profitability of marginal or degraded
areas within croplands and reported that the inclusion of perennials in these areas can increase the overall profitability by 80%.
It is important to further review and estimate the areal extent of
marginally productive or degraded croplands on a global scale
along the lines suggested by Gibbs and Salmon (2015). Also,
more research is needed on the biomass production potential
and generation of ancillary ecosystem services from marginally productive croplands under different conditions. Growing
perennial WSGs and SRWCs in marginally productive patches
of croplands and growing food crops in highly productive areas
852
of the croplands can enhance the heterogeneity and thus the
multifunctionality of agricultural landscapes. Further strategic
research, assessment of feasibility, and development of energy
policies are needed to address the synergies and challenges of the
association of food production with dedicated energy crop production as well as the delivery of ecosystem services (Manning
et al., 2015).
Energy Crops on Marginal Lands
and Ecosystem Services
Growing perennial WSGs and SRWCs on marginal or
degraded lands can provide a number of ecosystems services including biomass production, erosion control, C sequestration,
improvement of soil biodiversity and water quality, and others,
but experimental data on such ecosystem services, at this point,
particularly for SRWCs, are limited (Tables 1–3). The few field
studies indicate that growing dedicated energy crops on marginal
lands can have beneficial effects on ecosystem services (Tables
1–3). Establishing perennial WSGs or SRWCs on marginal sites
could be a strategy to enhance the potential of marginal lands to
provide ecosystem services.
Biomass Yield
A literature review indicated that biomass production on
marginal lands is highly variable, depending on the type of marginal site, management (e.g., fertilization), and vegetation species.
In general, biomass yields could vary between 1 and 14 Mg ha−1
for WSGs (Table 1) and between 0.5 and 9.5 Mg ha−1 for
SRWCs (Table 2). While field data on biomass production from
different types of marginal lands are few (Tables 1 and 2), the
following conclusions can be drawn:
• Intensively managed marginal lands with the addition
of fertilizers and organic amendments can produce
more biomass than those without intensive management (Table 1).
• Marginal lands can, in general, produce >5 Mg ha−1
of energy crop biomass if fertilizers or organic amendments are used (Table 1). Some studies have suggested
that WSG biomass yield on marginal sites should be at
least 5 Mg ha−1 to be profitable (Marra et al., 2013).
Biomass production on marginal lands can be lower
than on prime agricultural lands.
• Biomass yields for WSGs and SRWCs appear to be lowest on reclaimed minesoils with no amendments, which
may be due to the drastic disturbance and alteration of
the soil profile during mining operations.
• Flood-prone marginal lands (lowlands susceptible to occasional flooding) appear to support greater WSG biomass production than other marginal lands (Table 1).
• Switchgrass appears to perform better than other WSG
species on most marginal lands.
• Biomass yields for different types of marginal sites
should be assessed on a crop-specific basis.
Soil Science Society of America Journal
www.soils.org/publications/sssaj
853
Buffalo, OK
Milan, TN
Poorly drained floodplain
eastern gama grass
3
3
3
4
Time after
planting
yr
5
6.29§
2.59¶
170–391–743 kg ha−1 N–P–K
switchgrass as conservation buffer
switchgrass, big bluestem, and
miscanthus
Energy crop
Impact
Water erosion control
6
reduced runoff and soil loss by ?53% compared with no buffer
yr
Wind erosion control
5
reduced the soil’s susceptibility to wind erosion compared with row
crops
Time after
planting
Gilley et al. (2000)
Evers et al. (2013)
Reference
Krizek et al. (2003)
Mooney et al. (2009)
Venuto and Daniel (2010)
Marra et al. (2013)
Evers et al. (2013)
Reference
Pierrelaye, France
black locust
miscanthus and switchgrass
2, 3, 4, and 14
increased soil microbial biomass C and N (0–30-cm soil depth)
Soil biology and biodiversity
3
increased faunal diversity and abundance (Collembola) compared
with wheat
Matos et al. (2012)
Chauvat et al. (2014)
Soil C sequestration
Lincoln, NE
switchgrass as conservation buffer
15
0.85 Mg C ha−1 yr−1 compared with row crops (0–15-cm soil depth) Blanco-Canqui et al. (2014)
China
miscanthus
3
0.46 Mg C ha−1 yr−1
Mi et al. (2014)
northeastern Germany
black locust
2, 3, 4, and 14
4.0 Mg C ha−1 yr−1 (0–30-cm soil depth)
Matos et al. (2012)
Moody County, SD
switchgrass
4
Lee et al. (2007)
2.46 ± 0.9 Mg C ha−1 with inorganic fertilization
and 4.06 ± 1.0 Mg C ha−1 with manure (0–90-cm soil depth)
Kucharik et al. (2003)
Dane County, WI
mixed grasses–forbs and switchgrass
>8
0.25 Mg C ha−1 yr−1 (0–5-cm soil depth)
Council Bluffs, IA
Manhattan, KS
Location
Reclaimed minesoil
northeastern Germany
† CRP, Conservation Reserve Program.
Contaminated agricultural
land
CRP land (1–20% slope)
Heavily eroded
Reclaimed minesoil
Erodible land (i.e., CRP†)
Sloping cropland (5.4%)
Sloping cropland (8–16%)
Flood-prone cropland
Type of marginal land
Biomass
produced
Mg ha−1 yr−1
10.9†
10.9
13.8
0.8
5.76
3.8
1.9
0, 67, 134, and 202 kg N ha−1
none
sewage sludge (225 Mg [dry] ha−1)
none
45 kg N ha−1
Fertilization or amendment
Table 3. The few studies reporting soil ecosystem services of dedicated energy crops grown on different types of marginal lands.
Acid, compact, and sloping soils
Beltsville, MD
† Biomass yield corresponds to biomass harvested in the fifth year.
‡ Conservation Reserve Program (CRP) lands.
§ Averaged across the 3 yr and N fertilization rates.
¶ Averaged across all harvests throughout the study.
Old World bluestem
mixture of native grasses
West Virginia
Reclaimed minesoil 1 yr prior to this study
Reclaimed minesoil 10 yr prior to this study
Highly erodible lands‡
switchgrass
switchgrass
big bluestem
miscanthus
switchgrass
Warm-season grass
Manhattan, KS
Location
Flood-prone cropland
Type of marginal land
Table 2. Biomass yield of perennial warm-season grasses grown on some marginal lands.
Water Erosion and Water Quality
Soil Carbon Sequestration
Growing WSGs on marginal lands such as sloping fields
can provide a vital ecosystem service including the reduction of
water erosion and improvement in water quality (Table 3). The
establishment of WSGs on sloping marginal lands can reduce
runoff and losses of sediment and sediment-associated nutrients, although field data under different scenarios of energy crop
management are limited. Perennial WSGs can reduce the risks of
water erosion by providing a protective cover and by improving
soil properties.
Shorter cutting heights during harvesting of WSGs can
reduce the protective cover and increase the risks of water erosion on erodible lands. In Illinois, under low-intensity storms,
biomass removal to the 10-cm height from switchgrass, big
bluestem, smooth bromegrass (Bromus inermis Leyss), and corn
plots on erodible lands (i.e., CRP lands) increased runoff and
the loss of sediment by 15%, but runoff and the loss of sediment
were the least under grasses and greatest under corn (Wilson et
al., 2011). Grass cutting heights, harvest frequency, grass species
selection, soil slope, and climate warrant further evaluation for
sustainable biomass production and the reduction of water erosion on erodible lands.
Warm-season grasses can improve soil properties, thereby
reducing the susceptibility of the soil to water erosion. Perennial
grasses, through their deep roots, increase soil aggregate stability
and macroporosity in the soil profile. Soils with stable aggregates
are more porous and resistant to detachment than soils with
weak aggregates. The increased macroporosity can increase water
infiltration and thus reduce runoff. The increased soil aggregate
stability and porosity under WSGs is positively correlated with
increased total soil organic C concentration (Blanco-Canqui et
al., 2014).
The few studies assessing soil C sequestration under WSGs
on marginal sites have indicated that WSGs can sequester C, but
the rates are variable. The limited data in Table 3 show that perennial WSGs can sequester between 0.25 and 4 Mg ha−1 yr−1
of C in the soil. Similar to the effects on biomass production,
factors that affect C sequestration include the type of marginal
land, the type of land transition, management, climate, and others. For example, WSGs on former CRP lands can sequester as
much as 4 Mg ha−1 of C in the soil if large amounts of animal
manure are added (Table 3). It is important to consider that C
added with manure may be partly responsible for the high C accumulation under WSGs on marginal lands. Perennial WSGs
without fertilizers or organic amendments may not sequester
more than 1 Mg ha−1 of soil C per year (Blanco-Canqui et al.,
2014). Data on C sequestration potential under SRWCs are very
limited, but the study by Matos et al. (2012) suggested that a
black locust SRWC can sequester as much as 4 Mg ha−1 of soil C
on reclaimed minesoils.
Even when aboveground biomass is harvested, perennial
grasses can still sequester significant amounts of C through their
increased root biomass input. Additional research is needed,
however, to quantify the extent to which frequent aboveground
biomass removals of energy crops can reduce C sequestration
on marginal lands in the long term. In pasturelands, some studies have found that frequent aboveground biomass removal can
reduce soil C sequestration by reducing root biomass growth
(Skinner, 2008). When the aboveground biomass is completely
removed, the main mechanism for C sequestration under energy
crops can be the root biomass accumulation. The recommendation is, however, to harvest WSGs to about the 10-cm height,
which would still leave a significant amount of aboveground
biomass to contribute to C sequestration. It is also well recognized that perennial grasses can develop deep roots in the long
term, which can contribute to C sequestration at deeper soil
depths. Soil C accumulation under perennial WSGs also improves soil physical properties and microbial biomass and activity, further enhancing soil ecosystem services (Table 3; Bach and
Hofmockel, 2015).
It is important to briefly review how soil C is sequestered
or protected in the soil. The main mechanism for organic C sequestration in the soil is the occlusion of organic C inside the
soil microaggregates (Six et al., 2002; Denef et al., 2004; BlancoCanqui and Lal, 2004). The young or labile organic C is often
found within macroaggregates, whereas stable organic C is found
within microaggregates (Blanco-Canqui et al., 2004). Organic
C associated with macroaggregates can be more susceptible to
rapid turnover and less protected than that associated with microaggregates. Thus, the microaggregate-associated C under perennials can be crucial for the protection and sequestration of C
in the soil (Denef et al., 2004; Blanco-Canqui and Lal, 2004).
The extent to which perennial WSGs and SRWCs will
accumulate C in the soil following a land use change will depend not only on the type of marginal land and type of land
Wind Erosion
The potential of perennial vegetation to reduce wind erosion such as on CRP lands is well recognized. Successful establishment of WSGs on wind-erosion-prone soils can reduce wind
erosion risks (Fig. 3, bottom). In eastern Kansas, on a flood-prone
soil, WSGs reduced the wind-erodible fraction and increased
dry soil aggregate stability compared with row crops when
WSGs were cut to about 10-cm height on an annual basis (Table
1). Perennial WSGs can stabilize degraded soils and reduce wind
erosion through their deep, fibrous, and extensive root network.
Perennial WSGs with uniform and permanent surface soil cover
can intercept and buffer the erosive forces of the wind. On some
marginal lands, such as in water-limited regions, the potential
of WSGs to reduce wind erosion could be limited, however,
due to reduced biomass production, particularly in the first few
years. An appropriate cutting height (>10 cm) for energy crops
can provide a permanent surface cover to protect the soil from
wind erosion. Similar to water erosion control, more research is
needed to evaluate how different cutting heights and cutting frequencies can affect WSG performance for reducing wind erosion
on marginal lands.
854
Soil Science Society of America Journal
transition but also on the initial soil C concentration. Soils
with low initial C levels (Matos et al., 2012) can more rapidly
accumulate C after the establishment of perennials compared
with those with high initial C levels (Evers et al., 2013). For
example, as discussed above, highly disturbed soils such as minesoils can sequester C in the soil at high rates (Matos et al.,
2012). Regarding the type of land transition, Qin et al. (2016)
reported that cropland conversion to energy crops resulted in a
6 to 14% increase in the soil C concentration, while conversion
from grassland or forest to switchgrass, miscanthus, or willow
did not increase soil C levels. The rates of soil accumulation
can also vary with time following a land use change. Soil C sequestration rates under energy crops can be high in the first
10 yr and not significant at about 20 yr following land conversion (Qin et al., 2016). The large differences in both soil C sequestration rates among the different marginal lands (Table 3)
and land use change scenarios warrant more research to better
understand the changes in soil C induced by energy crops for
different marginal land types and land use transitions.
Wildlife Habitat
Growing WSGs on marginal lands can also provide other
ecosystem services such as improved wildlife habitat, pollinator
conservation, and pest and weed control. Bennett et al. (2014)
estimated that the conversion of annual crops on marginal soil
to perennial grasses increased bee abundance from 0 to 600%
and bee diversity between 0 and 53% across 20 soybean fields
in southern Michigan. Perennial grasses can also increase
bird abundance and richness as well as arthropod biomass
(Robertson et al., 2011; Cox et al., 2014). Birds often prefer heterogeneous landscapes with WSGs or tallgrass prairie relative
to cool-season and sparse vegetation. Werling et al. (2014) assessed biodiversity across 115 corn, switchgrass, and prairie systems in Michigan and Wisconsin and reported that switchgrass
and prairie plantings had greater plant, methanotrophic bacteria, arthropod, and bird diversity than cornfields. Increasing
landscape heterogeneity on marginal lands can be important to
improve wildlife habitat and diversity. Maintaining unharvested areas of WSGs (i.e., buffers) can be critical for bird nesting
and permanent habitat for wildlife. Mixtures or polycultures
of perennial WSGs can enhance wildlife habitat and diversity
as well as other ecosystem services more than monocultures
due to differences in composition, structure, and canopy cover
among plant species (Werling et al., 2014). Perennial grasses
can also be grown in rotation with SRWCs to create different
canopy heights and structure to further promote wildlife habitat and communities (Hartman et al., 2011).
Also, as indicated above, increasing the heterogeneity of
agricultural landscapes by growing perennials on marginally productive areas and food crops on highly productive areas of croplands can also benefit wildlife habitat and diversity. Growing
perennials on marginally productive croplands could be a strategy to potentially restore some of the lost wildlife community
and diversity due to intensive food cropping. Haughton et al.
www.soils.org/publications/sssaj
(2015), using large biodiversity data sets at the landscape level,
reported that miscanthus and willow had a higher abundance
of invertebrates and more complex invertebrate and plant communities relative to annual food crops, corroborating that perennial WSGs and SRWCs can enhance biodiversity. Establishing
a balanced alliance of perennials and food crops in the existing
agricultural landscapes will be critical to achieve both renewable
energy security as well as food security.
CHALLENGES AND OPPORTUNITIES
Growing dedicated energy crops on marginal lands offers
a potential opportunity to produce biofuel feedstocks and enhance ecosystem services. The few available studies have strongly
indicated that perennial vegetation can improve ecosystem services (Tables 1–3). Challenges still exist, however, for the largescale production of cellulosic biomass on marginal sites. For
example, marginal lands can produce cellulosic biomass while
improving the soil, the environment, and biodiversity, but the
economic and social implications warrant further comprehensive analysis. Producing perennial grasses on marginal lands may
not be profitable in some cases, especially under low biomass
production, unless other ecosystem services are valued and included in the economic analysis and proper incentives assigned.
Some have argued that marginal lands are marginal for a reason,
thereby generating marginal biomass yields or profits due to their
low productivity and adverse soil conditions.
Interactions among management, time after establishment,
type of marginal land, and climate will determine the performance of dedicated energy crops and their ecosystem benefits
on marginal lands. First, management will dictate their performance. Producing biomass will require fertilization, the addition
of amendments, possibly irrigation in water-limited regions, and
other inputs. If substantial inputs are used to produce biomass in
marginal environments, dedicated energy crops may not be lowinput systems. Second, the length of time after establishment
will determine the degree to which ecosystem services such as
soil erosion control, soil organic C accumulation, and biodiversity will change. Changes in soil C stocks, for example, are not
significant in the first few years after establishment depending
on the initial soil C levels (Evers et al., 2013; Schmer et al., 2012).
Third, marginal soils with low initial soil C (e.g., reclaimed minesoils) may more rapidly accumulate C by growing WSGs than
marginal soils with relatively high initial soil C levels.
Site-specific management strategies and guidelines for
feedstock production from energy crops on marginal lands are
needed. There is also a need to examine the tradeoff between
production costs of dedicated bioenergy crops on marginal lands
and the implications for ecosystem services. Biofuel production
from WSGs and SRWCs is still under development, and growing profitable energy crops may not be currently attractive for
some producers in some cases. However, the ecosystem services
(i.e., soil conservation, C sequestration, environmental quality,
and biodiversity) provided by WSGs can be incentives to establish WSGs on marginal lands.
855
RESEARCH NEEDS
The research needs for the production of biofuel feedstocks
on marginal lands include:
1. A need exists to better identify, locate, and classify marginal lands, quantify their extent, and determine their
potential for growing dedicated energy crops. Not all
marginal sites may produce economically viable energy
crops. A framework similar to that proposed by Gopalakrishnan et al. (2011) using multiple criteria (i.e., soil
health indicators) should be considered to better define
and classify marginal lands.
2. More field research data on the biomass yields of dedicated energy crops on different types of marginal lands
are needed. The few available studies have indicated
that energy crop biomass yields can vary with the type
of marginal land. Field data can also be useful for the
calibration and validation of models to estimate the
potential of marginal lands for producing biomass and
supporting related ecosystem services (Qin et al., 2015).
At present, the limited experimental data availability
limits the ability of models to accurately estimate biomass production potential for different marginal lands
at regional and global scales.
3. The few field studies have mostly focused on biomass
production and have not simultaneously quantified
the associated ecosystem services that dedicated energy
crops can provide including soil erosion control, C
sequestration, greenhouse gas flux mitigation, wildlife
habitat, water quality, and other services. More comprehensive studies assessing both biomass production and
related ecosystem services is needed for different scenarios of energy crop management under different types
of marginal lands and land use transitions.
4. Questions also remain about how biomass harvesting
from dedicated energy crop plantations will affect wildlife habitat and diversity. While it is well recognized
that native perennial grass vegetation can enhance the
wildlife environment, little is known about how wildlife
habitat and diversity respond to dedicated energy crops
grown for biofuel production in which aboveground
biomass is removed once or twice a year. Managed plantations of dedicated energy crops with biomass harvested could differ in their benefits for wildlife habitat and
diversity compared with perennials without biomass
harvesting.
5. It is also important to compare the effects of biomass
removal from dedicated energy crops on soil properties
with those of crop residue removal such as corn residues
for biofuel. Perennial vegetation provides abundant
aboveground and belowground biomass, but removal of
the aboveground biomass removes C, which may reduce
the ecosystem services provided by perennial vegetation
on marginal lands.
6. More research on developing herbaceous and woody
species with genetic characteristics tolerant to pro-
856
longed and frequent drought, flooding events, salinity,
acidity, and other adverse climatic, soil, and environmental conditions is needed (Xie et al., 2014).
7. Comprehensive cost–benefit analysis of dedicated energy crops grown on different types of marginal lands is
warranted to discern the financial viability. Some marginal sites may produce marginal yields, which requires
an objective analysis of production costs.
8. More studies on the rates of fertilizers and organic
amendments are needed to provide recommendations
for growing dedicated energy crops on different types
of marginal lands. Additional amendments such as
biochar (a C-rich material resulting from the pyrolysis
of biomass), flue gas desulfurization gypsum, and other
emerging industrial byproducts should also be studied
to increase biomass production on marginal lands.
CONCLUSION
A number of marginal or degraded lands have been tested
to assess their potential for the production of dedicated energy crops. Some of these lands include erodible lands (i.e.,
CRP lands), compaction-prone soils, flood-prone soils, sloping and acid soils, contaminated soils, reclaimed minesoils,
urban marginal sites, and abandoned or degraded croplands.
Experimental data on biomass yields and other ecosystem services from the different marginal lands are, however, few. These
few studies have indicated that growing dedicated energy crops
on marginal sites can, in general, provide a number of ecosystem services including biomass production, soil water and wind
erosion control, soil C sequestration, absorption or retention
of pollutants or metals, stabilization or reclamation of minesoils, and improvement in soil properties, among others. The
amount of biomass produced and ancillary soil and environmental benefits vary with the type of marginal land as well as
management. The addition of inorganic fertilizers or organic
amendments (i.e., animal manure) is needed to increase biomass production and soil C accumulation on marginal lands.
Further assessment of biomass production and other ecosystem services as well as the economic and social implications
of growing energy crops on marginal lands is warranted to
develop both field- and region-specific management strategies
for the sustainable production of bioenergy crops as well as the
development of bioenergy production facilities and policies.
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