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The Emissions Gap Report 2013 from the United Nations Environment Programme restates the claim that changing to no-till practices in agriculture, as an alternative to conventional tillage, causes an accumulation of organic carbon in soil, thus mitigating climate change through carbon sequestration. But these claims ignore a large body of experimental evidence showing that the quantity of additional organic carbon in soil under no-till is relatively small: in large part apparent increases result from an altered depth distribution. The larger concentration near the surface in no-till is generally beneficial for soil properties that often, though not always, translate into improved crop growth. In many regions where no-till is practised it is common for soil to be cultivated conventionally every few years for a range of agronomic reasons, so any soil carbon benefit is then lost. We argue that no-till is beneficial for soil quality and adaptation of agriculture to climate change, but its role in mitigation is widely overstated.
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The recent Emissions Gap Report 20131 makes bold statements
about agricultures potential to reduce greenhouse gas
(GHG) emissions. e authors of the chapter on ‘Policies
for Reducing Emissions from Agriculture’ estimate that at a mar-
ginal cost of less than US$50–100 per tonne of CO2 equivalent
(CO2e), direct emissions from agriculture could be reduced by 1.1
to 4.3GtCO2eyr−1 by 2020. ey claim that 89% of this poten-
tial could be realized through improved management practices
including conversion to no-tillage land preparation (Box 1), more
ecient use of water and fertilizers and addition of biochar to soil.
Optimistic assessment
Overall the United Nations Environment Programme (UNEP)
report1 is helpful: it demonstrates that current global eorts to
decrease emissions are far below what is necessary to avoid dan-
gerous climate change2 and it attempts to quantify opportuni-
ties for further reductions in dierent sectors. However, we have
substantial concerns that the report overstates the potential for
climate change mitigation in agriculture due to over-optimistic
assumptions concerning the impact of no-till practices (Box 1
and Fig. 1).
ere is abundant published evidence that no-till is benecial
for the functioning and quality of soil (Table 1) in many, though
not all, situations3–5. e soil conditions developed oer potential
for improved crop growth and increased resilience to weather
variability and likely impacts of climate change, so in some envi-
ronments can be regarded as a contribution to climate change
adaptation. But published data on the magnitude of climate
change mitigation from no-till through sequestration of organic
carbon (C) in soil is much more equivocal, so the UNEP report1
gives a false message of optimism regarding the ability of human-
ity to combat climate change by reducing GHG emissions from
Limited potential of no-till agriculture for climate
change mitigation
David S. Powlson1*, Clare M. Stirling2, M. L. Jat3, Bruno G. Gerard2, Cheryl A. Palm4, Pedro A. Sanchez4
and Kenneth G. Cassman5
The Emissions Gap Report 2013 from the United Nations Environment Programme restates the claim that changing to
no-till practices in agriculture, as an alternative to conventional tillage, causes an accumulation of organic carbon in soil,
thus mitigating climate change through carbon sequestration. But these claims ignore a large body of experimental evidence
showing that the quantity of additional organic carbon in soil under no-till is relatively small: in large part apparent increases
result from an altered depth distribution. The larger concentration near the surface in no-till is generally beneficial for soil
properties that often, though not always, translate into improved crop growth. In many regions where no-till is practised it is
common for soil to be cultivated conventionally every few years for a range of agronomic reasons, so any soil carbon benefit
is then lost. We argue that no-till is beneficial for soil quality and adaptation of agriculture to climate change, but its role in
mitigation is widely overstated.
agriculture. If, as we maintain, the contribution through promot-
ing no-till practices is substantially less than claimed, there is even
more pressure to deliver mitigation through other approaches —
both in agriculture and in other sectors.
Soil carbon stocks and climate change
Organic matter in the world’s soils represents a major stock of organic
C, storing about 1,500GtC (equivalent to 5,500GtCO2) to a depth
of 1m and a further 900GtC in the next 1m (refs 6,7). Organic C in
the surface 1m alone is three times the amount of C in atmospheric
CO2. Land-use changes — especially clearing of natural vegetation
to expand the area used for crop production — have signicantly
depleted global soil C stocks and contributed to increased CO2 emis-
sions8,9. It is therefore entirely appropriate to consider opportunities
to slow or reverse this trend through land-management practices.
It has been estimated that a 10% increase in the global soil C stock
would cancel out 30years of anthropogenic CO2 emissions6,7. But
there are numerous reasons to be cautious about the potential
for sequestering C in this way, including misunderstanding of C
ows10,11, limitations to the area of land that can be removed from
agriculture12 and the likelihood that organic C in soil will be sub-
ject to more rapid decomposition at elevated temperatures resulting
from climate change7,13.
Evidence from experiments and modelling
Several widely cited publications have alluded to the potential of
reduced tillage to increase soil organic matter, sequester C, and so
contribute to climate change mitigation14–16. ere is certainly evi-
dence that these practices oen lead to some increase in organic
matter (and hence C) concentration in the 15–20cm layer of top-
soil17 and this has positive benets such as reduced soil erosion
and improved physical properties that increase the extent to which
1Department of Sustainable Soils & Grassland Systems, Rothamsted Research, Harpenden, Hertfordshire AL5 2JQ, UK, 2International Maize and
Wheat Improvement Center, Conservation Agriculture Program, Apdo, Postal 6-641 06600 Mexico, Distrito Federal, Mexico, 3International Maize and
Wheat Improvement Center, India Oce, National Agricultural Science Centre Complex, Dev Prakash Shastri Marg, Pusa Campus, New Delhi 110012,
India, 4Agriculture and Food Security Center, The Earth Institute at Columbia University, 61 Route 9W, Lamont Hall, Palisades, New York 10964,
USA, 5Department of Agronomy and Horticulture, University of Nebraska-Lincoln, PO Box 830915, Lincoln, Nebraska 68583-0915, USA.
soil can absorb rainfall and hold water, making it available for later
crop use5,18–20. In some situations these soil improvements lead to
increased crop yields4,5. But the opposite has also been observed,
with decreased crop yields under no-till in cool moist climates21 and
in tropical environments, aer heavy rains, the surface crop residues
that accompany no-till in conservation agriculture can sometimes
cause waterlogging and reduce yields22.
So what is the evidence that soil organic carbon (SOC) stock
increases substantially under no-till and can be viewed as C seques-
tration and hence a contribution to climate change mitigation?
ere have been several global reviews6,17,23–25 with most of the
experimental evidence derived from the Americas and Australia
where no-till is widely practised on large, mechanized farms. A
key issue is that much, though not all, of the apparent increase in
SOC under no-till results from redistribution of C nearer to the
soil surface and is therefore not a net increase in SOC stock17,26–28.
A comparison of 69 sets of paired data for no-till and conventional
till, where soil had been sampled to at least 40cm depth, showed
no overall increase in SOC stock under no-till: larger stocks in the
surface 20cm compared with conventional tillage were counter-
acted by smaller quantities in the 20–40cm layer under no-till17.
is altered depth distribution is illustrated in Fig.2. In another
global meta-analysis23, SOC stock under conservation agricul-
ture (combination of no-till and residue return — see Box1) was
greater than in conventional practice in about half of the cases but
not dierent in 40%. Similarly, in a meta-analysis of experiments in
Mediterranean climatic conditions25 (mainly in the Mediterranean
basin), it was found that no-till led to small increases in SOC stock
of about 0.3–0.4 Mg C ha–1 yr–1. In an experiment in northern
France, one of the world’s longest-running and closely-monitored
experiments on tillage methods, no-till led to no increase in SOC
stock in 41 years29. us the optimistic assertion in the UNEP1
report, other claims or implications for major soil C gains through
no-till9,14,30,31 and in World Bank documents32 are at variance with
the conclusions from these detailed analyses of a large body of data.
A second issue results from confounding SOC mass versus
concentration. In many studies only the concentration of SOC
(expressed as % C or gCkg–1 soil) in specic soil layers is reported.
For assessing the potential for climate change mitigation through
C sequestration, it is necessary to express SOC as a mass or stock,
expressed in units such as MgCha–1 or GtC within a dened area.
is approach requires measurement of soil bulk density in addition
to SOC concentration, because bulk density is frequently altered by
a change to no-till: crop residues are not mixed in the topsoil layer
as occurs with ploughing or discing, so organic matter concentrates
near the soil surface. is can lead to decreased soil density in the
surface 5cm compared with conventional tillage but much of the
soil prole under no-till till almost invariably has increased bulk
density due to the absence of disturbance. ese trends are well
established33–35 but are oen ignored in published literature com-
paring the eects of tillage methods on soil carbon stocks. Even
when changes in bulk density are accounted for, the interplay of
changed soil bulk density and the strongly developed SOC concen-
tration gradient with depth under no-till leads to erroneous values
for SOC stock if tilled and no-till soil are sampled to equal depth36.
To obtain a valid comparison of SOC stocks, tilled and no-till soil
should be sampled on an ‘equal soil mass’ basis instead of ‘equal
soil depth34,37. Recently cited examples showed that an apparent
increase in SOC stock when calculated on an equal depth basis can
be decreased by 50% or eliminated completely if recalculated to an
equal soil mass basis37.
A third concern is that C sequestration in agricultural soil may
not be long term. To qualify as climate change mitigation long term
(more than 100years) or permanent removal of CO2 from the atmos-
phere is necessary. e extra carbon under no-till is predominantly
in labile forms that would certainly be decomposed if no-till prac-
tices ceased and a farmer reverted to conventional tillage38–40.
A more general limitation of climate change mitigation through
soil C sequestration is that the soil’s capacity to hold organic
No-till means reduced soil disturbance as an alternative to
traditional cultivation by ploughing or discing, in which the
soil is broken and then further cultivated to prepare a seedbed
for planting crops. In large-scale mechanized farms tillage
operations are performed with heavy machinery pulled by
tractor; in smallholder agriculture in less developed regions it
is generally achieved using a small animal-drawn implement, or
hand-held tools. Where conventional cultivation is eliminated
seeds are sown in a slot cut in the soil, causing minimum soil
disturbance. Large-scale tractor drawn no-till seeders are widely
used, but small-scale no-till seeders are increasingly available for
use with either animal traction or small tractors. In Subsaharan
Africa no till planting may also be achieved by making a hole
for individual seeds, such as those of maize, with a ‘dibble stick.
Although complete absence of tillage is called no-till or zero
till, reduced tillage or minimum tillage practices are also used
whereby there is an intermediate amount of soil disturbance.
No-till and reduced till sometimes form a component of a suite
of practices termed conservation agriculture (CA), comprising
retention of crop residues on the soil surface and diversication
of cropping systems in addition to reduced or no-till. Here we
specically address no-till agriculture rather than the complete
CA package because this was the focus of the UNEP report
with which we take issue, though in a few instances we refer
to published data for the full set of CA practices where this is
relevant or data is more readily available. For simplicity we use
the term ‘no-till’ throughout to include the range of reduced till
practices, from no-till to minimum till. e term ‘conservation
tillage’ is used by some authors but we avoid this as it can be
ambiguous, either meaning no-till/reduced till or, depending on
the context, it may refer to the no-till component of CA.
Box 1 | What is no-till?
Figure 1 | Mexican farmer practising no-till crop establishment.
Photograph shows use of a ‘swather’ to cut crop residues and distribute
them evenly over the surface of the undisturbed soil. Following this, seeds
will be sown using a no-till seeding machine that cuts a slot for seeds,
causing minimum disturbance of the soil.
C is nite. Soil organic carbon does not continue to increase
indenitely and annual rates of accumulation decline as the soil
approaches a new equilibrium, which can take from 25 to 100+
years depending on climate and soil type41–43. Hence, rapid rates
of SOC accumulation sometimes measured in the early years aer
a change in management, such as a shi to no-tillage, cannot be
extrapolated indenitely.
A new assessment but with many caveats
To assess the global potential for no-till practices to sequester
soil carbon and thus mitigate climate change we take a value of
0.3 Mg C ha–1 yr–1 as an annual carbon accumulation rate under
no-till, derived from the reviews cited above. We then apply this
accumulation rate to the global area under cereal crops as these are
the most likely systems where no-till can be practised. We exclude
land in the Americas and Australia because no-till is already widely
practised in these regions — where soils and climate are suitable —
so any climate change mitigation is already accruing. Applying the
value of 0.3MgCha–1yr–1 to the remaining global cereal crop area of
559Mha (ref. 44) gives an annual global rate of SOC accumulation
of 0.17GtC, equal to 0.6GtCO2e. If the calculation is restricted to
the areas under wheat, maize and rice (where no-till can be most
easily practised, though with limitations for rice) the gure becomes
Although these values for CO2 mitigation are smaller than
those proposed in the UNEP report1 (1.1 to 4.3GtCO2e yr–1 ) they
are of the same order so, supercially, could be taken as being in
moderate agreement. However, we consider our estimate of 0.4 to
0.6GtCO2eyr–1 to be highly optimistic for several reasons. First, the
annual rate of accumulation we have used for SOC under no-till is
probably too large. Although it approximates an average for those
situations where increases were measured, there were many cases
where the dierence in SOC stock between no-till and conventional
tillage was very small or zero6,17,23,24,26,27,45. Second, most of the reported
dierences will be overestimated due to the interplay of altered soil
bulk density and the SOC gradient with depth in no-till as discussed
above36,37. ird, in addition to the Americas and Australia, some
form of reduced tillage is already used in substantial areas of crop-
land on large mechanized farms in Europe and Asia, so part of the
‘potential’ SOC gain from no-till is already occurring and cannot be
counted as additional climate change mitigation. But there seems to
be considerable uncertainty about the area now under no-till in large
countries such as Russia, Kazakhstan, China and India46. Fourth, in
some regions, such as northwest Europe, periodic ploughing is com-
monly practised to control the perennial weeds and soil compaction
that are found to result from no-till in the soils and weather con-
ditions of this region42. Periodic tillage also occurs in regions with
wider adoption of no-till such as USA and Australia for a range of
valid agronomic reasons47,48. Periodic cultivation will lead to consid-
erable loss of any SOC accumulated in topsoil during the years of
no-till35,42,47,48 so the carbon sequestration and climate change mitiga-
tion benets are lost or greatly reduced. Finally, there are signicant
barriers to widespread adoption of no-till by resource-poor small-
holder farmers in less developed regions such as Subsaharan Africa
and South Asia due to a range of economic, social and infrastructure
factors that have been widely discussed elsewhere4,5,49–51. us, for
all of these reasons, the apparent potential for increased global SOC
stock from adopting no-till is unlikely to be realized.
In view of these major limitations and uncertainties regarding
the impact and degree of adoption of no-till, we conclude that its
global impact on soil C stocks will be only a fraction of the 0.4 to
0.6Gt CO2e yr–1 we estimate above, but we have insucient infor-
mation available to assess how small a fraction. It is possible that
the total extra soil C accumulation could be close to zero. It is also
known that a change to no-till can inuence emissions of nitrous
oxide, causing either increases or decreases52,53. As nitrous oxide is a
–1 012
(Additional organic C in no-till soil) / (Organic C in conventionally tilled soil)
Depth (cm)
Figure 2 | Changes in soil organic carbon (SOC) content in soil under no-till compared to conventional tillage. Based on a meta-analysis of data
from 43 sites where the two tillage systems had been applied for at least 5years, and in many cases for more than 15years. Large filled squares are
the geometric mean of data in each soil depth; this value was used because the data were not normally distributed. Bars on each side of large squares
represent the range of data from most studies. Values outside this range are shown by small points. An increase in SOC stock in no-till is indicated by an
x axis value greater than 0. A value less than 0 indicates a decrease compared to conventional tillage. The data show an accumulation of organic C in the
uppermost surface layers (0–10cm) but a greater amount of C in conventional tillage at the base of the plough layer (about 25cm). At greater depths
there was no significant dierence between tillage treatments. Redrawn from ref.26.
potent GHG with a global warming potential 298 times that of CO2
on a 100year basis54, even a small increase can easily outweigh the
benet of an increase in SOC. Short-term laboratory incubations of
soils from tilled and no-till elds in the UK show there is a poten-
tial for the overall impact to be decreased emissions55, but it is not
known if this is realized under eld conditions.
A regional assessment of the impact of a change to no-till was
made for wheat-based production systems in the Indian states
within the Indo-Gangetic Plain56, the breadbasket of South Asia.
IPCC methodology was used to estimate the potential for climate
change mitigation through soil C sequestration, applying the IPCC
factors to the dierent soils and climatic conditions in the region.
is modelling study led to calculated annual rates of SOC accumu-
lation under no-till in the range 0.2–0.4MgCha–1, broadly consist-
ent with annual rates measured in other regions of the world and
cited above6,24. e calculated annual rate of SOC accumulation in
the entire region was less than 0.01Gt CO2e yr–1 , less than 1% of
Indias total annual GHG emissions. Another modelling study, in
which two well-validated SOC models were applied to situations in
Africa and South America57, showed a smaller rate of SOC accu-
mulation from no-till of only 0.04Mg C ha–1 yr–1 . If this rate was
reproduced globally, total soil C accumulation would be an order of
magnitude less than our estimate.
Many assessments of potential climate change mitigation in agri-
culture rely on the estimate of ‘global technical mitigation’ by Smith
etal.15 of 5.5–6GtCO2eyr–1, with economic potentials in the range
1.5–4.3GtCO2eyr–1 depending on the assumed carbon price. ese
values can be misunderstood to imply a very large mitigation poten-
tial within cropped land. In fact 36% of the total estimate is from the
restoration of degraded land to its natural state and re-ooding of
organic soils that are now under cultivation. Although re-ooding
of organic soils is desirable for carbon sequestration, it is only likely
to be practicable on small areas and the area of productive land
that could be removed from agricultural production is limited as
it represents a trade-o against the goal of global food security58,59.
A further 28% of the total estimate refers to management of graz-
ing land and improved management of livestock and manure to
decrease emissions of nitrous oxide and methane. e mean values
for annual accumulation of SOC from a combination of reduced
tillage and return of crop residues cited in Smith etal.15 are in the
range 0.04 to 0.19MgCha–1yr–1 , depending on climate zone, rather
less than the value of 0.3MgCha–1yr–1 we used in our assessment
above and again indicating that our estimate is highly optimistic.
It is noteworthy that the estimates of soil C increases under no-till
used in the UNEP report rely heavily on Derpsch etal.46. However
this reference contains virtually no data on SOC, being mainly con-
cerned with the areas under no tillage in dierent regions of the
world and opinions, not measured data, about the potential impacts
on soil carbon. e UNEP report1 is also at variance with the more
balanced view of the benets and limitations of conservation agri-
culture (including no-till) expressed by 43 scientists with detailed
knowledge of the topic in the “Nebraska Declaration60.
e claims made for climate change mitigation through conver-
sion to no-till agriculture in the chapter ‘Policies for Reducing
Emissions from Agriculture’ in the 2013 UNEP report1 are
unrealistic and not based on thorough review of the scientic
literature. Although the authors mention the social, economic
and infrastructural barriers to adoption of no-till, especially
for smallholder farmers, they proceed to ignore these in mak-
ing their assessment. is leads to overstatement of the global
potential for soil C sequestration. ere are some genuine oppor-
tunities for mitigating climate change in the agricultural sector,
largely through improved management of water and nutrients —
especially nitrogen from fertilizer61,62 and manure63,64 — and
through improved feeding practices and management of ruminant
Table 1 | Some key benefits and limitations or problems observed from a change to no-till cultivation practices.
Benefits Potential problems/limitations
Soil properties, crop growth and environmental impacts
Additional organic C in surface layer—beneficial for soil structure, soil biological
activity and seedling emergence
Only small additional total organic C stock in whole soil profile—limited
benefit for climate change mitigation
More continuous pores allowing increased rainfall infiltration — beneficial for
water availability for crops and climate change adaptation
Increased crop yields in some situations—probably owing to improved soil
conditions and/or water availability
Crop yields decreased or unchanged in some situations, or increases only
emerge after several years. Possibly associated with uneven seedling
emergence or increased soil density causing inhibited root growth in
some environments
Increased soil biological activity–especially if combined with crop
residue retention
Decreased risk of soil erosion—particularly if combined with crop
residue retention
Nitrous oxide emissions may either increase or decrease—with negative or
positive impacts on climate change mitigation
Farm operations
Labour/time saved through elimination of tillage operations May need extra labour or use of herbicides for weed control
Earlier sowing of crop often facilitated, leading to possibility of improved growth
and yield in some environments
In wet climates delayed planting may occur owing to slower soil drying after
rainfall events
Fuel saved through elimination of tillage operations—decreased costs and
CO2 emissions
Suitable machinery for planting may not be available, a particular issue for
resource-poor farmers in less developed countries
Long-term increases in crop yields and farm incomes—especially if combined
with crop residue retention and crop diversification
May be little or no increase in farm income in the short-term, a major
limitation for small-holder farmers in less developed countries
Reduced tillage does lead to a reduction in GHG emissions
associated with tillage operations, whether CO2 from burning
tractor fuel in mechanized agriculture67,68 or production of feed
required for draught animals in smallholder systems69. In the case
of fuel use in mechanized agriculture, although this saving is ben-
ecial for climate change mitigation, a study from the central USA
indicates that its magnitude is small relative to possible changes in
N2O emissions68. For conditions in the USA, total GHG emissions
associated with growing non-legume crops (maize, wheat) are
dominated by those from the production and use of agricultural
lime and nitrogen fertilizer67. erefore although the emissions
saving from reduced use of fuel are signicant and benecial70,
a ‘whole system’ approach emphasizes the great importance and
potential of achieving improved eciency in the use of nitrogen
fertilizer for climate change mitigation in agriculture.
Reduced tillage certainly has a role to play as one of the strat-
egies contributing to global food security and the protection of
soils, and thus to climate change adaptation through building
agricultural systems that are more resilient to climate and weather
variability. In regions where no-till or reduced tillage is appropri-
ate it should be promoted on these grounds, but not on the basis
of equivocal evidence for climate change mitigation. No-till agri-
culture can deliver signicant benets for farmers and sustainabil-
ity in many (though not all) situations (Table 1): reduced GHG
emissions are a small but important additional benet, not the key
policy driver for its adoption.
Received 10 March 2014; accepted 4 June 2014; published
online 30 July 2014
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Parts of this work result from studies on the climate change mitigation impacts of
conservation agriculture conducted by the International Maize and Wheat Improvement
Center funded by the Climate Change, Agriculture and Food Security programme of the
Consultative Group on International Agricultural Research.
Additional information
Reprints and permissions information is available online at
Correspondence and requests for materials should be addressed to D.P.
Competing financial interests
e authors declare no competing nancial interests.
... An increasing share of chemical energy in the energy balance of intensive farming creates prerequisites for the reduction in mechanical energy input in soil cultivation. It defines global trends of minimizing primary soil cultivation with an increase in chemicals use in agriculture (Popova et al., 2013;Powlson et al., 2014;Vasin et al., 2020). ...
... foundational assumptions about the mechanisms that control SOM accumulation and loss are still debated. In particular, researchers are still addressing how quality of litter inputs (Rui et al., 2022;Schmidt et al., 2011), tillage intensity (Powlson et al., 2014), and cover cropping (Poeplau & Don, 2015) affect SOM levels, as well as accrual. As technical understanding about SOM evolves, there is increasing need for empirical inquiry into what soil and management factors are associated with greater amounts of SOM, and in relation with inherent soil properties such as drainage class, texture, and pH. ...
The accumulation of soil organic matter (SOM) is vital to the agronomic and environmental functioning of agroecosystems, yet the relative influence of inherent soil properties and agricultural management practices on SOM dynamics are not often addressed in individual studies. Using a network of 218 operating farm fields across Wisconsin and southern Minnesota, USA, this research employs single variable analysis (ANOVA and regression) and regression tree analysis to assess the effects of soil properties (texture, drainage class, and pH) and management variables related to crop rotation, tillage, cover cropping, and manure application on SOM, as well as total organic carbon (TOC) and total nitrogen (TN) in the upper 15 cm. Single variable analysis revealed that greater SOM, TOC, and TN were associated with poorly drained soil, tile‐drained fields, high clay content soil, and high biomass crop rotations. SOM and TOC were strongly related (R2 = 0.71), but different regression trees were produced; SOM was most influenced by clay content, while TOC was most influenced by drainage class. Future assessment for the building of SOM or TOC should be conducted with drainage and texture class categories and on a regional basis, given that these factors influence the practices that occur within landscapes. A rapid building of datasets through unstructured sampling, including an abundance of metadata, should be a research priority in agricultural science to identify practices to build SOM on a regional basis.
... For instance, Brilli et al. (2017), by reviewing several studies, found that flux discrepancies arose from errors in the simulation of soil water content (SWC), underlining the importance of adequately describing peculiar agroecosystem conditions such as a shallow water table, or thawing and ponding. Moreover, current models typically represent soils in a simplified way that limits the correct representation of deep SOC dynamics (Braakhekke et al., 2013;Jones et al., 2017;LeDuc et al., 2017), e.g., actual SOC accumulation versus SOC stratification under no-till conditions Powlson et al., 2014) or dissolved organic carbon leaching (Montanarella and Panagos, 2021). ...
Process-based models have been recognized as cost-effective tools to assess carbon farming mechanisms through quantifying the C fluxes in the agroecosystems. A result-based approach is suggested however the wide variability of agricultural environments makes further model implementation necessary to limit the uncertainty of the results, especially on deep soil organic carbon (SOC) stock estimation and stratification and in agro-ecosystems characterized by a shallow water table. In this study, a comprehensive soil and crop dataset collected over a seven-year period from different pedoclimatic conditions across the Veneto Region (NE Italy) was used for EPIC model calibration and validation of SOC stock dynamics. Experimental data included yields from several crops (corn, winter and spring wheat, rapeseed, and soybean), continuous monitoring of soil water content, and SOC stocks (1872 total samples within the 0-50 cm soil profile) under conventional, cover crop and conservation agriculture systems. Modelling was performed by testing two N-C sub-models (CENTURY and PHOENIX), which differentiated in terms of mineralization/immobilization rates. Results showed that the procedure was able to obtain parameters valuable for most of the management system and pedoclimatic condition, reproducing well the tested variables. The EPIC model acceptably captured soil water dynamics (Nash-Sutcliffe coefficient-NSE-was up to 0.26), especially in the topsoil. Furthermore, simulation of weed-crop competition in conservation agriculture strongly contributed to properly explain the variability in crop production among the contrasting agricultural systems (R 2 ranged from 0.51 to 0.71). Likewise , EPIC skillfully simulated SOC stocks within the 0-50-cm profile regardless of the sub-model used (NSE was up to 0.64). Moreover, the model acceptably captured the profile SOC stratification among the different management practices. This study highlights the EPIC robustness for predicting SOC stocks and assessing with high accuracy carbon farming results.
... In turn, they are higher than those observed in maize-soybean rotations including cover crops (Restovich et al., 2019), and in a meta-analysis where the effects of straw return on soil carbon are quantified (Liu et al., 2014). We recognize that the high carbon accumulation in the topsoil here documented might be partly a consequence of a vertical redistribution documented for transitions from conventional tillage to no-tillage (Powlson et al., 2014). Our data allows us to compare results between treatments; nevertheless, in the following seasons we will include the quantification of carbon contents of 20-40 cm and 40-100 cm of the soil profile to account for potential effects of vertical redistribution. ...
The design of sustainable, high-yielding continuous cropping systems requires to maintain, or even restore, critical ecosystem properties, such as soil functioning. In the rolling Pampa (Argentina), total soil organic carbon decreased by 15-40% due to continuous agriculture. Therefore, soils are far from their potential carbon saturation. The most promising strategies to increase yield and restore carbon rely on the sustainable intensification of the current cropping systems based on no-tillage practices. Such strategies also involve increasing resource use through cover crops, increasing cropping intensity, and performing accurate and flexible fertilization and crop protection schemes. This study evaluated the effects of different cropping systems on soil organic carbon stocks in the uppermost 20 cm of the soil profile. We performed a 5-year experiment combining five cropping systems with different cash crop sequence (soybean mono-cropping and two different rotations) and agronomic technology (genotypes, fertilization, and crop protection), which in turn were evaluated under both fallow and cover cropping. Five years after the beginning of the experiment, all systems had a net positive balance of soil carbon accumulation, which averaged 2.25 t C.ha-1 .yr-1. On average, 41% of plant carbon inputs remained within the first 20 cm of the soil profile. Cover crops increased plant carbon inputs, with larger effects as the cash crops occupied a shorter period in the field. Therefore, compared to fallow, cover crop doubled carbon input in soybean mono-cropping, had intermediate increments in the maize-soybean sequence, and had the lowest increments in the wheat/soybean-maize-soybean sequence. Under fallow, both rotations outperformed the plant carbon inputs of soybean mono-cropping. Management intensification, only evaluated for rotations, increased plant carbon inputs and soil carbon accumulation in a synergistic interaction with cover crop. Our results indicate that increasing carbon inputs through crop rotation, cover cropping and better agronomic technology is an opportunity to revert the long trend of soil carbon deficit of these agricultural lands.
Technical Report
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Competition for crop residues between livestock feeding and soil mulching is a major cause of the low and slow adoption of conservation agriculture (CA) in sub-Saharan Africa. Retaining crop residues in the field is not only a prerequisite for CA but may also be the most viable option for African farmers to retain their fields in a productive state. In this paper, (1) we explore the possibility of increasing the quantity of crop residue available by closing the maize yield, (2) we propose interventions that can reduce crop residue demand for livestock feed, and (3) we quantify the optimum amount of crop residues required as mulch, using empirical, secondary and modeling data from Western Kenya and the Ethiopian Rift Valley. Residue retention can also be increased by reducing livestock demand. Closing the maize yield gap-i.e. achieve 90% of the water-limited yield potential-and intensifying dairy production-which would promote the use of rations that are more energy-dense than cereal residue-based rations-would increase the estimated proportion of farmers retaining at least 1 t ha(-1) of crop residues from the current 36% to 97% in Western Kenya. In the Ethiopian Rift Valley, closing the maize yield gap and substituting mechanization to animal draught power would increase the estimated proportion of farmers retaining at least 1 t ha(-1) of crop residues from the current 3% to 83%. We conclude that the question is not 'if', but 'how' cereal residues can fulfill the demand of both the soil and the livestock.
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Soil organic matter plays a crucial role in maintaining soil health and its productivity potential. However, most of the world's agricultural soils have become depleted in organic matter compared with their state under natural vegetation. This is because the dominant form of agriculture is based on tillage, which accelerates the decomposition of soil organic matter. Tillage-based production systems should therefore be transformed so that the future production intensification can be achieved sustainably. Conservation Agriculture, a system avoiding or minimizing soil disturbance, combined with soil cover and crop diversification, is considered to be such sustainable production system. However, there appears to be certain degree of uncertainty about the role of Conservation Agriculture in carbon sequestration and in reducing green house gas emissions. This publication presents a meta analysis of global scientific literature with the aim to develop a clear understanding of the impacts and benefits of traditional tillage agriculture and Conservation Agriculture with respect to their effects on soil carbon pools. The study attempts to reduce the existing uncertainty about the impact of soil management practices on soil carbon and is addressing scientists as well as policy makers to facilitate decision making regarding future farming models. Soil organic matter plays a crucial role in maintaining soil health and its productivity potential. However, most of the world's agricultural soils have become depleted in organic matter compared with their state under natural vegetation. This is because the dominant form of agriculture is based on tillage, which accelerates the decomposition of soil organic matter. Tillage-based production systems should therefore be transformed so that the future production intensification can be achieved sustainably. Conservation Agriculture, a system avoiding or minimizing soil disturbance, combined with soil cover and crop diversification, is considered to be such sustainable production system. However, there appears to be certain degree of uncertainty about the role of Conservation Agriculture in carbon sequestration and in reducing green house gas emissions. This publication presents a meta analysis of global scientific literature with the aim to develop a clear understanding of the impacts and benefits of traditional tillage agriculture and Conservation Agriculture with respect to their effects on soil carbon pools. The study attempts to reduce the existing uncertainty about the impact of soil management practices on soil carbon and is addressing scientists as well as policy makers to facilitate decision making regarding future farming models.
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Soil tillage practices have a profound influence on the physical properties of soil and the greenhouse gas (GHG) balance. However there have been very few integrated studies on the emission of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) and soil biophysical and chemical characteristics under different soil management systems. We recorded a significantly higher net global warming potential under conventional tillage systems (26-31% higher than zero tillage systems). Crucially the 3-D soil pore network, imaged using X-ray Computed Tomography, modified by tillage played a significant role in the flux of CO2 and CH4. In contrast, N2O flux was determined mainly by microbial biomass carbon and soil moisture content. Our work indicates that zero tillage could play a significant role in minimising emissions of GHGs from soils and contribute to efforts to mitigate against climate change.
The effects of no-tillage (NT) and moldboard plowing (MP) on the distribution and storage of soil organic carbon (SOC) and different C fractions were determined along a transect on a private farm in southern Ontario, Canada, where a paired NT and MP strip traversing three soil series had been in existence for 19 yr. Soil samples were collected to a depth of 60 cm in seven increments. SOC was determined in each sample and for the top 30 cm, the organic carbon was fractionated into loose-, occluded-particulate organic matter (loose-POM and occluded-POM) and humified fraction (HF). After 19 yr, soils under NT contained significantly (P < 0.05) more SOC than soils under MP on both an equivalent depth basis and an equivalent mass basis. Greater concentrations of loose- and occluded-POM were found in NT than MP surface soils (0-10 cm). MP favored higher loose-POM contents than NT practices at a depth of 10-20 cm. The HF fraction accounted for most of the increase in SOC in the Huron and Brady soils, whereas the occluded POM accounted for more of the increase in the Fox soil. Our results indicate that the extent of SOC sequestration under NT is strongly dependent on soil type and cropping history.
The soil carbon (C) reservoir is an important component of the global C cycle. It comprises of soil organic C (SOC) and soil inorganic C (SIC). Soils of India are severely depleted of their SOC stock. Therefore, enhancing and maintaining SOC concentration to above the critical threshold (~1.5% in the 0-20cm depth) is essential to improving soil quality, increasing use efficiency of nutrients and water, minimizing vulnerability to extreme climatic events, decreasing susceptibility to erosion and other degradation processes, and sustaining agronomic production. Above all, recarbonization of the SOC stock is integral to any strategy towards adapting to and mitigating the abrupt climate change, advancing food security and improving the environment. The SOC stock is also important to provisioning of numerous ecosystem services (e.g., food security, water security). Thus, identification and adoption of recommended management practices (e.g., conservation agriculture, agroforestry, manuring and integrated nutrient management, diverse farming system) are important to C sequestration. The rate of SOC sequestration in cropland soils of India are low, but need to be credibly assessed for diverse soils and farming systems. Rate of formation of secondary carbonates for different practices and or leaching of bicarbonates in irrigated soils must be established. A way forward should consider: (i) improvement in education curricula at state agricultural universities to include courses on climate change, C sequestration etc.; (ii) establishment of National Climate-Resilient Agriculture Program (NACRAP), and (iii) development of mechanisms to compensate farmers and land managers through payments for ecosystems services (e.g., soil C sequestration).
The efficiency of energy utilisation in cattle is a determinant of the profitability of milk and beef production, as well as their environmental impact. At an animal level, meat and milk production by ruminants is less efficient than pig and poultry production, in part due to lower digestibility of forages compared with grains. However, when compared on the basis of human-edible inputs, the ruminant has a clear efficiency advantage. There has been recent interest in feed conversion efficiency (FCE) in dairy cattle and residual feed intake, an indicator of FCE, in beef cattle. Variation between animals in FCE may have genetic components, allowing selection for animals with greater efficiency and reduced environmental impact. A major source of variation in FCE is feed digestibility, and thus approaches that improve digestibility should improve FCE if rumen function is not disrupted. Methane represents a substantial loss of digestible energy from rations. Major determinants of methane emission are the amount of feed consumed and the proportions of forage and concentrates fed. In addition, feeding fat has long been known to reduce methane emission. A myriad of other supplements and additives are currently being investigated as mitigators of methane emission, but in many cases compounds effective in sheep are ineffective in lactating dairy cows. Ultimately, the adoption of ‘best practice’ in diet formulation and management may be the most effective option for reducing methane. In assessing the efficiency of energy use for milk and meat production by cattle, and their environmental impact, it is imperative that comparisons be made at a systems level, and that the wider social and economic implications of mitigation policy are considered.