Soil & Tillage Research 213 (2021) 105143

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Soil & Tillage Research

journal homepage: www.elsevier.com/locate/still

Stover management modifies soil organic carbon dynamics in the

short-term under semiarid continuous maize
Jorge Álvaro-Fuentes a, *, Samuel Franco-Luesma a, Victoria Lafuente a, Pablo Sen b, Asun Usón b,
Carlos Cantero-Martínez c, José Luis Arrúe a
a
Soil and Water Department, Estación Experimental de Aula Dei (EEAD), Spanish National Research Council (CSIC), Montañana Av. 1005, 50059 Zaragoza, Spain
b
Agrarian and Natural Environment Sciences Department, University of Zaragoza (UZ), Carretera Cuarte s/n 22071 Huesca, Spain
c
Crop and Forest Sciences Department, EEAD-CSIC Associated Unit, Agrotecnio Center, University of Lleida (UdL), Alcalde Rovira Roure Av. 191, 25198 Lleida, Spain

A R T I C L E I N F O A B S T R A C T

Keywords: In croplands, the adoption of certain management practices may increase soil organic carbon (SOC) levels. In this
Irrigation method study, we evaluated the short-term impact of crop stover management and the interaction between crop stover
Maize monoculture and irrigation method on SOC change in a continuous maize (Zea mays L.) system in Spain. Four years after the
Crop stover
beginning of the experiment, total SOC and C fractions (particulate organic matter carbon, POM-C; and mineral-
No-tillage
associated organic matter carbon, Min-C) contents, SOC stocks and SOC stock changes were measured in four
SOC
different soil layers (0− 5, 5− 10, 10− 25 and 25− 50 cm) in an experiment with two irrigation methods (sprinkler
and flood) and three stover management systems (conventional tillage with all the stover incorporated, CT; no-
tillage maintaining the stover, NTr; and no-tillage removing the stover, NT). Stover management resulted in
significant differences in SOC and POM-C but not in Min-C. In particular, NT reduced SOC and POM-C contents
compared with CT and NTr (about 10 and 60 %, respectively). After 4 years, SOC change was not affected by the
interaction between stover management and irrigation. Concurrently, both CT and NT showed SOC losses,
reaching 0.11 and 1.22 Mg ha− 1 yr− 1 in CT and NT, respectively. However, NTr showed SOC gains at a rate of
0.09 Mg ha− 1 yr− 1. Consequently, the removal of crop stover has been demonstrated as a detrimental strategy to
store SOC in the short-term in irrigated continuous maize systems.

1. Introduction irrigated periods (Pareja-Sánchez et al., 2020). Similarly, in Central

Great Plains (USA) greater SOC levels were observed in irrigated agro­
In croplands, different management practices have been identified to ecosystems when different rainfed and irrigated fields were compared
increase soil organic carbon (SOC) levels (Bai et al., 2019; Francaviglia (Denef et al., 2008). Even though, the conversion to irrigated land has
et al., 2019). A significant number of practices that increase SOC stocks been evaluated in several experiments located in different parts of the
are oriented towards the increase of carbon (C) inputs. Thus, addition of world (Trost et al., 2013), the impact of the irrigation method or man­
exogenous C (biochar, compost, manures), crop residue management, agement on SOC changes has been less studied. In particular, we have
improved fertilization or irrigation are examples of management prac­ not found any experiment in the literature studying the impact of irri­
tices which enhance SOC accrual by means of maximizing the addition gation method on SOC changes in the Mediterranean basin. Indeed, a
of C to the soil (Paustian et al., 2016). In dryland systems, irrigation is an few years ago, in a comprehensive SOC meta-analysis for the all the
excellent strategy to increase SOC levels through its positive effect on Mediterranean climate regions (Aguilera et al., 2013), irrigated systems
crop production and, consequently, crop residues returned to the soil were considered as a management class in the analysis but the irrigation
(Trost et al., 2013). In semiarid Spanish conditions, a significant increase method was not included.
in SOC levels was observed three years after the conversion from rainfed Crop stover management is also an effective management practice to
to irrigated cropland (Pareja-Sánchez et al., 2020). In this last study, an increase SOC levels (Aguilera et al., 2013; Stewart et al., 2018). Two
increase in C inputs under sprinkler irrigated conditions explained more recent meta-analysis have concluded that the removal of crop stover
than 70 % of the variability in SOC change rates between rainfed and results in a general decrease in SOC (Xu et al., 2019; Wang et al., 2020).

* Corresponding author.
E-mail address: jorgeaf@eead.csic.es (J. Álvaro-Fuentes).

https://doi.org/10.1016/j.still.2021.105143
Received 2 February 2021; Received in revised form 2 July 2021; Accepted 5 July 2021
Available online 13 July 2021
0167-1987/© 2021 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
J. Álvaro-Fuentes et al. Soil & Tillage Research 213 (2021) 105143

Furthermore, the removal of crop residues not only reduces total SOC occurred every 10–14 days, whereas in the sprinkler method irrigation
levels but also labile C fractions such as the particulate organic matter occurred two times per week. More information about crop and irriga­
carbon (POM-C), particularly in high residue crops such as maize tion management can be found in Franco-Luesma et al. (2020a, 2020b).
(Stewart et al., 2016; Obrycki et al., 2018). Likewise, in situations with
high residue production, stover management may be linked to tillage in 2.2. Soil and crop stover sampling and C analyses
order to facilitate field operations (Pareja-Sánchez et al., 2019). The
reduction of tillage intensity may affect SOC (Álvaro-Fuentes et al., In February 2019, soil was sampled at 0− 5, 5− 10, 10− 25 and
2014; Ogle et al., 2019) but there is still an open scientific debate about 25− 50 cm layers. A composite sample was obtained per plot and soil
the real potential of no-tillage (NT) for sequestering C (Powlson et al., layer. Once in the laboratory, soil was air dried and ground to pass a 2-
2014; VandenBygaart, 2016). Recent global studies have concluded that mm sieve. Soil physical fractionation was done to isolate the POM-C and
the positive effect of NT on SOC sequestration depends not only on Min-C fractions following the method of Cambardella and Elliot (1992).
climate (Sun et al., 2020), but also on climate and soil properties (Ogle Briefly, 20 g of <2 mm air dried soil was dispersed in 100 mL of 5 g L− 1
et al., 2019). Therefore, more information is still needed on the impacts sodium hexametaphosphate for 15 h on a reciprocal shaker. After this
of tillage systems on SOC changes under different climate and soil types. time, samples were passed through a 53-μm sieve to separate silt + ­
In this regard, in Mediterranean conditions, the number of studies in clay + Min-C (<53 μm size) from >53 μm size particles
which the impact of tillage systems on SOC has been studied under (sand + POM-C). The <53 μm fraction was collected in aluminium pans
rainfed conditions is significantly higher than under irrigated conditions and oven dried at 50 ◦ C overnight. Organic C concentrations of the bulk
(González-Sánchez et al., 2012). Furthermore, most of these studies are soil and the Min-C fraction were measured using a LECO analyser model
concentrated on the beneficial effect of NT on soil water conservation, RC-612 (Leco Corp., St. Joseph, MI, USA) and the POM-C was calculated
this being an asset in dryland conditions (Lampurlanés et al., 2016). by the difference between total SOC and Min-C.
Accordingly, the main aim of this study was to evaluate the short- Soil bulk density was measured for each soil layer using the soil
term impact of crop stover management and the interaction between cylinder method (Grossman and Reinsch, 2002). The SOC stocks were
irrigation method and stover management on SOC changes in a calculated considering the SOC concentration, the soil bulk density and
continuous maize system in semiarid conditions. the sampling depth. All the SOC stock values were corrected for the
equivalent soil mass following the procedure explained in Ellert and
2. Material and methods Bettany (1995). As the reference soil mass was considered the CT soil
management under flood irrigation as the historical management of the
2.1. Site characteristics and experimental design field. The cumulative soil mass in the 0− 50 cm soil layer was 7911 Mg
ha− 1. The SOC stock change in each treatment was calculated from the
The experiment was established in 2015 in the EEAD-CSIC experi­ difference between the SOC stock in 2019 and the initial SOC stock
mental farm located in Zaragoza, Spain (41◦ 42 ́ N, 0◦ 49 ́ W, 225 m measured in 2015 right before the setup of the experiment. The SOC
altitude). The farm occupies 40 ha and it is entirely irrigated. The stock measured at the beginning of the experiment for the 0− 50 cm soil
climate is Mediterranean semiarid with 14.1 ◦ C, 298 mm and 1243 mm layer was 59.43 Mg C ha− 1.
of mean annual air temperature, mean annual precipitation and refer­ In all four maize seasons, the stover yield was measured in three 2-m
ence evapotranspiration (ETo), respectively. The soil is classified as rows per plot at the physiological maturity stage by separating the grain
Typical Xerofluvent (Soil Survey Staff, 2014), with a pH (H2O, 1:5) of from the rest of the plant (stover). Stover subsamples were oven dried at
7.9, electrical conductivity (1:5) of 0.31 dS m− 1 and sand, silt and clay 60 ◦ C for 48 h, weighed and ground. The C concentration was measured
contents of 282, 534 and 184 g kg− 1, respectively, in the top 15 cm. on a LECO analyser model Truspec CN (Leco Corp., St. Joseph, MI, USA).
In March 2015 a 0.830 ha field was divided in two identical areas.
The field had been traditionally flood irrigated and intensively tilled 2.3. Statistical analyses
(maintaining all the stover in the field) and for the last 10 years maize
was the main crop. The two areas were used to differentiate the irriga­ Analyses of variance (ANOVA) were performed to evaluate the effect
tion system. Hence, one area remained with the traditional flood irri­ of the different factors (irrigation, stover management and soil layer)
gation system and in the adjacent area, a hand-move sprinkler irrigation and their interaction effects on the different soil variables measured. The
system was established. In each of the two areas (0.415 ha), nine experimental design consisted in a strip block experiment in which the
6 × 18 m plots were demarcated. The following three stover manage­ stover management factor was replicated three times but the irrigation
ment treatments were laid out randomly within three blocks forming a factor was not replicated. Due to the lack of replication, the irrigation
split-block design: conventional tillage with a pass of subsoiler to 30 cm factor was not evaluated, but the evaluation of the interaction between
followed by a pass of rotary tiller and all the stover incorporated into the the irrigation method and the stover management was possible (Federer
soil (CT); no-tillage with all the crop stover left on the soil surface (NTr); and King, 2007). In order to meet ANOVA assumptions, the homoge­
and no-tillage with all the crop stover removed from the field (NT). In neity of variances was tested with the Levene test and the normality with
this last treatment, after every season harvest, the maize stover was the Kolmogorov-Smirnov test. The POM-C content was squared- trans­
manually removed from the plots. From April 2015 to October 2018, formed because it was the only measured variable that did not fulfil the
four continuous maize growing seasons were established with a five- normality assumption. When significant differences were found at the
month fallow period (October-March) in between seasons. Maize cv. 0.05 or 0.10 level, the post-hoc test Fisher’s Least Significant Difference
Pioneer P1785 was planted in mid-April at a density of 89,500 plants (LSD) was used to compare differences among treatments. All the sta­
ha− 1 and harvested in the first week of October. Plots were equally tistical analyses were performed with the R software (R Core Team,
fertilized with 260 kg N ha− 1 split between planting and one top dres­ 2017).
sing application at V6-V8 maize growth stage. The amount of irrigation
water applied was calculated according to climate data obtained from a 3. Results
meteorological station located within the experimental farm and it was
the same amount in all tillage treatments within a same irrigation sys­ The soil bulk density was affected by the stover management, the soil
tem. The two irrigation methods presented differences in the amount of depth and the interaction between irrigation and stover management
water applied and in the irrigation frequency. The flood irrigation (data not shown). In both irrigation methods, soil bulk density increased
received about 25 % more water than the sprinkler irrigation (707 vs. with soil depth with the lowest soil bulk density measured in the surface
882 mm per growing season, respectively) and irrigation events soil layer (Table 1). Under both irrigation methods, with soil depth

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J. Álvaro-Fuentes et al. Soil & Tillage Research 213 (2021) 105143

Table 1 (Table 2). The Min-C was also affected by the interaction between irri­
Soil bulk density after four years of continuous maize as affected by stover gation and soil depth. In general, both irrigation methods showed a
management (CT, conventional tillage; NT, no-tillage removing the maize sto­ decreased in Min-C with soil depth. But in the 25− 50 soil depth, the
ver; and NTr, no-tillage retaining the maize stover) under flood and sprinkler Min-C content was significantly lower under flood than under sprinkler
irrigation. irrigation (data not shown).
Soil layer (cm) In flood irrigation, significant differences among stover management
Irrigation Stover management 0-5 5-10 10-25 25-50 systems were only found in the 5− 10 cm soil depth where CT presented
greater SOC than NT (Fig. 1). However, in sprinkler irrigation, signifi­
Flood
CT 1.35 ab† 1.39 bc 1.60 a 1.65 cant differences were only observed in the topsoil layer (0− 5 cm) where
NT 1.44 a 1.36 c 1.53 a 1.66 NTr resulted in greater SOC content than NT (Fig. 1). The POM-C frac­
NTr 1.32 ab 1.46 abc 1.60 a 1.63 tion in the 0− 5 cm soil depth was greater in NTr than in NT under flood
Average 1.37 B‡ 1.41 B 1.58 A 1.65 A irrigation (Fig. 2). However, in sprinkler irrigation, stover management
systems affected POM-C contents at both the 5− 10 and 10− 25 cm soil
Sprinkler
CT 1.24 b 1.50 ab 1.39 b 1.61
depths where this fraction was significantly greater in CT than in NT and
NT 1.39 ab 1.51 ab 1.67 a 1.57 NTr, respectively (Fig. 2).
NTr 1.44 a 1.53 a 1.64 a 1.63 The SOC stocks were affected by the stover management and soil
Average 1.36 B 1.52 A 1.57 A 1.60 A depth, and the interactions between irrigation and soil depth and be­
†
Within a soil layer, values followed by different lowercase letters are signi­ tween stover management and soil depth (data not shown). For flood
ficantly different at 0.05 level. irrigation, significant differences among stover management systems
‡
Within an irrigation method, mean values followed by different uppercase were found in the 5− 10 soil layer where NTr resulted in lower SOC
letters are significantly different at 0.05 level. stocks than CT, and in the 25− 50 cm soil layer where NT resulted in
lower SOC stocks than NTr (Fig. 3). When the entire 0− 50 cm soil depth
changes from the 0− 5 to the 25− 50 cm, soil bulk density increased was considered, NT had the lowest SOC stock. Significant differences in
about 17 and 20 % for sprinkler and flood, respectively (Table 1). There SOC were only found in the 0− 5 cm depth under sprinkler irrigation
were no clear differences in soil bulk density of the soil layers due to where SOC was significantly greater in NTr compared with NT (Fig. 3).
stover management. For example, in the 0− 5 cm soil layer, the soil bulk Furthermore, in flood irrigation, significant differences existed when the
density in the CT under sprinkler irrigation was significantly lower than entire 0− 50 cm soil layer was considered. In this case, NTr showed
in the NT and NTr under flood irrigation and sprinkler, respectively. But, significantly greater SOC stocks than NT (Fig. 3).
in the 5− 10 cm layer, the NT under flood irrigation resulted in signifi­ After 4 years of continuous maize, SOC changes in the 0− 50 cm soil
cantly lower soil bulk density than the NTr under sprinkler irrigation layer were only affected by the stover management and only at the 0.10
(Table 1). In the 10− 25 soil layer, the CT under sprinkler irrigation had significance level (p-value = 0.073). The CT and NT treatments showed
the lowest soil bulk density, and in the 25− 50 soil layer no significant SOC losses of -0.11 and -1.22 Mg ha− 1 yr− 1, respectively (Fig. 4). On the
differences were found (Table 1). contrary, NTr accumulated SOC during the experiment at a rate of
The SOC and POM-C contents were affected by the stover manage­ 0.09 Mg ha− 1 yr-1 (Fig. 4).
ment and soil depth and the interaction between stover management
and soil depth (Table 2). No-till resulted in a reduction of SOC and POM- 4. Discussion
C contents compared to CT and NTr, which showed similar values
(Table 2). Soil depth not only affected SOC and POM-C contents but also Changes in soil tillage may have a significant impact on SOC changes
Min-C content. All three soil variables decreased with soil depth. Soil depending on climate and soil conditions (Ogle et al., 2019). In our
organic C, POM-C and Min-C contents at the 25− 50 cm soil depth rep­ study, after four years, differences in SOC between tillage systems were
resented only the 57, 23 and 65 %, respectively, of that in the topsoil only observed when stover was removed from the field (Table 2). The
shift from CT to NTr (with both tillage systems maintaining crop stover)
Table 2 did not affect SOC contents. In contrast, when the shift was from CT or
Analysis of variance of soil organic carbon (SOC), particulate organic matter C
(POM-C) and mineral-associated organic matter C (Min-C) contents as affected
by stover management (CT, conventional tillage; NT no-tillage removing the
maize stover; and NTr, no-tillage retaining the maize stover) and soil layer, and
the interactions between both factors and the irrigation method (Irrigation).
Treatment SOC POM-C Min-C
1
g C kg soil−

Stover CT 8.85 a† 1.43 a 7.42

NT 7.91 b 0.87 b 7.04
NTr 8.73 a 1.38 a 7.35

Soil layer 0− 5 11.21 a 2.37 a 8.84 a

(cm) 5− 10 8.77 b 1.27 b 7.50 b
10− 25 7.65 c 0.71 c 6.94 c
25− 50 6.35 d 0.55 c 5.80 d

ANOVA p values
Stover (Stv) <0.01 <0.05 ns
Soil layer (Layer) <0.001 <0.001 <0.001
Irrigation x Stv ns ns ns
Irrigation x Layer ns ns 0.03 Fig. 1. Soil organic carbon (SOC) content after four years of continuous maize
Stv x Layer 0.03 0.04 ns
under flood and sprinkler irrigation methods as affected by stover management
Irrigation x Stv x Layer ns ns ns
(CT, conventional tillage; NT, no-tillage removing the maize stover; and NTr,
ns, non-significant. no-tillage retaining the maize stover). Within a soil layer and irrigation method,
†
Values followed by different letters are significantly different at 0.05 level. values followed by different letters are significantly different at 0.05 level.

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J. Álvaro-Fuentes et al. Soil & Tillage Research 213 (2021) 105143

Fig. 2. Particulate organic matter C (POM-C) content after four years of

continuous maize under flood and sprinkler irrigation methods as affected by
stover management (CT, conventional tillage; NT, no-tillage removing the
maize stover; and NTr, no-tillage retaining the maize stover). Within a soil layer
and irrigation method, values followed by different letters are significantly
different at 0.05 level.

NTr to NT (NT with all the stover removed) a significant decrease in SOC
was observed. It is well established the positive relationship between C
inputs and SOC gains (Virto et al., 2012; Luo et al., 2017). In our
experiment, in only four years, SOC content decreased by 10 % with only
removing crop residues from the soil surface. In a global meta-analysis,
it was estimated that SOC decrease due to maize stover removal was 8%
(Xu et al., 2019). In this same study, it was observed that the greatest
reduction in SOC levels were observed for short-term experiments (<5
years) (Xu et al., 2019). In our study, as expected, the reduction in SOC
contents due to the removal of stover was mainly observed in the upper
soil layers (Fig. 1), as observed in other studies (Chowdhury et al.,
2015). Indeed, the analysis of variance showed that the SOC and the
other two C fractions measured (POM-C and Min-C) significantly
decreased with soil depth.
Besides total SOC, stover management also affected only POM-C not
the Min-C fraction. As observed for total SOC, the removal of stover
decreased POM-C. The POM is a C fraction derived from partially un­
decomposed plant-derived materials while Min-C is mostly of microbial
origin (Lavallee et al., 2020). Compared with the Min-C fraction, POM-C
is not associated with soil minerals, and more accessible to microbial
decomposition and cycling (Cotrufo et al., 2019). Consequently, crop Fig. 3. Soil organic carbon (SOC) stock after four years of continuous maize
residue inputs directly contribute to the formation and build-up of under flood and sprinkler irrigation methods as affected by stover management
(CT, conventional tillage; NT, no-tillage removing the maize stover; and NTr,
POM-C in the topsoil which would explain the decrease found in this C
no-tillage retaining the maize stover). Bars represent standard error. Within a
fraction when the residue was not left on the soil in the 0− 5 cm soil
soil layer and irrigation method, values followed by different letters are signi­
depth (Fig. 2). Several studies have also shown decreases in POM-C ficantly different at 0.05 level.
levels when maize stover is removed (Osborne et al., 2014; Stewart
et al., 2016; Obrycki et al., 2018). Indeed, this decrease in the content of
particular, these same authors observed increases of about 75 % in
POM-C occurs rapidly as observed in two experiments located in USA
POM-C levels when rainfed systems were converted to irrigated maize
where, three years after the start of the experiment, differences in
systems (Pareja-Sánchez et al., 2020). Similar values of Min-C among
POM-C between stover management treatments already existed (Sin­
stover management treatments were observed (Table 2) since this
delar et al., 2014; Ruis et al., 2018). The POM-C fraction is an early
fraction is characterized by its inherent high mean residence time and
indicator of SOC changes due to changes in management (Plaza-Bonilla
thereby less affected by management compared with POM-C (Cambar­
et al., 2014). In our study, both total SOC and POM-C contents showed
della and Elliot, 1992).
significant reductions when the maize stover was removed. However,
The comparison between CT and NTr (NT maintaining maize stover)
when the percentage of reduction was compared between fractions there
did not show differences in either SOC contents nor SOC stocks. Changes
existed differences. When the maize stover was removed the SOC
in SOC are the result of the balance between C inputs and losses
decreased about 10 % compared with the treatments in which the crop
(Paustian et al., 2016). In our case, no differences in above-ground C
residues were left on the soil (NTr and CT). However, when comparing
inputs were observed among the three stover management systems
the POM-C, this proportion reached almost 38 %. In an experiment
tested. During the 2015–2018 period, the total stover C yield was 20.04,
located under similar Mediterranean conditions, the POM-C fraction was
18.92 and 19.15 Mg C ha− 1 in CT, NT, NTr, respectively (data not
identified as an early indicator of SOC changes when a rainfed cropping
shown). Consequently, it might be assumed that, in order to compensate
system was converted to irrigated maize (Pareja-Sánchez et al., 2020). In
the balance between C inputs and losses, decomposition rates did not

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Fig. 4. Soil organic carbon (SOC) stock change after four years of continuous Fig. 5. Linear relationship between soil organic carbon (SOC) change and total
maize as affected by stover management (CT, conventional tillage; NT, no- stover C during the 2015-2018 period for different irrigation and stover man­
tillage removing the maize stover; and NTr, no-tillage retaining the maize agement treatments: conventional tillage under flood irrigation (white circle);
stover) Vertical bars represent standard error. Values followed by different conventional tillage under sprinkler irrigation (black circle); no-tillage
letters are significantly different at 0.10 level. removing the maize stover under flood irrigation (white triangle); no-tillage
removing the maize stover under sprinkler irrigation (black triangle); no-
tillage retaining the maize stover under flood irrigation (white square); no-
change between CT and NTr. However, in the same experimental plots, tillage retaining the maize stover under sprinkler irrigation (black square).
during the 2015, 2016 and 2017 maize seasons, Franco-Luesma et al.
(2020a) observed about 25 % higher soil CO2 emissions under CT than
are usually observed during the first years right after the new manage­
under NTr which would be partly explained by a higher decomposition
ment practice is adopted (West and Six, 2007). In Spain under rain-fed
rate in CT. Despite this difference in soil CO2 emissions, we still found
Mediterranean conditions, the greatest SOC change rates were
similar SOC stocks between both management systems. Thereby, we
observed 4 years after the change from CT to NT (Álvaro-Fuentes and
could hypothesize that the higher decomposition rates under CT might
Paustian, 2011). Consequently, in our experiment, the short period for
be offset by higher root C inputs in CT as observed in some studies
evaluation have contributed to the high SOC losses measured in the
(Barber, 1971; Li et al., 2017) or, simply, that more time needs to pass to
stover removal treatment. Therefore, it would be necessary to continue
determine whether C changes between tillage systems really exist
evaluating the impact of these management strategies over the
(Smith, 2004). Therefore, it is important to highlight that several dis­
long-term and to identify possible future variations in the rate of SOC
cussion papers have been published in the last decade questioning the
changes.
potential for SOC sequestration when NT is adopted (Powlson et al.,
2014; VandenBygaart, 2016). Consequently, it would be likely that after
5. Conclusions
several years of the establishment of the experiment, similar SOC levels
still exist between tillage systems.
After four years, stover management has resulted in significant SOC
During the four years of experiment, SOC stocks changed differently
changes in a maize monoculture system. In the two irrigation methods
depending on the stover management system. However, after 4 years,
studied (flood and sprinkler), the removal of maize stover is a detri­
SOC change was not affected by the interaction between stover man­
mental practice for SOC sequestration since, after four years, it resulted
agement and irrigation (data not shown). The average SOC change
in a decrease in SOC and POM-C contents and SOC stocks compared with
values of the irrigation and stover management treatments presented a
the maintenance of crop stover. At the same time, SOC and fraction
significant relationship with the amount of stover C yield produced in
contens and SOC stock changes were not affected by the interaction
the 4 years (Fig. 5). But, after this time, differences between irrigation
between irrigation method and stover management. The removal of crop
and stover management treatments were not still enough great to be
stover has been demonstrated as a detrimental strategy to store SOC in
statistically significant in neither yield C stover nor SOC change.
the short-term in irrigated maize systems.
The historical crop and soil management of the field (CT maize)
resulted in a slight decrease of SOC during the 4-yr period (Fig. 4). It
Declaration of Competing Interest
would be expected a situation in which no changes in SOC stocks
occurred, but in reality, the historical management was not in steady
The authors report no declarations of interest.
state conditions. The sequestration duration is controlled by several
factors such as soil properties, climate, C inputs level and management
Acknowledgements
(West and Six, 2007). In a modelling study, Álvaro-Fuentes and Paustian
(2011) estimated that, under Mediterranean conditions, shifting from
The authors wish to thank Eva Medina and Estela Luna for laboratory
rainfed to irrigated in a continuous barley system would need 90 years to
and field assistance and Jorge Lampurlanés for statistical advice.
achieve steady state conditions.
Financial support of the Ministry of Economy and Competitiveness of
In our study, after four years, NTr resulted in slightly gains in SOC
Spain (Grant AGL2013-49062-C4-4-R), the Spanish State Agency for
stocks. But the most abrupt change was observed in the NT treatment
Research (AEI) (Grant AGL2017-84529-C3-1-R) and the European
with a mean SOC loss rate of 1.22 Mg C ha− 1 yr− 1. Compared to other
Union (FEDER funds) is gratefully acknowledged.
studies in Mediterranean conditions, the annual SOC loss rate obtained
in our study for NT is high (Álvaro-Fuentes and Paustian, 2011; Aguilera
et al., 2013). After a shift in management, the greatest SOC change rates

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