1 | INTRODUCTION
Soil
degradationis a major impediment to global crop productionandimproper
management in arable land is the main driver of land degradation
(Ye&Van Ranst, 2011;Sampietro et al., 2018; Lorenz et al., 2019). With
drier climates and increasing pressure on resources, land degradation
has become a major issue that continues to negatively affect human and
natural ecosystems in some parts of the world (Guillaume et al., 2016;
Djuma et al., 2020).Continuing degradation in arable soils results
indeclines insoil organic carbon(SOC) stocks, crop productivity, and
ecosystem service values of increasing agricultural systems (Ma et al.,
2020;Raimondo et al., 2020). TheSOCdepletion is also acknowledged as a
major source of greenhouse gas emissions, resulting further in losses of
soil fertility and ecosystem stability (Amundson et al., 2015; Rüegget
al., 2019).Even small changes inthe SOC caused by
anthropogenic disturbance in
terrestrial ecosystems can profoundly affect the atmospheric C
dioxide(CO2)and thus get feedback to climate changes
(Sayer et al., 2011). In recent years, increasingattentionshave been
paid to SOC sequestration by
optimizing appropriate crop rotation, integrated soil fertility
management, and conservation tillage including crop residue management
in agricultural ecosystems (Xia et al., 2018; Gonçalves et al., 2019;
Berhane et al., 2020;Ryan et al.,
2020; Sun et al., 2020).Therefore, understanding the SOC dynamics and
the role that the soil plays in sequestering more atmospheric
CO2into soils are of incredible concern due to their
great potential for both climate change mitigation and agricultural
sustainability (Zhao et al., 2018a; Feng et al., 2020).
With a straw yield of 703.3 million tons (Mt) in 2014, and an average
annual straw increase of 4% over the decades, China has become one of
the most abundant countries in terms of straw resources (Hong et al.,
2016; Yin et al., 2018). However, the agricultural soils in China have a
relatively low SOC level due to the long cultivation history, highly
intensive field management, and lower straw-return rates caused by large
amounts of straw used as fuel and animal feeds or were burnt in fields
(Zhao et al., 2018a;Hou et al.,
2019; Berhane et al., 2020). Since crop residue contains large amounts
of nitrogen (N), phosphorus (P), and potassium (K), adopting
straw-return management practices in farmland facilitates the
maintenance of soil nutrient balance and soil quality, and boosts the
sustainability of agricultural production (Yin et al., 2018; Guan et
al., 2020). As the largest producer and consumer of
mineral fertilizers, China has
consumed approximately 35% of the global mineral fertilizers for
agricultural production (Sun et al., 2012; Yin et al., 2018). The
application of mineral fertilizers
with low levels of straw-return generally enhances grain yields in the
short term, but exacerbates soil organic matter
(SOM) depletion, deteriorates soil
nutrient availability, resulting in the decline of agricultural
sustainability in the long term (Gaffney et al., 2019). Conversely,
straw return significantly enhanced SOC contents (14.9%) and crop
yields (5.1%) with the same amounts of mineral-N applied in comparison
with straw removal in global agro-ecosystems (Xia et al., 2018).
Likewise, Zhao et al. (2018a) have reported an increase of 140 kg C
ha−1yr−1 SOC stock from 1980 to 2011
in China’s croplands (0−20 cm), and that approximately 40% of the
incremental increase could be accounted for by straw return. However, it
remains uncertainty that how agricultural soils respond to straw return
(Liu et al., 2014; Berhane et al., 2020). For instance, Liu et al.
(2014) reported that SOC sequestration was enhanced under straw return
during the first 3 years, but afterwards that effect gradually decreased
over time. Some studies have also reported that the effects of straw
return may be negligible or negative (García-Orenes et al., 2009; Wang
et al., 2011). The distinctions might be due to various ecological
conditions, soil conditions, methods of disposing straw, straw-returned
rate, and experimental duration (Liu et al., 2014).
Straw incorporation through conventional tillage, such as
plowing tillage and
rotary tillage, is a common and
effective field management practice with a strong influence on soil
fertility, soil physical and biological properties and crop yields (Yu
et al., 2017; Liu et al., 2021). On the one hand, frequent adoption of
conventional tillage destroys soil structural stability, decreases the
water holding capacity of soils, worsens the biological characteristics,
and nutrient reserve and supply
(Wang et al., 2011; Xu et al.,
2019; Nouri et al., 2019).
However, increasing evidences from
manipulative experiments (Zhao et al., 2019a; Li et al., 2019) and
meta-analyses (Zhao et al., 2019b; Jat et al., 2020) have showed that
adopting conservation agriculture (CA) could improve soil quality and
agricultural sustainability. The
CA mainly consists of various reduced and
even no-tillage techniques with
more than 30% of crop residue retained on soil surface, providing
effective strategies for combating soil degradation (Liu et al., 2020).
It has been reported that SOC contents of topsoil increased with years
under CA for its superiority on the protection of soil structure and
reduced rates of soil degradation (Somasundaram et al., 2017; Reeves et
al., 2019). The effects of CA on grain yields are highly variable,
varying from increase (Liu et al., 2018; Peng et al., 2020), neutral
(Zhang et al., 2018) to decrease (Pittelkow et al., 2015; Fiorini et
al., 2020).
The
intensive wheat (Triticum
aestivum L.)-maize (Zea mays L.)
double cropping systemis the major
agricultural practice in
the southern Loess Plateau of
northwest China (Deng et al., 2006; Liu et al., 2017). The growth
periods for wheat from mid-October to early June of next year, and for
maize were from mid-June to early October. The high intensity with short
time interval between wheat and maize growth periods in this
agricultural system have been widely reported (Li et al., 2019). To
achieve high grain yields, the excessive uses of mineral fertilizers and
tillage, especially the plowing and rotary tillage, are indispensable
(Yang et al., 2017; Xu et al., 2019). Under favorable conditions of
water and fertilizer, the intensive field managements stimulate the
degradation of plant residues and SOM, and thus result in SOC loss (Liu
et al., 2014; Guan et al., 2020). For a long time, straw burning was
adopted by farmers after crop harvest, which did not only lead to a
waste of biomass resources, but also gave rise to an excessive emissions
of greenhouse gases, and even left these regions in a thick haze (Hou et
al., 2019; Li et al., 2019). As such, adopting sustainable, cleaner
field management practices (i.e.,
conservation tillage and straw return) is essential to promote SOC
sequestration and grain yields, thus attaining
economic and
environmental sustainability in
grain production (Zhao et al.,
2018a).
Moreover, most studies relate to
SOC sequestration and grain yields affected by both straw return and
tillage in the
intensive wheat-maize system have
focused on the period after maize harvest (Tian et al., 2016; Kan et
al., 2020), but did not consider the effects
of both straw return and tillage
management practices after wheat harvest. Although long-term straw
return is clearly an effective field management practice for
sequestering C in soils, and a linear relationship exists between
SOC sequestration and grain yields
(Liu et al., 2014; Zhao et al., 2018a; Xu et al., 2019), there is a
paucity of information on the effects of both
no-tillage before maize planting
and maize straw return on SOC sequestration and its relationship with
grain yields and yield stability in the intensive wheat-maize system.
Therefore, the present study utilized a long-term field experiment
initiated in 2008 and aimed to examine the combined effects of
no-tillage before maize planting and maize straw return on SOC
sequestration, grain yields, yield stability and agricultural
sustainability. The information obtained can be used to optimize both
no-tillage and straw return management practices, enhance crop
production, and improve
agricultural sustainability for the
wheat-maize rotation system in dry
sub-humid areas of northwestern China and other areas with similar
climates and cropping systems.