Keywords
Conservation Tillage; SOC Sequestration; Crop Yield; Northeast China;
Soil Degradation; Synthesis Analysis
Introduction
Soil has the largest organic carbon pool of the terrestrial ecosystems,
containing three to four times that present in the atmosphere (Lal,
2008; Sanderman, Hengl, & Fiske, 2017). However, the conversion of
natural lands to cropping causes depletion and degradation of soil
organic carbon (SOC) (Don, Schumacher, & Freibauer, 2011; Guo &
Gifford, 2002; X. R. Wei, Shao, Gale, & Li, 2014). The destruction of
soil aggregate during tillage, which exposes previously protected SOC to
decomposition, combined with decreased inputs of organic matter under
cropping are the main reasons for the SOC loss after conversion to
cropland. This depletion and degradation of SOC can affect crop yield
due to its role in sustaining soil quality (Page, Dang, & Dalal, 2020;
Reeves, 1997). Therefore, agricultural practices that sequester SOC are
needed to restore soil fertility and advance food security.
Northeast China (NEC) (Fig. 1) , including Heilongjiang, Jilin, Liaoning
Province, and the northeast part of Inner Mongolia Autonomous Region, is
responsible for a large proportion of China’s grain production, with
three of its provinces (Heilongjiang, Jilin, and Liaoning Province)
accounting for 30.9% and 44.4% of China’s total production of maize
(Zea mays L.) and soybean (Glycine max Merril.),
respectively (NBSC, 2020). The black soil (Mollisols) region (43 - 50°N,
124 - 127°E) in NEC covers an area of 5.96 million hectares (Xiong &
Li, 1987) and is extensively used for grain production, playing an
important role in national food security (T. C. Wang, Wei, Wang, Ma, &
Ma, 2011).
However, because of long-term cultivation and erosion caused by poor
agricultural practices, soil degradation is severe in NEC, and it
seriously threatens the sustainable development of agriculture (Jia, Ma,
Li, & Chen, 2010). Conventional tillage (CT) in NEC, which is
characterized by crop residue removal after harvest and deep moldboard
or rotary plowing in the fall, has led to large losses of SOC
(Somasundaram et al., 2018; Xie et al., 2014; Zhao et al., 2015). It has
been reported that the annual loss of SOC stocks in NEC could reach 2.05
Mg ha−1 (Qiu, Wang, Tang, Li, & Li, 2004).
To alleviate this soil degradation, conservation tillage practices,
e.g., no-tillage (NT), ridge tillage (RT) and subsoiling tillage (ST)
with minimal soil disturbance, have been considered as an alternative to
CT and have been greatly popularized in NEC. After conversion to
conservation tillage, SOC accumulation and soil quality in the region
are often improved in upper soil depths due to reduced disruption of
soil aggregates (Sarker et al., 2018; Song et al., 2016; X. Wang et al.,
2019). The restoration of SOC can not only reverse the degradation
trends, but also enhance ecosystem services (Banwart et al., 2015; Lal,
2020). Moreover, subsoiling can effectively reduce soil compaction and
increase root distribution in deeper soil, which eventually increases
soil water storage and has a positive effect on grain yield in China
(Qiang et al., 2019; X. F. Sun et al., 2017) and around the world
(Getahun et al., 2018; Yalcin & Cakir, 2006).
While the effectiveness of conservation tillage in reducing soil erosion
and enhancing soil quality are generally expected to increase crop yield
(Lal, 2004; Lal, Reicosky, & Hanson, 2007; Triplett & Dick, 2008),
previous research has indicated that its impact can vary depending on
climate. Positive effects are generally observed on crop yield in warm
and dry climate zones (Cullum, 2012; Govaerts, Sayre, & Deckers, 2005;
Kan, Liu, He, et al., 2020; Pittelkow, Liang, et al., 2015; Verhulst et
al., 2011; Zhao et al., 2017), while in cool-humid areas, conservation
tillage can have a negative impact (Anken et al., 2004; Arvidsson,
Etana, & Rydberg, 2014). Some other studies have also reported no
effect of SOM on crop yield (Hijbeek et al., 2017; Oelofse et al., 2015;
W. L. Wei et al., 2016).
In the past five years, conservation tillage has been recommended by
government in NEC, and the area using conservation tillage grew to 2.67
million hectares in 2020 with the aim of 9.33 million hectares by 2025
(The Ministry of Agriculture and Rural Affairs of China, 2020). However,
the application of conservation tillage is region-specific, and the
effect of application is closely related to environmental and
socioeconomic conditions. Compared to other areas where conservation
tillage has been widely adopted, such as the US, the application of
conservation tillage in NEC still needs improving and perfecting. At
present, conservation tillage machines, especially no-tillage planters,
still have some problems, such as poor adaptability, low operating
efficiency, and high price (Y. F. Liu, Lin, & Li, 2017; X. R. Wei et
al., 2014). In addition, the mode of conservation tillage suitable for
development in different regions also needs to be better determined. The
mean annual temperature in NEC varies from < 0 to
> 10 ℃, and annual precipitation ranges from 400 - 800 mm.
Under global warming, the climate in NEC will also change, leading to
uncertainty for the effects of conservation tillage, yet little is known
about this. Therefore, it is important to identify different tillage
effects on yield and SOC under different conditions.
The objectives of this study were to: (i) assess the effects of
different tillage practice on crop yield and SOC sequestration in NEC;
(ii) estimate the relation between SOC and crop yield in NEC; and (iii)
provide some recommendation for the application of different
conservation tillage practices in NEC. We hypothesize that there is no
single tillage method suitable for the whole area of NEC, and different
conservation tillage measures will have their own advantages under
different planting and meteorological conditions in crop yield and
carbon sequestration.