ABSTRACT
Soil erosion decreases topsoil depth, and hence soil fertility and crop
productivity in agricultural systems. However, it is not clearly
elucidated how different crop species adapt to the soil erosion
regarding root function, nutrient uptake and rhizosphere biochemical
properties, which is pivotal to cropping strategy under soil erosion. We
established three simulated erosion severities with topsoil depths of
10, 20 and 30 cm in a Mollisol farmland under a maize-soybean rotation
system with no-tillage. After three consecutive years of field
experiment,
the
decrease in topsoil thickness from 30 to 10 cm resulted in 9−22% of
decrease in maize yield but not soybean. Compared to the 30 and 20-cm
topsoil thickness, the 10-cm topsoil significantly lowered root and
shoot biomass of maize at the
jointing
(V7) and milk stages (R3) and of soybean at the mid-seed filling stage
(R6). Compared to the 30-cm topsoil, the 10-cm topsoil decreased
available
nitrogen
and phosphorus in soil by 42% and 36% under maize, and by 25% and
19% under soybean, respectively, while
the
shallow topsoil also decreased N, P and K uptake per unit root length
with the decreases being less for maize than soybean. Compared to the
30-cm topsoil,
the
10-cm and 20-cm topsoil significantly increased the activities of
urease, phosphatase and invertase in maize-grown soil, but not in
soybean-grown soil except for the activity of urease in 10-cm topsoil.
Maize was more sensitive to soil erosion than soybean due to the greater
decreases in soil nutrient availability and its capability of nutrient
uptake. The greater stimulation of nutrient mineralization processes in
soil did not alleviate the nutrient constraint to maize yield under
severe erosion conditions.
Key words : soil erosion; topsoil depth; black soil; soil
enzymes
Introduction
It is estimated that 15.1% of global land suffers degradation, of which
83.6% results from soil erosion
(Lal, 2001; Gao et al., 2015). Soil
erosion is a gradual process of removal, transport and deposition of
topsoil caused by wind and water (Liu et al., 2010). The reduction of
topsoil thickness is one of significant impacts of erosion on farmland.
Topsoil thickness is a major indicator of soil quality and productivity
(Sui et al., 2013). The reduction of topsoil thickness worsens soil
physical, chemical and biological properties, and thus reduces crop
productivity (Christensen and McElyea, 1988; Larney et al., 2000;
Sarapatka et al., 2018). Therefore, preventing soil erosion and
understanding the response of crop yields to the erosion is important in
assessing the vulnerability of agriculture to erosion
(Lal
et al., 2000; Bakker et al., 2004).
It is difficult to establish the relationship of soil erosion and crop
productivity as the process of degradation is slow (Bakker et al., 2004;
Zhou et al., 2015). Previous studies have been conducted to assess the
effects of soil erosion on crop
productivity
through artificial erosion approaches such as cut-and-fill experiments
(Larney et al., 2000; Jagadamma et al., 2009), transects characterized
by different erosion phases (Kosmas et al., 2001;
Rejman and Iglik, 2010) and variable
past erosions
(Graveel
et al., 2002; Fenton et al., 2005). Furthermore, simulation modeling has
been established to estimate the long-term effect of soil erosion on
plant growth (Pierce et al., 1983; Duan et al., 2016). For instance,
Wang et al. (2009) demonstrated that soybean yield was exponentially
decreased with increasing soil erosion depth due to the loss of soil
organic matter and nutrients using the Agriculture Land Management
Alternatives with Numerical Assessment Criteria (ALMANAC) model.
However, these researches did not clarify the relationship of soil
erosion and crop productivity, which may exhibit linear, concave and
convex response curves (Bakker et
al., 2004). Besides different experimental methods, the response of crop
yield to soil erosion also depends on variables such as crop type, soil
properties, management practices and climate characteristics (Bakker et
al., 2007).
The negative effects of soil erosion on crop productivity can be
attributed to the loss of soil organic carbon and plant nutrients,
especially nitrogen (N), phosphorous (P), and potassium (K) (Kaspar et
al., 2004; Herbrich et al., 2018). Quinton et al. (2010) reported that
topsoil erosion decreased 23–42 Tg of nitrogen, 2.1–3.9 Tg of organic
P and 12.5–22.5 Tg of inorganic P per year on the global scale. Plants
obtain nutrients from soil mainly through roots; however, root growth in
the soil vary with soil physical, chemical, and biological properties
(Wang et al., 2015; Shinohara et
al., 2016; Herbrich et al., 2018). It has been reported that a reduction
of topsoil thickness caused by soil erosion results in decreases in soil
organic matter (Liu et al., 2003; Srinivasan et al., 2012; Li et al.,
2019a; Miao et al., 2019), available nutrients (Bakker et al., 2004; Sui
et al., 2013; Xiong et al., 2018) and the effective rooting zone
(Graveel et al., 2002). In addition, soil enzymes play an important role
in soil quality and soil nutrient availability to plants (Jia et al.,
2005; Stott et al., 2010; Sarapatka
et al., 2018). Researchers have used soil enzyme activities as
indicators of soil deterioration caused by erosion (Chaer et al., 2009;
Sui et al., 2013; Nosrati, 2013). However, there are limited studies on
nutrients uptake of crop and activities of enzymes as affected under
zero tillage and residue cover in the eroded areas of China (Sui et al.,
2013).
As an important grain production area, northeast China
produces
18.7% of China’s total grains of which 45% and 33% are soybean, and
maize, respectively (National Bureau of Statistics of China, 2012).
However, soil erosion increasingly becomes a major limiting factor for
productivity of agricultural land in this region (Liu et al., 2010).
Zhang et al. (2008) showed that the average thickness of topsoil layer
decreased from 43.7 cm in 1982 to less than 30 cm in 2002. Sui et al.
(2009) reported that the yield reduction in maize and soybean were 13%
and 9% for the removal of every 10-cm topsoil. A survey with soil
erosion in cropland in northeastern China over the past 300-year history
conducted by Xie et al. (2019) showed that the soil loss of cropland
exponentially increased due to the increasing cropland acreage in the
steep slope areas.
In this study, we constructed three levels of topsoil depth in a
Mollisol with the same physical,
chemical and biological properties
to explore how maize and soybean responded to topsoil erosion under
zero
tillage, residue cover and maize-soybean rotation conditions. The
objectives were (1) to quantify the influence of
topsoil thickness on crop yield; (2)
to compare
nutrient
uptake of crops under three topsoil depths; (3) to analyze the effect of
topsoil thickness on root development and biochemical characteristics in
the rhizosphere of the crop plants.