1 Introduction
Soils provide multiple services for ecosystems and humans (Brevik et
al., 2015; Gu et al., 2018). It was evaluated that 95% of food on the
earth comes from soil (Borek et al., 2018). However, human activities,
including but not limited to unreasonable farming (Amundson et al.,
2015), deforestation, fire, and overgrazing usually increase the rate of
ecological degradation, destroy the natural ecological balance, and lead
to continuous expansion and intensification of soil erosion worldwide
(Stanchi et al., 2015). Soil erosion caused by or stimulated by human
activities is reaching rates that are tens to hundreds of times those of
natural erosion (Wuepper et al., 2019). Because of soil erosion, fertile
soils are disappearing at a faster rate than natural replenishment. Some
severely eroded soils are not useable for further crop production.
Mathieu et al. (2019) reported that approximately 75 billion metric tons
of soil is removed annually from arable lands by wind and water, and
around 80% of the world’s land suitable for cultivation is moderately
or severely eroded (Pimentel, 2006). According to Wuepper et al. (2019),
global average soil erosion rate reached
2.4 t ha−1 yr−1.
Soil erosion affects carbon cycling (Lugato et al. 2016) by
redistribution of soil organic matter (SOM) (Wang et al., 2009; Gu et
al., 2018), increases water runoff, and decreases water-storage capacity
of soils (David and Michael, 2013). The most severe negative impacts of
soil erosion include decreased soil fertility (Mahdi et al., 2001; Gu et
al., 2018), degraded soil structure (Tenberg et al. 2014), and reduced
effective plant rooting depth. When nutrient resources are depleted by
erosion, plant growth is stunted and productivity is reduced (Pimentel,
2005; Dominati et al., 2010; Li et al. 2015). Erosion-induced
variabilities of soil nutrient significantly alters agricultural
productivity in cropping systems (Montanarella et al., 2015; Gu et al.,
2018). In May 2019, The Food and Agricultural Organization (FAO) led
Agriculture and food reports that the impact of erosion on crop
production has been estimated at a 0.4 percent reduction in global crop
yields per year due to erosion. It is clear that soil erosion is a
threat to world food production (David and Michael, 2013; Liu et al.,
2015; Zhou et al., 2015; Xie et al., 2019). Pierce and Lal (2017)
established the essential for research on erosion’s impact on
productivity. Consequently, a thorough understanding of soil erosion
effects on crop yield is critical for assessing agricultural production
dynamics (Lin et al., 2019) to ensure food security (Bakker et al.,
2004; Pierce and Lal, 2017; Gu et al., 2018).
Quantitative relationships between erosion variables and crop yield are
the basis for determining soil loss tolerance and evaluating regional
sustainable development (Zhou et al., 2012). Since the 1930s, American
scientists have taken the lead in observing effects of soil erosion on
crop yields at soil and water conservation observation stations
(Musgrave et al., 1923; Hays et al., 1949). In 1950s, research on the
impacts of soil erosion on soil productivity has received a wider
attention with the enactment of the US Soil and Water Conservation Act
and the establishment of the National Soil Erosion-Soil Productivity
Research Planning Committee (Williams et al., 1981). Using various
research methods including field observation as well as model
estimation, research area has extended from the United States to other
developed countries and regions (Schmidt et al., 1982; Olson and
Nizeyimana, 1988; Sasal et al., 2010; Gao et al., 2015; Duan et al.,
2016). Although global efforts to assess degradation by soil erosion
often measure degradation in terms of erosion rate rather than by its
impact on productivity (Pierce and Lal, 2017). So far, numerous studies
focused on erosion-crop yield relations (Larney et al., 1995; Larney et
al., 2000; den Biggelaaret al., 2004; Bakker et al., 2007), and included
research methods, climatic conditions, agricultural systems, soil
characteristics (Bakker et al., 2004), and soil types.
Most research confirmed the negative effects of soil erosion on land
productivity (Bakker et al., 2004; den Biggelaaret al., 2004). For
example, Larney et al. (2008) showed that 16-year average yield
reductions were 10.0, 19.5, 29.0, and 38.5% for 5, 10, 15, and 20-cm
topsoil removal treatments, respectively. Additionally, the observed
relationships between crop yield and soil erosion varied in different
studies from linear (Lal, 1981; Rosa et al., 2000), exponential (Wang et
al., 2009; Zhao et al., 2012) to quadratic (Larney et al., 1995).
Although several publications confirmed the influence of erosion on crop
yield, their quantitative relationships at global scale have yet to be
investigated. This is the key to developing practices and policies for
the restoration of eroded soils. To address this, which is essential to
assess degradation of soil, we tested the overarching hypothesis
that
soil erosion leads to a decline in crop yield and follows a common
yield-erosion relationship across different soil types and grain types
worldwide. We conducted a meta-analysis of crop yield variability along
erosion gradients worldwide using data from 13 published studies. Our
primary objectives were to (a) demonstrate variability of those
relationships across different regions; (b) determine the overall
effects of erosion on crop yields; and (c) identify quantitative
relationships between erosion and crop yield.