Research PaperThe spatial-temporal coupling pattern of grain yield and fertilization in the North China plain
Graphical abstract
Introduction
Fertilizers containing N (nitrogen), P (phosphorus), and K (potassium) contribute 40–60% of the increase in grain yield (Cordell et al., 2009). Both over- and under-fertilization, however, have implications for the long-term sustainability of agricultural systems (Potter et al., 2010). Excessive, inefficient, and regionally unbalanced fertilizer application (Mueller et al., 2012; Lu and Tian, 2017) have caused serious negative impacts on agricultural systems (Tilman et al., 2002; Liu et al., 2013). This highlights the importance of understanding the geographic correlation between fertilization and grain yield and its dynamics in different areas at various scales. Determining the spatial-temporal relationship between historical grain yield and fertilization in various regions provides a solid base for proposing rational fertilization strategies. Such strategies are undoubtedly of global significance in increasing grain yield to feed the rapidly growing population while also preserving the agricultural system.
Among the various methods used to quantify the relationship between grain yield and fertilizer application, field experiments, traditional statistics, and geostatistics have been widely acknowledged. Based on field experiments, a relatively precise relationship between grain yield and fertilization can be obtained, which is significant for proposing rational fertilization strategies (Ortuzar-Iragorri et al., 2018). Such a relationship, however, is usually based on short-term experiments with strictly controlled environments in a specific small area, which is very different from practice in a large region over the long term. As observational data and survey data accumulate, statistical methods have been widely applied to quantify the relationship between grain yield and fertilization over a large area using longer time-series data (Halbrendt and Gempesaw, 1990; Bélanger et al., 2000; Dobermann and Cassman, 2002). Nevertheless, traditional statistical methods still lack the ability to reveal regional differences in the quantitative relationship between grain yield and fertilization. Great differences exist in the spatial-temporal coupling patterns of fertilizer usage and grain yield among regions and countries.
Recently, geostatistics, a method integrating geographic information system (GIS) and mathematical approaches, has demonstrated significant potential for revealing the spatial-temporal pattern of fertilizer usage and its dynamics from global (Potter et al., 2010; Bouwman et al., 2017; Lu and Tian, 2017), national, and regional scales (Cao et al., 2018; Gao et al., 2020). Geostatistics also can be applied to analyze the spatial-temporal coupling relationship between grain yield and fertilization in different areas and over long time periods (Sun et al., 2008; Wang et al., 2014). For example, GIS and SPSS have been used to analyze the differences in the yield-increasing effects of chemical fertilizers in different regions (Xin et al., 2012). Compared with field experiments and traditional statistics, geostatistics can better describe regional differentiation patterns, especially with the support of data over larger areas and longer time series. However, the differences in the driving effect of fertilization on grain yield among various regions have only been explored in a few studies.
To feed its population using limited cultivated land, China has the highest fertilizer application rates in the world (Potter et al., 2010; Zhang et al., 2015). However, overfertilization has caused serious environmental problems in some regions of China (Guo et al., 2010; Liu et al., 2013) without equivalent harvests because of its low fertilizer use efficiency (Lassaletta et al., 2014; Zhang et al., 2015; Li et al., 2019). Nevertheless, China has had long-term success in ensuring food security, partly through continuously improving fertilization strategies (Frink et al., 1999). Studies on the spatial-temporal patterns of historical grain yield and fertilization in China are of global significance, considering that many developing countries are following the same fertilization pathways as China.
The North China Plain, one of China's major agricultural areas with a wheat-corn double cropping system, produces more than 10% of China's total grain (Zheng et al., 2010), including more than 75% and 32% of the nation's wheat and corn, respectively (Tian et al., 2020). To promote grain yield, farmers often opt to increase fertilizer usage. Therefore, the issues caused by fertilization and the effect of fertilizer on grain yield in the North China Plain have been extensively studied (Zhu and Chen, 2002; Zhao et al., 2013; Wang et al., 2015; Li et al., 2017; Li et al., 2019). However, the spatial-temporal coupling patterns of fertilizer usage and grain yield and the effects of fertilization on grain yield among various regions in the North China Plain have been rarely explored.
In summary, few previous studies have demonstrated the mechanism driving the interactions between grain yield and fertilization over large areas and long time periods from the spatial-temporal coupling perspective. For this purpose, and to propose reasonable fertilization strategies referring to regional practical experience, using the North China Plain as an example, the present study first revealed the spatial patterns of grain yield and fertilization individually using global spatial autocorrelation analysis. Subsequently, the coefficients of the spatial-temporal coupling relationship between grain yield and fertilization were detected using the geographically weighted regression (GWR) model. Finally, the effects of different fertilizer types on grain yield were observed using a geodetector. Additionally, the patterns of regional differentiation and trends in the dynamic evolution of grain yield and fertilization, as well as the effects of chemical fertilizers on grain yield, were discussed.
Section snippets
Study area and data sources
The North China Plain (32°00′–40°24′N, 112°48′–122°45′E) includes Beijing, Tianjin, and Shandong provinces, as well as the main part of Hebei and Henan provinces and the northern region of Anhui and Jiangsu provinces, totaling 55 prefecture-level cities (Fig. 1).
Prefecture-level cities were set as the basic research units. We collected data on grain yield (rice, wheat, and corn) and fertilizer application (N, P, and K fertilizers) for each prefecture-level city from 1991 to 2016 (data from 1990
Changes in grain yield and fertilization intensity
We observed a fluctuating growth trend in the North China Plain grain yield from 1990 to 2015 (Fig. 2). Compared with that in 1990–1995, the annual yield of rice, wheat, and corn increased by 17.83%, 48.27%, and 20.74%, respectively, in 2010–2015. That is, the yield increased from 6068.8, 4221.3, and 5190.3 kg/ha to 7151.2, 6259, and 6266.8 kg/ha, respectively. Moreover, the fluctuation range of grain yield was narrower year by year, demonstrating that the yield of rice, wheat, and corn was
Discussion
Grain yield in the North China Plain significantly increased and the fluctuation narrowed year by year from 1990 to 2015 (Fig. 2), which was also reported in a prior study (Lu et al., 2016). Another study, however, reported that yield gains did not occur across 79% of rice cropland areas, 56% of wheat cropland areas, and more than half of corn cropland areas in China (Ray et al., 2012). Therefore, promoting grain yield in the North China Plain is undoubtedly crucial to ensuring China's food
Conclusions
Motivated by proposing rational fertilization strategies based on regional and historical practices, this study sought a contextual understanding of the geographic correlation between fertilization and grain yield and its dynamics. It was found that the grain yield consistently increased in the North China Plain in the past few decades, but there is still room for further growth. We also found significant differences in grain yield among prefecture-level cities, showing unbalanced agricultural
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This research was financially supported by the National Natural Science Foundation (Nos. 41877521, 41271515) and the National Key Research and Development Program (No. 2016YFA0602402) of China.
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