Water productivity of irrigated maize production systems in Northern China: A meta-analysis
Introduction
Global freshwater supplies are facing unprecedented challenges and risks (de Fraiture and Wichelns, 2010). Irrigation is the largest water-use sector, accounting for about 70 % of global water withdrawals and nearly 90 % of consumptive water use (Grasby, 2004). Water withdrawals for agriculture are projected to increase by 40 % unless water productivity (WP) substantially increases in the coming decades (de Fraiture and Wichelns, 2010). The WP is defined as the ratio between grain yield and seasonal water supply, which includes soil water change from planting to maturity, in-season rainfall, and applied irrigation water (Sinclair et al., 1984; van Ittersum et al., 2013). Intensive field research and statistical models have demonstrated that WP varies widely dependent on multiple factors, such as climate conditions (Sun et al., 2013), soil properties (Katerji and Mastrorilli, 2009) and management practices (Hatfield et al., 2001). In practice, WP is synergistically affected by crop yield and seasonal water supply, and high WP indicates higher crop production from the same water supply or the same crop production from low water supply (Zwart and Bastiaanssen, 2004; Brauman et al., 2013; Mekonnen and Hoekstra, 2014). Detailed analysis of the spatial distribution of current WPs and their potentials is useful for identifying efficient use of water resources, and avoiding inefficiencies in crop production (Zwart et al., 2010).
Although the WP variation has been analyzed at the national, regional, and global scales (Zheng et al., 2018; Zwart and Bastiaanssen, 2004; Zhang et al., 2014), such analyses are lacking for major maize-producing zones in China. Maize in China accounts for more than one-third of the country’s cereal production and 18 % of global maize output (FAO, 2017). Maize production has increased rapidly when compared with the relatively stable rice and wheat production in China, and is planted across several agro-ecological zones, spanning from cold to subtropical, from arid to humid, and from single to double cropping production systems (Tao and Zhang, 2011). The variation in Chinese maize production and the crisis of limited water resources provide a need to quantify WP under different climate, soil and management practices to determine the impact of factors and improve water management for maize production.
Many field measurements have indicated that agricultural practices that reduce soil surface evaporation (e.g., soil surface plastic mulch, reduced tillage, and surface residue) (Qin et al., 2015; Wang et al., 2015, 2018a, 2018b), improved irrigation efficiency (e.g., drip irrigation, sprinkling irrigation, alternate furrow-irrigation) (Kang et al., 1998) or increase yield (e.g. fertilizer inputs, varieties) (Wang et al., 2010; Bu et al., 2015) may achieve high WP. Besides, some other measures like super absorbent polymers (Polymer) also may improve maize WP by increasing soil water storage (Liu et al., 2007). However, there is great variation in the magnitude of the increase in WP with improved management practices under different environmental conditions. It would be useful to provide practical guidance for maximizing production with the least amount of water for Chinese maize production.
The boundary function for WP can be determined by the highest attained yield for a given seasonal water supply (kg grain produced per ha per mm water supply (Grassini et al., 2009, 2011; Rattalino Edreira et al., 2018). Previous evaluations have been demonstrated and quantified the boundary function for WP as benchmarks for Chinese maize production (Zhang et al., 2014; Lin and Liu, 2016). However, differences in boundary function methods and datasets have resulted in inconsistent conclusions. For example, attainable water productivity was estimated at 40 kg ha−1 mm−1 based on French and Schultz’s boundary function across 36 studies of maize experiments between 1996 and 2012 (Zhang et al., 2014). The potential WP was also calculated as 60 kg ha−1 mm−1 across 65 articles published between 1987 and 2014 based on the quantile regression theory (Lin and Liu, 2016). An integrated assessment of the boundary function for WP at the regional levels for China is therefore needed to establish realistic goals of agricultural production considering available water resources, and to determine the related factors that constrain WP.
In China, the irrigated maize area accounted for 46 % of cropped area in 2008 (FAO, 2018). Irrigation water need is projected to increase due to increased drought affected area due to climate change (Piao et al., 2010; Wu et al., 2010). We conducted a meta-analysis of maize yield and water use data presented in peer-reviewed studies in Northern China (2354 observations from 282 studies) to: 1) investigate the current state of irrigated maize WP and influencing factors, 2) evaluate management practices to improve WP, and 3) estimate the boundary function for WP within different maize-production regions.
Section snippets
Research area
The research regions are divided into three agro-ecological zones: Northwest China (NW; 34–40 °N, 95–115 °E), Northeast China (NE; 40–55 °N, 110–135 °E), and North China Plain (NCP; 32–41 °N, 113–120 °E) (Wu et al., 2013). These three zones accounted for 88 % maize planted area and 90 % of production in 2011–2016 (China Agriculture Database, 2017). The NE agro-ecological zone experiences a cold, humid, or semi-humid temperate climate with a mean precipitation of 530 mm, 60 % of which falls from
Current WP and boundary function
The maize grain yield from 282 published articles covering 442 site-years averaged 9.81 Mg ha−1 (Fig. 1), and the WP averaged 22.3 kg ha−1 mm−1, and ranged from 6 to 45 kg ha−1 mm−1 (Fig. 1). The mean WP followed the order NE (mean: 25.8 kg ha−1 mm−1, 95 % CIs: 25.6-26.9 kg ha−1 mm−1, range: 15–38 kg ha−1 mm−1) > NCP (mean: 22.3 kg ha−1 mm−1, 95 % CIs: 21.7-22.5 kg ha−1 mm−1, range: 6–42 kg ha−1 mm−1) > NW (mean: 21.6 kg ha−1 mm−1, 95 % CIs: 21.2-22.0 kg ha−1 mm−1, range: 7–45 kg ha−1 mm−1) (
WP comparisons between our study and previous estimates
The estimated WP between 2000 and 2018 in the northern China was 22 kg ha–1 mm–1, which is substantially higher than that determined in previous research on irrigated maize in China (17.4 kg ha–1 mm–1) (Deng et al., 2006). In this study, the WP of maize production was estimated based on data from experimental plots. In general, experimental plots were managed carefully under optimal conditions (e.g., nutrient supply, pest management, tillage, and irrigation technology), which together increased
Conclusions
Across a large set of maize experiments between 2000 and 2018 for China, the mean WP was 22 kg ha–1 mm–1. WP varied with latitude, VPD, ST, N application, agro-ecological zone, year, and farming management practices. We identified large potential for improving the WP, and estimated the boundary function for WP has slope of 42.5, 36.8 and 40.4 kg ha−1 mm−1 for NW, NCP and NE, respectively. This study provides information for managers aiming to improve WP.
Declaration of Competing Interest
The authors declare that there are no conflicts of interest.
Acknowledgment
The present study was funded by the Taishan Scholarship Project of Shandong Province (No. TS201712082); National Natural Science Foundation of China (Key Program, U1706211); the Shandong Provincial Key Research and Development Program of China (2017CXGC0304).
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