Deficit irrigation enhances contribution of shallow groundwater to crop water consumption in arid area
Introduction
Worldwide, irrigated agriculture accounts for approximately 70% of the world’s freshwater withdrawals and produces 40% of the food (Ayars et al., 2006). With water becoming scarce especially in semi-arid countries, pressure is mounting to produce more food with less water (Khouri et al., 2011, Wright and Cadiero, 2011). In addition, insufficient and unreliable water supply in less developed countries are often the main cause of poverty and hunger (Ringler and Zhu, 2015).
In China, one of the most water-short countries in the world, irrigation and food supply are intrinsically linked. Seventy percent of the food required for 1.3 billion people is produced on irrigated land. In addition, rapid development of urbanization and industrialization will use more water in the future and then the already decreasing resources require agriculture to produce more food with less water. Therefore, improving the irrigation efficiency in China while maintaining its original yield is an important challenge and a priority for Chinese government (Meng et al., 2013, Long et al., 2003).
Deficit irrigation has been shown to reduce evapotranspiration in regions with deep groundwater (Zhang et al., 2004, Fereres and Soriano, 2007) and in several cases without reducing the crop yield (Jaimez et al., 1999, Kirnak et al., 2002, Kirda et al., 2005). Also, lots of studies (Kang et al., 2002, Sun et al., 2006, Mojaddam et al., 2011) have shown that water use efficiency WUE (i.e., the ratio of crop yield and the amount of water irrigated) can be improved by applying less irrigation water. These studies, however, usually consider the crop-soil system and neglect the water for crop evapotranspiration from groundwater in the shallow groundwater regions.
Generally, with the recharging of excess irrigation water in the irrigated land with flooding irrigation practice, many irrigation areas with shallow groundwater appeared. In such districts, groundwater upflow can play an important role in contributing to crop water use and then the vertical water flux in groundwater tables needs to be quantified (Yang et al., 2007). Fluxes in a groundwater table depend on several factors such as groundwater table depth, soil hydraulic properties, crop growth stage, weather and irrigation. Several studies that have quantified the amount of water derived from groundwater found that 20%-40% of the evapotranspiration can be met by capillary rise from water tables at depths of 0.70–1.50 m (Ragab et al., 1988, Khandker, 1994, Ayars and Schoneman, 2006, Gowing et al., 2009, Fan and Miguez-Macho, 2010, Gao et al., 2015). Based on a lysimeter experiment, Yang et al. (1999) reported that the contribution of groundwater to maize was 16% with groundwater depth of 0.7–1.3 m. Similarly, Babajimopoulos et al. (2007) reported that 18% of the water transpiration originated from a mean groundwater of 0.58 m. For a long term and regional scale, Chen et al. (2016) reported that the contribution of groundwater to evapotranspiration in regions has an obvious increasing trend with reduction of water diversion, accounting for 20% in 2013, which is doubled compared with that in 1980. Furthermore, Huo et al., 2012a, Huo et al., 2012b found a linear relationship between groundwater contribution and groundwater depth for a lysimeter experiment with water table depths between 1.5 m to 3.5 m.
Recently, some empirical equations and numerical models have been used to quantify the contribution of groundwater to crop water consumption at shallow groundwater areas (Sepaskhah et al., 2003, Raes and Deproost, 2003, Liu et al., 2006). Torres and Hanks (1989) reported that the contribution of water table to evapotranspiration simulated by WATABLE model varied from 92% to 9% for fine sandy loam at 50 cm to 150 cm. Sepaskhah et al. (2003) found that a linear descending relationship between water table contribution and groundwater depth. A number of studies including experimental and model work have proved that shallow groundwater can contribute to part of the water use of crops and enhance crop yield. To our knowledge, however, few studies describes the impact of different irrigation amount on the contribution of shallow groundwater to crop water consumption.
Therefore, the general objective of the study is to (1) study the variation of upward capillary flux under deficit irrigation; (2) investigate the impact of deficit irrigation on the evapotranspiration and water productivity of maize in shallow groundwater areas; (3) investigate the contribution of groundwater to crop water consumption and the impact of deficit irrigation on the contribution of groundwater in shallow groundwater areas.
Section snippets
Study area
Field experiments were conducted in 2013 and 2014 at the experimental farm Shuguang (Fig. 1) in the 12000 km2 Hetao irrigation district with severe water scarcity and high groundwater tables (Yang et al., 2009), which is located at an elevation of 1040 m in the north-west of Inner Mongolia in China. The district has a typical arid and semi-arid continental climate. Mean annual rainfall is 136–222 mm per year, and potential evaporation is 1940–2400 mm per year. Winters are cold with minimal snow
Soil moisture content during growing period
Through analyzing the soil moisture (Fig. 2), at planting time at the end of April, the moisture contents for all treatments for both years were nearly the same and varied from a low 0.10 cm3/cm3 to a high of 0.16 cm3/cm3. Then as the soil thawing further at deeper depth, the moisture contents declined by about 0.02–0.03 cm3/cm3 over a 40-day period in 2013 for all treatments. The moisture contents were not greatly affected in any of the irrigation treatments by the same amount of irrigation on
Conclusions
Based on two-year deficit irrigation experiments in shallow groundwater regions, the impact of deficit irrigation on evapotranspiration and water use was investigated. Results show that the upward flux at the bottom of root zone was greater for low irrigation treatment than that for the other irrigation treatments with more water application. Increasing irrigation rates resulted in increased maize yield per unit area, but did not affect the water use efficiency. Upward movement of water from
Acknowledgements
This research was supported by project from the National Nature Science Foundation of China (51322902) and the Ministry of Water Resources of China (201401007). The authors would like to thank the editor and all the reviewers for their insightful comments and constructive suggestions.
References (55)
- et al.
Contribution to irrigation from shallow water table under field conditions
Agric. Water Manage.
(2007) - et al.
Quantitative response of greenhouse tomato yield and quality to water deficit at different stages
Agric. Water Manage.
(2013) - et al.
An improved water use efficiency of cereals under temporal and spatial deficit irrigation in north China
Agric. Water Manage.
(2010) - et al.
The effect of salinity on water productivity of wheat under deficit irrigation above shallow groundwater
Agric. Water Manage.
(2009) - et al.
The effect of irrigation frequency on water and carbon relations in three cultivars of sweet pepper (Capsicum Chinense Jacq), in a tropical semiarid region
Sci. Hortic.-Amsterdam
(1999) - et al.
Effect of shallow groundwater table on crop water requirements and crop yields
Agric. Water Manage.
(2005) - et al.
Effects of limited irrigation on yield and water use efficiency of winter wheat in the Loess Plateau of China
Agric. Water Manage.
(2002) - et al.
Crop coefficient and ratio of transpiration to evapotranspiration of winter wheat and maize in a semi-humid region
Agric. Water Manage.
(2003) - et al.
Effects of the shallow water table on water use of winter wheat and ecosystem health: implications for unlocking the potential of groundwater in the Fergana Valley (Central Asia)
Agric. Water Manage.
(2014) - et al.
Crop Yield Response and N-fertiliser recovery of maize under deficit Irrigation
Field Crops Res.
(2005)