HYDRUS Simulation of Sustainable Brackish Water Irrigation in a Winter Wheat-Summer Maize Rotation System in the North China Plain

Kangkang He,Yanmin Yang,Suying Chen,Xiaojing Liu,Yonghui Yang,Feng Gao,Qiuli Hu

doi:10.3390/w9070536

Abstract

Freshwater resources in the North China Plain (NCP) are near depletion due to the unceasing overexploitation of deep groundwater, by far the most significant source of freshwater in the region. To deal with the deepening freshwater crisis, brackish water (rich but largely unused water in agriculture) is increasingly being used in irrigation in the region. However, inappropriate irrigation with brackish water could lead to soil salinization and cropland degradation. To evaluate such negative impacts, the HYDRUS-1D model was used to simulate soil salt transport and accumulation under 15 years of irrigation with brackish water. The irrigation scenarios included brackish water irrigation during the wintering and jointing stages of winter wheat and then freshwater irrigation just before the sowing of summer maize. Freshwater irrigation was done to leach out soil salts, which is particularly vital in dry years. For the littoral region of the plain, HYDRUS-ID was used to simulate the irrigated cropping system stated above for a total period of 15 years. The results showed that it was feasible to use brackish water twice in one year, provided freshwater irrigation was performed before sowing summer maize. Freshwater irrigation, in conjunction with precipitation, leached out soil salts from the 100 cm root-zone depth. The maximum salt accumulation was in the 160–220 cm soil layer, which ensured that root-zone soil was free of restrictive salinity for crop growth. Precipitation was a critical determinant of the rate and depth leaching of soil salt. Heavy rainfall (>100 mm) caused significant leaching of soluble salts in the 0–200 cm soil profile. Salt concentration under brackish water irrigation had no significant effect on the variations in the trend of soil salt transport in the soil profile. The variations of soil salinity were mainly affected by hydrological year type, for which the buried depth of soil salt was higher in wet years than in dry years. The study suggested that 15 years of irrigation with brackish water is a reliable and feasible mode of crop production in coastal regions with a thick soil column above the water table. The scheme proposed in this study allowed the use of brackish water in irrigation without undue salinization of the crop soil layer, an intuitive way of resolving the deepening water crisis in the NCP study area and beyond.

Highlights

A deepening water shortage is gradually developing into one of the most pressing global crises.Nearly 1.7 billion of the world’s population are faced with groundwater shortage, and it is projectedWater 2017, 9, 536; doi:10.3390/w9070536 www.mdpi.com/journal/waterWater 2017, 9, 536 that half of the world will face this worsening crisis by 2030 [1]
It shows that whereas EC of the saturated extract (ECe) varied with time for the 0–200-cm soil layer under the scenarios, it was almost constant for thefor
Theprofile soil profile was divided sub-layers based on thebased salt tolerance ofcapacity winter wheat andwheat summer layerThe above into two sub-layers on the saltcapacity tolerance of winter and maize

Summary

Introduction

A deepening water shortage is gradually developing into one of the most pressing global crises.Nearly 1.7 billion of the world’s population are faced with groundwater shortage, and it is projectedWater 2017, 9, 536; doi:10.3390/w9070536 www.mdpi.com/journal/waterWater 2017, 9, 536 that half of the world will face this worsening crisis by 2030 [1]. Over-pumping of water for crop production has resulted in rapid depletion of these aquifers, which are the largest in the world [6]. The plain is one of the most important grain production regions, with a pervasive water scarcity driven by excessive groundwater exploitation. Based on analysis of research studies [8,9], agriculture is the main sector with chronic over-exploitation of groundwater resources in the plain region [10]. The coastal plain in the east of the NCP is a classic groundwater resource depletion zone, where water levels in both the shallow and deep aquifers have been rapidly declining for decades and deep aquifer water levels have fallen by 110 m [12,13]

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