Cotton-producing area in Xinjiang of China tripled during the past 20 years. Currently, more than 50% of the national cotton production is supplied by Xinjiang. Aksu oasis, located in Southern Xinjiang, is a major cotton-producing area of Xinjiang. This region is characterized by an arid climate with extremely high ratio of evaporation to precipitation. Thus, water resource is one of the most critical factors that restricts the sustainable production of cotton.
In the Aksu oasis with low precipitation, groundwater is important to the development of the society and economy, as well as the production of cotton. It also plays an important role in the water balance of the soil-plant-atmosphere system. However, the effect of groundwater on cotton growth and the root zone water balance is not very clearly.
Recent years, the inappropriate land management has resulted in many problems in this ecologically fragile region (i.e. Aksu oasis). Therefore, it is necessary to evaluate the impact of groundwater on cotton growth and the root zone water balance to design a sustainable land management in this arid region.
To study the impact of groundwater on cotton growth and soil water dynamics, HAN Ming et al. implemented a crop growth model based on the crop growth model of the SWAT model into Hydrus-1D (one-dimensional) model. They simplified the SWAT crop growth model to simulate (only) cotton growth, including its phenological development based on daily accumulated heat units. Researchers firstly calibrated and validated the coupled model by using field observations of soil water content, leaf area index, cotton height, the above ground biomass, and cotton yield comparisons between measured and modeled variables, and the results showed a reasonable agreement for all variables.
The results indicated that groundwater is a major water resource for cotton growth in the Aksu oasis. The depth of groundwater table has significant positive and negative effects on cotton growth and various components of the soil water balance. For example, groundwater has a positive effect on cotton growth by making more water available in the root zone and reducing cotton water stress and thereby enhancing the maximum cotton leaf area index and yield in this region when the groundwater table depth is raised from its positions (i.e. 0.52 m in 2007); however, if the groundwater table is raised by more than 0.52 m, it then has a negative effect on cotton growth, mainly by creating anaerobic conditions in the root zone.
The suitable seasonal averaged groundwater depth of experiment field is 1.84 m, and the capillary rise from groundwater contributes almost 23% of crop transpiration when the average groundwater depth is 1.84 m. Thus, groundwater needs to be taken into consideration when evaluating agricultural land management in this arid region. This study provides a useful modeling tool for evaluating local land management and for designing sustainable conditions of arid oases.
This study was published in Agricultural Water Management in October 2015.
Prof. ZHAO Chengyi
State Key Laboratory of Oasis Desert and Ecology, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences