Evaluating the impact of groundwater on cotton growth and root zone water balance using Hydrus-ID coupled with a crop growth model

Authors: HAN, MING - Chinese Academy Of Sciences; ZHAO, CHENGYI - Chinese Academy Of Sciences; SIMUNEK, JIRI - University Of California; Feng, Gary

Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/30/2015
Publication Date: 7/15/2015
Publication URL: http://handle.nal.usda.gov/10113/61119
Citation: Han, M., Zhao, C., Simunek, J., Feng, G.G. 2015. Evaluating the impact of groundwater on cotton growth and root zone water balance using Hydrus-ID coupled with a crop growth model. Agricultural Water Management. 160:64-75.

Interpretive Summary: Groundwater is an important factor that needs to be considered when designing sustainable land management. However, its impact on plant functioning and the root zone water balance has not been sufficiently examined, partly because numerical models have not fully considered all the interactions between the soil water balance and plant growth. In this study, simulations were performed to examine the influence of groundwater on cotton growth and the root zone water balance using a numerical model, which coupled Hydrus-1D with a simplified crop growth model from SWAT. The simulation results of the coupled model were compared with experimental data obtained from cotton field experiments. Results suggest that volumetric soil water contents, LAIs, above ground biomass and cotton yields simulated by the coupled model were in good agreement with the measurements. Additional model simulations showed that groundwater is a major source of water for cotton growth. Compared to a control simulation that had no groundwater, 23% of crop transpiration is supplied by a capillary rise from groundwater, producing an increase in cotton yield by 20%. The model simulations also showed that the cotton growth and root zone water balance are very sensitive to the depth of the groundwater table and that cotton growth, in turn, affects subsurface water fluxes, such as capillary rise. When the groundwater table depth was raised from its positions in 2007 by less than 0.52 m, it had 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 LAI and yield in this region. 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. Similarly, when the groundwater table has a positive effect on cotton growth, cotton growth would in turn increase capillary rise from groundwater by increasing LAI, and potential transpiration. On the other hand, when the groundwater table is raised more than 0.52 m, decreasing cotton LAI and actual transpiration decrease capillary rise from groundwater. It can be concluded that groundwater is a crucial factor that needs to be taken into consideration when evaluating agricultural land management in this region. Our work, presented in this manuscript, provides a useful modeling tool for evaluating local land management and for designing sustainable water management.

Technical Abstract: Groundwater is an important factor that needs to be considered when evaluating the water balance of the soil-plant-atmosphere system and the sustainable water management. However, the impact of shallow groundwater on the root zone water balance and cotton growth is not fully understood. In this study, we have first analyzed the influence of the groundwater table depth on the seasonal maximum leaf area index of cotton, the average seasonal water stress, cotton yield, actual transpiration, actual evaporation, and capillary rise, using the Hydrus-1D variably-saturated soil water flow model coupled with a simplified crop growth model from SWAT. The coupled model has been first calibrated and validated 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 has shown a reasonable agreement for all variables. Additionally, with a validated model, we have carried out numerical experiments from which we have concluded that groundwater is a major water resource for cotton growth in this region. The capillary rise from groundwater contributes almost 23% of crop transpiration when the average groundwater depth is 1.84 m, which is the most suitable groundwater depth for this experimental site. We have concluded that cotton growth and various components of the soil water balance are highly sensitive to the groundwater table level. Different positions of the groundwater table showed both positive and negative effects on cotton growth. Likewise, cotton growth has a significant impact on the capillary rise from groundwater. As a result, groundwater is a crucial factor that needs to be considered when evaluating agricultural land management in this arid region. The updated Hydrus-1D model developed in this study provides a powerful modeling tool for evaluating the effects of the groundwater table on local land management.