Articles | Volume 20, issue 1
https://doi.org/10.5194/hess-20-487-2016
https://doi.org/10.5194/hess-20-487-2016
Research article
 | 
29 Jan 2016
Research article |  | 29 Jan 2016

Sensitivity of water stress in a two-layered sandy grassland soil to variations in groundwater depth and soil hydraulic parameters

M. Rezaei, P. Seuntjens, I. Joris, W. Boënne, S. Van Hoey, P. Campling, and W. M. Cornelis

Abstract. Monitoring and modelling tools may improve irrigation strategies in precision agriculture. We used non-invasive soil moisture monitoring, a crop growth and a soil hydrological model to predict soil water content fluctuations and crop yield in a heterogeneous sandy grassland soil under supplementary irrigation. The sensitivity of the soil hydrological model to hydraulic parameters, water stress, crop yield and lower boundary conditions was assessed after integrating models. Free drainage and incremental constant head conditions were implemented in a lower boundary sensitivity analysis. A time-dependent sensitivity analysis of the hydraulic parameters showed that changes in soil water content are mainly affected by the soil saturated hydraulic conductivity Ks and the Mualem–van Genuchten retention curve shape parameters n and α. Results further showed that different parameter optimization strategies (two-, three-, four- or six-parameter optimizations) did not affect the calculated water stress and water content as significantly as does the bottom boundary. In this case, a two-parameter scenario, where Ks was optimized for each layer under the condition of a constant groundwater depth at 135–140 cm, performed best. A larger yield reduction, and a larger number and longer duration of stress conditions occurred in the free drainage condition as compared to constant boundary conditions. Numerical results showed that optimal irrigation scheduling using the aforementioned water stress calculations can save up to 12–22 % irrigation water as compared to the current irrigation regime. This resulted in a yield increase of 4.5–6.5 %, simulated by the crop growth model.

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Short summary
The sensitivity of the combined model (LINGRA-N and HYDRUS-1D) to hydraulic parameters, water stress, crop yield and lower boundary conditions was assessed. We showed that it is sufficient to estimate limited amount of key parameters in optimization strategies. A combined modelling approach could increase water use efficiency (12–22.5 %) and yield (5–7%) by changing irrigation scheduling. Result calls for taking into account weather forecast and soil water content data in precision agriculture.