Two-dimensional modeling of nitrogen and water dynamics for various N-managed water-saving irrigation strategies using HYDRUS

Abstract

a b s t r a c tNitrate losses are the dominant cause of the non-point source pollution under agricultural fields. In this study, the HYDRUS-2D model was first calibrated and validated using data collected during a two-year field investigation in a drip-irrigated maize field and then applied to evaluate the influence of 176 different N-managed water-saving irrigation scenarios on water and N dynamics and maize grain yield. Various scenarios were defined by combining 11 irrigation levels (IL = 0-100% with a 10% interval), 8 N fertilization rates (NR = 0-400 kg ha −1 with a 50 kg ha −1 interval) and two water-saving irrigation strategies: deficit irrigation (DI) and partial root-zone drying (PRD). Reliable estimates of soil NO 3 − -N concentrations (RMSE = 0.39-10.9 mg l −1 and MBE = −8.9-8.4 mg l −1 ), crop N uptake (RMSE = 3.9-8.9 kg ha −1 and MBE = −5.3-6.25 kg ha −1 ), and soil water contents (RMSE = 2.3-5.11 mm and MBE = 1.63-4.93 mm) were provided by HYDRUS-2D. Based on the simulated results, the fertigation strategy with NR = 200 kg ha −1 is an optimum strategy. For the higher fertigation rates (NR ≥ 250 kg ha −1 ), the NO 3 − -N leaching out of the surface layers (0-20 cm) increased by 0.1-183% while N uptake was enhanced by only 0.3-15%. On the other hand, reducing NR below this level would have resulted in severe economic losses. A 30% reduction in IL at NR = 200 kg ha −1 shows an enormous potential in lowering N leaching below different soil layers (12-99%) while reducing crop N uptake by only 5.4%. In addition, higher crop yield by 0.2-20.2% can be expected under PRD since crop N uptake is enhanced by more water available in the surface layers. While on the one hand, PRD ensures environmentally safer fertilizer applications, on the other hand, the economic objectives are met more easily under PRD than under DI. Additionally, it could be concluded that the HYDRUS-2D model, instead of labor-and time-consuming and expensive field investigations, could be reliably used for determining the optimal scenarios under both the DI and PRD strategies.

An application of the water footprint assessment to optimize production of crops irrigated with saline water: A scenario assessment with HYDRUS

“…Water or salinity stresses may reduce crop N uptake (Karandish and Šimůnek, 2017;Ramos et al, 2012) and lead to higher nutrient loads into aquifers as a byproduct of N leaching out of the root zone (Zhu et al, 2005;Thompson et al, 2007;Dudley et al, 2008;Burow et al, 2010;Dahan et al, 2014;. If fresh water is applied, N leaching may be lower under PRD than under DI due to a higher crop N recovery (Kang and Zhang, 2004;Kirda et al, 2005;Li et al, 2007;Wang et al, 2009;Hu et al, 2009;Wang et al, 2012;Karandish and Šimůnek, 2017), which could translate into lower groundwater contamination. Even so, no earlier studies have ever attempted to find the optimal combination of N fertilization rates and applied water levels under PRD irrigated with saline water.…”

“…Instead of carrying out laborious, time-consuming, and thus expensive field investigations with a limited number of treatments, an optimal N application rate can be estimated using a modeling approach (Karandish and Šimůnek, 2016a(Karandish and Šimůnek, , 2016b(Karandish and Šimůnek, , 2017. This may be especially advantageous in situations where it may be economically or technically impossible to carry out the project in the field (Li and Liu, 2011).…”

“…The concept behind PRD is different than behind DI and thus soil-watercrop relationships may be affected by these differences. While the HYDRUS model has been previously used to simulate soil water and nutrient dynamics under PRD (Karandish and Šimůnek, 2016a(Karandish and Šimůnek, , 2016b(Karandish and Šimůnek, , 2017, this has not yet been done while taking into account simultaneously both water and salinity stresses and their effects on soil-watercrop relationships. (ii) Similarly, little research has been carried out to find optimal management strategies with respect to both economic and environmental factors.…”

“…This may be especially advantageous in situations where it may be economically or technically impossible to carry out the project in the field (Li and Liu, 2011). Among a large number of analytical and numerical models simulating soil water and solute dynamics (e.g., Johnsson et al, 1987;Hutson and Wagenet, 1991;Ma et al, 2001;Šimůnek et al, 2008, 2016Doltra and Munoz, 2010), the HYDRUS (2D/3D) model (Šimůnek et al, 2008, 2016) is among the most powerful models for evaluating sound agricultural practices due to its flexibility in accommodating different types of boundary conditions for water flow and solute transport, its ability to simultaneously consider root uptake of water and nutrients, and its sophisticated graphical user interface (Li et al, 2015;Karandish and Šimůnek, 2017). The literature review reveals that there are many research gaps in this field of research.…”

“…After sowing, the experimental plots were irrigated every other day during both growing seasons. For the FI treatment, the net irrigation depth ( I [ ] n FI , mm) was calculated as follows (Karandish and Šimůnek, 2016a(Karandish and Šimůnek, , 2016b(Karandish and Šimůnek, , 2017: Soil water content (SWC) measurements TDR probes were used at least two times a day to measure SWCs in 5-cm depth increments during both growing seasons. Moreover, information about the movement of the wetting front during irrigation events was collected at least 10 times in each treatment by measuring SWCs one hour before, and immediately and 2, 6, 12, 24, 48, 72, and 96 hours after irrigation events in the 2010 growing seasons.…”