Calibration and Verification of the AquaCrop Model in Simulating the Yield, Dry Matter and Water Productivity of Grain Corn (Zea mays L.) under Different Irrigation Methods and Nitrogen Fertilizer Levels

بوم شناسی کشاورزی

Article 8, Volume 16, Issue 4 - Serial Number 62, December 2025, Pages 729-744   

Document Type: Research Article

DOI: 10.22067/agry.2024.88850.1201

Authors

zhaleh zarei¹; Hassan Heidari^{* 1}; Saeid Jalali Honarmand¹; Ali Bafkar²

¹Department of Plant Production and Genetics Engineering, Faculty of Agricultural Science and Engineering, Razi University, Kermanshah, Iran

²Department of Water Engineering, Faculty of Agriculture, Razi University, Kermanshah, Iran

Abstract

Introduction
The decrease in rainfall in recent decades and the occurrence of drought in Iran, which is one of the arid and semi-arid regions, as well as the significant wastage of water in the agricultural sector, have caused many researchers to look for new irrigation methods that lead to improve water consumption. Therefore, the importance of conducting this experiment is to reduce surface water evaporation, save water, reduce leaching and use of nitrogen fertilizer in maize cultivation. Nowadays, due to the decrease in rainfall and the excessive water consumption in the agricultural sector, the importance of water resources management has received more attention from researchers. Therefore, simulation models an effective role in evaluating irrigation management methods to improve water consumption in the agricultural sector. This study aimed to assess the AquaCrop model in terms of simulating the yield and biomass of maize under two methods of irrigation (wick and surface) and nitrogen fertilization (topdressing and fertigation).
Materials and Methods
This experiment was carried out in 2020 and 2021 in the Faculty of Agriculture of Razi University. Experimental treatments included wick irrigation and surface irrigation (at three levels of 100, 70, and 50%) and two levels of nitrogen fertilizer 100 and 50% of the plant's fertilizer requirement. The statistical design was factorial in the form of randomized complete blocks and was implemented in three replications. In the wick irrigation method, fertilizer was provided to the plant through tanks and in solution. In the surface irrigation method, fertilizer was topdressing on the soil surface. Nitrogen fertilizer was applied in three stages. In each watering, the amount of water used will be measured and recorded through the meter. At the end of the experiment, the data measured in the first and second years were used for calibration and validation, respectively. For both stages of calibration and validation of the model, the measured (observed) and simulated values of yield, biomass, canopy cover, and water productivity were compared and statistically analyzed. For statistical evaluation, root mean square error (RMSE), efficiency coefficient of the Nash-Sutcliffe model (EF), and Wilmot agreement index (d) were used.
Results and Discussion
The results indicated that the root mean square error (RMSE) for simulating canopy cover development under various irrigation and fertilizer treatments ranged from 1.5% to 6.1% during the calibration stage (2020) and from 2% to 6.4% during the verification stage (2021). The model's efficiency factor (EF) for canopy cover simulation was between 0.91 and 0.99 during the calibration stage and between 0.93 and 0.99 during the validation stage. For biomass simulation, the RMSE values ranged from 1.07 to 2.1 tons/ha in the calibration stage and from 1.4 to 2.9 tons/ha in the validation stage. The model's EF for biomass simulation ranged from 0.87 to 0.98 in the calibration stage and from 0.92 to 0.99 in the validation stage. These results demonstrate the model's high accuracy and reliability in simulating both canopy cover and biomass development across different treatments. AquaCrop simulation results showed that the model was able to simulate water productivity better than yield and total biomass so the coefficient of determination (R²) related to water productivity, yield, and biomass of maize was obtained as 0.82, 0.52, and 0.54 respectively.
Conclusion
The simulation of yield, dry matter, and water productivity in the calibration and verification stage was lower than the actual value in all treatments. The biggest difference between the observed and simulated values of yield, biomass and water productivity was observed in the wick treatment (first and second year). According to the obtained results, it can be concluded that AquaCrop was chosen well and within the expectations for the studied area and the ability of AquaCrop in the field to provide a low irrigation model like the wick method is suitable and practical.

Keywords

Calibration; Irrigation management; Modeling; Urea fertilizer; Verification

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