نوع مقاله : مقاله پژوهشی
عنوان مقاله English
نویسندگان English
Iran is facing a serious water crisis due to limited resources, climate change, and excessive extraction of groundwater, which has increased the importance of optimizing water consumption, especially in the agricultural sector. This study, aiming to improve agricultural water management, investigated an irrigation scheduling method based on canopy temperature (Tc) and Crop Water Stress Index (CWSI) for forage maize (SC704) under surface drip irrigation in Karaj. The experiment was conducted with three irrigation levels (60, 80, and 100 percent of water requirement) and three replications in the summer of 2024, and a handheld infrared thermometer was used to monitor corn leaf temperature. Utilizing the empirical IDSO method, baseline upper canopy temperatures for forage corn in July, August, and September were determined to be 4.55, 3.98, and 5.00 °C, respectively. Furthermore, baseline lower canopy temperature relationships for the aforementioned months were established as follows: (Tc-Ta)c = -0.0781(AVPD)+3.7018, (Tc-Ta)c = -0.0694(AVPD)+3.3326, and (Tc-Ta)c = -0.0859(AVPD)+4.0814. The coefficient of determination (R²) values for these relationships were 0.86, 0.81, and 0.83, respectively, indicating the high accuracy of the regression relationships derived between canopy-air temperature difference (Tc-Ta) and atmospheric vapor pressure deficit (AVPD). Finally, the CWSI was extracted for different irrigation treatments. The average CWSI in irrigation treatments of 60, 80, and 100 percent of water requirement was calculated as 0.57, 0.48, and 0.29, respectively. Considering the non-stress treatment (full irrigation treatment), specific equations for determining irrigation timing during three different growth stages were respectively presented as (Tc–Ta)c = –0.0679(AVPD) + 3.8121, (Tc–Ta)c = –0.0341(AVPD) + 3.6628, and (Tc–Ta)c = –0.0653(AVPD) + 4.3019, based on air vapor pressure deficit (AVPD) and the temperature difference (Tc–Ta), which enables more precise and climate-adapted irrigation scheduling.
کلیدواژهها English
Water scarcity in Iran, exacerbated by population growth, drought, and excessive groundwater use, poses serious threats to agricultural sustainability and food security. Given the urgent need to improve water productivity, particularly in agriculture, accurate irrigation management based on real-time plant responses is essential. The Crop Water Stress Index (CWSI), calculated from canopy temperature (Tc), has emerged as a reliable and quantitative indicator for assessing plant water status and has proven effective in irrigation scheduling and enhancing water use efficiency across diverse crops and climates.
This study focuses on forage maize, a strategic crop in Karaj, where water resources are limited. Despite the widespread adoption of CWSI-based irrigation scheduling globally, its application in Iranian agriculture remains limited. This research aims to apply the CWSI approach under surface drip irrigation to optimize irrigation scheduling. Objectives include determining upper and lower baseline equations for CWSI calculation and establishing crop stage-specific irrigation relationships based on Tc and AVPD, with the potential to improve water management in arid regions.
The study was conducted in 2024 at the Research Farm of the College of Agriculture and Natural Resources, University of Tehran, in Karaj (50°95′ E, 35°80′ N, 1293 m elevation). Prior to planting, soil samples were taken from three depths across the field, and irrigation water was tested for quality. A randomized complete block design (RCBD) was used with three irrigation treatments (60, 80, and 100 percent of crop water requirement) and three replications, using forage maize (SC704). Each 12 m² plot contained four rows (75 cm row spacing, 20 cm intra-crop). Irrigation was applied via drip tape. Crop water requirements were estimated using reference evapotranspiration (ET₀), calculated with ET₀ Calculator V3.2 software based on meteorological data. Actual crop evapotranspiration was determined by applying crop coefficients (Kc) from FAO-56 guidelines, adjusted for local climate. Water Stress treatments began at the four- to five-leaf stage.
The Crop Water Stress Index (CWSI) was calculated based on the difference between canopy temperature (Tc) and air temperature (Ta), using lower limit (non-stressed) and upper limit (fully stressed) baseline equations. The lower baseline, dependent on AVPD and relative RH, indicates maximum transpiration, while the upper baseline represents zero transpiration. Canopy temperature was measured with a handheld infrared thermometer at multiple plant heights and four cardinal directions, hourly from 8:30 to 14:30. Leaf temperature data from post-irrigation (non-stressed) and pre-irrigation (all treatments) were used to develop baseline equations and calculate CWSI, enabling assessment of plant water status under different irrigation levels.
Upper and lower limit baseline equations were established using the Idso method for different maize growth stages. Field data showed that as AVPD increased, the absolute (Tc−Ta) difference also rose, with variations influenced by growth stage and irrigation level. Using the developed baselines, CWSI was calculated for the three irrigation treatments, and its relationship with crop evapotranspiration was analyzed. Results revealed that CWSI increased as irrigation decreased, with the highest values observed in August under the severe deficit treatment (60 percent of crop water requirement). To facilitate accurate irrigation scheduling under non-stressed conditions, specific equations were developed to estimate allowable (Tc−Ta)c based on AVPD during three distinct growth periods. These equations enable optimized irrigation timing using real-time temperature and humidity data.
Irrigation scheduling based on canopy temperature (Tc) was evaluated for forage maize in Karaj using an infrared thermometer. Three drip irrigation treatments (60, 80, and 100 percent of water requirement) were applied, yielding CWSI values of 0.57, 0.48, and 0.29, respectively. Using the full irrigation (non-stressed) treatment as reference, equations were developed to determine irrigation timing at three growth stages based on AVPD and the canopy-to-air temperature difference (Tc−Ta). One of the limitations of this approach is the need to establish site- and growth-stage-specific baselines using field data, along with challenges in measuring canopy temperature during early growth stages due to sparse foliage. It is recommended that infrared thermometry be used to determine irrigation timing, while water volume be estimated through complementary methods such as soil moisture monitoring or meteorological data.
The study was funded by the University of Tehran, Faculty of Agriculture and Natural Resources, Department of Irrigation and Reclamation, Iran, Tehran.
Data curation: Mohammad Mahdi Jafari; Investigation: Mohammad Mahdi Jafari; Formal analysis: Mohammad Mahdi Jafari.
All authors contributed equally to the study design and execution, data collection, statistical analysis, interpretation of data and results, preparation of the original draft, validation of results, and revision and finalization of the manuscript.
The authors’ specific contributions based on the thesis are as follows:
First Author (Student): Investigation, Data curation, Formal analysis, Writing—original draft preparation.
Second Author (Supervisor): Conceptualization, Methodology, Supervision, Validation, Writing—review and editing.
Third Author (Supervisor): Conceptualization, Supervision, Writing—review and editing.
Fourth Author (Co-supervisor): Conceptualization, Supervision, Writing—review and editing.
All authors contributed equally to the conceptualization of the article and writing of the original and subsequent drafts.
This declaration does not apply to the use of basic tools for checking grammar, spelling, references, etc..
Data available on request from the authors.
We would like to express our gratitude to the esteemed Vice Chancellor for Research of the University of Tehran / Faculty of Agriculture and Natural Resources for their financial support / moral support / cooperation in conducting the present study.
The authors avoided data fabrication, falsification, and plagiarism, and any form of misconduct.
The authors declare no conflict of interest.
