Determination of Crop Water Stress Index for Irrigation Scheduling of Turfgrass (Cynodon dactylon L. Pers.) under Drought Conditions

Document Type : Research Paper


The crop water stress index (CWSI) is a valuable tool for monitoring and quantifying water stress as well as for irrigation scheduling. A field experiment was conducted during spring and summer 2012 at Research Station of College of Agriculture and Natural Resources of Darab, Shiraz University, Iran, to determine CWSI of  turfgrass for irrigation scheduling. Four levels of water regimes including well watered [Irrigation according to 100% field capacity (FC)], mild drought stress (75% FC), severe drought (50% FC), and most severe drought (25% FC) stress were arranged in a randomized complete block design with four replicateions. The highest monthly average value of CWSI for all treatments was reached in August and decreased in September slightly. In all treatments the CWSI values showed an increasing trend from June (0.097 in well watered treatment) to August (0.684 under most severe drought) as a result of higher vapor pressure deficit values and negatively increase in Tc-Ta differential. Also, significant differences were observed between mean CWSI values of well watered and mild drought, with severe drought and most severe drought treatments. The color grading number for mild drought treatment in turfgrass decreased sharply from 8 to 4 at the start of the experiment in July, and remained constant (3) for August and September. The amounts of irrigation water more than 75% FC did not affect visual quality of turfgrass, which appeared to be sufficient to fulfill an acceptable turfgrass quality. A negative relationship was found between CWSI with water applied and color quality under different irrigation regimes. It appeared that under arid and semi-arid conditions, such as southern Iran, where the amount of water is a major limiting factor, the amount of applied water could be lowered to 75% FC without any loss in visual quality of turfgrass with the seasonal CWSI being kept about 0.15.


Article Title [Persian]

تعیین شاخص تنش خشکی گیاه برای برنامه ریزی آبیاری چمن (Cynodon dactylon L. Pers.) در شرایط تنش خشکی

Abstract [Persian]

شاخص تنش خشکی گیاه ابزاری سودمند برای پایش و به کمیت در آوردن تنش خشکی در برنامه ریزی آبیاری است. آزمایشی مزرعه­ای در بهار و تابستان 1392 در ایستگاه تحقیقاتی دانشکده کشاورزی و منابع طبیعی داراب، دانشگاه شیراز برای تعیین شاخص تنش خشکی گیاه در برنامه ریزی آبیاری به اجرا در آمد. چهار سطح رژیم رطوبتی شامل آبیاری مطلوب (آبیاری بر اساس 100% ظرفیت مزرعه)، تنش ملایم (75% ظرفیت مزرعه)، تنش شدید (50% ظرفیت مزرعه) و تنش خیلی شدید (25% ظرفیت مزرعه) در قالب طرح کاملا تصادفی با چهار تکرار به اجرا در آمد. بیشترین میزان شاخص تنش خشکی گیاه در همه تیمارها در مرداد ماه مشاهده شد و در شهریور ماه این شاخص به صورت جزئی کاهش یافت. در همه تیمارها شاخص تنش خشکی روندی افزایشی از خرداد ماه (097/0 در آبیاری مطلوب) تا مرداد ماه (684/0 در تنش شدید) داشت که تابعی از میزان کمبود فشار بخار محیط بود و رابطه منفی با تفاوت دمای سایه انداز و دمای هوا داشت. همچنین تفاوت میانگین مقدار شاخص تنش خشکی در شرایط آبیاری مطلوب و تنش خشکی ملایم با تنش خشکی شدید و بسیار شدید معنی­دار به دست آمد. در خرداد ماه در شروع آزمایش بر اساس شاخص درجه بندی رنگ در تنش ملایم این شاخص از 8 به 4 کاهش یافت و تا مرداد و شهریور در حد 3 ثابت باقی ماند. مقدار آبیاری بیشتر از 75% ظرفیت مزرعه تاثیری روی کیفیت رنگ چمن نداشت. به نظر می­رسد که تنش ملایم برای رسیدن به کیفیت مطلوب چمن کافی باشد. شاخص تنش خشکی گیاه رابطه منفی با میزان آب آبیاری و کیفیت رنگ چمن در شرایط مختلف رژیم آبیاری داشت. به نظر می­رسد که در شرایط خشک و نیمه خشک مانند جنوب ایران که میزان آب عامل مهمی در آبیاری است مقدار آب آبیاری می تواند به 75% ظرفیت مزرعه کاهش یابد بدون این که در کیفیت ظاهری رنگ چمن تغییری حاصل شود به طوری که در این شرایط شاخص تنش خشکی فصلی گیاه در حد 15/0 باقی بماند.

Keywords [Persian]

  • تنش خشکی
  • چمن
  • شرایط نیمه خشک
  • کیفیت ظاهری
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Table captions:
Table 2. Soil physicochemical characteristics of  the experimental site
Table3. Page numbers of Munsell Color Chart, color numbers and visual quality values (Wilde and Voigt, 1977)
Table 4. Monthly and mean CWSI values for turfgrass as affected by drought treatments  
Table 5. Visual color quality values of turfgrass during the experiment as affected by drought treatments
Figure captions:
Figure 1. Stressed and non-stressed baselines for calculation of CWSI in turfgrass.
VPD = vapor pressure deficit.
Figure 2. Relationship between CWSI and water applied in turfgrass.
Figure 3. Relationship between CWSI and visual color quality values in turfgrass.