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A dynamic and fuzzy logic analysis of crop water -stress index for tall fescue (Festuca arundinacea)

Abdulelah A Al-Faraj, University of Nebraska - Lincoln

Abstract

The goal of this study was to study the effects of irradiance and vapor pressure deficit (VPD) on canopy temperature under different levels of soil moisture. Canopy-air temperature differential (Tc - Ta) was affected by the plant water status, irradiance level, and VPD levels. Tc - Ta increased with the decrease in the soil moisture content. The increase in canopy temperature coupled with a decrease in transpiration rate are signs of water stress progression. Tc - Ta increased as irradiance level increased regardless of the plant water status. Canopy temperature of well-watered plants decreased around 2.42°C for each 1 kPa decrease in air vapor pressure deficit under all irradiance level. For each 100 W m-2 increase in irradiance level, canopy temperature of well-watered plants increased around 0.6°C. ^ The fescue canopy was modeled using Laplace transfer functions, with irradiance and vapor pressure deficit as input variables and plant temperature as the output variable. Well-watered plants tended to respond as a second-order model, with a critical and under-damped response for most levels of step irradiance inputs. Moderately stressed plants approached critical and under-damped response conditions. Severely stressed plants tended to respond closely to a first order model. ^ A fuzzy logic crop water stress index (FL-CWSI) was developed, based on fuzzy logic theory. The FL-CWSI index is fast to develop and eliminates the need to include measurements of special variables i.e. canopy resistance, aerodynamic resistance, net radiation and sod heat flux needed for calculating the theoretical crop water stress index CWSI. Additionally, the use of FL-CWSI also eliminates the need to calculate baseline limits needed to make new calibrations of empirical CWSI's. The FL-CWSI was tested using growth chamber and greenhouse data. The results of testing demonstrated that the FL-CWSI model can predict water stress development. ^

Subject Area

Agriculture, Agronomy|Engineering, Agricultural

Recommended Citation

Al-Faraj, Abdulelah A, "A dynamic and fuzzy logic analysis of crop water -stress index for tall fescue (Festuca arundinacea)" (1999). ETD collection for University of Nebraska - Lincoln. AAI9929181.
http://digitalcommons.unl.edu/dissertations/AAI9929181

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