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 Title: Crop-water stress index models for cool season turfgrasses Author(s): Martin, Dennis Loren Doctoral Committee Chair(s): Wehner, D. Department / Program: Agriculture, AgronomyEngineering, Agricultural Discipline: Agriculture, AgronomyEngineering, Agricultural Degree Granting Institution: University of Illinois at Urbana-Champaign Degree: Ph.D. Genre: Dissertation Subject(s): Agriculture, Agronomy Engineering, Agricultural Abstract: Crop Water Stress Index (CWSI) technology has shown potential in improving irrigation timing as it determines timing based on the plant's need. Research was conducted to better apply this technology to turf management. The objectives of this study were (i) to determine the complexity of model needed to accurately calculate the CWSI, (ii) to determine if a single model is appropriate across both Kentucky bluegrass (Poa pratensis L.) (KB) and creeping bentgrass (Agrostis palustris Huds.) (CB), and (iii) to evaluate the performance of CB when managed under different CWSI models.Models were developed for predicting the upper and lower limits of the canopy-air temperature difference ((T$\sb{\rm c}$-T$\sb{\rm a}$)$\sb{\rm UL}$ and (T$\sb{\rm c}$-T$\sb{\rm a}$)$\sb{\rm LL}$) of five KB and one CB for use in calculating the empirical CWSI. Cultural regimes were 196 kg N ha$\sp{-1}$ yr$\sp{-1}$ for all grasses, and cutting heights of 9.5 and 48 mm for CB and KB respectively.Use of vapor pressure deficit (VPD), net radiation (R$\sb{\rm n}$), and wind speed (WS) was required to accurately predict (T$\sb{\rm c}$-T$\sb{\rm a}$)$\sb{\rm LL}$. When tested on a validation data set, an energy balance equation accounted for less variation in T$\sb{\rm c}$-T$\sb{\rm a}$ of turf than a model using VPD, R$\sb{\rm n}$, and WS. Net radiation and WS terms were required to best predict (T$\sb{\rm c}$-T$\sb{\rm a}$)$\sb{\rm UL}$.Irrigation of CB was scheduled by 4 CWSI models at 3 CWSI set points (0.25, 0.50, and 0.75). Irrigation (1.3 cm) was applied when the CWSI was $\geq$ the CWSI set point. Variables groups used to calculate (T$\sb{\rm c}$-T$\sb{\rm a}$)$\sb{\rm LL}$ in models I-III were VPD; VPD and R$\sb{\rm n}$; and VPD, R$\sb{\rm n}$, and WS. Model I calculated (T$\sb{\rm c}$-T$\sb{\rm a}$)$\sb{\rm UL}$ by solving the equation for (T$\sb{\rm c}$-T$\sb{\rm a}$)$\sb{\rm LL}$ where the vapor pressure gradient equals 0. Variables used to calculate (T$\sb{\rm c}$-T$\sb{\rm a}$)$\sb{\rm LL}$ in models II and III were R$\sb{\rm n}$; and R$\sb{\rm n}$ and WS. Model IV utilized an energy balance approach.The number of irrigation events, quantity of water applied, and color ratings of CB declined with increasing model complexity and increasing value of the CWSI set point.At locations where environmental conditions are variable, empirical CWSI models must account for the effects of VPD, R$\sb{\rm n}$, and WS in order to accurately assess the CWSI. A single CWSI model may be appropriate for KB cultivars managed alike. A separate CWSI model for CB appears necessary. Color of CB depends on both CWSI model type and CWSI at which irrigation is applied. Issue Date: 1990 Type: Text Language: English URI: http://hdl.handle.net/2142/22835 Rights Information: Copyright 1990 Martin, Dennis Loren Date Available in IDEALS: 2011-05-07 Identifier in Online Catalog: AAI9026263 OCLC Identifier: (UMI)AAI9026263
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