Turf loss from freezing injury results in costly re-establishment, especially with turfgrasses such as perennial ryegrass (Lolium perenne L.) having poor low-temperature hardiness. Studies are limited as to the influence of N and K on cold tolerance during dehardening periods in late winter when grasses are most susceptible to freezing injury. The objective of this study was to evaluate perennial ryegrass low temperature hardiness during deacclimation in response to N and K and associated effects on crown hydration, median killing temperature (LT50), shoot growth rate, tissue K concentration, soil exchangeable K, and low temperature disease. Treatments included five rate levels of N (49, 147, 245, 343, and 441 kg·ha-1·yr-1) in all factorial combinations with 3 rate levels of K (49, 245, and 441 kg·ha-1·yr-1). Low temperature tolerance was assessed using whole plant survival and electrolyte leakage (EL). Interactions between N and K were detected for all field measurements. The effects of N and K on survival LT50 were detected only during late winter periods in February 2004, N and K differences were lost by March. Late winter cold survival was negatively correlated with crown moisture, growth rate, and tissue K. Tissue K concentrations ranged from 28.6 to 35.9 g·kg–1 DM while soil K ranged from 121 to 261 mg·kg–1. Soil extractable K was not correlated with tissue K. Survival and EL LT50 were uncorrelated due to N and K interaction. Survival LT50 ranged from –9.0 to –13.6 °C. Maximum cold hardiness occurred when low to moderate N (49 to 147 kg·ha-1·yr-1) was applied with medium-high to high levels of K (245 to 441 kg·ha-1·yr-1), which corresponded to soil exchangeable K levels ranging from 200 to 260 mg·kg–1. Alternatively, similar K fertilization and soil K levels combined with high rates of N (343 and 441 kg·ha-1·yr-1) increased freeze stress and low temperature fungi (Typhula incarnata). At N rates routinely applied to perennial ryegrass, higher soil extractable K beyond those levels currently recommended for optimum shoot growth could provide some benefit in enhancing cold hardiness. Late fall applied N did not appear to increase the potential for winter injury.
Weihong Huang is a senior lecturer with Kingston University London, UK. Weihong's recent research focuses on semantic context-aware computing and its application in multimedia and knowledge management towards the Semantic Web. David Webster and Dawn Wood are PhD students at the University of Hull. Tanko Ishaya is a lecturer with the Centre for Internet Computing, the University of Hull, UK. His research focuses on the use of ontologies and agents for personalised e-learning services.
AbstractRecent developments of e-learning specifications such as Learning Object Metadata (LOM), Sharable Content Object Reference Model (SCORM), Learning Design and other pedagogy research in semantic e-learning have shown a trend of applying innovative computational techniques, especially Semantic Web technologies, to promote existing content-focused learning services to semantic-aware and personalised learning services. To facilitate this transforming process, this paper presents a novel context-aware semantic elearning approach to integrate content provision, learning process and learner personality in an integrated semantic e-learning framework. As the basis of the computational framework, a scalable and extensible generic context model is proposed to structure the semantics of contextual relations and concepts in various contexts, such as learning content description, learning model, knowledge object representation and learner personality. Corresponding technical and pedagogical developments of this framework also consider compatibility issues with existing technologies (eg, XML/Resource Description Framework) and specifications (eg, IEEE LOM) in order to achieve the best interoperability.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.