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Keywords: Precision Agriculture, Site Specific Agriculture, Global Positioning System, GPS, Fertilizer Application, Information System.Spatial and temporal variability in soil, crop and climate characteristics results in non optimal use of fertilizers when the application rate is kept constant within agricultural fields. Components to adapt the fertilizer rate to site specific conditions are identified and discussed. One of the basic components is positioning; both for data acquisition and for site specific control, a reliable and accurate positioning device has to be available. For a correct description of the spatial variability of soil properties often many samples are required. The possibility to reduce the number of soil samples by means of correlation with recorded plough draught is presented. Next to data recording, site specific control of a fertilizer spreader is discussed. Not just adaption of fertilizer rate to local requirements but also recording of applied fertilizer amount is important. Calculation of the required amount of fertilizer is based on information from different sources. To accommodate this data exchange, an information model for processing of spatial and temporal data is presented. Field experiments were conducted to evaluate the components and determine the required spatial scale of operation. To describe the soil variability, a grid with a cell size of 5 by 5 meter was necessary. The positioning system was sufficiently accurate but the implements for the application of fertilizer had to be modified to vary application rate that precise.

This study is aimed at making a contribution toward the didactic development of Environmental Education (EE).The issue under question is as follows (Part I): Which criteria govern commitment-oriented EE learning processes? To answer this question a number of theories were studied (Part II) and the practical experiences of several EE tutors evaluated (Part III). Then comparisons were made between the results (Part IV). The outcome of the comparison consists of several didactical clues for the didactics of EE learning processes. A brief description of the content of the different parts is given below.Part I: Underlying principles, issues and research questionsThe emergence of nature and environmental education is strongly linked to society's increased concern about the deterioration of nature and the environment. The introduction of EE in schools is believed to contribute toward solving the existing problems of the environment by teaching children to behave in a more environmental-friendly way. In this study we distance ourselves from this one-sided instrumental view. We perceive a form of education which transforms students into active participants in an ever-changing society. It demands a critical attitude and the willingness to shoulder joint responsibility. It does not include the provision of codes of behaviour. With this perception of education we see EE's primary objective as being man's commitment to nature.Someone committed to nature is taken to mean:a person prepared to and capable of weighing up the pros and cons of the interests of nature, against personal interests and society's interests;;a person who understands nature and the value of the environment for our mental and material well-being;a person who understands and values nature as the bearer of all life; anda person who is willing to personally take on the responsibility for nature and whose deeds give shape to this responsibility.Part II: The cornerstone of this studyThe question now arises as to h

This thesis investigates the disappointing use of computers and courseware in Dutch agricultural education. The central question is: How to develop courseware that will be used by teachers in agricultural education practice? On the basis of a theoretical frame of reference and by means of two case studies, the use of courseware in the context of Dutch agricultural education is described, understood and explained; and use influencing factors are established. Prescriptions are formulated that reckon with these factors and presumably increase the likelihood of use in practice. In two additional case studies, both the process and the organisation of courseware development for Dutch agricultural education are described, understood and explained. On the basis of this understanding, the prescriptions, phrased in the two preceding case studies, are adjusted and extended. The resulting prescriptions fit into five categories:a) courseware should address needsb) courseware should lead to lower costs of usec) courseware development should match teacher learningd) courseware development should reckon with contexts of usee) courseware development should be organised in manner that facilitates useincreasing developmentEssentially, the formulation of these use-increasing prescriptions as described above amounts to tailoring the courseware-development process to the context in which the courseware will be used. For this process of tailoring, insight is needed in the contingencies between courseware- development characteristics and the attributes of a context of use. These contingencies are described in the last chapter of this thesis. Risk prevention is the most important argument in selecting a specific courseware-development characteristic for a given context.In this research, this tailoring process is applied to Dutch agricultural education. The resulting alternative and supposedly use-increasing approach of courseware development can be characterised as situation specific, teach