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INFLUENCE OF TIME OF APPLICATION ON THE PERFORMANCE OF GLIRICIDIA PRUNINGS AS A SOURCE OF N FOR MAIZE
- WILKSON MAKUMBA, BERT JANSSEN, OENE OENEMA, FESTUS K. AKINNIFESI
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- Journal:
- Experimental Agriculture / Volume 42 / Issue 1 / January 2006
- Published online by Cambridge University Press:
- 16 January 2006, pp. 51-63
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Asynchrony between nitrogen (N) released by organic materials and N demand by the crop leads to low N use efficiency. Optimizing the time of application could increase the N recovery. A field experiment was designed to determine the effects of time of application of Gliricidia sepium prunings and of the addition of small doses of inorganic N fertilizer on N recovery and yield of maize. Six split applications of gliricidia prunings (in October, December and February) were compared. The prunings were incorporated into the soil while fresh. The application in October was done four weeks before planting the maize. Higher N uptake and maize yields were obtained when gliricidia prunings were applied in October than when applied in December and February. The corresponding substitution values were 0.66, 0.32 and 0.20. Split applications of prunings prolonged mineral N availability in the soil until March but did not increase N uptake and maize grain yield compared to a sole application in October. Combinations of gliricidia prunings and inorganic fertilizer increased N uptake and maize yield over prunings alone but the effect was only additive. We concluded that application of gliricidia prunings in October was more efficient than application in December and February.
5 - The energy submodel: TIME
- from Part One - The TARGETS model
- Edited by Jan Rotmans, National Institute of Public Health and Environment (RIVM), The Netherlands, Bert de Vries, National Institute of Public Health and Environment (RIVM), The Netherlands
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- Book:
- Perspectives on Global Change
- Published online:
- 06 July 2010
- Print publication:
- 16 October 1997, pp 83-106
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Summary
This submodel simulates the supply and demand for fuels- and electricity, given a certain level of economic activity. It is linked to other submodels, for example through investment flows, population sizes and emissions. The energy model consists of five modules: Energy Demand, Electric Power Generation, and Solid, Liquid and Gaseous Fuel supply. Effects such as those of depletion, conservation, fuel substitution, technological innovation, and energy efficiency are incorporated in an integrated way, with prices as important signals. Renewable sources are included as a non-thermal electricity option and as commercial biofuels.
Introduction
Modern societies as they have developed over the last two centuries require a continuous flow of processed fuels and materials. Until some 200 years ago energy needs were largely met by renewable fluxes such as water and biomass. Since then energy has increasingly been derived from the fossil fuels coal, oil and gas. To be useful these fuels have to be extracted, processed and converted to heat and chemicals. For all these steps the production factors labour, land, capital, and energy and material inputs, are required. All three steps are also accompanied by waste flows, the largest being the emission of carbon dioxide (CO2) during combustion. Figure 5.1 shows the use of fossil fuels in million tonnes of oil equivalents over the period 1800–1990. The graph shows an increase in the use of coal, followed by the penetration of oil and later natural gas.
19 - Global change: fresh insights, no simple answers
- from Part Two - Exploring images of the future
- Edited by Jan Rotmans, National Institute of Public Health and Environment (RIVM), The Netherlands, Bert de Vries, National Institute of Public Health and Environment (RIVM), The Netherlands
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- Perspectives on Global Change
- Published online:
- 06 July 2010
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- 16 October 1997, pp 417-434
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Summary
Introduction
We know that the future is inherently uncertain, yet we are fascinated by insights into ways in which we may be influencing the planet. This interest is intensified because there is widespread perception that the world is changing at an unprecedented speed. Undeniably, many parts of the global system are accelerating or decelerating compared to previously observed, natural rates of change. For some people these processes of change may just look like more of the same. There are, however, underlying behavioural and structural changes at work which suggest deeper, more radical change in the longer term. Many of those long-term changes can be viewed as part of transition processes. Several of these are within the human system: from many to 1 or 2 children per family, twice as many older people per thousand compared to today, a factor of 3 to 5 less energy and water use per unit of economic activity, increasing pressure to cultivate more land and use it more intensively to feed the population. More gradual, but possibly of overriding importance, are the changes in the environmental system, such as the accelerating increase in the concentration of some atmospheric gases and increasing accumulation of pollutants in soils and water bodies which are the result of past and present practices. It is difficult to disentangle the human-induced, structural long-term changes from the natural changes, which makes it even harder to see where the world is heading.
13 - Energy systems in transition
- from Part Two - Exploring images of the future
- Edited by Jan Rotmans, National Institute of Public Health and Environment (RIVM), The Netherlands, Bert de Vries, National Institute of Public Health and Environment (RIVM), The Netherlands
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- Perspectives on Global Change
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- 06 July 2010
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- 16 October 1997, pp 263-290
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Summary
In this chapter we present simulation experiments and outcomes of the energy submodel TIME. First, the major controversies and uncertainties are discussed. Next, the cultural perspectives are introduced with reference to world energy, after which we clarify the way in which these are linked to assumptions and model routes. Some results of sensitivity and uncertainty analyses are also given. We discuss a few energy dystopias which could emerge if, for a given population-economy scenario, the world view and the management style within the energy system are discordant. Some conclusions are presented about the plausibility of and risks related to the utopian energy futures. The impacts of the emissions from fossil fuel combustion on water, land, and element cycles are discussed in the next three chapters.
Introduction
In 1886 Jevons warned in his book ‘The coal question’ about the rapid depletion of British coal fields threatening the British Empire. Numerous appraisals of coal, oil and gas availability have been made since then, many of them for strategic reasons. Environmental issues and the two oil crises in the 1970s have intensified the debate on fossil fuel use. Later on, it has been broadened by incorporating demand side management and renewable supply options and by including macro-economic aspects. Controversies and uncertainties about the future development of the world energy system abound.
3 - The TARGETS model
- from Part One - The TARGETS model
- Edited by Jan Rotmans, National Institute of Public Health and Environment (RIVM), The Netherlands, Bert de Vries, National Institute of Public Health and Environment (RIVM), The Netherlands
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- Book:
- Perspectives on Global Change
- Published online:
- 06 July 2010
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- 16 October 1997, pp 33-54
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Summary
When tackling a subject as complex as global change and sustainable development, it is essential to be able to ‘frame the issues’. This was one of the main reasons for developing the TARGETS model, an integrated model of the global system, consisting of metamodels of important subsystems. In this chapter we introduce TARGETS. Building on the previous chapters, we elaborate on the possibilities and limitations of integrated assessment models. Some of the key issues discussed are aggregation, model calibration and validation, and dealing with uncertainty.
Introduction
One of the main tools used in integrated assessment of global change issues is the Integrated Assessment (IA) model. This chapter introduces such an integrated model, TARGETS, which builds upon the systems approach and related concepts introduced in Chapter 2. Previous integrated modelling attempts either focused on specific aspects of global change, for instance the climate system (IPCC, 1995), or consisted merely of conceptual descriptions (Shaw et al., 1992). We have tried to go one step further, linking a series of cause-effect chains of global change. Although we realise the shortcomings in our current version of the TARGETS model, we felt there was a need to present our model to a wide audience. We first give some advantages and limitations of IA models. Next, we discuss issues of aggregation, calibration, validation and uncertainty. We proceed with a brief description of the five TARGETS submodels which coincides with the PSIR concept and the vertical integration as introduced in Chapter 2. A more detailed description of these submodels is given in Chapters 4 to 8.