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Wageningen Universiteit (1997)

Hierarchical levels in agro-ecosystems : selective case studies on water and nitrogen

Ridder, N. de

Titre : Hierarchical levels in agro-ecosystems : selective case studies on water and nitrogen

Auteur : Ridder, N. de

Université de soutenance : Wageningen Universiteit

Grade : PhD thesis 1997

Résumé partiel
Today, agronomic research faces the triple challenge to develop knowledge and insight to manage agro-ecosystems which are inherently sustainable, to diminish the undesirable side effects and to meet the increasing demand of food of a still growing world population, without claiming all the available land. Sound management of agro-ecosystems is not solely a matter of the individual farmer, nor of only field and farm level. Local, national and international policy levels demand guidance from the agricultural research community in management of the natural resources. Thus, agronomic processes, so far studied at the level of plots, have to be studied and applied at higher hierarchical levels, i.e. larger entities such as toposequences, watersheds, river systems, continents and even the entire globe, and over longer time periods. Furthermore, agronomic research must switch from a reductionistic to a more holistic approach. Agro-ecosystem analysis at multiple hierarchical levels, the subject of this thesis, is such an approach.

In the first chapter, several issues related to this subject are introduced : agro- ecosystem analysis, hierarchical levels, scales, scaling and spatial up-scaling in agronomy. In the subsequent chapters examples are presented, that deal with agro- ecosystem analysis at hierarchical levels varying from plant to watershed. In addition, they touch upon issues of agro-ecosystem analysis at multiple hierarchical levels.

Agro-ecosystem analysis at multiple hierarchical levels

At the hierarchical level of the plant (and crop), the reproductive effort of annual species in Mediterranean pastures is analyzed (Chapter 2). The reproductive effort is defined as the reproductive ratio (proportion of biomass invested in the reproductive organs in relation to the total biomass produced) and as harvest index (proportion of harvestable seed in relation to the total biomass produced). It appears that the proportion of the total production invested in reproductive tissue may be as high as that of cultivated species. The variation within a species of both ratios is high, owing to environmental conditions. A model is introduced which describes the relation between the harvest index and the nutrient (mainly nitrogen) transfer from vegetative organs to the reproductive organs in the period between flowering and maturity. This model explains to a large extent the possible variation within a species.

Mots clés : biology / systems / measurement / scaling / indicators / hydrology / water balance / soil / nitrogen / farming systems / geostatistics / hydrological cycle / agroecosystems

Présentation et version intégrale

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