Agriculture in the industrial world has gone A common interest of the contributors is increas­ through dramatic changes over the past decades. ing the understanding of the turnover of carbon Mechanization in combination with high inputs of and inorganic nutrients in terestrial ecosystems. fertilizers and pesticides has turned deficits of agri­ The authors approach this topic from different cultural products into surplus. Over the same directions depending on their interests and ex­ period we have experienced increased environment­ pertise. Difficulties are identified in the quantifica­ al problems in both the atmosphere and our water tion of below-ground production where death and resources, which have been associated with the re-growth, if incorporated into the calculations, changes in management practices. can change production figures considerably as Concern about the potential pollution by compared to values derived from "peak" estimates. nitrogen fertilizers as well as the low utilization The role of root-derived carbon is investigated in efficiency of applied nitrogen by plants has created relation to nutrient competition between roots and a need for a better understanding of nitrogen microorganisms, the cost of N2 fixation and the cycling in the plant-soil-water system. To achieve decomposition of organic nitrogen. Mycorrhizae this, it is neccessary to study process interactions use root-derived carbon and their roles in phos­ and process regulation in an ecosystem context. phorus conservation and in supplying nutrients to During the last decade many ecosystem studies the host are exemplified.

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The application to agriculture of predictive plant production models based on regional experimental data.- Primary productivity of natural grass ecosystems of the tropics: A reappraisal.- A reassessment of shoot/root and root/ organic matter interactions.- Why and how to estimate the cost of symbiotic N2 fixation? A progressive approach based on the use of 14C and 15N isotopes.- Plant- and soil-related controls of the flow of carbon from roots through the soil microbial biomass.- Carbon and nitrogen dynamics along the decay continuum: Plant litter to soil organic matter.- Nitrogen cycling in farming systems derived from savanna: Perspectives and challenges.- Influences of elemental interactions and pedogenic processes in organic matter dynamics.- Modelling land use effects of soil organic matter dynamics in the North American Great Plains.- Simulating regional patterns of soil C, N, and P dynamics in the U.S. central grasslands region.- Management of earthworm populations in agro- ecosystems: A possible way to maintain soil quality?.- Impact of human activities on nematode communities in terrestrial ecosystems.- Cycling of nutrients from dying roots to living plants, including the role of mycorrhizas.- Mycorrhizal mycelia and their role in soil and plant communities.- Activity of nitrifiers in relation to nitrogen nutrition of plants in natural ecosystems.- Nitrogen availability and nitrification during succession: Primary, secondary, and old-field seres.- The influence of invertebrates on soil fertility and plant growth in temperate grasslands.- Role of soil animals in C and N mineralisation.- Inferring trophic transfers from pulse-dynamics in detrital food webs.- Can population and process ecology be combined to understand nutrient cycling?.- Perspectives on measurement of denitrification in the field including recommended protocols for acetylene based methods.- Impact of agricultural landscape structure on cycling of inorganic nutrients.- The movement of nutrients across heterogeneous landscapes.- Development, validation and applications of simulation models for agroecosystems: Problems and perspectives.- Statistical opportunities for analyzing spatial and temporal heterogeneity of field soils.- Models by decision makers and ecologists, can they be coupled?.- The use of nitrogen fertiliser in agriculture. Where do we go practically and ecologically?.