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.