A better understanding of the effect of environmental factors on growth and nitrate accumulation in plants is necessary to develop cultivation practices, and in particular for providing lettuces with a low nitrate content. This study was conducted to analyse the effect of nitrogen supply on the interception and conversion of the PAR in dry matter, and on the nitrate and water accumulations in fresh tissues of the lettuce, for various conditions of temperature and radiation. The growth, and water and nitrate concentrations of two soilless cultures of lettuce (summer and autumn) were measured for two levels of radiation and two levels of nitrogen supply. RUE ranged from 2.12 to 3.50 g•MJ-1 , being higher for a low radiation level and for a high nitrogen supply. There was a positive correlation between the lettuce nitrate and water contents. The slope of this relationship was not affected by environmental conditions, indicating a strong interdependance between nitrate and water accumulation in lettuce. radiation use efficiency / RUE / nitrate / water / shading / sand culture / drip irrigation / greenhouse Résumé-Effet de la nutrition azotée sur la croissance et l'accumulation du nitrate chez la laitue (Lactuca sativa L.), sous des conditions variées de rayonnement et de température. Pour concevoir des itinéraires techniques permettant d'obtenir une faible teneur en nitrate des laitues, il est nécessaire de mieux comprendre les effets des conditions de culture sur la croissance et l'accumulation de nitrate dans la plante. L'objectif de cette étude est d'analyser l'effet de la nutrition azotée sur l'efficience d'interception et de conversion du rayonnement en matière sèche, et sur l'accumulation de nitrate et d'eau dans la laitue, pour différentes conditions de température et de rayonnement. La croissance des laitues et les concentrations en eau et en nitrate ont été mesurées sur deux cultures hors-sol (en été et en automne) avec deux niveaux de rayonnement incident et de nutrition azotée. L'efficience de conversion de l'énergie lumineuse en

Abbreviations: IBSF, irrigated before seed filling and not during seed filling; IDSF, irrigated during seed filling and not during the period from the start of flowering to the 2 initiation of seed filling; NI, non-irrigated treatment; WI, irrigated as needed during the whole growing season.

Pierre Donadieu, André Fleury Die Landwirtschaft als Natur für die Stadt ? Der von der industriellen Verstädterung lange verdrängte ländliche Raum wird heute als kulturelles Erbe und Lebensmilieu reintegriert. Die landwirtschaftlichen Nutzflächen am Stadtrand entsprechen aber nicht immer der Idealvorstellung, die Stadtbewohner sich von der Natur machen. Landwirtschaftliche Nutzung und Freizeit der Städter miteinander verbinden, setzt symbolische Vermittlungen voraus, unter denen der Landschaft eine vorrangige Rolle zukommt.

The modem construction of a « country town » in Europe. This paper deals with the role of agriculture, in the broad sense of the word, in a « country town » project, where agriculture is an integral component of nature. The first part describes the change in social status of the peri-urban area. For a long time, this area was devoted to carrying out useful, essential urban tasks (from a urban point of view), but was often dirty and ugly and, for this reason, an unpleasant environment in which to live. The peri-urban area was also movable, gradually being pushed further from the centre under the influence of urban spreading. More recently, however, the area has provided a more pleasant environment, where new inhabitants seek to maintain countryside amenities. Indeed, urban planning has endorsed this conception by creating green belts and by including agriculture as an integral element of natural spaces, with special properties (nearness, landscape attraction). The second part of the paper analyzes the expectations of urban residents, and discusses the role of the peri-urban area as a market for the delivery of rural goods, services and amenities. A new type of agriculture is emerging, the aims of which are to provide and promote pleasure (farming as a hobby, gardening), social integration (community gardens), heritage, symbolic values, and so on. This is the product of both private and public initiatives, and the landscape constitutes an integral part. The last part considers how agriculture can adapt to these new circumstances while maintaining its customary role. Even though farmers continue farming in peri-urban areas, they do not produce for the local market, because of modern commodity chains, but for the global market. However, by improving its environmental impact and the quality of its products, agriculture is now perceived more favourably by the local population. Agriculture may thus become a partner in local development, not because of its products but more by virtue of its landscape qualities.

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