Agroecosystem management and biotic interactions: a review

Increasing the use of synthetic fertilisers and pesticides in agroecosystems has led to higher crop yields, accompanied by a decline in biodiversity at the levels of field, cropping system and farm. Biodiversity decline has been favoured by changes at landscape level such as regional farm specialisation, increases in field size, and the removal of hedgerows and woodlots. The loss of biodiversity in agroecosystems has increased the need for external inputs because beneficial functions are no longer provided by beneficial species as natural enemies of crop pests and ecosystem engineers. This trend has led to a strong reliance on petrochemicals in agroecosystems. However, many scientists have been arguing for more than two decades that this reliance on petrochemicals could be considerably reduced by a better use of biotic interactions. This article reviewsoptions to increase beneficial biotic interactions in agroecosystems and to improve pest management and crop nutrition whilst decreasing petrochemical use. Four agronomic options are presented. First, it has been shown that the choice of cultivar, the sowing date and nitrogen fertilisation practices can be manipulated to prevent interactions between pests and crop, in either time or space. Nevertheless, the efficacy of these manipulations may be limited by pest adaptation. Second, beneficial biotic interactions may result from appropriate changes to the habitats of natural enemies and ecosystem engineers, mediated by soil and weed management. Here, knowledge is scarce, and indirect and complex effects are poorly understood. Third, changes achieved by crop diversification and, fourth, by landscape adaptation are promising. However, these practices also present drawbacks that may not necessarily be outweighed by beneficial effects. Overall, these four management approaches provide a powerful framework to develop sustainable agronomic practices

Expropriated from the hereafter: the fate of the landless in the Southern Highlands of Madagascar

During the period following the abolition of slavery by the French colonial government in 1896, the Southern Highlands of Madagascar was settled by ex-slaves. These early settlers constructed a foundation myth of themselves as tompon-tany, or 'masters of the land', a discourse not only equating land with tombs, kinship and ancestors, but also coupled with a skilful deployment of 'Malagasy customs'. In order to exclude later migrants who also wanted to settle, the 'masters of the land' attempted to establish control over holdings in the area. To this end, and to reinforce their own legitimacy as landholders, the tompon-tany labelled subsequent migrants andevo ('lave' or of 'slave descent') who - as a tombless people - have no rights to land. Because they have neither tombs nor ancestors, the landless andevo are socially ostracised and economically marginalised. As an 'impure people', they are not entitled to a place in the hereafter

Contribution à l'étude des abcès de la rate

Thèse : Médecine : Université de Bordeaux : 1911N° d'ordre :

Effect of nitrogen nutrition on growth and nitrate accumulation in lettuce (Lactuca sativa L.), under various conditions of radiation and temperature

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$\cdot$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.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 matière sèche (RUE) était comprise entre 2.12 et 3.5 g$\cdot$MJ$^{-1}$. Elle était plus élevée pour les faibles rayonnements et les forts niveaux de nutrition azotée. Une corrélation positive entre les teneurs en nitrate et en eau a été observée. Cette relation, dont la pente n'est pas affectée par les conditions de croissance, semblerait indiquer une forte interdépendance des accumulations d'eau et de nitrate chez la laitue

Effects of soil structure on pea (Pisum sativum L.) root development according to sowing date and cultivar

International audienceSpring peas are known to be very sensitive to compaction, particularly when sowing takes place soon after winter. Winter peas, which are sown in autumn, should present an opportunity to sow the crop in better soil structural conditions than for spring peas, because of more favourable moisture conditions at that time. As environmental conditions have a big influence on root systems, it is important to determine the effects of soil structure on pea root systems for different cultivars and sowing dates. A spring pea cultivar and a winter pea cultivar were both sown at two dates (one in autumn and one in spring) on soils with different plough-layer structures (compacted and uncompacted) at two sites in 2002 and one site in 2003. Soil structure was characterised by bulk density and the percentage of highly compacted zones in the ploughed layer. Root distribution maps were produced every month, from February to maturity. Root development was described in terms of general root dynamics, root elongation rate (RER) in the subsoil, final maximum root depth (Dmax) and root distribution at maturity. Root depth dynamics depended on compaction and its interaction with climatic conditions. The effects of compaction on RER in the subsoil depended on the experimental conditions. Dmax was reduced by 0.10 m by compaction. Compaction also reduced root distribution between 10 and 40% in the ploughed layer only. Pea cultivars differed in sensitivity to soil compaction, with a direct effect on the final depth explored by roots. These results are discussed in terms of their relevance to water and nutrient uptake

Evaluer les effets des pratiques agricoles pour optimiser les services écosystémiques rendus par les sols cultivés

Evaluer les effets des pratiques agricoles pour optimiser les services écosystémiques rendus par les sols cultivés. Salon International de l'Agriculture (SIA) : " Les sols : des services et des usages

L'état des sols de France

Cet ouvrage a fait l'objet d'une synthèse éditée par le Groupement d'Intérêt Scientifique sur les Sols : Gis Sol. 2011. Synthèse sur l'état des sols de France. 24 p.absen

Synthèse sur l'état des sols de France

Cette synthèse est issue d'un ouvrage édité par le Groupement d'Intérêt Scientifique sur les Sols : Gis Sol. 2011. L'état des sols de France. 188 p.absen