The aim of this study was to determine the effect of the rhizosphere of maize on the diversity of denitrifying bacteria. Community structure comparison was performed by constructing a collection of isolates recovered from bulk and maize planted soil. A total of 3240 nitrate-reducing isolates were obtained and 188 of these isolates were identified as denitrifiers based on their ability to reduce nitrate to N2O or N-2. 16S rDNA fragments amplified from the denitrifying isolates were analysed by restriction fragment length polymorphism. Isolates were grouped according to their restriction patterns, and 16S rDNA of representatives from each group were sequenced. A plant dependent enrichment of Agrobacterium-related denitrifiers has been observed resulting in a modification of the structure of the denitrifying community between planted and bulk soil. In addition, the predominant isolates in the rhizosphere soil were not able to reduce N2O while dominant isolates in the bulk soil evolve N-2 as a denitrification product.

Un bilan des éléments rejetés par une porcherie engraissant près de 11000 porcs par an, et de leur devenir avant épandage, a été réalisé sur les lisiers soumis à un tamisage centrifuge puis à un stockage en lagune anaérobie. Ces rejets par porc produit sont respectivement de 3,77 ; 1,31 et 1,44 kg de N, P, et K, et de 30 et 76 g de Cu et Zn. La volatilisation d'ammoniac est évaluée à 28% de l'azote excrété : 11% à partir du bâtiment et 17% au dessus de la lagune. Les émissions de méthane par la lagune sont estimées entre 4,9 et 5,9 kg par porc produit. Une importante décantation dans la lagune permet de recueillir 82% de P, Cu, et Zn rejetés, 32% de la DCO et 13,8% de l'azote excrété, dans des sédiments manipulables après séchage sur lit. Les transformations dans la lagune produisent un lisier partiellement épuré plus facile à gérer par épandage que le lisier initial ; la filière peut être encore améliorée.

Nitrous oxide emission from agricultural soils is an important environmental concern as this gas contributes to the partial destruction of the stratospheric ozone layer and to global warming. European farmers are being encouraged to develop crops for producing biofuel. However, the excessive use of nitrogenous fertilizers on these crops could substantially increase agricultural emissions of N2O and hence eliminate the beneficial effects of recycling CO2. N2O fluxes were estimated from soil under four treatments: (1) bare soil, (2) unfertilized grassland fallow, (3) soil cropped to rapeseed and fertilized at rate of 180 kg N ha−1 yr−1 and (4) as for (3) but fertilized at 280 kg N ha−1 yr−1. Measurements were made using the static chamber method throughout spring and summer 1994. No particularly beneficial effect on N2O production was observed under reasonable fertilized rapeseed. Fluxes in the order of 1 kg N ha−1 yr −1 were measured under rape fertilized at 180 kg N ha−1 yr−1. The amount of fertilizer applied to rape has a very definite effect on the amount of N2O released. Bare soils constitute a risk in terms of N2O release as a ‘hot spot’ was observed after the harvest. Grass fallow seemed to be best adapted to limiting N2O release.