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Typologie des bilans d'azote de divers types d'exploitation agricole: recherche d'indicateurs de fonctionnement

Abstract : Typology of nitrogen balances on a farm scale: research of operating indicators. A farm survey based on the method of the nitrogen apparent balance at the farm scale quantified the nitrogen inputs and outputs due to the farm commercial transactions. A total of 555 farms, partly situated in France and partly in north-west Italy, was analyzed. This method considers the farm as a "black box" and also takes the nitrogen fixation into account. However, nitrogen input due to atmospheric deposition, or nitrogen losses due to volatilisation, denitrification or leaching are disregarded: this is the reason why it is called "apparent balance". The study quantified the excess of nitrogen and its most important sources of variation in 11 important types of farm production systems including stockless farming, crop-less intensive rearing, forage crop-livestock integrated farming systems, mixed farming with livestock. The surplus of N was smaller in the stockless farming system (50 kg.N.ha$^{-1}$.y$^{-1}$, on average), intermediate in dairy cow or beef breeding farms (from 30 to 250 kg.ha$^{-1}$), and higher in intensive stocking systems where forage was not produced in the farm (from 250 to 500 kg.ha$^{-1}$, or even more). In general, where the apparent N surplus was small ($< 200 {\rm kg.ha}^{-1}$) the excess of N was mainly caused by the purchase of mineral fertilizers, while in farms with a high surplus ($> 200 {\rm kg.ha}^{-1}$) the N surplus was highly dependent on N input of purchased animal feedstuffs. Two groups of farming systems were clearly identified: one was oriented to crop production and was characterized by a favourable N efficiency or N conversion (72% ); the other one was oriented to livestock production, with very variable N fluxes, but little outputs, and was characterized by lower values (22-44% ). The very large variability in N surplus and in indicators (N efficiency, N conversion and N losses) suggests that in many situations it should be possible to reduce the environmental impact of a farm without drastic changes in the production system.
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Jean-Claude Simon, Carlo Grignani, Alain Jacquet, Louis Le Corre, Jérome Pagès. Typologie des bilans d'azote de divers types d'exploitation agricole: recherche d'indicateurs de fonctionnement. Agronomie, EDP Sciences, 2000, 20 (2), pp.175-195. ⟨10.1051/agro:2000118⟩. ⟨hal-00886003⟩



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