Impact de l'exploitation des alpages sur la qualité des eaux

Agricultural fertiliser (farmyard manure), covers partially the nutrient elements demand of the vegetation cover. However, its application is difficult as regards the unknown concentration of fertilising elements contained and their biological availability for the plants, the important volumetric masses to manage and the general uneven land application. An inaccurate management of farmyard manure may cause groundwater pollutions with sometimes serious consequences, especially in the case of karst aquifers. The objective of this research was to specify various aspects of the farmyard manure cycle. It consists of three major parts: a general study of the difficulties related to the farmyard manure management in mountainous regions with the aim to provide practical recommendations to reduce the risk of groundwater contaminations, the evaluation of an alternative method of pig farming in liberty the study of the impacts of agricultural activities on the surface- and groundwater quality. Based on the analysed farmyard manure managements, the following practical recommendations have been made: split up the land application, but concentrate the input of nutrient elements in spring, during the period of plant growth. For sanitary reasons, a delay of at least 1 month has to be respected between the last land application and the beginning of pasture; collect in adequate installations all agricultural effluents which potentially cause water pollution, except if they are spread out immediately. minimise the production of fertiliser by the following two possibilities: infiltrate low contaminated waste water (from the roof, spring, eventually from the farm) reduce the time the animals stay in the stable. An alternative method of pig farming in liberty has been tested in the field. 25 pigs have been raised on a field of ca. 2 ha, representing a density of 0.71 LiveStock Unit/ha/y, respectively 0.18 LSU/ha/m during 4 months. Amongst others, the study has considered the impacts of pig pasture on the environment (vegetation cover, soil) and the animals health. The most important impact is in fact the destruction of the vegetation cover, with its direct repercussions on the botanical diversity and the concentration of nutrients in the soil. The experiment has made evident the importance to keep the vegetation cover intact, in order to adsorb the nutrient elements in the manure. An advantageous method to reduce the impacts on the vegetation cover is to equip the pigs with nose-rings. It is furthermore necessary to altemate the pasture parks in order to enable the vegetation to recover (2 to 3 different parks). The important impacts observed around the pig feeding through can be avoided by two ways: first, by changing the throughs placement during the pasture period or second, by the construction of a concrete place and the collection of the manure in the slurry pit. For the pasture of pigs in liberty one has to chose grasslands with thick soils of good quality but a