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Permanent grassland is the most complex natural ecosystem due to the biodiversity of the structural and functional elements that characterize the space and time unit of this ecosystem. From this point of view, in the case of this ecosystem, biodiversity is manifested by the richness of species as a result of the interactions between species and the biotope, the interspecific relations and the effects of the technology and usage applied to the improvement of these surfaces. The paper presents the results obtained in an experimental device placed on a permanent grassland of Festuca valesiaca + Festuca rupicola, from Caraş-Severin County, under conditions of mineral and organic fertilizers application (sheep manure and direct fertilization by sheep folding). [ABSTRACT FROM AUTHOR]

In any agricultural system based on legumes, nitrogen balance should take into account the flow of N2 by legume species. In this flow, the amount of N2 fixed by legumes is considered a reserve amount of nitrogen which, through harvesting, is removed from the nitrogen balance. The aim of the present paper is to assess the amount of nitrogen fixed biologically (NFB) in some legume species sowed in association and of the share of this amount of NFB of the total amount of nitrogen from the productions obtained. Thus, in the fodder system made up of Italian ryegrass + red clover cultivated for two years, the amount of NFB in the first year was 60 kg/ha. If we relate the amount of NFB to the amount of nitrogen exported through the fodder biomass, we see that the share of NFB varies between 22 and 42%. [ABSTRACT FROM AUTHOR]