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To point out the photosynthetic ability of perennial legume species, we measured the following parameters: chlorophyll content and soluble sugar content. Sampling was done on permanent pastures at different altitude levels: 90 m, 330 m, 900 m, and 1,800 m. Soluble sugar content was measured in samples from variants fertilized with mineral nitrogen and with organic fertilizers (through animal folding). Results showed that, as far as chlorophyll content is concerned, there is a negative relation between this parameter and the altitude level of the pasture. Perennial legume species on the pastures had a lower content of soluble sugars in all the variants fertilized with mineral fertilizers and with organic fertilizers compared to the control variant.

The forage system proposed by the continuous land cultivation has taken under research 5 structures of forage plants, grown one after the other over a period of 2 agricultural years (2009/2010, 2010/2011). In every type of structure the silage corn culture was introduced. Each structure has been studied both under conditions of non fertilization with nitrogen (N0) and with fertilization (N+). As compared to the cultivation structure of the silage corn in monoculture, for 2 years, in other structures, in which were introduced legumes sowed in association, the cumulated quantities of forage biomass have been 30-50% bigger, and the soil has been covered with vegetation in a proportion of over 80% during the entire period of the forage system.

The determination of the colonization capacity with permanent nitrogen fixating bacteria has been achieved indirectly through the method of using soil extracts, taken from the rhizosphere of leguminous species existing in the 4 types of permanent grasslands, located on different altitudinal levels (90m, 330m, 900m, 1800m). Treatments with soil extracts taken have been made at three species of legumes (Lotus corniculatus, Trifolium repens, Trifolium pratense), seeded on a sown perlite layer and grown in the growth chamber. Between the total amount of nodosities formed and the altitude of grasslands there is a negative correlation. At treatments with extracts taken from grasslands situated between 90-330m, there has been observed the highest number of nodosities formed on roots of tested leguminous species.

For achieving some culture structures that would ensure, through rotation, a continuous coverage of the agricultural land, 6 types of such structures have been studied, based on aristate ryegrass. Each forage structure, that covers the land for a consecutive period of two years, has been cultivated in two variants: one non fertilized with nitrogen (N0) and the other fertilized (N+) according to the specific dose to each culture. Based on results obtained it has been demonstrated that: in natural experimental conditions, the forage system of continuous cultivation of the land ensures a growth of 2-3 times higher in the forage production as compared to the conventional system based on one culture sown in an agricultural land.