[Fixation of free nitrogen in the soil and on the roots of citrus trees in the subtropics of the Georgian SSR].

The rate of biological nitrogen fixation was determined by the acetylene technique in soils and on the roots of orange, mandarin and lemon trees growing in red, yellow, podzolic, alluvial brown forest, and humus-calcareous soils. The minimum nitrogen fixation in podzolic soils was 3--8 kg of nitrogen per hectare per vegetative period. The maximum nitrogen fixation (48--51 kg N per hectare) was found in red and humus-calcareous soils of orange plantations. One dose of nitrogen fertilizers with liming increased the nitrogen fixing activity of subtropic podzolic soils of mandarin plantations whereas a triple dose inhibited the activity. The rate of nitrogen fixation by the root microflora was 3--4 times higher than that by the soil microflora.