Mineral Fertilisers as a Factor Regulating the Number of Azotobacter under Different Fertiliser Rates

Abstract

The paper presents the research results on the effect of different mineral fertiliser rates on the microbiological activity of alluvium under plum over the 2003-2005 period. The trial was conducted in an experimental plum plantation of the Fruit Research Institute and at the Microbiology Department of the Faculty of Agronomy in Cacak. The soil was treated with 8:16:24 + 3% MgO mineral fertiliser, as follows: the N-1 variant - 400 kg/ha; the N-2 variant - 600 kg/ha; the N-3 variant - 800 kg/ha; the N-4 variant - 1,000 kg/ha and the N-5 variant (the control - non-fertilised soil). The effect of the used fertiliser was determined three times during the growing season and was monitored through determinations of the number of azotobacter (by the fertile drop method on Fyodorov's medium). The obtained data showed that the soil azotobacter development was affected by the fertilisation variants employed, the sampling periods and the research years. The use of high mineral fertiliser rates (N-3 and N-4) induced a decrease in the number of azotobacter. The use of lower rates resulted in an increase in the number of this group of microorganisms. The most pronounced fertiliser effect was recorded in the second sampling period and in 2003. The highest plum yield was achieved by the use of the mineral fertiliser rate of 600 kg/ha.