Effect of NPK Fertilizer on the Soil Microorganisms Growth in 'Cacanska Rodna' Planting

Abstract

The paper shows the effect of increasing NPK fertilizer rates on the developement of the Azotobacter and oligonitrophyles over the three-year period (2003-2005). The investigation was carried out in the plum planting established by Fruit Research Institute Cacak (Serbia) according to the randomised block design with three replications. The soil was treated with 8:16:24 + 3% of MgO mineral fertilizer as follows: treatment N-1 - 400 kg ha(-1); treatment N-2 - 600 kg ha(-1); treatment N-3 - 800 kg ha(-1) and treatment N-4 - 1000 kg ha(-1). Unfertilized soil was used as the control. The effect of the studied mineral fertilizer rates was determined three times over the growing season. It was checked by identification of the number of Azotobacter (by the fertile drop method on Fyodorov's medium) and oligonitrophyles (by indirect rarefaction method on Fyodorov's medium). The data obtained showed that the use of high mineral fertiliser rates (N-3 and N-4) induced a decrease in the number of Azotobacter and oligonitrophyles. On the other hand, the use of lower fertilizer rates (N-1 and N-2) enhanced the number of the studied group of microorganisms. The most pronounced fertiliser effect was recorded in the second sampling period and in the first year of the experiment. Considering the soil biological properties, the N-2 treatment (600 kg ha(-1)) can be recommended as the most favourable one for 'Cacanska Rodna' growing in the stated agro ecological conditions.