engleski

The effect of mineral nitrogen fertilization on microbial properties of terra rossa soil in Istria

Soil is a unique natural environment that contains enormous populations of bacteria, fungi, algae and protozoa. Microorganisms play a key role in the soil ecosystem functioning and their role is essentional in numerous soil processes, thus also in the nitrogen cycling process. Nitrogen is one of the most common limiting factors for the plant production. Therefore, mineral nitrogen fertilizers are widely used, since they contain nitrogen in the plant available form or readily transformable into this form. The aim of the present study was to determine the effect of soil covering and different nitrogen fertilizer rates on total number of bacteria and on microbiological processes involved in nitrogen cycling. For this purpose, a stationary field trial was set up on hydromeliorated terra rossa soil in Istria. Nine trial plots were formed, with three replications, which differed from one another in the amounts of nitrogen fertilizers applied (60 kg N/ha, 120 kg N/ha, 180 kg N/ha) as well as in soil surface covering (uncovered soil, straw covered soil and soil covered with black polyethylene film). Watermelon was used as the test crop. Sampling was carried out three times during the growing season - in the spring, summer and autumn periods. Effect of sampling season on total number of bacteria was determined. Highest values for the total number of bacteria were determined in the spring period. Also, in dependence on the season, different impacts of the studied trial factors upon total number of bacteria as well as on the abundance of free-living nitrogen fixers were determined. At the first sampling, different soil covering resulted in significant differences of data obtained. Statistically significant effect of mineral nitrogen application was determined at the second sampling as well, when the lowest values were obtained with the application of 60 kg N/ha. Significant effect of nitrogen fertilization upon the number of ammonifiers was determined in the spring period while this effect was less expressed in the summer and autumn periods. Values obtained for the abundance of nitrifiers and denitrifiers clearly indicate a downward trend from the spring to the autumn period. Soil covering with film resulted in the highest number of nitrifiers in all seasons. Application of different rates of nitrogen fertilizers had different effects on the abundance of both nitrifiers and denitrifiers, in dependence of the sampling season.

microbial properties; nitrogen cycle; terra rossa; Istria; nitrogen fertilization

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