102(1)_str2

 

ISSN 1392-3196 / e-ISSN 2335-8947
Zemdirbyste-Agriculture, vol. 102, No. 1 (2015), p. 15–22
DOI  10.13080/z-a.2015.102.002

Nitrogen cycle bacteria in soils of organically and conventionally managed crop rotations

Malle JÄRVAN, Liina EDESI

Abstract

The aim of the current research was to investigate the influence of organic and conventional farming on certain bacteria (nitrifiers, denitrifiers and azotobacteria) involved in the soil nitrogen cycle. During 2007–2013, field experiments were performed in Central-Estonia (58º33′ N, 25º34′ E) on a sandy loam Albeluvisol (AB) in a five-field crop rotation (winter rye → potato → oats → barley with undersowing → red clover). The following treatments were carried out: organic without manure, organic with cattle manure, and conventional where manure, mineral fertilizers and pesticides were used. In the treatments, solid cattle manure (60 t ha-1) was applied for potato. In 2007–2013, soil samples for microbiological tests were taken from the two fields of the crop rotation from 0–20 cm layer. All soil samples were examined for the total number of bacteria, azotobacteria, denitrifying and nitrifying bacteria using the plate-count method.

In the organic farming, the application of cattle manure significantly (P < 0.05) increased the total bacteria communities. Also the nitrifying bacteria responded greatly to the soil nutritional status. Their abundance in the organic without manure treatment was significantly (P < 0.05) lower than that in the other treatments. There were no significant (P < 0.05) differences in the counts of denitrifying bacteria between the treatments. The repeated application of fungicides and insecticides for potato protection decreased the number of azotobacteria as direct effect by 2.7 times and had a harmful aftereffect on these sensitive bacteria also in succeeding years.

Key words: azotobacteria, denitrifying and nitrifying bacteria, pesticides, plate-count method, total bacteria, solid cattle manure.

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