Abstract:
It is well known that chemical inputs are the main determinant of yields, but their impact is considerable, causing
significant changes in the soil. Soil microbiota is a very important component of the agricultural ecosystem and is
involved in nutrient cycling. Its structure and dynamics are easily influenced by tillage, fertilizers and crops. The aim of
the present study was to observe the effects of different tillage systems combined with the application of inorganic
fertilizers and a phosphorus-solubilizing bacterial fertilizer in different rates and combinations on nitrogen-fixing
bacteria in the soil. The study was conducted in 2023 growing season at the Ezareni Farm from Iasi. The tillage systems
were represented by conventional (CT) and no-tillage (NT). Sunflower and maize crops were fertilized with: NPK (20%
N, 10% P2O5, 5% K2O), phosphorus solubilizing bacteria (PSB) fertilizer containing Bacillus megaterium var.
phosphaticum, applied twice, and Corona N foliar fertilizer (21% N), applied to 3 of the 5 treatment formulations. For
the quantification of nitrogen-fixing bacteria populations (Azotobacter spp. and Clostridium pasteurianum), soil
samples were collected four times and the method used in the laboratory was that of successive dilutions. During the
growing season, an increase in colony numbers was observed in CT maize when treated with the manufacturer's
recommended dose (10 l/ha) of biofertilizer in combination with foliar application of nitrogen. In contrast, in sunflower,
the number of bacterial populations was higher in NT under biofertilizer treatment at the prescribed dose but without
foliar fertilizer application. At the beginning of the growing season, Clostridium sp. is more numerous, but this is
reversed 4 weeks after the second application of PSB, which corresponds to the flowering period of the plants, when
Azotobacter spp. predominates. The results indicate increased populations of nitrogen-fixing bacteria in both the
recommended and higher-dose PSB treatments, and in sunflower this is more evident in the no-tillage system.
