Summary:

Chosen chemical, physical and biological properties of a fallow soil as well as plant succession in the first year after cultivation of chosen cereals (buckwheat, millet, maize) and potatoes under sprinkler irrigation, were determined in the paper. Trials were conducted in 2005 at Kruszyn Krajeński near Bydgoszcz on a very light soil classified to weak rye complex of agricultural suitability. It was found that in regard of granulation, humus horizons of the studied soil belonged to two textural groups: loose sandy soil and coarse sandy soil. They contained from 3 to 6 % silt and clay whereas the content of organic carbon was typical for sandy soils and ranged from 9,40 to 9,90 g*kg^-1. There were no marked and oriented differences in the organic carbon content between control fields and those which were previously irrigated. On the basis of available phosphorus and potassium contents, the humus horizons of the studied soil can be included to I–III and I–IV classes of soil fertility, respectively. Soil pH was very differentiated. In the first year of fallow, annual plants of arable lands were dominant (mostly Conyza canadiensis). It was connected with properties of habitat, and on the other hand with agricultural practices which were previously carried out. Loose sandy soils, characterized by large permeability and low nitrogen content, were favourable to the development of xerothermic weeds such as Agropyron repens and Filago arvensis. Concentration of mites on the studied areas ranged from 3,46 to 6,65 thousand individuals *m^-2. These arthrpods were most numerous on the fallow field after cultivation of maize in previous year. This field as well as fields after buckwheat and millet cultivation were characterized by domination of Actinedida, whereas that after potatoes – by Tarsonemida. The studied area was characterized by the low number of predacious Gamasida and saprophagous Oribatida. On the studied fallow fields 4 species of oribatid mites occurred only. Most species (3) were found on the field with maize as forecrop. From among oribatid mites, Scutovertex sculptus was the most numerous species and it was noted on all the sites.