Soil structure is one of the most important factors affecting soil fertility. In the structure-forming process the main role is played by organic matter and biological processes occurring in soil. The role of plants largely depends on their influence on the content of organic matter in the soil. The favourable influence of continuous pasture and red clover on formation of the granular structure are commonly known. The aim of these studies was to determine the effect of annual plants grown in narrow (spring barley, winter rye, winter oilseed rape, white mustard) and wide row-spacing (potato, maize) on the structure of light soil. The plants were cultivated in four-year crop rotation: potatoes (or maize) - spring barley - oilseed winter rape (or white mustard) - winter rye. In a permanent fertilization experiment at yczyn near Warsaw established in 1960 soil crumb composition and water resistance were investigated in years 1994-1997. The field was situated on lessive soil, the upper layer of which constitutes light loamy sand on boulder loam. The soil for studies was taken from the arable layer of 0-20 cm. The cultivated plants significantly influenced soil structure and water resistance of soil aggregates. The soil from plots in which winter plants were grown in narrow row-spacing (winter oilseed rape, winter rye) was characterised by the best structure. The highest water resistance of aggregates was formed on these plots. Potato and maize, grown in wide row-spacing had the worst influence on the soil crumb composition and water resistance of aggregates. Their action on the soil started relatively late, what had an effect on the formation of water resistance of aggregates. Plants shading the soil well over the year favour the increase in water resistance of aggregates and those shading poorly like potatoes and maize - its decrease.
