Greater vigour of plants that border with unsown areas, known as border effect, compensates for the use of tramlines in the lowland meadow but also gives an error to the results of field experiments. This phenomenon is well-known for certain cultivated plant species. However, there is a lack of publications which would make it possible to analyze and compare the border effect of several plant species in similar habitat conditions and evaluated in the same way. The aim of the study was to recognize and compare the border effect in the cultivation of spring cereals: wheat, triticale, barley, oat, pea, and yellow lupine, as well as to determine the effect of this phenomenon on yield overestimation in plot experiments. In years 2004-2010 at the University of Technology and Life Sciences Research Station at Mochełek (53^o13' N; 17^o51' E), a series of plot experiments was carried our, each according to the same methodology. Experimental factor was the situation of plant rows on the plot; four rows into the plots from the unsown path 50 cm wide were evaluated. It was found that the border effect resulted in greater values of nearly all the evaluated plant characteristics. Oat was the most susceptible to the effect. Border effect in cereals, in relation to most characteristics, was limited only to the row of plants directly adjacent to the path, while in the subsequent two rows the values of the particular characteristics were usually close to the evaluation of the fourth row. In the case of legumes, the effect was visible also in the subsequent two rows into the lowland meadow. Yields of plants harvested from the whole plot were greater by 18.3%-28.0% than in the mid area of the plot, depending on the plot area and plant species. It was also found that in order to avoid the border effect influencing yield size estimation, it is recommended to omit during harvest one border row of oat plants from both sides of the experimental plots and two rows of triticale and barley. In the case of wheat, lupine and pea, three rows of plants from each side of the plot should be excluded from harvest.

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