A two-factorial pot experiment was carried out in 2005 to estimate the effect of soil moisture on competition intensity between oat and yellow lupine plants in mixtures Factor I was soil moisture: 40, 60, 80% of field water capacity, and factor II: the composition of oat and lupine mixture (pcs·pot^-1) respectively – 30 + 5, 20 + 5, 10 + 5, 0 + 5 (pure sowing of lupine), 10 + 0, 20 + 0, 30 + 0 (pure sowings of oat). Indexes worked out by Rudnicki and Kotwica [2007] were applied for the assessment of competition intensity. Competitive effect of oat on lupine increased along with a growing oat plant density in mixtures, in inverse proportion to the soil humidity. Lupine plants exerted a weaker competitive pressure on oat plants than vice versa, which resulted from their smaller density. Single oat plants turned out to be weaker competitors than single lupine plants in the mixture.

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