In the years 2005 to 2008, the consumption of water by selected cultivated and weed species under the field conditions and the values of the actual evapotranspiration in selected stands of cultivated crops were evaluated. The values of the transpiration flow were measured with a T4.2 EMS Brno (CZ) 12 channel sap-flow meter, and the actual evapotranspiration by BREB method (Bowen Ratio-Energy Balance) using the equipment of the same firm. The recording of the values obtained during the

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... urements was carried out in 10-min intervals. The sap flow was measured on the following weed plants <I>Amaranthus retroflexus</I>, <I>Artemisia vulgaris</I>, <I>Cirsium arvense</I>, <I>Conyza Canadensis</I>, and <I>Lactuca serriola </I>as weeds in the cultivated crops of <I>Brassica napus </I>and <I>Zea mays</I>. The actual evapotranspiration using the BREB method was determined over the stands of <I>Beta vulgaris</I>, <I>Brassica napus</I>, <I>Hordeum vulgare</I>, <I>Medicago sativa</I>, and <I>Zea mays</I>. On the basis of the measurements carried out, the average daily values of the sap flow of the evaluated plants ranged from 0.016 to 0.193 kg/day of water per plant. The maximum daily values ranged from 0.025 to 0.309 kg/day of water per plant. The average daily value of the evapotranspiration flow in <I>Hordeum vulgare </I>during the period under observation amounted to 2.9 mm, while the daily values ranged from 1.2 to 4.6 mm H<SUB>2</SUB>O/day. In the other evaluated plants, the daily values of evapotranspiration ranged from 0.9 mm to 5.9 mm/day of water, on average 3.4 mm/day of water (<I>Beta vulgaris</I>), and from 1.7 mm to 5.2 mm/day of water, on average 3.2 mm/day of water (<I>Brassica napus</I>).