THE CHANGES OF WEED ECOLOGICAL GROUPS IN THE WINTER RYE CROP GROWN IN DIFFERENT CROP ROTATIONS

The investigations were carried out over the period of 2003-2007 at the Experimental Station of the Lithuanian University of Agriculture on an Endocalcari-Epihypogleyic Cambisol (CMg-n-w-can). The objective of this investigation was to compare the weediness of winter rye (Secale cereale L.) 'Duoniai' in different crop rotations (intensive, three-field, eight-field with a row crop, six-field without a row crop and sideral) after various pre-crops. The highest number and dry matter mass of weeds were established in the winter rye crop grown after winter rape for green manure (sideral crop rotation). The number of weeds increased from 62.3 to 133.2% and the dry matter mass of weeds increased from 2.1 to 4.7 times compared with the other crop rotations. The number of silky bentgrass (Apera spica-venti (L.) P. Beauv.) increased from 2.2 to 25.1 times, the dry matter mass from 2.1 to 25.6 times. The least dry matter mass of weeds was established in the winter rye crop grown after perennial grasses of the 1(st) year of use (intensive crop rotation). The dry matter mass of weeds significantly decreased from 55.4 to 78.8% compared with a six-field rotation without a row crop and a sideral crop rotation (after winter rape for green manure). According to soil pH and nitrogen demand the weeds were divided into 7 ecological groups. Most of the weed species found in winter rye, grown in different crop rotations after various pre-crops, belonged to indifferent plant groups (growing at a wide soil pH and nitrogen range). According to soil pH and nitrogen demand, indifferent weed species and those Occurring on soils very rich in nitrogen were found to be most numerous. Qualitative distribution of weeds within ecological groups was even, quantitative distribution uneven, because in 2007 abundance of moderately acid soil weed species and indifferent weed species according to nitrogen demand increased.