Potential of industrial hemp (Cannabis sativa L.) genotypes to suppress weeds

Abstract

Field experiments designed to explore weediness of hemp crops of industrial varieties were carried out at the Upytė Experimental Station of the Lithuanian Research Centre for Agriculture and Forestry in 2010–2012. Eight monoecious industrial hemp varieties from France (5), Poland (2) and Ukraine (1) were grown in a conventional crop rotation after winter wheat. Hemp was sown at a seed rate of 50 kg ha -1 with 10 cm interrows at the beginning of May and harvested when the first matured seeds appeared. No mechanical or chemical weed control was applied during hemp growth period. Density of weeds at full hemp emergence was relatively high, with the highest average value of 202 plants m -2 in 2011, the year with relatively high air temperatures at the end of May – beginning of June and adequate rainfall. At hemp harvesting, the highest weed density and above-ground biomass was found in 2010, the year characterised by high temperatures in July and August, in the plots of the USO 31, the variety with the shortest growth period and the lowest plant height. A total of 31 weed species were identified in hemp experiments – 26 species of broad-leaf and grass weeds and 5 species of perennial weeds. At full hemp emergence, weeds typical of spring crops of the region were most abundant: Chenopodium album L. dominated in 2010, Veronica arvensis L. in 2011, while in 2012 the domination was shared by the four weed species Lamium purpureum L., Thlaspi arvense L., V. arvensis and Poa annua L. At harvest, in total 8 weed species were found; however, only C. album and partly Polygonum aviculare L. were relatively abundant in all years.