Effects of cultural practices on weed flora in Virginia (flue-cured) organic tobacco (Nicotiana tabacum L.): green manure and irrigation systems

Abstract

Organic tobacco is a new industrial crop. Field experiments were conducted, during 2005-2006, to determine the effects of irrigation system and green manure on weed flora in organic tobacco crops (Nicotiana tabacum cv. NC 71). The experiments were designed as a split plot design with 4 replicates, 2 main plots (drip and sprinkler irrigation), and 3 sub-plots (vetch and red clover as green manure, and control). The greatest number and dry weight of weeds was observed in sprinkler irrigation. Our results indicate that weed distribution under drip and sprinkler irrigation is related not only to the surface soil water content but also to competition from the crop for water and light. Moreover, there were no significant differences between vetch, red clover, and the control in terms of number of weeds at site 1. In addition, at site 2, the lowest number of weeds was found in red clover plots. The main reason for weed suppression at site 2 may be attributed to the amount of red clover incorporated into the soil, 390 kg ha^{-1} and 270 kg ha^{-1}, for site 2 and site 1, respectively. Red clover strongly inhibited germination and growth of barnyardgrass (Echinochloa crus-galli (L.) P.Beauv.) but only at the first sample date after transplanting of tobacco (35 days after transplanting). These results indicated that green manure and drip irrigation could be used for the suppression of weeds in organic row-crops.