Weed flora and weed management under different soil tillage systems in small scale sorghum (Sorghum Bicolor(L) Moench) production in Chiawa

A research study on sorghiun (Sorghum bicolor (L) Moench) production under small scale farming was conducted in Chiawa, during the 1993/94 cropping season. It consisted of three components, namely the weed flora survey, the socio-economic weed management survey and a field trial. The main objective of the research study was to determine the weed flora and weeding requirements on two different tillage systems practised in the area i.e., conventional and conservation tillage. The weed flora survey covered 30 sorghum fields, while the socio-economic survey involved 30 farmers from 17 villages across Chiawa. A two factorial split-plot design was used on the field trial, with tillage systems and weeding frequencies arranged on the main and sub-plots, respectively. Weeding frequencies comprised zero, one, two, three and clean weedings. The field trial was replicated 4 times. Data on soil moisture, weed cover, sorghum cover and sorghum height were collected a day before any weeding treatment was applied, while sorghum yields were- recorded at harvesting time. Paspalum scrobiculatum was the most dominant weed in Chiawa, while Commelina benghalensis, Cyperus esculentus and Digitaria milanjiana were considered the most difficult weeds to be controlled by hand hoeing. Yields under conventional tillage of 989 Kg/ha were significantly higher (p < 0.05) than those realised under conservation tillage of 733 Kg/ha. There was a significant negative correlation(p< 0.05)between weed infestation and sorghiim yield (r = - 0.90), while sorghum cover and height were positively correlated with sorghum yield across tillage systems. There was no interaction between tillage systems and weeding frequencies. Three timely weedings at 2, 4 and 6 WAP was more economical, practical and resulted in crop performance and yields which didn't differ from that of clean and two weedings. These observations however, need to be investigated further over several seasons in order to obtain tangible conclusions.