Relationships among planting time, chemical weed control and weed cover in cabbage (Brassica oleracea L. var. capitata).

In order to investigate on the influence of planting time and chemical weed control on weed flora evolution and on yield and crop growth in cabbage, research was carried out in 1994 and 1995 in Sele Plain (SA) on a clay-loam soil. Three planting times (March 15th, April 21st, May 29th in 1994; April 6th, May 9th, June 5th in 1995) in factorial combination with two treatments regarding weed control (pre-transplanting chemical application with chlorthal-dimethyl + propachlor and no weed control) were compared. A split-plot design, with three replications, was arranged. In comparison with the highest yield obtained with the first planting time (62 t•ha-1 as an average) reductions of 20.4% and 45.1% were recorded for the second and the third planting time respectively; no weed control caused a mean yield reduction of 27.3% compared to herbicide treatment. Crop biomass and LAI attained the highest values at harvest with the first planting time and the chemical weed treatment (662 g•m-2 and 3.9 m2•m-2 respectively). CGR showed an increasing trend (with a maximum of 72.6 g•m-2•d-1 with the second planting time and herbicide treatment) but a decrease in the last growth phase. Shannon-Wiener diversity index (H'), calculated on the base of weed species biomass, displayed at harvest a decreasing trend from the first to the third planting time (respectively 1.46 and 0.98) corresponding to herbicide treatment but it didn't vary evidently with no weed control (1.30 with the first planting time and 1.32 with the third one). The greatest mean influence to diversity index was given by Amaranthus retroflexus, Chenopodium album, Cynodon dactylon and Cyperus esculentus.