Yields, weeds, pests and soil nitrogen in a white cabbage living mulch system

The purpose of the present studies was to screen for suitable cover crops and seeding rates and investigate the influence of non-suppressed and mechanically suppressed living mulch on white cabbage yield, weed growth, pest damage and green manuring effects. Because no differences in weed suppression between the species/cultivars were found in the first experiment, Trifolium repens L. cv. Pertina, which had least negative impact on cabbage yield was chosen for the second experiment. In addition, Trifolium subterraneum L. cv. Geraldton was included. The competition between cover crop and cabbage was considerable in the second experiment. Mowing once or twice did not improve cabbage yield compared with unmoewed treatments. A considerable increase in cabbage yield was achieved both in subclover and white clover by rototilling between the rows 6 weeks after transplanting. The cover crops did not reduce weed biomass or number of weeds early in the season compared with monoculture, but weed biomass in late summer became significantly lower in living mulch. Rototilling was more effective for weed suppression than mowing. Cover crop combined with rototilling reduced weed biomass by 89% compared with untreated monoculture. Subclover living mulch gave the earliest and most ground coverage and the lowest cabbage yield, but it also gave the least insect damage. Both subclover and white clover living mulches gave significantly more marketable cabbage heads than monoculture due to less insect damage. However, damage from caterpillars, primarily Mamestra brassicae L., was too great in all treatments to produce a commercially viable crop. White clover intercropping in cabbage gave significantly higher oat (Avena sativa L.) yield the subsequent year than monocropping. The implications of the current findings on future efforts to improve intercropping are discussed.