Broccoli Growth, Yield and Level of Aphid Infestation in Leguminous Living Mulches

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Abstract
A living mulch is an intercropping system which combines an annual crop with a cover crop in order to achieve better weed and insect control, enhance soil fertility and reduce soil erosion and compaction. In this study broccoli (Brassica oleracea var. botrytis L.) was grown under clean cultivation (no cover crop) and in living mulches using three leguminous cover crops: white clover (Trifolium repens L.), strawberry clover (Trifolium fragiferum L.) and a mixture of birdsfoot trefoil (Lotus corniculatus L.) and red clover (Trifolium praetense L.). Aphid infestation of harvested broccoli heads, leaf area, leaf water content, leaf nitrate-nitrogen and yields were assessed. Fertiliser was applied at commercial rates as synthetic fertiliser or compost crossed with cover crop regime. In plots fertilised with compost aphid infestation on harvested broccoli heads was consistently less in living mulches than under clean cultivation. Nitrogen availability was lower in all compost subplots, as indicated by low leaf nitrate levels compared to synthetic fertiliser. Compost lowered levels of leaf area, leaf water content and yields. Leaf water content was lower in the clean cultivated treatment when fertilised with compost, probably because low soil nitrogen levels limited root growth and therefore restricted water uptake. Broccoli size and yields were equivalent between living mulches and clean cultivation in synthetic fertiliser plots, and when fertilised with compost broccoli in living mulches outyielded broccoli under clean cultivation.