The use of living or surface mulch to supply nutrients and control weeds in organic vegetable growing

Clover/grass material as a surface mulch and the planting of crops in rotovated strips in a red clover/grass sward were compared using white cabbage and red beet. Growing in rotovated strips was unsuccessful, even though the sward was mown frequently. The negative effect was lessened by applying mulch material, but not avoided entirely. Surface application of a 3 cm deep layer of red clover material to tilled soil gave good control of annual weeds, but not of perennials. One application was almost as effective as two. Incorporation by inter-row rotovation reduced subsequent weed control and gave only a small increase in plant nutrient uptake. The use of two surface mulchings, containing 587 kg N ha(-1), gave 12% and 32% increases in saleable yields of red beet and white cabbage respectively. The practice is, however, labour-intensive and requires an area of two to three times that of the vegetable plots, in order to provide 3 cm of mulch. An additional treatment included 60 kg N ha-1 of dried chicken manure, followed by mulching at a later date with a green manure mixture grown alongside the vegetables. This treatment supplied 128 kg N ha(-1) and gave yield increases of 12% in beet and 17% in cabbage. It did not give as good weed control as red clover mulching, since the material was applied later. The apparent recovery by the crops of the nitrogen applied in the mulches was very low, ranging from 2-9% in the case of beet and 12-19% in cabbage. Residual amounts of mineral-N at 0-60 cm depth were increased after beet by 30 and 55 kg ha(-1) with one or two mulchings, respectively. The corresponding figure for the chicken manure/green manure treatment was only 10 kg ha. Much smaller differences were found after cabbage, reflecting the greater uptake of nitrogen by this crop.