THE EFFECT OF PLANTING DATE AND PLANT-DENSITY ON YIELD AND GRADING OFBRUSSELS-SPROUTS

During three seasons the effects of planting date and plant density, a nd their interaction, on marketable yield and grading of Brussels spro uts (Brassica oleracea var. gemmifera) were studied in field experimen ts. The marketable yield, as an average of three or four successive me chanical harvests, decreased with delay in planting from the end of Ap ril-early May to the end of June-early July. Final marketable yield le vels varied between 29.4 tonnes per hectare when planting was early, t o 17.4 tonnes per hectare when planting was late in the season. A decr ease in yield with an increase in plant density from 2.7 to 4.4 plants per m(2) was found in only one year. Grading (percentage of buds >31m m) was not consistently influenced by planting date, but increasing th e plant density increased the proportion of small buds. There were no or interactions of only limited importance between the effects of plan ting date and plant density on yield and grading, indicating that, wit hin one year, for the whole range of planting dates the effects of den sity on yield and grading are similar. For a high yield of small buds, plant density should be increased and the harvest date delayed. For h arvest planning, better use should be made of variation in maturation time between cultivars, rather than of variation in the date of planti ng. Maturation time within a cultivar can be manipulated by varying th e plant density.