YIELD FORMATION IN BRUSSELS-SPROUTS

The effects of three planting dates and three plant densities, coverin g most of the planting dates and densities used in the Netherlands, on yield determining factors of Brussels sprouts (Brassica oleracea var. gemmifera), were studied in field experiments during three seasons. P lanting dates were between the end of April and early July. Plant dens ity ranged between 2.7 and 4.4 plants per m(2). Planting late in the s eason initially resulted in more leaves being formed, a higher Leaf Ar ea Index and a longer stem. During crop growth this trend was reversed to a lower number of leaves formed, and in two of the three years a l ower LAI and stem length when planting was delayed. The effect of plan t density on these characteristics was generally either less pronounce d than that of planting date or was absent. There was no, or only limi ted, interaction between the effects of planting date and plant densit y on these characteristics. The initial rate of dry-matter accumulatio n after planting was higher after planting late in the season, but the final amount of standing dry matter was reduced by the late planting. Plant density did not influence the final amount of standing dry matt er. There was no interaction between the effects of planting date and plant density on dry-matter accumulation. Planting date and plant dens ity hardly influenced the radiation use efficiency. Overall radiation use efficiency was 2.2 g MJ(-1). The time of bud initiation expressed as numbers of days after planting was advanced by delayed planting, bu t was not influenced by plant density. Planting late in the season dec reased the number of buds per plant and in one of the three years also reduced the weight per bud. A decrease in the number of buds per plan t due to increased plant density was more than compensated for by the increase in number of plants per hectare. The final number of buds as a percentage of the final number of leaves, was either not, or not con sistently, influenced by treatment. Bud dry-matter concentration at fi nal harvest decreased when planting was delayed, but was not influence d by plant density. There was no interaction between the effects of pl anting date and plant density on bud dry-matter concentration. The dry -matter harvest index of 30-45% was not greatly affected by treatments . To aim for high yields, planting should be as early as field conditi ons allow.