PLANTING AND HARVEST DATE EFFECTS ON PRODUCTIVITY AND ROOT SHOOT QUOTIENT OF 4 BRASSICA CULTIVARS/

Summer-planted turnip (Brassica rapa L.) is a highly productive crop, and may allow farmers to extend the grazing season and tower animal pr oduction costs. A field study was conducted to determine the influence of planting date and harvest date on morphological development and pr oductivity of leafy plants like turnip in late fall. Turnip and a spin ach x mustard hybrid were seeded in rows on Hagerstown silt loam soil (fine, mixed, mesic Typic Hapludalfs), using a factorial treatment str ucture (6 planting dates x 4 cultivars) in a split-plot design, with p lanting date as whole plot, cultivar as subplot, and four replicates. Three to six harvest dates were used, depending on planting date, resu lting in an overall incomplete factorial treatment structure. Mean yie ld of all cultivars with optimal planting date-harvest date combinatio ns was 11.5 Mg ha(-1) without severe foliar disease and 9.7 Mg ha(-1) with alternaria leaf spot (caused by Alternaria spp.). The interaction of planting date and harvest date on morphological development depend ed on resource allocation characteristics of the cultivar for top and root production. Delay of planting from late July to late August decre ased top and root production more in 1990 than 1989. An optimum harves t date for maximizing fall top yield occurred each year regardless of planting date. Root yields increased in November and early December, w hereas top yields did not. In general, total yields were high for crop s planted in late July and harvested in late October or early November . Top/root quotient (top yield divided by root yield) was increased by delaying summer planting, and decreased by delaying fall harvest. Sav anna had the highest, and Purple Top had the lowest top/root quotient. Turnip offers very high production potential for late-fall grazing, w ith a wide range of top/root yields.