Planting and Harvest Date Effects on Productivity and Root/Shoot Quotient of Four Brassica Cultivars

Abstract

AbstractSummer‐planted turnip (Brassica rapa L.) is a highly productive crop, and may allow farmers to extend the grazing season and lower animal production costs. A field study was conducted to determine the influence of planting date and harvest date on morphological development and productivity of leafy plants like turnip in late fall. Turnip and a spinach ✕ mustard hybrid were seeded in rows on Hagerstown silt loam soil (fine, mixed, mesic Typic Hapludalfs), using a factorial treatment structure (6 planting dates ✕ 4 cultivars) in a split‐plot design, with planting date as whole plot, cultivar as subplot, and four replicates. Three to six harvest dates were used, depending on planting date, resulting in an overall incomplete factorial treatment structure. Mean yield of all cultivars with optimal planting date‐harvest date combinations 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 depended on resource allocation characteristics of the cultivar for top and root production. Delay of planting from late July to late August decreased top and root production more in 1990 than 1989. An optimum harvest date for maximizing fall top yield occurred each year regardless of planting date. Root yields increased in November and early December, whereas top yields did not. In general, total yields were high for crops 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. Savanna had the highest, and Purple Top had the lowest top/root quotient. Turnip offers very high production potential for late‐fall grazing, with a wide range of top/root yields.