Effect of planting bed shape, mulch and soil density on root yield and shape in North American ginseng (Panax quinquefolius L.)

Abstract

Ginseng root value varies with shape. To increase understanding of factors affecting root shape and growth, we conducted a 4-yr field experiment with three planting bed shapes with and without straw mulch cover, and 3-yr duplicate experiments with varied soil textures and bulk densities (BD). Panax quinquefolius L. plants either remained undisturbed for 3 yr in vertical tiles where sand or loam soil was compacted to differing BD, or were transplanted into low BD soil after 1 yr. Transplanting aimed to demonstrate the influence of conditions encountered in the first year of growth on mature root shape, and to explore opportunities to manage beds and manipulate root shape in transplanted ginseng, which may be a common practice in future. Without mulch, 4th year root yields were reduced by 65%, primarily due to a 60% reduction in plant stand which occurred by the end of the seedling year. Seeding directly into the ground resulted in yields similar to conventional rounded beds and a greater proportion of roots of favourable shape, likely due to greater soil BD in ground plots than round beds. Relative to low BD, high BD soil resulted in shorter, rounder "chunk" grade roots after 1 and 3 yr growth in situ. After 3 yr, roots were shorter and rounder in loam than in sand. Soil BD effects were not retained after 3 yr for replants, so high BD pre-treatment of transplants will not improve root shape over the longer term. Moderate soil compaction may reduce production of undesirable pencil-grade roots, but there is a yield trade-off with high BD soils. A high BD must be maintained for >1 yr, and a decline in stand is likely in compacted loam soil which has slow drainage. Key words: Root grade, North American ginseng, American ginseng