The influence of soil preparation, seedling rates, and organic mulch on the production of woods-cultivated ginseng

Abstract
North American ginseng (Panax quinquefolius L.) has long been recognized as a valuable horticultural crop because of the properties of its roots for both herbal and medicinal purposes. The wild root is generally described as having the highest quality. Unfortunately, over-harvesting and inappropriate management in 1800's led to its decline. Today, ginseng production can be divided in three distinct categories: 1- wild simulated root, 2- woods-cultivated root, and 3- field-cultivated root. The aims of this study were to compare different treatments in natural forests and in pesticide and chemical free environments in order to produce high quality roots. To achieve this goal, three soil preparations (1- wild simulated, 2- tillage, and 3- preparation of beds), three kinds of organic mulch (1- forest floor, 2-decidious leaves, and 3-wood chips/leaves), and three plant densities (25 to 35 kg per ha) were studied. The effects of these treatments on germination rate, plant growth, mortality and root morphology were analysed on seedling. Our results have shown that mulch type has an effect on plant mortality, whereas soil preparation (tillage and bed preparation) improved the germination rate and growth of ginseng seedling. Plant density had no significant effect for the first year of growth. Data will be discussed in terms of improved crop management for better plant growth.

Introduction

Ginseng, an obligate shade plant, is grows naturally in broadleaf forests of Northern Asia and North America (Proctor and Bailey 1987). American ginseng (Panax quinquefolius L.) ranges from southeastern Canada southward to the Carolinas and Georgia and westward to states bordering the Mississippi River. Habitat destruction through the cutting of deciduous forests and intensive harvesting for their medicine properties, however, have contributed to its progressive disappearance in North America (Charron and Gagnon 1991). North American ginseng has long been recognised as a valuable horticultural crop because of the properties of its roots for both herbal and medicinal purposes. Traditional Asian medicines use this valuable root extensively. Data from Statistics Canada indicate that the average Canadian export price on field-cultivated ginseng root in 1997 was 23.93 Canadian $/lb. For 1996, the U.S. exports of wild ginseng root (including wild simulated root, woods cultivated ginseng and wild root altogether) were also recorded as having an average price about 242 Canadian $/lb. Unfortunately, new fungal diseases affecting large-scale ginseng fields are now threatening the profitability of this culture. Moreover, ginseng root quality has decreased noticeably over the last few years, resulting in significantly lower prices. Growing ginseng in its native forest environment is another approach, which is less expensive, and produces high quality roots in pesticide and chemical free environments.

Numerous studies have been conducted on the ecology of natural populations of ginseng (Charron and Gagnon 1991, Lewis and Zenger 1982, Stathers and Bailey 1986), reproductive biology (Lewis and Zenger 1982), chemical composition (Kim et al. 1995, Ma et al. 1994), medicinal properties (Carlson 1986), field-cultivated growth, yield, photosynthetic rate, respiration and transpiration under various solar radiation and/or temperatures conditions (Konsler 1986, Lee et al. 1980, Proctor and Tsujita 1986). Unfortunately, the wild simulated root, and woods-cultivated root production techniques have received limited attention. Quantitative differences in total ginsenosides and qualitative differences in individual ginsenosides between wild and cultivated plants have been reported (Betz et al. 1984) which might be attributed to physiological stresses and differences in growth rate (Konsler et al. 1990). Woods growing is potentially profitable in the United States and is now practiced by more people (Persons1 1994). In New Zealand, Smallfield and al. (1995) have shown that American ginseng can be grown successfully under canopies of Pinus radiata planted on volcanic ash soil in the Central North Island. Cultivating ginseng within natural forest (Korean pine forests) is the future direction for ginseng plantations in China (Wang et al. 1994).

There are two different approaches for growing ginseng under natural forest shade: 1- the wild-simulated method (minimal disturbance to the forest floor), and 2- woods cultivation (preparing cultivated beds) (Persons1 1994). Wang et al. (1994) observed that root weight decreased with increasing shade density and that soil preparation could produce an increase in ginseng weight when ginseng was cultivated for 7 years under different forest canopies using the seed scattering method with no soil preparation or with soil preparation. Root characteristics also changed with the type of forest (fertility, climate, shading).

It is well known that the natural leaf mulch under the forest canopy plays an important role in the growth of ginseng as it conserves moisture during dry periods in the summer and provides protection for roots from excessively low soil temperatures during the winter (Stathers and Bailey 1986). A study done by Konsler (1982) during 4 years has shown that oak and poplar mulches produced the highest yields while straw was among the lower yielding mulches. Roots from pine needle mulch tended to be among the largest during the first two years but by the fourth year were among the smallest while wheat straw and hardwood leaf mulches consistently produced smallest roots.

Root growth and incidence to diseases are strongly influenced by plant spacing. Under field growing conditions many studies have been done in order to optimise plant spacing (Konsler 1982, Konsler and Shelton 1984). However, little is known about the response of American ginseng to plant spacing in its woodland habitat. The objective of this study was to study the effects of soil preparation, plant density and mulches on germination rate, plant growth and mortality and root morphology for the first year of ginseng growth under its natural forest environment.

 

Experimental Methods

Experimental site

The experiment was conducted in a sugar maple-beech forest located at Ile d'Orléans, Québec, Canada (lat. 46.58, long. 70.58). The woodland soil is a loam-clay with 11.7 % organic matter and pH of 4.6. Total precipitation for may to September 1997 is 436.2 mm. Normal daily air temperatures for the month of May, June, July, August and September are 15.9, 22.8, 24.9, 24.3 and 17.7 °C, respectively. Natural forest canopies provide 70-80% of shading. Preparation of the wooded sites consisted in the removal of all brush and small saplings. For wild-simulated planting, the leaves were raked aside and the soil surface was loosened on 2.5 cm with a heavy-tined rake. Seeds were scattered, raked in, mulched by returning the original leaf litter, and left to grow naturally. In wood tilled cultivation, seeds were planted 2.5 cm deep and mulched with natural leaf cover or according to the mulch treatments. Beds of 9 x 2 x 0.10 m were made and seeds planted 2.5 cm deep according to the plant spacing treatments. Fifteen cm of wood chips or deciduous leaves mulch was put on individual plots. In the second experiment, beds of 11 x 1 x 0.10 m were made and seeds planted 2.5 cm deep according to the plant spacing treatments.

Treatments

In the first experiment, three soil preparation treatments (1- wild simulated, 2- tillage on 15 cm depth, and 3- preparation of beds on 10 cm), and three plant densities (1- 25 kg per ha, 2- 30 kg per ha, and 3- 35 kg per ha) were compared. The experimental design was a completely randomized blocks with three replications and two repetitions for a total of 54 plots. In the second experiment, three soil preparation treatments (1- wild simulated, 2- tillage on 15 cm depth, and 3- preparation of beds on 10 cm), and three kinds of organic mulch (1- natural forest floor, 2- 15 cm of deciduous leaves, and 3- 15 cm of wood chips/leaves mixing) were studied. The seedling rate for the second experiment was 30 kg/ha. The experimental design was a completely randomized blocks with four replications for a total of 36 plots. Each plot of the first experiment was 2 x 9 m in size and 2 x 11 m for the second experiment. Stratified American ginseng seeds were purchased from commercial source and planted in October 1996.

Monitoring, sampling and analysis

The number of seedlings found in a 2 m2 in each plot was recorded weekly during the 1997 growing season (09/06/97 to 07/08/97). Nine plants per experimental unit were dug in mid-August and stem length, root and shoot fresh and dry weights measured as well as leaf area. Morphological analysis of nine plants per experimental unit was done with WinRhizoÔ software (Régent Instruments, Qué., Canada). The GLM procedure was used for the contrast analysis of this two factorial experiments (SAS Institute Inc.). The contrasts were determined a priori and the number of comparisons was equal to the degrees of freedom of the treatments.

Results and discussion
Effect on emergence and mortality
In the first experiment, soil preparation treatments had a significant effect (P=0.01) on plant emergence, mortality and survival while plant densities did not affect significantly these parameters (table 1). Soil preparation gave better results than wild simulation (more than twice as high emergence). However, large variation within experimental units was observed. The soil preparation increased drainage and soil temperature. Seed germination occurred when soil temperature reached 5 oC (Wang et al. 1994). Plant spacing had no effect on these parameters very likely because the seedlings were too small to observe density effect. Under optimal conditions, the germination rate of stratified seeds is ~ 60-70 % (Oliver 1996). With densities of 25, 30 and 35 kg/ha and a germination rate of 65 %, the emergence rates are 54, 64 and 75 plants/2 m2, respectively. The poor results obtained could be explained by the cold rainy conditions that prevailed in spring 1997, by insufficient soil drainage and by seed diseases. In fact, pathogens propagation, causing damping-off such as Rhizoctonia, Pythium, Fusarium and Phytophtora, are favored under cold and wet conditions (Persons2 1994).
In the second experiment, wood chips/leaves mulch favored plant emergence (P=0.01), more than twice as high emergence compared natural forest floor and 4 times with deciduous leaves. The wood chips mulch is less humid than the two other ones, and might increase temperature. Adding deciduous leaves to the forest floor is generally no recommended because soil humidity increases and as a consequence, the thick layer of mulch affects seedlings emergence. The slugs were responsible for most of the mortality rate. Their impact is lower when wood chips were used because this mulch has an abrasive effect on the slugs (Oliver 1996).
Effect on growth and morphology
Soil preparation treatments had a significant effect (P=0.05) on plant growth and root morphology (Tables 3, 4 and 5). Bed cultivation and soil tillage increased leaf area by 16% while shoot and root fresh weights increased by 18-24% and 40%, respectively. No significant effect was observed on stem length and shoot and root dry weights. The total length (cm), area (cm2) and volume (m3) of smaller roots (<1 mm) were 80-83%, 60-63% and 44-50 % higher, respectively, under disturbed soil (tillage and bed cultivation) compared with the not-disturbed soil (wild simulated plants; Table 4). However, no significant effect of soil preparation on these parameters was found for bigger roots (>1 mm). Moreover, root projected area (cm2), and the number of root apex and root divisions increased by 55-60%, 36-51% and 60-65%, respectively, under disturbed soil in comparison with the not-disturbed soil while mean root diameter decreased by 13-22% (carrot shaped with soil preparation for the first year of growth). These results suggest that under disturbed soil, rootlet development is favored very likely as a way to increase water and nutrient uptake. An increase in the latter two physiological functions is generally linked to higher leaf area, plant fresh weight and seedling survival.
After the first growing season, seed rates did not affect significantly: 1) the growth (leaf area, root and shoot fresh and dry weights), 2) the morphology of wood-cultivated American ginseng (Tables 3, 4 and 5) or 3) the incidence of diseases. Plant spacing effects may eventually show up later during plant development (up to 3-4 years). For field-cultivated American ginseng, Konsler and Shelton (1984) have observed a strong influence of plant spacing (29 to 258 plants m2) on root growth during the 6 years of the study. Average root size was proportional to the space available per plant, while root yield per unit area was closely related to plant population. They reported the increased probability of disease epidemics and alleopathic reaction with increasing plant population.

Conclusion
Results from this study have shown that woodland soil preparation by tillage or cultivated beds improved the establishment and growth of wood-cultivated American ginseng after the first growing season, due to better root development for water and nutrient uptake. However, no significant difference was observed between soil tillage and beds cultivation. In general, mulch wood chips favored plant emergence and survival. It is too early to report on any effect of plant spacing on growth, root quality, and incidence of diseases of wood cultivated ginseng. In order to better know the long term effects of soil preparation, plant spacing and mulch treatments on American ginseng root growth and quality, further observations and analysis will be done in the next 4 years.

	Betz J.M., A.H. Der Morderosian and T.M. Lee. 1984 Continuing studies on the ginsenoside content of commercial ginseng products by TLC and HPLC. II. Proc. 6th North American Ginseng Conference, Guelph, ON, p.65-83.
	Carlson A.W. 1986. Ginseng: America's botanical drug connection to the orient. Econ. Bot. 40:233-249.
	Charron D., D. Gagnon. 1991. The demography of northern populations of Panax quinquefolium (American ginseng). J. Ecology 79:431-445.
	Kim, D.C., S.M. Chang et J. Choi. 1995. Effects of the chemical properties of field soils on the contents of sugars and saponin in ginseng roots. Agr. Chem. biotechnol. 38(1): 72-77.
	Konsler T.R. 1986. Effect of stratification temperature and time on rest fulfilment and growth in American ginseng. J. Am. Soc. Hortic. Sci. 111:651-654.
	Konsler T.R. 1982. Some responses of American ginseng (Panax quinquefolium L.) to kind of bed mulch and to plant spacing thru four growing season. Proceeding of the fourth national ginseng conference, Kentucky, USA Eds C.R. Roberts and J English.
	Konsler T.R. and J.E. Shelton. 1984. Plant spacing, mulches and soil effects on cultivated American ginseng (Panax quinquefolium L.). Sixth North American ginseng conference, University of Guelph, Canada, Eds J.T.A. Proctor.
	Konsler T.R., S.W. Zito, J.E. Shelton and E.J. Staba. 1990. Lime and phosphorus effects on American ginseng:II. Root and leaf ginsenoside content and their relationship. J. Amer. Soc. Hort. Sci. 115:575-580.
	Lee J.C., SK Cheon, Y.T. Kim and J.S. Jo .1980. Studies on the effect of shading materials on temperature, light intensity, photosynthesis and root growth of Korean ginseng (Panax ginseng C.A. Meyer). Korean Soc. Crop Sci. 25:91-98.
	Lewis W.H.and V.E. Zenger. 1982. Population dynamics of the American ginseng, Panax quinquefolium (Araliaceae) Am. J. Bot. 69:1483-1490.
	Ma Y.C., J. Zhu, L. Benkrima, L. Sun, S. Sain, C. Kont, and Y.Y. Plaut-Carcasson. 1994. A comparative study on ginsenosides in different commercial ginseng products and tissue culture samples using HPLC. International Ginseng Conference Proceeding, Vancouver, Canada. Eds W.G. Bailey, C. Whitehead, J.T.A. Proctor and JT Kyle.
	Oliver, A. 1996. Ginseng Production Guide for commercial growers. 1996 ed., British Columbia: Ministère de l'Agriculture, des pêcheries et de l'Alimentation.
	Persons,1 W.S. American ginseng farming in its native woodland habitat. 1994. In The challenges of the 21st century in Vancouver, edited by W.G. Bailey, C. Whitehead, J.T.A. Proctor, and J.T. Kyle, Simon Fraser University, B.C., 78-83.
	Persons,2 W.S. 1994. American ginseng: green gold. Revised ed., Asheville, North Carolina: Bright Mountain Books, Inc.
	Proctor J.T.A. and W.G. Bailey. 1987. Ginseng: Industry, botany and culture. Hort. Reviews 9:187-236.
	Proctor J.T.A. and M.J. Tsujita. 1986. Air and root-zone temperature effects on the growth and yield of American ginseng. J. Hortic. Sci. 61:129-134.
	Stathers R.J. and W.G. Bailey. 1986. Energy receipt and partitioning in a ginseng shade canopy and mulch environment. Agricultural and Forest Meteorology 37:1-14.
	Smallfield B.M., J.M. Follett, M.H. Douglas, J.A. Douglas and G.A. Parmenter. 1995. Production of Panax spp in New Zealand. Acta Hort. 390:83-89.
	Wang H., J. Fan, X. Yang, G. Fan, Q. Liou and H. Dai. 1994. A study on ginseng cultivation under forest conditions and its physiological and ecological characteristics. International Ginseng Conference Proceeding, Vancouver, Canada. Eds W.G. Bailey, C. Whitehead, J.T.A. Proctor and JT Kyle.