PECAN PRODUCTION IN CHINA, 2000

Background: Several Chinese scientists contacted the National Clonal Germplasm Repository in late 1998 and 1999, requesting pecan propagation materials. We received requests for either graftwood or seedstock from Hunan, Yunnan, Anhui and Henan Provinces. Shipments of graftwood were sent to Hunan (37 cultivars) and Yunnan (6 cultivars) in 1999, and seed was sent to Anhui in 2000 (4 seedstocks) through the China National Forestry Seed Company. The request from Henan was for 5000 lbs. of pecan seed, and we were not able to accommodate the order. In late 1999, I was invited to visit some of the tests that had been established with graftwood we sent, and to discuss further cooperation on the exchange of materials. I invited Larry Womack, of Womack's Nursery, DeLeon Texas, to accompany me in order to address aspects of nursery culture and propagation, and to contribute the perspective of a private nurseryman concerning this international germplasm exchange.

USDA ARS sponsored a trip to Vietnam and China from Sept. 16-Oct 25, 1990, primarily for the purpose of obtaining seed from the Asian Carya species. Participants in that trip were Dr. Bruce Wood (USDA-ARS, Research Horticulturist, Byron, GA), Dr. Jerry Payne (USDA-ARS, Research Entomologist, Byron, GA) and myself (Dr. L. J. Grauke, USDA-ARS, Research Horticulturist and Curator, National Clonal Germplasm Repository for Pecans and Hickories, College Station, TX). In China, the team visited Beijing, Zhejiang, Hunan, and Guizhou Provinces. The report of the collection trip has been published (Grauke et al., 1991).  Unfortunately, we were not permitted to collect according to our understanding of the agreement, and the few materials we collected were taken from us for later shipment. When we received them, nothing was viable. However, we obtained herbarium materials that contributed to the treatment of the Juglandaceae in the Flora of China (Lu et al., 1999). We gained insight and information on that trip that was not reported, and that is valuable for understanding the current situation in China as it relates to pecan.

Farm and Industry Structure: In 1990, our team was briefed by Chen Jianbo (Agronomist, Ministry of Agriculture, Beijing) concerning the status of the Chinese pecan program. Pecan was introduced by research units, not by production units, and was being grown in pilot test plots. More information was needed before sending the crop to production units. The Ministry of Forestry is responsible for the future market development of pecan. When asked if China was interested in increasing production of walnut, Chen replied that as far as the government was concerned, there was no expansion planned. Expansion was based on market demand. When asked if there was oil production from tree nuts, the response was that it was not economic. When asked if nut trees were being used in reforestation efforts, for erosion control, or for timber production, the response was negative. When asked if there were Federal programs for conservation of the native genetic resources, the response was negative: new plant introductions are based on economics, with the China National Seed Company supplying seed at the request of industry groups. The Technical Extension Stations provide seed of improved hybrids, there are small seed companies, and farmers save their own seed. The National Seed Company is only involved with importation. The picture we formed from this interview is that interest in pecan will be based on its ability to make economic profit. Establishment of economically profitable orchards is fastest from grafted trees.

Economics: In order to understand the potential for agricultural market development in China, it is necessary to understand the economic structure of the country, as defined by its political system. China's economy currently operates under the guidelines set forth in 1978 by the Third Plenary Session of the Eleventh Central Committee of the CPC. Those guidelines involved the adoption of policies designed to transform China's rural economy from a "self-supporting or semi-self-supporting economy to a commodity economy, and from traditional agriculture to modern agriculture" (see Agriculture, chapter 3, in vol 2, Chinese Academy of Social Sciences, 1989). The primary policy is an "output-related system of contractual responsibility" which functions as a form of sharecropping. Land is controlled by "co-operative economic units" or "production teams", which are administrative units at a sub-county level. The production teams contract their business projects to individuals, households or groups. The two parties sign a contract, with the contractor having full rights of independent management and ownership of all proceeds, minus the share of the crop demanded by the contract. The contractor improves his personal income by increasing his production, giving an incentive to good management. When the contractor finishes the contracted task, he is free to engage in other individual or cooperative enterprises.  The period of contractor's use of contracted land is generally 15 to 20 years, with longer terms authorized in some cases.  Implicit in the "small-scale peasant economy" is the understanding that "every family tills some land and every household engages in every trade by itself". The Chinese government encourages development of "specialized households" that develop business enterprises in addition to the basic farming contract. Those enterprises include many aspects of natural resource utilization, such as reforesting barren hills, or setting up nurseries, orchards, farms and fisheries on undeveloped land. The Federal and local governments offer support by "prolonging the contract validity periods, giving preferential treatment to contractors in profit distribution and providing technology free of charge" (ibid.).  

My interpretation is that the initial work with pecan in China indicated economic potential, and the effort to transfer the program from research to production is now underway. The success of that effort will depend on the establishment of economically productive model orchards. Our trip to China in 2000 gave us the opportunity to evaluate those systems.

Purpose: The purpose of this trip was to evaluate the Chinese pecan program in order to better understand the potential for cooperation and the long-term threat of competition.

Trip Structure: We were the guests of the Pecan Introduction Project of the South Central Forestry University, in Zhuzhou, Hunan. The itinerary was developed by the leaders of that project, Dr. Lu Defang and Dr. Zhang Riqing to give us an understanding of their program so we could better establish long-term cooperation in the exchange of germplasm and possibly contribute to the development of the Chinese pecan industry.  They accomplished this by introducing us to the faculty and showing us the facilities at the University, showing us their germplasm collections (grafted trees and seedling nurseries), and taking us to model orchard sites where pecan culture will be pursued and must be economically profitable for the program to succeed.

Trip Itinerary

Thursday, May 11. Arrive in Beijing

Friday, May 12. AM Travel to Changsha (by plane). PM Meet faculty at South Central Forestry University, tour labs.

Saturday, May 13. AM Travel to Yongzhou (by train). PM Field trip to see cultivar collections, provenance collection, model planting.

Sunday, May 14. AM Field trip, propagation demonstration by Larry Womack, Chinese staff. PM Travel to Zhuzhou (by train)

Monday, May 15. AM Presentations at Forestry University. PM Visit Changsha

Tuesday, May 16. AM Travel to Kunming (by plane). PM Travel to Dali (by car)

Wednesday, May 17. AM Travel to Yangbi (by car). PM Tour Yangbi pecan and walnut plantings, return to Dali

Thursday, May 18. AM Travel to Kunming (by car). PM Visit International Horticulture Expo

Friday, May 19. AM Final meeting with Dr. Lu Defang, Travel to Beijing (by plane). PM Tiananmen Square, Beijing

Saturday, May 20. AM Badaling, Great Wall. PM Beijing, Forbidden City. Met with Dr. Wu Zemin from Anhui

Sunday, May 21. Returned home

Observations and Findings

Climate The temperature and rainfall patterns for the areas we visited in Hunan and Yunan Provinces, as well as targeted areas for pecan culture in Anhui Province are shown in Table 1. Temperature and rainfall information was obtained from online records (www.worldclimate.com) and from a climatic atlas (Domros and Gongbing, 1988). The pecan growing areas of Hunan and Yunan are classified as the Middle Subtropical Zone (Domros and Gongbing, 1988), and are characterized by a year round positive temperature mean with humid moisture conditions. Areas in Hunan and Yunan are classified in Hardiness Zone 9, with mean annual minimum termperatures of -6.6 to -1.2C (20 to 30F)(Widrlechner, 1997) (fig 1). Comparable areas of the United States with that hardiness rating (see USDA Plant Hardiness Zone Map, Cathey, 1990) include parts of Florida, coastal Louisiana, the Rio Grande Valley of South Texas below the 30th parallel, and western California (fig. 2). In Mexico comparable hardiness zones are found in Coahuila, Durango, Nuevo Leon, Zacatecas, San Luis Potosi, Aguascalientes, Guanajuato, Queretaro, and Hidalgo as well as portions of several more southern states. 

Locations in Anhui Province are classified in the Northern Subtropical Zone (Domros and Gongbing, 1988). The climate is humid and only slightly colder than middle Subtropical Zone, still having positive monthly temperature means year round. The areas would be classified as Hardiness Zone 8 (fig 1) with mean annual minimum temperatures of –12.2 to –6.7C (10 to 20F). These areas are comparable in hardiness to the Gulf Coast and California in the United States. 

Rainfall amounts vary from 1081 mm per year at Dali, Yunan Province, to nearly 1500 mm per year at Chenzhou, Hunan Province. Patterns of seasonal occurrence of rainfall vary greatly also (fig 4), with rainfall at Dali being concentrated in the summer (June to September) with a peak in August. At both Hunan locations, rainfall occurs primarily in the spring, with large amounts received in April, May and June. Both patterns are in contrast to distribution patterns found in the US. Disease pressure is expected to be great in all of the Chinese locations.

Soils The pecan growing region of China that we visited lies south of the Changjiang River (Yangtze River) in the Provinces of Hunan and Yunnan. The soils in that region are classified primarily as Acrisols by the Chinese (Chinese Academy of Social Sciences, Vol. 1, p. 77):

"This is dispersed in the damp and hot region of the sub-tropical zone. Its soil-forming process consists of strong leaching and clayization processes, a fairly strong ferrallitic process, as well as the action of humus accumulation under acid conditions. The feature of the soil section shape is that the surface is covered with withered branches and dead leaves, with a grey-brown humus horizon about 10-20 cm thick, possessing a grain or granular shape structure; under the humus horizon there is red, sticky and heavy clayization B horizon, sometimes with iron nodules below. Under the red clayization B horizon there is also a matrix horizon. The organic content on the acrisol surface is one to five per cent. Due to the action of strong leaching, the soil is strongly acidic."

The "Acrisol" classification corresponds to the Ultisols Order in the soil classification system used in the United States. The description of the characteristics and distribution of Ultisols by Brady (1974) is helpful, and is given below:

"Ultisols (Latin ultimus, last). This order contains most soils formerly called Re-Yellow Podzolic and Reddish-Brown Lateritic soils and Rubrozems along with some called Humic Gley, Low Humci Gley, and Ground Water Laterited soils. They are usually moist soils and develop under warm to tropical climates. Ultisols are more highly weathered and acidic than the Alfisols but generally are not so acid as the Spodosols. They have argillic (clay) horizons with base saturations lower then 35 percent. Except for the wetter members of the order, their subsurface horizons are commonly red or yellow in color, evidence of accumulation of free oxides of iron. They still have some weatherable minerals, however, in contrast to the Oxisols. Ultisols are formed on old land surfaces, normally under forest vegetation, although savannah or even swamp vegetation is common. "

"Most of the soils of the southeastern part of the United States fall in this order. Udults, the moist but not wet Ultisols, extend from the east coast (Maryland to Florida) to and beyond the Mississippi river Valley and are the most extensive of soils in the humid southeast. Humults (high in organic matter) are found in Hawaii, eastern California, Oregon, and Washington. Xerults (drier Ultisols) are common in southern Oregon and northern and western California."

"Ultisols are prominent on the east and northeast coasts of Australia. Large areas of Udults are located in southeast Asia, including southern China. Important areas are also found in southern Brazil and Paraguay. "

"Although Ultisols are not naturally as fertile as Alfisols or Mollisols, they respond well to good management. They are located mostly in regions of long-growing seasons and of ample moisture for good crop production. Their clays are usually of the 1:1 type along with oxides of iron and aluminium, which assures ready workability. Where adequate chemical fertilizers are applied, these soils are quite productive. In the United States the better Ultisols compete well with Mollisols and Alfisols as first-class agricultural soils."

Skinner, Fowler and Alben (1938) evaluated the soils of the Southeastern United States in relation to their suitability for pecan production. Among the Ultisols that might be recognized by pecan growers was the Ruston series, one of 7 soils that those authors estimated accounted for 95 percent of the pecan acreage on upland soil series.

We did not have time to attempt characterization of the pecan soils at the sites we visited. However, we discussed the need for full physical and chemical characterization of the soils with Drs. Zhang and Lu, who intend to undertake that work. At the Yongzhou nursery site, the soil was an yellow-orange sandy clay (fig. 5, fig 6). In the provenance planting, the soil was a darker red, and was apparently a well drained sandy clay (fig. 7 ). Both sites were relatively small acreage and were level. At the model orchard site, the soil was again an orange red sandy clay soil, but with steep slopes (estimated 15-30%) (fig. 8, fig. 9 ). The picture of the model orchard (figure 9) shows an interesting aspect of the Chinese effort: the primary crop in the area is rice, which commands the best soils in the more level bottoms. The model orchard is established on higher, dryer, less desirable sloping sites. On the train trip to the orchard sites, we passed many brick factories that were evidently using very similarly colored local soils (fig. 10).

     The soils in the Anhui region are classified as Inceptisols, in both the Chinese (Chinese Academy of Social Sciences, Vol. 1, p. 77) and U.S. systems (Brady ,1974). Inceptisols are young soils with horizons that show little weathering. These soils are variable in terms of their agricultural utility

Rootstocks Two groups of seedstocks are being used in the nursery and provenance plantings: domestic and introduced. The domestic seedstocks are from selected trees that originated in Anhui or Zhejiang provinces. Seed was planted in spring, 1998 and seedlings are doing very well. The other seedstocks were sent by Dr. R. D. O'Barr in 1998, from trees at LSU as well as seedstocks sent by Dr. Bill Reid, Chetopa, KS, and from our collections. Those seed were not planted until July, due to shipment delays. Introduced seedlings were much smaller than the domestic seedlings as would be expected based on the cultural differences. Ultimate seedstock performance may be influenced by the genetic differences. Measurements are being taken of the seedling growth. 

Table 2. Pecan seedstocks sent from LSU to cooperators in Hunan and Yunan Province, 1998
Cooperator	Seedstock	Source
Research Institute of Nontimber Forest Crops	Choctaw	NCGR
South Central Forestry University	Kiowa	LSU
Zhuzhou, Hunan 412006	Caddo	LSU
PRC	Elliott	LSU
	Desirable	LSU
	Moreland	LSU
	Cape Fear	LSU
	O'Barr	LSU
	Oconee	LSU
	Forkert	LSU
	Sumner	LSU
	Surprize	LSU
	Melrose	LSU
	Jackson	LSU
	Candy	LSU
	Maramec	LSU
	Pawnee	LSU
	Gloria Grande	LSU
	Mississippi 10	LSU
	Wichita	NCGR
	Western Schley	NCGR
	Shawnee	LSU
	Cheyenne	LSU
	Giles	KS
	Peruque	KS
	Colby	KS
	Witte	KS
	Kanza	KS

Cultivars The cultivars sent to Dr. Zhang in 1999 are shown in Table 3. Dr. O’Barr provided wood of ‘Candy’ and a selection called ‘Pyzner’. That is a selection made by Glenn Hamm of Fairfax, Louisiana for outstanding resistance to aphids. Hamm called it ‘Catwalk’, and it is in the NCGR under that name. Dr. John Pyzner, Extension Specialist in Louisiana has been instrumental in distributing the wood, and his name was associated with the material sent to China. Cultivars have been established by grafting onto the seedling rootstocks in the nurseries, with all accessions being successfully grafted either in Hunan or in Yunan Province.

Table 3. Pecan cultivars sent by the NCGR to cooperators in Hunan and Yunan Province, 1999
Cooperator	Cultivar	Orchard	Row	Tree
Zhang Ri Qing	Western	BW	7	19
Research Institute of Nontimber Forest Crops	Maramec	BW	13	4.5
South Central Forestry University	Moreland	BW	106	29
Zhuzhou, Hunan 412006	Gloria Grande	BW	111	20
PRC	Barton	CSHQ	0.3	1
	Choctaw	CSHQ	2.3	1
	Wichita	CSHQ	3.3	1
	Sioux	CSHQ	5.3	1
	Mohawk	CSHQ	6.3	1
	Caddo	CSHQ	7.3	1
	Shawnee	CSHQ	8.3	1
	Cheyenne	CSHQ	9.3	1
	Tejas	CSHQ	13	2
	Kiowa	CSHQ	13	3
	Pawnee	CSHQ	13	4
	Osage	CSHQ	13	5
	Oconee	CSHQ	13	7
	Kanza	CSHQ	13	9
	Elliott	CSV	2	2
	Giles	CSV	2	3
	Desirable	CSV	5	2
	Forkert	CSV	5	5
	Mississippi 10	CSV	7	3
	Surprize	CSV	7	11
	Owens	CSV	8	1
	Jackson	CSV	8	7
	Colby	CSV	9	3
	Hirschi	CSV	9	5
	Posey	CSV	9	12
	Witte	CSV	9	17
	Prilop	CSV	14	17
	Curtis	CSV	16	2
	McMillan	CSV	17	7
	Melrose	CSV	17	22
	Sumner	CSV	18	4
	Cape Fear	CSV	18	11
	Peruque	CSV	19	8
	Candy	LSU
	Pyzner (Catwalk)	LSU
Hu Xu Lan
Yunnan Agricultural Extension Center	Oconee	CSHQ	13	7
3 Xinwen South Rd	Pawnee	CSHQ	13	4
Kunming	Caddo	CSHQ	7.3	1
Yunnan 650032	Elliott	CSV	16	10
Peoples Republic of China	Curtis	CSV	16	2
	Baker	CSV	17	16

Cultural Management

Hunan    

Cultivar Nursery: Seedlings were initially established in beds and have been transplanted to permanent sites in the nursery, on beds about 4 ft wide, with trees at about 15X15 ft spacing. This leaves a bed in the middle that is planted to other crops (ornamentals, chestnuts, pine). Seedlings are watered as needed, apparently in a furrow-type system. They are fertilized with both organic and inorganic fertilizer. Seedlings are being grafted with a modified miniature inlay bark graft. The graft is composed of a 1 bud scion dressed with a sloping cut to the back and a chisel cut on the base (fig. 11), inserted into a cleft slot made to one side at the top of the small (3/8 inch dia.) seedlings and tied with budding tape (fig. 12). Many of the trees we saw had graft unions below ground, since the seedlings being worked were so small, although some seedlings were grafted above ground (fig. 13). Workers are skilled and can perform as many as 1000 per 8 hour day. Larry Womack estimated that a skilled worker in the US doing patch buds could do about 500 per 8 hour day. He demonstrated the patch bud, and we discussed the potential for extending the season of propagation with that technique. However, the double bladed budding knife is not locally available and is expensive, while the tools used for the current technique are simple, inexpensive and available.

Provenance orchard: Ungrafted seedlings from the domestic and introduced seedstocks are being grown for comparison.  Patterns of performance indicate the advantage of the domestic seedlings, primarily due to establishment methods rather than genetics. However, some of the introduced seedstocks were from northern cultivars and may also have genetic limitations under the conditions of the test.

     Seedlings are planted in beds with generally the same organization as in the nursery plots. Beds with pecan seedlings are intercropped with peanut, while the middle bed was planted to pine and chestnut seedlings. The influence of the intercrops is not uniform across the entire plot. As in the nursery, seedlings are irrigated as needed.

Model orchard: Seedlings in the model orchard were grown from domestic seedstock, and are currently ungrafted. Seedlings are planted in terraces, about 10 feet wide, with 1.5 -3 ft of drop to the next terrace. Seedlings have peanuts planted in the terrace with them, and are being encroached upon by weeds (see fig. 8, ) more than at either of the other planting sites. Irrigation is more challenging on this site, with water being delivered to individual seedlings by bucket. Leaf feeding caterpillars infested some seedlings (fig. 14).

Yunan

Yangbi Research Center: The plots at Yangbi were not as systematically established for particular purposes as in Hunan Province.  Mature pecan trees of several genotypes are being grown:

‘Jin Hua #1’ (fig. 15) This is a selected seedling from Nanjing. On May 17, mature trees had catkins shedding pollen (with few fully spent) and pistillate flowers currently receptive (mostly past) (I rated it as protogynous)(fig. 16). There were up to 8 nuts per cluster. Several ‘Jin Hua #1’ grafts showed pistillate flowers on the first growth of the graft (fig. 17), indicating either unusual precocity or that smaller diameter wood contains buds that are initiated to bloom more than the larger diameter wood we typically use for seedling propagation. We saw nuts with damage similar to that caused by shuckworm (Cydia caryana Fitch) (fig. 18)

 ‘Shao Xing’ is a selected seedling from Zhejiang Province. The trees were past receptivity but shedding pollen on May 17, making them protogynous.

 There were grafts of Carya cathayensis on pecan and C. tonkinensis seedling rootstocks. A large C. tonkinensis seedling (over 30 ft tall, 8 in dbh, planted 1990) was the source of those seedlings (fig. 19).

We saw extensive damage from a borer that created galleries in the trunk and limbs, sometimes completely girdling the limb and causing death (fig. 20, fig. 21, fig. 22). An empty pupal case was found protruding from one of the galleries (fig. 23). Sun and He (1982) reported that “the main pest in Nanjing was the yellow-tailed borer (Sesiidae). The larvae damage the tree trunk by destroying the phloem around the trunk. It has been shown in an investigation in Nanjing that the borer damage was as high as 85 percent in trees from 11 to 30 years old.” In the United States, similar damage is caused by the Pecan Carpenterworm (Cossidae,  Cossula magnifica (Strecker)) found in the Southeastern US. Zeuzera pyrina L. (Leopard moth) is another Cossid that could cause this type of damage.

The Yangbi Research Station is also involved with walnut research and has developed a cultivar of Juglans sigillata named ‘Yangbi’ (fig. 24). ‘Yangbi’ kernels shelled out as full halves, were an appealing cream color, and had excellent flavor. The only accessions of Juglans sigillata in the NCGR for Walnuts at Davis, California are seedling selections collected by Anthony Allen (Dr. Charles Simon (curator), pers. commun.)

Research and Extension

The Chinese researchers involved with the pecan project freely provide information and materials to their cooperators. Their program will benefit from the free exchange of germplasm and information from the United States. Our Chinese colleagues are interested in receiving copies of periodicals and the Proceedings of grower association meetings.

Production Capability

The California Walnut Commission initiated an investigation of the potential for market development or competition with China in 1989, and revisited the country in 1999. They found exceptional growth in the Chinese walnut industry over that time period. The perspective of that commission is reported detail (Balint et al, 1999) and is valuable reading. Walnuts are an established commodity in China, with 175,000 short tons being produced in 1989, which increased to almost 215,000 produced in 1998. The Chinese pecan industry is in its early development. Appropriate selection of rootstocks and scion cultivars must be accompanied by careful attention to management constraints to determine if economically enticing production can be accomplished and sustained. The stated objective of production is economic profit, as opposed to conservation via reforestation or on-farm consumption of nuts, fuel and high grade lumber (which will be accomplished secondarily, if the commodity is successfully established). Given the relative lack of disposable income by most rural Chinese, economic returns must be targeted at the large cities (if not the export) market. Increasing awareness of the palatability of pecans by urban Chinese provides a short-term opportunity for export by the US pecan industry. 

Potential for Collaborative Research Efforts

Chinese hickory (Carya cathayensis) is grown commercially in the eastern China, primarily Zhejiang Province, while Hunan hickory (Carya hunanensis) is produced to a smaller extent in Hunan and Guizhou Provinces. Cultivars have been selected, and interspecific hybridization with pecan has been accomplished (Ruan et al, 1992). We would like to obtain accessions of those species, cultivars and hybrids for inclusion in our germplasm repository, for characterization in relation to other species in the genus. We also see potential value in obtaining accessions of the Juglans sigillata cultivar ‘Yangbi’ selected by the Chinese.

Our Chinese colleagues are actively involved in molecular genetic characterization of pecan and other Carya species. They mentioned intriguing results from chromosome counts of some Asian Carya species, and we expressed interest in seeing the publication. No one in the United States is actively using microscopy to characterize chromosomes in Carya, and their expertise in that area could be beneficial.

References Cited

Balint, D., Barton, G, Sibbett, S. and Siebert, J. 1999. China Mission: Findings and Conclusions. California Walnut Commission.

Brady, N. C. 1974. The Nature and Properties of Soils. 8th Edition. MacMillan Publishing Co. Inc., New York.

Cathey, H. M. 1990. USDA Plant Hardiness Zone Map. United States Department of Agriculture, Agricultural Research Service Miscellaneous Publication Number 1475.

Chinese Academy of Social Sciences. 1989. Information China: the comprehensive and authoritative reference source of new China. Pergamon Press.

 Domros, M. and Gongbing, P. 1988. The Climate of China. Springer Verlag. New York.

Grauke, L.J.; Wood, B.W.; Payne, J.A. 1991. Genetic resources of Carya in Vietnam and China. Annu. Rpt. N. Nut Growers Assn. 82:80-87.

Lu, A. M, Stone, D. E., and Grauke, L. J. Juglandaceae. p 277-285. In Wu Z. Y. and Raven, P. H. (eds) Flora of China, Volume 4, Cycadaceae through Fagaceae. Co-published by Science Press (Beijing) and Missouri Botanical Garden Press (St. Louis). 1999.

Ruan, Y. L., Wood, B. W. and Payne, J. A. 1992. Chinese hickory: an emerging nut-tree crop. Fruit Varieties Journal 46:16-22.

Skinner, J. J., Fowler, E. D., and Alben, A. O. 1938. Pecan soils of the gulf and southeastern states and maintenance of their fertility. United States Dept. of Agriculture Circular 492.

Sun, Z. J. and He, S. A. 1982. The history, present and prospect of pecan in China. Pecan South.

Widrlechner, M. P. 1997. Hardiness Zones in China (map). USDA ARS North Central Regional Plant Introduction Station, Iowa State University, Ames IA 50011.