Production and Cultivation Technology of Selenium-enriched Pueraria thomsonii Benth

Kunpeng OU Risheng HUANG Yuanning YANG Hengwen HUANG Yan WANG

Abstract The cultivation technology of selenium-containing plant Pueraria thomsonii Benth was summarized from the producing area conditions， variety selection， field management and other aspects， which is of great significance for increasing the selenium concentration in humans or animals.

Key words Selenium enrichment; Pueraria thomsonii Benth; Cultivation; Environment

Selenium （Se） is one of the micronutrients necessary for the human body， and is an important contituent part of the bodys antioxidant enzymes. It has the effects of enhancing human immunity， preventing cardiovascular diseases and resisting aging and cancer[1]. Se in agricultural products is the main source of Se in humans. Studies have shown that inorganic selenium can be converted to organic selenium by applying selenium to crops， thereby increasing the selenium content in humans or animals， which is a safe and effective way to supplement Se. It has important practical significance for the prevention and treatment of human selenium deficiency.

Pueraria thomsonii Benth belonging to Leguminosae is a medicinal and food plant jointly recognized by the Ministry of Agriculture and National Health and Family Planning Commission of Peoples Republic of China， and is mainly produced in Guangxi， Guangdong and other places[2]. The annual cultivated area of P. thomsonii in Guangxi is 10 000 hm2， accounting for one fifth of the total planted area in the China， mainly distributed in Tengxian， Yulin， Lingui， Pubei and other places， and the annual production has exceeded one million tons[3].

Guangxi has a relatively large area of Se-rich soil[4]， which provides unique conditions for the production of natural Se-enriched agricultural products. Because of its relatively simple cultivation management technology， P. thomsonii is suitable for large-scale industrialization due to its storage resistance and easy transportation， and its market potential is very broad.

Environmental Conditions of Producing Areas

P. thomsonii is highly adaptable to topography and soil. It is advisable to choose loose sandy loam soil with an organic matter layer of not less than 60 cm and a pH value of 6.0-7.0. P. thomsonii is not tolerant to waterlogging， and the field should have good drainability.

Selection of Variety

It ought to choose high-quality high-yield disease-resistant varieties with strong Se enrichment capability， such as Guifenge 1， Guangdong Huoshan Fange， Guangdong Heshui Fange and so on.

Base Fertilizer and Soil Preparation

The amount and type of base fertilizer applied can be determined according to the actual situation in various places. If possible， the base fertilizer can be applied as much as possible. After applying the fertilizer to the ground， the soil should be ploughed under to great depth， so that the base fertilizer can be evenly mixed with the soil. The ploughing depth of the soil can be 30-40 cm. After the ploughing， the soil should be harrowed in time and raked and ridged in a line spacing of 170 cm. The ridge surface is turtle-shaped and has a ridge width of 110-120 cm and a ridge height of 30-40 cm， and the ditch width is 50-60 cm. One row of plants are planted per ridge with plant spacing of 35-40 cm.

Plantlets Raising and Planting

Healthy and disease-free P. thomsonii cuttings are inserted into seedling cups. The plantlets are raised at temperatures of 15-25 ℃ for 20-30 d. The plantlets with a height of no more than 10 cm having 1-3 fibrous roots each， which grow strongly and are free of pests and diseases and damage， are used for cuttage on soil piles according to one plantlet per soil pile at a density of 12 750-16 500 plants/hm2.

Field Management

Water management

After field planting， if it is sunny， the plantlets should be watered once in the morning and evening for 3 consecutive days， followed by scientific water management depending on the weather conditions. If it is dry and rainless， the plantlets should be watered every 10 d or so. In rainy weather， furrowing and drainage should be performed timely.

Weeding

When the soil of P. thomsonii is compacted， a shallow-tooth harrow is used to till and loosen the soil. The tillage can be combined with weeding. Manual weeding must adhere to the principle of "weeding small weeds early and thoroughly". Weeding is performed once in May， June， August and October， to keep the soil loose and free of weeds.

Plant management

Pruning： After the plantlets survive， they often grow out several branches. When they grow to 10-20 cm in April， it is necessary to remove excess branches from the base when retaining strong branches. Generally， only 2 branches are left per plant to cultivate strong main veins. Topping： When the remaining two main vines grow to 1.5 m， topping must be done or the heart must be removed to prevent the main vines from growing too long. Thinning out of branches： Before and after topping of the main vines， a large number of side vines will grow on the main vines. It is necessary to thin the vines from June to August， for 2-3 times depending on the situation.

Fertilization Techniques

Base fertilizer： For P. thomsonii fields with a yield of 30 000 kg/hm2. According to the type of fertilizer and the level of fertilizer efficiency， it is generally controlled to apply 15 000 kg of fermented and rotten organic fertilizer and about 450 kg of compound fertilizer per hectare. The fertilizers are mixed and applied evenly into the tillage layer when preparing the land.

Seedling topdressing： The first topdressing is performed 20 d after planting with 45-60 kg of urea per hectare by dissolving in water. The second topdressing is performed 35-40 d after planting with 75-112.5 kg of urea per hectare by dissolving in water. The third topdressing is performed 55-60 d after planting with 375 kg of ternary compound fertilizer.

Topdressing in tuber formation stage： Eighty days after planting， the fourth fertilizer application is carried out with 525 kg of compound fertilizer， 30 kg of urea and 60 kg of potassium chloride per hectare， all of which are mixed and broadcasted. The fifth fertilizer application is carried out from July to August according to the method and quantities the same as the fourth topdressing.

Topdressing at tuber expansion stage： The sixth fertilizer application in September is the same as the fourth fertilizer application in quantities， but the fertilizers are dissolved in water and poured to the field. The water management in whole stage is aimed to keep the soil wet. The seventh topdressing is carried out with 525 kg of compound fertilizer per hectare by dissolving in water and poured to the soil. The selenium fertilizer is sprayed once in the mid and late September， respectively， and it should be noted that there should be no rain for 24 h after each time of spraying.

Topdressing at adult tuber stage： The eighth fertilizer application is in early to mid October， and 525 kg of high potassium fertilizer is applied per hectare by dissolving in water and poured to the soil.

Selenium Enrichment Measures

Production of natural selenium-enriched P. thomsonii

When the total selenium content of the soil is greater than 0.55 mg/kg， and the soil is sandy or loamy soil， P. thomsonii with strong selenium enrichment capacity can be selected， and standard selenium-enriched P. thomsonii products in accordance with DB45/T 1061 can be produced under conventional planting management without applying external selenium.

Exogenous selenium-regulated production

If the total selenium content of the soil for planting P. thomsonii is less than 0.55 mg/kg， necessary external selenium control measures shall be taken to produce selenium-enriched P. thomsonii products that meet the requirements. One of following two exogenous selenium control measures can be taken：

Regulation with selenium-containing organic fertilizer

When applying base fertilizer， selenium-containing organic fertilizer and compound fertilizer are mixed and used， and the amount of the organic fertilizer containing 0.02% of Se is 9 750-12 000 kg/hm2.

Regulation with organic selenium-chelated foliar fertilizer

The organic selenium-chelated foliar fertilizer with a selenium content of 8.8 g Se/L was sprayed at a rate of 15 000-18 000 ml/hm2 once at the initial expansion stage of P. thomsonii tubers. The foliar fertilizer is diluted 300 to 600 times and sprayed evenly on the leaves of P. thomsonii. If it rains within 10 h after spraying， the fertilizer should be sprayed again.

Control of Pests and Diseases

Diseases of P. thomsonii are mainly rust which is controlled by triadimefon， stem rot which is controlled by DuPont Zengweiyinglv， and black heart disease which is controlled by piling up the soil and forming deep ditches for water control， and mainly prevented. The pests in are mainly black cutworms in the seedling stage， and inchworms， night moths， and red spiders damaging the leaves in the middle stages. Trichlorfon or phoxim is sprayed to control black cutworms; inchworms and night moths are controlled by spraying beta-cypermethrin， Gongfu， chlorfluazuronto， etc. Red spiders are controlled by spraying Saomanjing once during peak occurrence. The pesticide applied must be strictly in accordance with the standards of pollution-free vegetables.

Harvesting and Storage

The roots of P. thomsonii are edible and are harvested from October to March of the following year. The tuber pieces should not be hurt when harvesting to ensure the appearance quality. The tubers without damage can be buried with loess， and the storage period can be as long as 6 months.

References

[1] LI J， ZHANG ZC. Trace element selenium and human health[J]. Studies of Trace Elements and Health， 2011（5）： 62-66. （in Chinese）

[2] ZHOU JH， GIE YC， DU XH， et al. RAPD analysis of arrowroot （Pueraria L.） germplasm genetic relationship[J]. Crop Research， 2013（4）： 347-350. （in Chinese）

[3] YANG ZX， LONG P， MO GS， et al. Key points of high-yield and high-efficiency cultivation of Pueraria[J]. Southern Horticulture， 2012， 23（1）： 42-43. （in Chinese）

[4] XIE QX. Guangxi wants to build the nations largest selenium-rich agricultural product base[J]. Nong Jia Zhi You， 2015（1）： 23. （in Chinese）