Study on the Activation Effect of Fermented Organic Fertilizers on Selenium in the Soil of Southern Dragon Fruit Orchards

Boqian CHEN Liping PAN Ying XING Jinping CHEN Kun DENG Yongxian LIU

Abstract ［Objectives］This study was conducted to explore the effects of using fermented organic fertilizers such as cow manure on the activity of selenium in the soil.

［Methods］The project team applied the organic fertilizer prepared by fermenting cow manure and other raw materials to activate selenium in the soil at two dragon fruit orchard bases in Shilong Town, Guiping City and Dingdang Town, Longan County, and carried out many years of experiments.

［Results］ The contents of available selenium in the two experimental orchards in Shilong Town and Dingdang Town increased by 10% and 5%, respectively, and the selenium contents in dragon fruit increased by 228.6% and 200.0%, respectively.

［Conclusions］The application of fermented organic fertilizers such as cow manure can increase available selenium content in the soil, thereby increasing the selenium content of dragon fruit.

Key words Cow manure; Organic fertilizer; Soil; Selenium; Activating agent

Received: June 20, 2021  Accepted: August 22, 2021

Supported by Nanning Science and Technology Research and Technology Development Key R&D Program (20202087, 20212020); Guangxi Science and Technology Major Project (GK AA17202026); Special Project of the Science and Technology Vanguard Special Action of Guangxi Academy of Agricultural Sciences (GNKM 202114); Guangxi Selenium-rich Featured Crops Experimental Station (G TS2016011).

Boqian CHEN (1997-), male, P. R. China, master, devoted to research about rural and regional development.

*Corresponding author. E-mail: liuyx27@163.com.

Selenium is one of the indispensable and important trace elements in the human body. It plays an important role in maintaining human health, such as resisting oxidation, delaying cell aging, reducing the incidence of cancer and other diseases, and is especially effective in preventing prostate cancer［1］. However, the distribution of selenium in the soil is extremely uneven. More than two-thirds of Chinas areas are generally deficient in selenium. In low-selenium soils, it is often impossible to produce selenium-rich crops. The inability to get enough selenium from the diet all the year round can lead to long-term low selenium intake in some people, which seriously affects human health［2］. Through a comprehensive geochemical survey, it is found that Guangxi has selenium-rich soil with an area of 6 575 700 hm2, which is the largest selenium-rich soil resource area in China that has been discovered so far. However, Guangxi is located in the acid soil area of southern China, and the bioavailability of selenium in the soil is low. Selenium in the soil exists in many forms, not all forms of selenium can be absorbed and used by crops from the soil. The selenium that can be directly absorbed by crops from the soil is collectively called available selenium［3］. Therefore, in order to better transform the advantages of selenium-rich soil resources into industrial advantages and make crops better absorb and utilize selenium in the soil, it is necessary to add some selenium activation conditioners to improve the availability of selenium in the soil and promote the absorption and utilization of crops.

The total selenium content in the soil refers to the sum of different forms of selenium in the soil. The absorption and utilization of selenium by crops mainly depends on the content of available selenium in the soil, rather than the total selenium content in the soil［4］. There is often a misunderstanding in peoples perception that crops grown in the soils with high total selenium content will definitely have high selenium content, which is wrong. The selenium content in crops is not necessarily high when the total selenium content in the soil is high. Crops can absorb and accumulate available selenium, while non-available selenium cannot be absorbed and utilized by plants. Studies have shown that available selenium content in acid soil can be increased by applying organic fertilizers, thereby promoting the absorption and accumulation of selenium by crops［5］.

Aiming at the problems of low availability of selenium in acidic soils of Guangxi and difficulties in being absorbed and utilized by crops, selenium in the soil were activated by applying fermented organic matters such as cow manure to the soil, thereby increasing the content of available selenium in the soil. Cow manure not only contains a lot of organic matter, but also is rich in phosphorus, while phosphorus and selenium have similar chemical behaviors in the soil, because both phosphorus and selenium exist in the form of anions in the soil. Phosphorus in cow manure competes with selenium for adsorption sites on the surface of soil colloid, releasing selenium from the adsorption by the soil to form available selenium, thereby increasing the availability of soil selenium.

Materials and Methods

General situation of experimental field

The experimental field was the two long-term location point bases of dragon fruit orchards in Dingdang Town, Longan County, Nanning City, Guangxi and Shilong Town, Guiping City, Guigang City, Guangxi. The selenium content of the experimental orchard in Dingdang Town was 0.28 mg/kg, and the soil pH was 5.2. The selenium content of the experimental orchard in Shilong Town was 0.52 mg/kg, and the pH was 4.6. Both places have a typical subtropical monsoon climate with high temperature and rain, and the soil is acidic.

Experimental materials

Cow manure was used as the main raw material, which was added with a certain amount of bagasse ash powder and bone meal, and then fermented into a functional organic fertilizer using scientifically prepared auxiliary materials, microbial agents, etc., through a reasonable process.   The pH value of the organic fertilizer increased after the materials was fermented, and the bone meal in the raw materials was not only alkaline but also had a high phosphorus content, which provided conditions for improving the availability of selenium in the soil.

Results and Analysis

Effects of organic fertilizer application on the content of available selenium in the soil

It can be seen from Fig. 1 that by applying the organic fertilizer, the available selenium content in the soil of the dragon fruit orchard in Dingdang Town, Longan County increased by 0.004 mg/kg, which was an increase of 5% compared with the CK (0.08 mg/kg). The content of available selenium in the soil of the dragon fruit orchard in Shilong Town, Guiping City increased by 0.015 mg/kg, which was an increase of 10% higher than that of the CK (0.15 mg/kg). Therefore, the application of organic fertilizer could effectively activate selenium in the soil and increase available selenium content in the soil.

Effects of organic fertilizer application on the content of available selenium in dragon fruit

It can be seen from Fig. 2 that the selenium content in dragon fruit in the test site of Dingdang Town, Longan County was 0.012 mg/kg by applying the organic fertilizer. Compared with the CK (0.004 mg/kg), the selenium content in the dragon fruit increased by 200.0%. The selenium content of dragon fruit in Shilong Town, Guiping City was 0.023 mg/kg. Compared with the CK (0.007 mg/kg), the selenium content of dragon fruit after fertilization increased by 228.6%. It showed that increasing an appropriate amount of organic fertilizer could promote the absorption and accumulation of selenium in the soil by dragon fruit.

Conclusions and Discussion

Organic matter has the ability to adsorb selenium in the soil. The higher the content of organic matter in the soil, the stronger the activity of selenium in the soil and the higher the available selenium content. After the application of organic fertilizer, a large number of organic compounds in the organic fertilizer can complex with the selenium element in the soil, thereby reducing the chemical activity of bound selenium in the soil［6］. After fermented organic matters such as cow manures are applied to the soil, a large amount of organic matter is complexed with selenium, so that selenium is released from the adsorption and fixation of the soil, forming available selenium that can be absorbed and utilized by plants. In addition, organic fertilizer can improve the physical and chemical properties of soil and affect the activity of microorganisms. Studies have shown that organic fertilizer can strengthen the metabolic activity of microorganisms in the soil, and their metabolic activity can activate some non-available forms of selenium into available forms of selenium, eventually promoting the release of available selenium from the soil［7］. The content of organic matter in the soil often has a greater impact on the availability of selenium than other factors［8］. In this study, after the addition of fermented organic fertilizers such as cow manure, available selenium content in the soil increased significantly, indicating that the application of organic matter could increase the available selenium content in the soil, which is consistent with the research results of Yang et al.［9］. Zhao et al.［10］ found that the application of bio-organic fertilizer alone could significantly increase available selenium content of acidic tea garden soil. Yao et al.［11］ found that the application of phosphate fertilizer accompanied by biological organic fertilizer, compared with phosphate fertilizer alone, could effectively improve the availability of selenium in the soil of strongly acidic tea gardens. Fermented organic fertilizers such as cow manure are rich in phosphorus, which can promote the release of selenium in the soil and effectively increase available selenium content in the soil of dragon fruit orchards, thereby facilitating the absorption and utilization of crops.

On the other hand, the results of Qu et al.［12］ showed that soil pH was also one of the important factors affecting the availability of selenium in the soil, and the lower the soil pH, such as in the large area of red soil in Guangxi, the lower the availability of selenium in the soil. Therefore, the application of alkaline organic fertilizers could improve the availability of soil selenium, and conversely, in the soil with higher pH, the availability of selenium was relatively higher, and the effect of applying organic fertilizers to improve the availability of soil selenium was less obvious. The soil pH of the two experimental sites in this study was about 5, which was acidic soil with a low pH, while the bagasse ash powder in the test materials was alkaline, so after applying the fermented organic fertilizer such as cow manure to the soil, it was beneficial to the increase of Soil pH, thereby increasing the availability of selenium in the soil.

After the application of organic fertilizer, the available selenium contents of the two experimental sites in Dingdang Town, Longan County and Shilong Town, Guiping City increased by 5% and 10%, respectively, and the selenium contents in dragon fruit increased by 200.0% and 228.6%, respectively. Therefore, applying fermented organic fertilizers such as cow manure to acidic selenium-rich soil can increase the available selenium content in the soil, and simultaneously promote the absorption and utilization of selenium in the soil by dragon fruit.

Boqian CHEN et al. Study on the Activation Effect of Fermented Organic Fertilizers on Selenium in the Soil of Southern Dragon Fruit Orchards

References

［1］ QIAO ZQ, ZHOU CP, CHEN WX, et al. Effect of root application of organic-inorganic compound humic acid Se fertilizer on Se content in vegetable and soil［J］. Guizhou Agricultural Sciences, 2020, 48(6): 23-25. (in Chinese)

［2］ LIU YF, DENG HJ, LIU XN, et al. Preliminary report on the effect of different types of selenium-enriched foliar fertilizer on selenium enrichment in rice［J］. Hubei Agricultural Sciences, 2019, 58(8): 67-70, 78. (in Chinese)

［3］ LIANG RY, HE J, CHEN J, et al. Bioavailability and profile distribution of selenium in soils of typical Se-enriched agricultural base［J］. Environmental Chemistry, 2017, 36(7):1588-1595. (in Chinese)

［4］ WANG SS. Study on the form, valence and bioavailability of selenium in soil［D］. Yangling: Northwest Agriculture & Forestry University, 2012. (in Chinese)

［5］ MA X, ZHU XD, ZONG LG, et al. Effects of Mixed Application of Calcium Magnesium Phosphate and Aminoacid Foliar Fertilizer on Se Availability in Acid Se-rich Soil and on Trait of Rice Yield［J］. Soils, 2018, 50(2): 284-290. (in Chinese)

［6］ CHEN TB, CHEN ZJ. Cadmium adsorption soil influenced by dissolved organic matter derived from rice straw and sediment［J］. Chinese Journal of Applied Ecology, 2002(2): 183-186. (in Chinese)

［7］ JUNIPER DT, PHIPPS RH, RAMOS-MORALES E, et al. Effect of high dose selenium enriched yeast diets on the distribution of total selenium and selenium species within lamb tissues［J］. Livestock Science, 2008, 122(1).

［8］ COPPIN F, CHABROULLET C, MARTIN-GARIN A, et al. Methodological   approach to assess the effect of soil ageing on selenium behaviour: First results concerning mobility and solid fractionation of selenium［J］. Biology and Fertility of Soils, 2006, 42(5): 1-5.

［9］ YANG N, ZONG LG, YAN J, et al. Effects of applying modes of bio-organic fertilizer and conditioners on selenium bioavailability of highly acidid se-rich soil in tea gardens［J］. Soils, 2014, 46(6): 1069-1075. (in Chinese)

［10］ ZHAO Y, MA AJ, ZONG LG, et al. Application of different adjustment measures in highly acidic Se-rich soil in tea garden［J］. Journal of Agro-Environment Science, 2011, 30(11): 2306-2312. (in Chinese)

［11］ YAO H, ZONG LG, MENG D, et al. Effect of enhancing availability of selenium by increasing phosphate fertilizer in highly acidic Se-rich soil in tea plantations［J］. Journal of Safety and Environment, 2015, 15(4): 288-293. (in Chinese)

［12］ QU JG, XU BX, GONG SC. Study on speciation distribution and availability of selenium in different soils of Shanghai［J］. Acta Pedologica Sinica, 1998(3): 398-403. (in Chinese)