An Exploration of Growth and Selenium Enrichment of Selenium-enriched Rice

Maohui WANG, Keqing LI, Chunyan ZHONG, Jinquan NIE

Zhaoqing Institute of Agricultural Sciences, Zhaoqing 526070, China

Abstract [Objectives] To explore the effects of selenium fertilizer on rice growth and selenium enrichment. [Methods] Using high-quality rice varieties as experimental materials, exogenous selenium fertilizer was sprayed at two critical periods of tillering stage and full heading stage to explore the effects of different selenium treatments on rice agronomic traits, leaf SPAD value and yield. [Results] Spraying selenium fertilizer could promote the growth of rice, and the selenium enrichment effect in the aboveground parts of the plant was obvious. The selenium content of rice (milled rice) was 0.04-0.07 mg/kg. [Conclusions] This study lays a foundation for the promotion of suitable leaf fertilizers in Zhaoqing City, and is expected to promote the cultivation and promotion of selenium-enriched rice.

Key words Rice, Selenium fertilizer, Agronomic traits, Selenium enrichment

1 Introduction

As an essential trace element for human body, selenium has been recognized by the World Health Organization (WHO) as one of the essential nutrients for organisms[1]. Although the content of selenium in the human body is very low, it is an important component of some antioxidant enzymes and selenium-P protein, and has certain health care functions[2]. Studies have found that selenium has a variety of health care effects on humans, such as anti-virus, anti-aging, anti-oxidation, anti-radiation, and improving human immunity, thus the intake of selenium is directly related to human health[3-4]. With the improvement in material living standards, various health products, nutritional additives, complementary food and other products have been developed to meet people’s living needs. Plants are the main source for supplementation of human selenium[5]. In recent years, selenium-enriched agricultural products have been widely planted in China as characteristic agricultural products, and the selenium-enriched industry has developed vigorously, receiving tremendous support from local governments. Some regions also promote selenium-enriched products as targeted poverty alleviation projects, such as Fujian’s Mingxi County, Liancheng County, and Yunxiao County promoting the planting of selenium-enriched grapes, selenium-enriched rice, and selenium-enriched loquat[6]. With the development of selenium-enriched industries in Fujian, Hubei, Guangxi, and Shandong provinces, there is a trend of development from primary selenium-enriched agricultural products to selenium-enriched health products[7].

Rice is the main food crop in China. At present, more than 65% of China’s population consumes rice as the staple food, with a total annual consumption of 200 million t. The rice industry is the largest grain industry in China and plays a vital role in ensuring national food security[8]. Selenium-enriched rice is to accumulate selenium through rice selenium-enriched cultivation. It uses the principle of biofortification to produce rice with high selenium content, and then processes the rice into selenium-enriched rice. Its selenium content is 6-9 times higher than common rice. The main forms of selenium in soil are selenate and selenite, metal selenide, organic, elemental and volatile selenium[10]. China is a selenium-deficient country, and 72% of the soil is low or deficient in selenium. The selenium content of crops grown on this soil is also very low, which cannot meet the needs of the human body. Therefore, adding exogenous selenium to increase the selenium content of plants is the main way to produce selenium-enriched agricultural products, and it is also a common method for artificially producing selenium-enriched rice at the present stage. Studies more than 10 years ago have found that the content of selenium in domestic rice was about 0.032 mg/kg, and the lowest was only 0.016 mg/kg, which was far from meeting the needs of human health[11].

Selenium-enriched rice is characterized by selenium enrichment, high quality, health care, disease prevention, safety, and high efficiency. Due to its special health care function, selenium-enriched rice is favored by consumers and has an excellent market prospect. In recent years, it has developed rapidly. More and more areas and researchers get devoted to the selenium-enriched rice industry. In this experiment, through foliar spraying of exogenous selenium fertilizer at the two critical stages of rice tillering stage and full heading stage, we explored the effects of selenium fertilizer on rice growth and its selenium enrichment mechanism, to lay a foundation for Zhaoqing City to promote suitable foliar fertilizers and promote the planting and promotion of selenium-enriched rice.

2 Materials and methods

2.1 Experimental materialsThe experimental material adopted the main rice variety indica rice in Guangdong Province, Meixiangzhan 2. Selenium fertilizer: Microbial nano-selenium has the characteristics of easy absorption and can increase the absorption of selenium by crops and increase the selenium content of crops. It would be diluted 200 times when used. The highest grade chelated selenium is a soil and crop selenium content regulator. It needs to be used with chelated selenium additives. This product has the characteristics of good stability. When using, it is necessary to take 33 mL of chelated selenium and auxiliary agent and add 15 kg of water to dilute and spray. Both selenium fertilizer application methods are foliar spray.

2.2 Experimental methodsThe experiment was carried out in the base of Zhaoqing Institute of Agricultural Sciences. The rice samples (harvested at late autumn) were divided into four groups (treatments): control (CK), microbial nano selenium (Se1), highest grade chelated selenium (Se2), microbial nano selenium + highest grade chelated selenium (Se1+Se2). Each treatment was planted with 20 m2in 3 replicates and foliar spraying of selenium fertilizer at tillering stage (ridge closure) and full heading stage. Cultivation management measures were the same as conventional field management. After the mature stage, the main agronomic traits were investigated, including indicators of plant height, panicles per plant, total grains per panicle and number of filled grains, seed setting rate, 1 000-grain weight andetc.The SPAD value of rice leaves was measured at tillering, jointing, grain filling and waxy ripe stages using a plant nutrition analyzer (model LYS-4N). The effects of selenium fertilizer on rice yield were analyzed by measuring the plot yield. At the same time, aboveground parts of plants were sampled to analyze the selenium enrichment in stems, leaves, brown rice and milled rice at the mature stage of rice.

2.3 Data analysisThe statistical analysis of experimental data was carried out with the aid of Excel and SPSS software

3 Results and analysis

3.1 Effects of different selenium fertilizer treatments on rice agronomic traitsAccording to the survey results of agronomic traits (Table 1), the rice panicles per plant, seed number and total number of rice treated by spraying with microbial nano-selenium and highest grade chelated selenium were all higher than those in the control. Specifically, spraying the highest grade chelated selenium treatment was significantly higher than other treatments, indicating that selenium fertilizer could increase tillering number and number of seed setting in rice. However, the differences in plant height, panicle length, seed setting rate and 1 000-grain weight among different treatments were not significant, indicating that spraying selenium fertilizer had little effect on agronomic traits such as plant height, panicle length, seed setting rate and 1 000-grain weight.

Table 1 Effects of different selenium fertilizer treatments on rice agronomic traits

3.2 Effects of different selenium fertilizer treatments on leaf SPAD valueSPAD (Soil and Plant Analyzer Development) value can be used to measure the greenness of leaves[12]. From Table 2, it can be seen that with the advancement of the rice growth stage (tillering stage, joining stage, grain filling stage, and waxy ripe stage), the SPAD value of the leaves gradually decreased, and the leaves turned from green to yellow. The SPAD values of rice treated with microbial nano-selenium and highest grade chelated selenium were all lower than those of the control in four stages, indicating that spraying selenium slightly affected the photosynthesis of rice leaves.

3.3 Effects of different selenium fertilizer treatments on rice yieldAt the mature stage of the rice, the actual yield of each plot was measured. Three replicates were set up for each treatment using the 3-point sampling method, the actual yield per square meter was calculated, and then converted into the yield of 667 m2. The results showed that the yield of rice treated by spraying microbial nano-selenium alone or highest grade chelated selenium was slightly higher than that of the control, but the difference was not significant. By comparison, the yield of rice treated with simultaneous spraying of microbial nano-selenium and highest grade chelated selenium was 8 833.33 kg/ha, which was significantly higher than that of other treatments, indicating that foliar spraying of selenium fertilizer at tillering stage and full heading stage of rice could increase the rice yield (Table 3).

Table 2 Effects of different selenium fertilizer treatments on leaf SPAD value

3.4 Comparison of selenium content in aboveground parts of plants treated with different selenium fertilizersAt the mature stage of rice, the aboveground parts of plants were divided into stalks and grains (brown rice and milled rice) for measurement of selenium content determination. The results showed that the milled rice, brown rice and culm treated with selenium fertilizer had certain selenium enrichment. Specifically, the selenium content of milled rice sprayed with highest grade chelated selenium was 0.07 mg/kg, the selenium content of brown rice treated with microbial nano-selenium and highest grade chelated selenium was 0.21 mg/kg, and the selenium content of culm was 0.44 mg/kg. Foliar spraying of selenium fertilizer can increase the selenium content of aboveground parts of rice (Table 4).

Table 3 Effects of different selenium fertilizer treatments on rice yield

Table 4 Comparison of selenium content in aboveground parts of plants treated with different selenium fertilizers mg/kg

4 Conclusions

At present, in the development and application of selenium-enriched rice, the major method is the application of exogenous selenium fertilizer to increase the selenium content in rice, and develop a selenium-rich fertilizer that can be easily absorbed and utilized by plants according to the physiological absorption and metabolism of selenium by rice. The accumulation of selenium in rice grains can be increased by soil spraying or foliar spraying of selenium fertilizer, thereby producing selenium-enriched rice with significantly higher selenium content than the control. Regarding the foliar spraying of selenium fertilizer, some studies have found that the selenium-increasing effect of one-time spraying of selenium fertilizer is full heading stage> tillering stage> booting stage> grain filling stage, and the selenium-increasing effect of two times of sprays of selenium fertilizer is tillering stage=full heading stage>booting stage=grain filling stage[13]. The application of selenium fertilizer in rice production can not only increase the selenium content in rice, but also increase rice yield to a certain extent, improve rice quality, enhance rice stress resistance, and alleviate the toxic effects of heavy metals such as chromium, cadmium and lead on rice[14]. The practice of nearly 20 years at home and abroad has proved that spraying selenium-enriched foliar fertilizer to produce selenium-enriched rice is a very mature, popular and safe technical measure, which is basically consistent with the spraying of ordinary foliar fertilizer.

In this experiment, through spraying biological nano-selenium and highest grade chelated selenium on the foliage of tillering stage and full heading stage, it was found that spraying selenium fertilizer could increase plant tillering, increase the effective tillering number and number of seed setting, as well as the yield; the SPAD value of leaves showed a decreasing trend with the growth process of rice, and the leaves changed from green to yellow; the selenium enrichment in the aboveground parts of rice was obvious, and the selenium content of milled rice was 0.04-0.07 mg/kg, which was higher than the national standard of selenium content of 0.032 mg/kg. Through spraying selenium fertilizer on the leaves of rice tillering stage and full heading stage, we explored the effects of different selenium fertilizer treatments on rice growth and its selenium enrichment rules. It is expected to lay a foundation for Zhaoqing City to promote suitable foliar fertilizers and promote the planting and promotion of selenium-enriched rice.