Effects of Plant-derived Humic Acid Organic Fertilizer on Selenium Content of Rice in Northern Guangxi

Yunwei JIANG Lixiu HUANG Dongmei WANG Liping PAN Qianchi MO Ri MING Zongji ZHANG Jinping CHEN Hengzhi

Abstract This study was to find out the suitable application amount of plant derived humic acid organic fertilizer for selenium rich rice production in northern Guilin area by applying the fertilizer at different amounts. The results showed that plant derived humic acid organic fertilizer could effectively activate selenium in selenium rich soil， and then promote the uptake of selenium by rice. With costs， selenium enrichment and rice yield as the main evaluation indicators， A4 was chosen as the best treatment， that is， the application of 4 500 kg/hm2 of plant derived humic acid organic fertilizer as base fertilizer could achieve the best benefit.

Key words Plant derived humic acid organic fertilizer; Rice; Selenium rich

Selenium is a very important trace element in the ecological environment. In China， Keshan disease and Kashin Beck disease are closely related to selenium deficiency in the environment[1]. Many studies have shown that selenium has anti cancer， anti tumor and anti aging effects[2]. Rice is one of the three major food crops in China， and selenium content in rice is directly related to the selenium nutritional status of most people. Increasing the selenium content in rice is recognized as the most direct and effective way to supplement selenium in the world[3]. At present， there are many reports about natural selenium enrichment in rice， but the stability of natural selenium enrichment in rice can not be controlled for various reasons， and the results are not satisfactory[4].

Application of exogenous selenium and activation of soil selenium are two main methods to increase selenium content in crops. Some studies have shown that although the total selenium content is relatively high in the soils from selenium rich areas， the available selenium content that can be absorbed by crops is only a small part[5]. Some studies have found that the conditioner composed of humic acid， organic fertilizer and other organic materials can activate soil selenium， effectively improve the content of available selenium in soil， and then promote the absorption of selenium by crops[6-8]. Adding conditioners can make good use of the advantages of selenium rich soil， reduce the pollution caused by the addition of exogenous selenium， and improve the selenium content of crops. In production practice， there are still many problems about the effectiveness of  applying exogenous selenium and activated soil selenium in the using process， such as application variety， application time， application amount and so on. In the production of selenium rich crops， it can easily lead to the blindness of the application of selenium fertilizer if the application is not carried out with target according to the soil selenium content， physical and chemical properties and the rules of selenium absorption of crops， resulting in fail to achieve the goal of selenium enrichment in crops.

Two thirds of the land area in China is deficient in selenium. However， it has found that there are abundant selenium rich soil resources in Guangxi. The investigation and analysis of soil environment in the whole region by Guangxi Geological Survey Institute from 2006 to 2010 showed that there were selenium rich soils in the north of Xianggui Railway in Guilin， including the area throughout Yongfu[9]. In this study， plot planting test was used to study the effects of plant derived humic acid organic fertilizer on rice yield and selenium content of rice in the selenium rich areas of northern Guangxi， so as to provide a basis for the production of selenium rich rice by rational application of plant derived humic acid organic fertilizer.

Materials and Methods

Test materials

The test rice variety was Baixiangzhan， a conventional rice variety planted in large area in northern Guangxi. The test fertilizer was compound fertilizer （15 15 15）. The test organic fertilizer was the plant derived humic acid organic fertilizer produced by Beihai Lidi Fertilizer Industry Co.， Ltd. with N+P 2O 5+K 2O 5≥5% and organic matter≥45%.

General situation of test areas

Field trials were conducted in Fushang Village， Dabu Township， Yanshan District， Guilin City from May to October， 2017. Rice was the preceding crop in the field， and the test soil was clayey yellow soil with pH of 7.7， available phosphorus content of 11.8 mg/kg， organic matter content of 62.2 g/kg， hydrolytic nitrogen content of 199 mg/kg， available potassium content of 125 mg/kg and selenium content of 0.62 mg/kg.

The field was prepared in time by drawing off the water. The rice seedlings were raised on June 25， and the seedlings with consistent size and good growth vigor were selected and transplanted on July 13. Before transplanting rice seedlings， the plant derived humic acid organic fertilizer was applied as base fertilizer， and compound fertilizer of 300 kg/hm2 was applied as topdressing fertilizer when the seedlings resumed green. Field management measures such as weeding， spraying and irrigation were the same in the later growth period of rice.

Test design

The test was carried out with single factor design， and there were 5 setting levels of humic acid organic fertilizer， namely A1=0 kg/hm2， A2=1 500 kg/hm2， A3=3 000 kg/hm2， A4=4 500 kg/hm2， A5=6 000 kg/hm2. The area of the test plot was 20 m2， and with 3 repetitions for each treatment， there were a total of 15 plots， which were arranged in randomized block.

Test items and methods

Selenium content

In this study， the test of selenium content was commissioned to Guangxi Yipu Testing Technology Co.， Ltd.， which had the testing qualification. The test was based on the first method of GB 5009 2017. The rice was harvested and dried before sending for testing.

Rice yield

During the mature period， 10 rice plants were collected in succession from the plot to investigate the 1 000 grain weight and setting percentage of rice. The rice from each plot was harvested and dried separately to measure the actual yield.

Data analysis

Excel was used for data processing， and variance analysis was used for data variance analysis.

Results and Analysis

Effects of plant derived humic acid organic fertilizer on rice plant height

As shown in Table 1， the plant height of rice increased gradually with the increase of the application amount of plant derived humic acid organic fertilizer. The highest plant height was found in treatment A5， which was 109.2 cm. This was in line with the growth law of rice that the vegetative growth of rice plants became more vigorous with better water and fertilizer conditions.

Effects of plant derived humic acid organic fertilizer on effective tillers of rice

As shown in Table 1， the number of effective tillers of rice increased gradually with the increase of the application amount of plant derived humic acid organic fertilizer. The difference reached the significant level between the treatments applied with plant derived humic acid organic fertilizer and the control A1. The number of effective tillers was the greatest in treatment A5 which had the largest application amount， and it showed significant difference with the other treatments.

Effects of plant derived humic acid organic fertilizer on rice setting percentage

As shown in Table 1， the difference in rice setting percentage reached the significant level between the treatments applied with plant derived humic acid organic fertilizer and the control A1. The highest seed setting rate was found in treatment A4， reaching up to 87%， which was significantly different from other treatments. With the increase of application amount of plant derived humic acid organic fertilizer， the seed setting rate of rice increased gradually， but decreased when the application amount reached a certain level. The main reason was that after excessive fertilization， the vegetative growth of rice plants was vigorous， while the reproductive growth was inhibited， resulting in a decrease in seed setting rate.

Effects of plant derived humic acid organic fertilizer on 1 000 grain weight of rice

As shown in table 1， there was little difference in 1 000 grain weight of rice among the treatments， and the highest 1 000 grain weight was found in treatment A4.

Effects of plant derived humic acid organic fertilizer on rice yield

As shown in Table 1， with the increase of the application  amount  of plant derived humic acid organic fertilizer， the yield of rice first increased gradually， and then decreased when the amount of fertilizer reached a certain level. The main reason was that after excessive fertilization， the vegetative growth of rice plants became more vigorous， while the reproductive growth was inhibited， resulting in a lower seed setting rate， and therefore the yield was low. The difference in rice yield reached the significant levels between the treatment applied with plant derived humic acid organic fertilizer and the control A1. And treatment A4 had the higest yield， which showed significant differences from other treatment.

Effects of plant derived humic acid organic fertilizer on selenium enrichment in rice

In 2014， Guangxi issued and implemented its local standard "Selenium Content Classification Requirements for Selenium rich Agricultural Products. The requirement clearly stipulates that the selenium content in selenium rich agricultural products is 0.15-0.50 mg/kg. As shown in Table 1， the content of selenium in rice reached the standard for selenium rich agricultural products after applying plant derived humic acid organic fertilizer， and the difference with the control treatment A1 reached the significant level. With the increase of the application amount of plant derived humic acid organic fertilizer， the content of selenium in rice increased gradually， and the selenium content was the highest in treatment A5， reaching 0.24 mg/kg. However， there was no significant difference between treatment A4 and treatment A5.

Discussion

With the increase of the application amount of plant derived humic acid organic fertilizer， the selenium content in rice increases gradually， which indicates that plant derived humic acid organic fertilizer can effectively activate organic selenium in soil， improve the content of soil available selenium， and then promote the absorption of selenium by rice， which is consistent with the results of previous studies like An et al.[7].

Plant height and the number of effective tillers increase with the increase of the application amount of plant derived humic acid organic fertilizer. The main reason is that after excessive fertilizer application， the vegetative growth of rice becomes more vigorous， and the biomass increases gradually， which is conductive to the selenium enriched breeding industry with rice straw as feed. As for rice yield， different fertilization levels significantly affect the seed setting rate of rice， but there is no significant difference in 1 000 grain weight between different fertilization levels. Therefore， the yield increasing effect of plant derived humic acid organic fertilizer on rice is mainly achieved by improving the seed setting rate.

Conclusion

（1） Plant derived humic acid organic fertilizer can effectively activate the selenium in selenium rich soil， and then promote the absorption of selenium by rice.

（2） In this test， the selenium content of rice in all treatments is 0.18-0.24 mg/kg， which meets the standard of selenium rich agricultural products.

（3） With costs， selenium enrichment and rice yield as the main evaluation indicators， A4 is the best treatment， that is， the application of 4 500kg/hm2 of plant derived humic acid organic fertilizer as base fertilizer can achieve the best benefit.

Agricultural Biotechnology2019

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