Effects of Comprehensive Control Technology on Heavy Metal Content and Rice Yield in Northern Guangdong Province

Yupeng ZHANG, Xianpeng YANG, Jianbing ZHOU, Yongjun GUO, Xiaoyuan CHEN, Wangmin YANG, Yuanye XIAO

Abstract In order to explore the application effect of the comprehensive control technology of "soil conditioning-organic planting-foliar control" in the rice area of northern Guangdong， the effects of combined application of different dosages of soil conditioner， bio-organic fertilizer and foliar control agent on heavy metal contents and yields of early and late rice were investigated based on field experiments. The results showed that different treatments of early rice and late rice all increased the yield. The yield increase rates of treatments 2， 3 and 4 reached 4.9%， 7.2% and 8.7% in early rice， respectively， and those in late rice reached 7.7%， 7.8% and 9.7%， respectively. And the cadmium contents of early rice and late rice in treatments 2， 3 and 4 were significantly reduced below the safe value. Taking into account factors such as cost， yield increase rate， and heavy metal compliance rate， the recommended application rate for early and late rice is conventional fertilization+soil conditioner 6 000 kg/hm2+bio-organic fertilizer 1 800 kg/hm2+foliar control agent 6 000 ml/hm2.

Key words Heavy metal; Rice; Soil; Control

Received： May 7， 2022  Accepted： July 9， 2022

Supported by Enterprise Science and Technology Commissioner Project of Guangdong Province （GDKTP2020020800）; Natural Science Foundation of Guangdong Province （2021A1515010851）; Undergraduate Innovation and Entrepreneurship Project （S202110576028X， 202010576002X）; Science and Technology Innovation Strategy Special Fund Project of Guangdong Province （pdjh2021b0455）.

Yupeng ZHANG （1989-）， Male， P. R. China， lecturer， PhD， devoted to research about plant nutrition.

*Corresponding author. E-mail： guo_yongjun2022@163.com.

With the rapid development of society and economy and the rapid growth of population， more and more harmful substances flow into the farmland system， in which the farmland soil is particularly seriously polluted by heavy metals[1]. Northern Guangdong is rich in mineral resources and is also the main rice producing area. However， the problem of farmland pollution caused by mineral mining is also very prominent. The problem of heavy metal pollution in the soil around mining areas is becoming more and more prominent， which seriously restricts the agricultural production in such areas and endangers human health[2].

For heavy metal pollution of cultivated soil， there are several commonly used technical methods such as physical engineering remediation， chemical remediation， and phytoremediation.  Physical engineering measures have wide adaptability and good effect， but the cost is high; chemical remediation is highly operable， and there is also the risk of secondary pollution; and phytoremediation has little impact on the environment， but the effect is slow[3]. Soil conditioners and bio-organic fertilizers can improve soil structure， adjust soil pH， improve soil water and nutrient status， and reduce the activity of heavy metal elements in soil. Meanwhile， foliar control agents can also effectively reduce the absorption of heavy metal ions by crops[4-5]. Therefore， the comprehensive control technology of "soil conditioning-organic planting-foliar control" is more and more widely used to improve soil fertility while remediating soil.

There are great differences in soil properties， climatic conditions and crop growth in different regions. Affected by climatic conditions， early rice and late rice also have certain differences in growth， yield and quality. In this study， the effects of different dosages of soil conditioner， bio-organic fertilizer and foliar control agent on the heavy metal contents and yields of early and late rice in the heavy metal-contaminated areas in northern Guangdong were investigated， aiming to put forward reasonable fertilization suggestions， provide reference for improving the treatment of heavy metal-polluted cultivated land in northern Guangdong and ensure the quality and safety of rice.

Materials and Methods

Experimental area

The experimental area is located in Shuili Village， Shitang Town， Renhua County， Shaoguan City， Guangdong Province. In order to explore the results of continuous experiments， both early rice and late rice were planted on the same field.

Test rice

The rice variety tested was Meixiangnian， the main local cultivar.

Test fertilizers

The soil conditioner， bio-organic fertilizer and foliar control agent tested were provided by Foshan Zhibao Ecological Technology Co.， Ltd. Among them， the technical indicators of the soil conditioner were： CaO≥20%， SiO2≥10%， organic matter≥12%， pH： 10.0-12.0 （main raw materials： oyster shell， limestone， stevia residue）， and the fertilizer registration number was agricultural fertilizer （2018） Zhunzi No. 9965. The technical indicators of the bio-organic fertilizer were： effective viable count ≥0.20·108/g， and organic matter≥40.0%， and the fertilizer registration certificate number was Microbial Fertilizer （2018） Zhunzi No. 3805. The technical indicators of the foliar control agent were： organic matter≥120 g/L， N+P2O5+K2O≥170 g/L， Cu+Mn+Zn+B+Mo： 30-50 g/L， pH： 4.0-6.0， water insoluble matter ≤20 g/L， and the fertilizer registration certificate number was Agricultural Fertilizer （1994） Zhunzi 0009.

Test soil

The soil properties of the experimental paddy fields are shown in Table 1， and the soil pollution level was moderate to mild cadmium pollution.

Experimental design

The experiment was carried out in 2021. Early and late rice were planted， with 4 treatments. The random block design method was adopted， and the plot area was 5 m×5 m=25 m2. After the ridges were formed， plastic films were used to isolate the water （the arrangement is shown in Fig. 1）. In order to explore the results of continuous experiments， the distribution of the experimental plots was consistent for the early and late rice. Except for the application of soil conditioner， bio-organic fertilizer， and foliar control agent， other agricultural operations were the same for each treatment. The soil conditioner was mechanically spread on the whole layer 7-10 d before rice seedling transplanting when the paddy fields were ploughed. The bio-organic fertilizer was applied to the whole layer， combined with the basal fertilizer or top-dressing fertilizer. The foliar control agent was respectively sprayed once in the tillering stage and heading stage of rice growth， and the spraying time was selected before 10 am or after 4 pm. The experimental treatments for both early and late rice were as follows：

Treatment 1： conventional fertilization （CK）;

Treatment 2： conventional fertilization+soil conditioner 3 000 kg/hm2+bio-organic fertilizer 900 kg/hm2+foliar control agent 3 000 ml/hm2;

Treatment 3： conventional fertilization+soil conditioner 6 000 kg/hm2+bio-organic fertilizer 1 800 kg/hm2+foliar control agent 6 000 ml/hm2;

And treatment 4： conventional fertilization+soil conditioner 9 000 kg/hm2+bio-organic fertilizer 2 700 kg/hm2+foliar control agent 9 000 ml/hm2.

Index determination

Lead， chromium， cadmium， arsenic and mercury in rice; ICP-MS method （food）; yield by weighing after manual harvesting; yield increase rate=（treatment yield-control yield）/control yield×100%.

Statistics

The experimental data were analyzed using IBM SPSS software.

Results and Analysis

Effects of different treatments on heavy metal content in early rice

From the results in Table 2， it can be seen that treatments 2， 3 and 4 can significantly reduce the content of chromium， arsenic and cadmium in early rice， but the control effects on lead and mercury were not significant. Among them， the contents of chromium， arsenic and cadmium in treatment 2 were 66.45%， 64.00% and 79.17% of the control treatment， respectively; the contents of chromium， arsenic and cadmium in treatment 3 were 69.67%， 68.00% and 58.33% of the control treatment， respectively; and the contents of chromium， arsenic and cadmium in treatment 4 were 66.45%， 72.00% and 62.50% of the control treatment， respectively. With the increase of the application rate， chromium and arsenic in rice did not change significantly， and the cadmium content showed a decreasing trend， but the difference between treatment 3 and treatment 4 was not significant.

Effects of different treatments on yield of early rice

The results in Table 3 showed that the rice yields of treatments 2， 3 and 4 all increased， and the yield increase rates reached 4.9%， 7.2%， and 8.7%， respectively.

Effects of different treatments on heavy metal contents in late rice

The results in Table 4 showed that treatments 2， 3 and 4 could significantly reduce the contents of arsenic and cadmium in late rice， but the control effects on chromium， lead and mercury were not significant. Among them， the contents of arsenic and cadmium in the rice of treatment 2 were 60.00% and 50.00% of the control treatment， respectively; the contents of arsenic and cadmium in the rice of treatment 3 were 56.00% and 46.43% of the control treatment， respectively; and the contents of arsenic and cadmium in the rice of treatment 4 were 48.00% and 50.00% of the control treatment， respectively. However， there was no significant difference in the contents of arsenic and cadmium in rice with the increase of application rate. However， there were no significant differences in the contents of arsenic and cadmium in rice with the increase of the application rate.

Effects of different treatments on yield of late rice （2020）

The results in Table 5 showed that the rice yields of treatments 2， 3 and 4 all increased， and the yield increase rates reached 7.8%， 7.8%， and 9.7%， respectively.

Conclusions and Discussion

Soil conditioners are used to make plants grow better by improving soil properties， rather than directly providing nutrients for plant growth. Soil conditioners can effectively improve soil physical structure， reduce soil bulk density， change soil chemical properties， enhance soil microbial activity， increase the content of soil water-stable aggregates， significantly improve the quality of aggregates， and can also increase the total soil porosity， adjust the three-phase ratio， improve its air and water permeability， increase soil enzyme activity， and increase soil fertility[4].  Therefore， the role of soil conditioners in the comprehensive control technology is mainly to adsorb and fix harmful heavy metal ions in the soil by improving soil properties， thereby reducing the absorption of heavy metal ions by crops.

Bio-organic fertilizers are rich in organic and inorganic nutrients and various physiologically active substances and beneficial microbial flora， which enable them to increase yield， improve quality， and improve soil fertility and soil quality in agricultural production[5-6]. Meanwhile， the metabolites such as vitamins， amino acids， nucleic acids， indole acetic acid and other physiologically active substances produced in the process of microbial activities in bio-organic fertilizers can promote the growth of plant roots， enhance the metabolic capacity of crops， and increase the biomass of crops[7-10]. Therefore， the role of bio-organic fertilizers in the comprehensive control technology is to further reduce the absorption of heavy metal ions by crops by improving the absorption and metabolism of crops.

Various nutrients contained in the foliar control agents are rapidly absorbed by leaves and participate in plant metabolism through various pathways[8]. Phosphorus and other elements prevent the migration of heavy metals to the aboveground part by forming phosphates with heavy metals such as cadmium and deposit in the cell wall and vacuoles of plant roots[9]. Among them， the acetic acid-extractable state of cadmium mainly forms chelates with heavy metals through the secondary phosphates[10]， so as to reduce the mobility of cadmium in plants and reduce the toxicity of cadmium to plants. Phosphorus can also increase the thickness of the cell wall to hold more cadmium[11]. Experiments found that spraying 0.3% potassium dihydrogen phosphate solution on the foliar surface at the booting stage could increase the yield of rice and reduce the accumulation of heavy metals such as lead， cadmium and zinc in rice[12]. Therefore， in the comprehensive control technology， the function of foliar control agents is mainly to reduce the migration of heavy metal ions from underground to above-ground through antagonism.

Under the comprehensive control of "soil conditioning-organic planting-foliar control"， the cadmium contents of early and late rice in treatments 2， 3 and 4 were significantly reduced to below the safe value. With the improvement of soil fertility， the yields of early rice and late rice increased with different treatments.

Different treatments of early rice and late rice all increased the yield. The yield increase rates of treatments 2， 3 and 4 reached 4.9%， 7.2% and 8.7% in early rice， respectively， and those in late rice reached 7.7%， 7.8% and 9.7%， respectively. And the cadmium contents of early rice and late rice in treatments 2， 3 and 4 were significantly reduced below the safe value. Taking into account factors such as cost， yield increase rate， and heavy metal compliance rate， the recommended application rate for early and late rice is conventional fertilization+soil conditioner 6 000 kg/hm2+bio-organic fertilizer 1 800 kg/hm2+foliar control agent 6 000 ml/hm2.

References

[1] CHEN T. Status quo of heavy metal pollution in soil in China and countermeasures for remediation[J]. Xiang Cun Ke Ji， 2018（23）： 118-121. （in Chinese）.

[2] XU KR. Effects of heavy metal pollution in soil on the quality and safety of agricultural products[J]. The Farmers Consultant， 2020（23）： 70. （in Chinese）.

[3] FENG HM， LI HB. Countermeasures and suggestions for remediation of heavy metal pollution in vegetable soils in Northern Guangdong Province： Taking Shaoguan as an example[J]. Journal of Hunan Ecological Science， 2018， 5（3）： 48-56. （in Chinese）.

[4] HAN XX. Research review on soil conditioner[J]. Anhui Agricultural Science Bulletin， 2009， 15（19）： 110-112. （in Chinese）.

[5] ZHOU L， TAN SY， YANG LL， et al. Review of bio-organic fertilizer research[J]. Soil， Fertilizer and Plant Protection， 2015， 32（12）： 125-126. （in Chinese）.

[6] LIU GL， JIN WX. China organic fertilizers[M]. Beijing： China Agriculture Press， 1991： 157-194. （in Chinese）.

[7] TIAN M， JIANG BL， LI XH， et al. Research of organic manure and its effect analysis[J]. Journal of Xian University of Architecture & Technology： Natural Science Edition， 2004（3）： 321-324. （in Chinese）.

[8] WANG YL， WANG J， LIU GS， et al. Expression of high-affinity phosphate transporter genes， phosphorus absorption and utilization in flue-cured tobacco under deficient phosphorus stress [J]. Acta Botanica Boreali-Occidentalia Sinica， 2015， 35（7）： 1403-1408. （in Chinese）.

[9] CHEN SB， ZHU YG， YANG JC. Mechanism of the effect of phosphorus on bioavailability of heavy metals in soil-plant systems[J]. Techniques and Equipment for Environmental Pollution Control， 2003， 4（8）： 1-7. （in Chinese）.

[10] YANG ZM， ZHENG SJ， HU AT. Accumulation， chemical forms and physiological characterization of cadmium in plants affected by phosphorus[J]. Chinese Journal of Applied & Environmental Biology， 2000（2）： 121-126. （in Chinese）.

[11] LI T， LI J， HAN Y， et al. Effects of phosphorus on subcellular distribution and chemical speciation of cadmium in rice[J]. Journal of Agro-Environment Science， 2017， 36（9）： 1712-1718. （in Chinese）.

[12] HUANG YZ， ZHU YG， HUANG FT， et al. Effects of cadmium and iron and their interactions on plants growth： A review[J]. Ecology and Environment， 2004（3）： 406-409. （in Chinese）.