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Article

A Two-Year Study of Bioorganic Fertilizer on the Content of Pb and As in Brown Rice and Rice Yield in a Contaminated Paddy Field

by
Huaidong He
1,2,*,
Jun Zhou
3,
Anwen Xiao
4,
Yehan Yan
1,
Aimin Chen
1 and
Bangxing Han
2
1
School of Environment and Tourism, West Anhui University, Lu’an 237012, China
2
Anhui Engineering Research Center for Eco-Agriculture of Traditional Chinese Medicine, West Anhui University, Lu’an 237012, China
3
Library, West Anhui University, Lu’an 237012, China
4
Institute of Agricultural Resources and Environment, Guangdong Academy of Agricultural Sciences, Guangzhou 510640, China
*
Author to whom correspondence should be addressed.
Agriculture 2024, 14(7), 1061; https://doi.org/10.3390/agriculture14071061
Submission received: 1 June 2024 / Revised: 25 June 2024 / Accepted: 28 June 2024 / Published: 30 June 2024
(This article belongs to the Section Agricultural Product Quality and Safety)
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Versions Notes

Abstract

:
Bioorganic fertilizer (BOF) represents favorable potential for agricultural production, but the safe and residual effects of BOF application in heavy-metal-contaminated soils still remain unclear. A two-year field experiment of four rice-growing cycles were conducted to study the effects of the one-time addition of BOF (low and high dosages, 0.45 and 0.9 kg/m2, namely, BOF1 and BOF2, respectively) on the lead (Pb) and arsenic (As) accumulations in brown rice, rice yield, and soil properties in an acidic and Pb-As-contaminated paddy field. The results show that BOF application enhanced the rice yields by 7.9–25.5% and increased the soil pH, organic carbon contents, and fluorescein diacetate hydrolase activity in the former two rice-growing cycles, while these attributes declined gradually and were not significant in the last two cycles. The soil bulk density decreased marginally due to the BOF. Furthermore, the BOF1 treatment barely affected the rice Pb and As concentrations during all cycles, whereas the BOF2 treatment clearly increased the Pb concentrations in brown rice, exceeding the food quality standard limit of 0.2 mg/kg in the last three cycles, and slightly increased the rice As in the former three cycles. The BOF effects on Pb and As in brown rice were due to the changes in the available soil Pb and As, respectively. Our results indicate that a one-time application of BOF could ameliorate the soil conditions of rice growth in two rice-growing cycles, while the high-dose BOF seemed undesirable in toxic-metal-contaminated soils. BOF application at the rate of 0.45 kg/m2 per annum may be a potential strategy for safe rice production in Pb-As-contaminated fields.

1. Introduction

In recent decades, heavy metal contamination in agricultural soils has become a prominent environmental problem, principally due to human activities, such as the use of fertilizers and metal mining [1]. Lead (Pb) and arsenic (As, which is a metalloid but commonly regarded as a heavy metal) are potentially toxic metals and can easily accumulate in crops, posing health hazards to humans via the food chain [2,3]. Rice (Oryza sativa L.) is one of the foremost cereals and is essential for global food security, but acts as a reservoir of toxic metals, like Pb and As. The difference in geochemical behaviors of Pb and As under a field environment is a risk for rice farming [2]. In addition, the indiscriminate use of chemical fertilizers can aggravate the heavy metal uptake by crops [4]. Due to arable land shortage and population demand, crops are still commonly cultivated in large areas of lightly contaminated soils. Consequently, there is an urgent needed to improve paddy soil conditions and regulate the heavy metal concentrations of rice, ensuring safe cereal production. In situ chemical amelioration by adding soil amendments (e.g., organic matter, biochar, alkaline materials, clay minerals, phosphates, and Fe-based materials) is a widely employed technology because of its agro-environmental compatibility [5]. Among these amendments, organic fertilizers have been recognized as alternatives to chemical fertilizers [6,7] and the potential amelioration materials for heavy-metal-contaminated soils [5,8]. The efficiency of amendments to soil amelioration is related to their dosages [5]. As reported, polyhalite applied with appropriate dosages improved mustard yield in a field [9], and manure application at recommended rates might be a suitable practice to reduce agricultural pollution [10]. However, the effects of organic fertilizers on heavy-metal-contaminated soils are uncertain and may change with dosages and over time, which has attracted more attention [8].
Bioorganic fertilizer (BOF) is a kind of organic fertilizer prepared through raw materials (farmyard manures, crop straws, organic wastes, etc.) and processed by functional microorganisms. The application of BOF has become more popular in some countries with the intensive production of agriculture and the decreased requirements of chemical fertilizers [11,12,13]. BOF amendments have been reported to control Fusarium wilt or weeds [14,15,16], reduce the utilization rate of chemical fertilizers [6,11,12], and promote plant growth with the improvement of soil quality [6,17,18]. Furthermore, BOF application can promote rice growth in toxic-metal-contaminated soils and also improve the yield of Chinese flowering cabbage in phthalate-acid-esters-contaminated soils [19,20,21]. Nevertheless, information is lacking regarding the residual effects of BOF on soil properties and crop growth in contaminated fields.
BOF, which consists of rich organic matter and a large number of microorganisms, may change the bioavailability of heavy metals in soil and thereby affect their accumulations within plants [13]. It is noted that the amount of organic matter can influence the mobility and availability of soil metals [22]. Schemes of organic fertilizers have uncertain roles on metal(loid) movement in soil, possibly decreasing, increasing, or not affecting the metal(loid) uptake by crops [8]. As reported, pig manure addition markedly reduced the concentrations of rice Pb in the first rice-growing season but enhanced them in the second season [23]. Zheng [24] showed that Pb in rice grains was not significantly affected by supplementing biochar in a paddy field. The amendments of organic fertilizers can also alter the activity and phytoavailability of soil As and react on the concentrations of As in crops [4,8,25]. Considered as a soil amendment, BOF may have the potential to repair heavy-metal-contaminated soils. A previous study indicates that bioorganic fertilizer addition improves the phytoremediation efficiency in a multiple-metal-contaminated soil [26]. Nonetheless, the effects of BOF on the synchronous alteration of Pb and As in soil and their accumulations in crops have been rarely studied. It is noted that most previous studies of heavy metal decontamination tested with the treatments of organic fertilizers were focused on laboratory or glasshouse conditions [5,27]. Due to the particularity of BOF, the lab-scale results may not be applicable to fields. Thus, it is necessary to explore the effects of BOF on heavy metals in soil–rice systems under field-scale conditions over continuous cultivation cycles.
Based on the aforementioned observations, the objectives of this study were (1) to investigate the residual effects of one-time BOF application on rice yield and soil properties in a heavy-metal-contaminated paddy field; (2) to explore the continuous effects of BOF on the alteration of Pb and As in rice–soil and the possible mechanisms involved; (3) to evaluate the dosage (low and high dosages) effects of BOF on Pb and As accumulation in brown rice and rice yield. This study provided theoretical basis and data support for the agricultural application of bioorganic fertilizer in heavy-metal-contaminated soils. To our knowledge, it is the first to explore the effects of BOF on the synchronous alteration of Pb and As in rice–soil. Field experiments of continuous cultivation cycles were conducted for determining rice grain yields; concentrations of Pb and As in brown rice; available soil Pb and As; and other soil properties, e.g., pH, total organic carbon (TOC) content, bulk density, and fluorescein diacetate (FDA) hydrolase activity.

2. Materials and Methods

2.1. Experimental Site, Bioorganic Fertilizer, and Rice Variety

The experiment was performed in a paddy field located in Tongxi village (23°51′ N; 113°39′ E, Qingyuan City, Guangdong Province, China) (Figure 1). This area has a subtropical humid climate with a mean annual temperature of 21.2 °C and a mean annual rainfall of 2206 mm. Due to mining operations and acid mine drainage from a local lead–zinc mine, paddy soils in the area have been subject to contamination by toxic metals (e.g., Pb and As) and acidification. The soils in the site contained 31.6 g/kg TOC, 1.7 g/kg total N, 1.14 g/cm3 bulk density, 106.9 mg/kg total Pb, and 31.3 mg/kg total As, and had a pH of 4.3. The concentrations of Pb and As in the paddy soil were slightly higher than the risk-screening values for the soil contamination of agricultural land (Pb 80 mg/kg and As 30 mg/kg in GB15618-2018 of China). If the risk-screening value is exceeded, the monitoring of agricultural products and soil characteristics should be enhanced, and moderate agriculture measures should be also employed. In this study, BOF was obtained from the Fogang Tianran Biological Engineering Technology Co., Ltd., in Guangdong Province, and was a black mixture of cow manure composts, amino acid fertilizer, and functional strains of Bacillus subtilis. It had a pH of 7.65 and contained 198 g/kg TOC, 5.5 g/kg phosphorus (P), 3.5 g/kg potassium (K), 57 g/kg calcium (Ca), 3.6 g/kg iron (Fe), 0.31 g/kg manganese (Mn), 77 mg/kg zinc (Zn), 22.5 mg/kg copper (Cu), 9.8 mg/kg Pb, and 1.6 mg/kg As, conforming to the national security standard (Pb ≤ 50 mg/kg and As ≤ 15 mg/kg in NY 884-2012 of China). The concentration of B. subtilis in the BOF was 0.86 × 108 CFU g−1, which was determined at the Guangdong Detection Center of Microbiology. Seeds of rice (Oryza sativa cv. Wuyou 308), which were supplied by the Rice Research Institute of Guangdong Academy of Agricultural Sciences, were applied in the experimental field.

2.2. Field Experiment Design

The experiment was set up with three treatments, including a control (without BOF), BOF1 (low dosage, 0.45 kg/m2), and BOF2 (high dosage, 0.9 kg/m2), and each treatment had four replicates. As a consequence, 12 plots were established in the paddy field. The area of each plot was 10 m2 (4 × 2.5). Then, 30 cm ridges were set up around each plot, along with a 20 cm interspace between neighboring plots. Subsequently, BOF was applied into eight random plots and mixed fully with the paddy soils in a 15 cm cultivation layer. Rice seedings were first cultivated for 20 days in a seed bed in an uncontaminated field and were then transplanted equally into each experimental plot. Rice plants were planted for 90–100 days (Figure 2) and were harvested during the maturation stage. The experiment was carried out for four rice-growing cycles (double-cropping rice per annum) in 2015–2016. After harvesting, the plots and their ridges were kept intact. Before the next planting season, the plots were ploughed manually, and the earth ridges were strengthened. All field plots followed the same agriculture operations, such as fertilization, clean water irrigation, and weeding [20].

2.3. Sampling and Analytical Methods

At harvest, the paddy soils were sampled from each plot by the method of the five-point mixed sampling. Soil pH was measured in the slurry of soil and deionized water (1:2.5) using a portable pH meter (pH 510, Eutech Instruments, Singapore) [28]. The FDA hydrolase activity was determined by referring to the method of Liu [29]. The TOC contents were determined using a TOC analyzer (TOC-VCPH, Shimadzu, Japan). The measurement of the soil bulk density was conducted by using the ring knife method. The fractions of available soil Pb and As were extracted using 0.01 M CaCl2, which provided a useful indication for assessing the metal phytoavailability [30,31]. Metal concentrations in the extracts were determined by inductively coupled plasma–optical emission spectrometry (ICP-OES; Optima 2000 DV, Perkin Elmer, Shelton, CT, USA) for Pb and atomic fluorescence spectrometry (AFS, Beijing, China, Jitian Instrument Co., Ltd.) for As. Grain yields of rice in each plot were measured by manual harvesting at maturity. Dried grains were obtained randomly from each plot collection and then were dehusked and milled to a powder in a grinding machine (IKA A11 basic, IKA-Werke GmbH, Staufen im Breisgau, Germany). The subsamples were acid digested with HNO3 (superior grade) at 190 °C in a microwave oven (MARS-X; CEM, Matthews, NC, USA), and were analyzed for Pb and As concentrations in brown rice according to the method of Li [32]. Quality controls were executed using blanks, soil standard material (GBW-07435), and rice standard material (GBW-10045) (China Standard Materials Research Center, Beijing, China) [28].

2.4. Statistical Analysis

All statistical analyses were carried out using SPSS (version 20.0) for Windows. All results were presented as the mean ± standard error, and the means were examined for statistical differences using a one-way analysis of variance (ANOVA), followed by the least significant difference (LSD) tests that were used to execute multiple comparisons between treatments (p < 0.05) [28]. Pearson’s correlation coefficient was calculated to analyze the relationship between the Pb and As concentrations in brown rice and the available soil Pb and As.

3. Results

3.1. BOF Effects on Available Pb and As in Soil

The effects of the BOF application [0.45 kg/m2 (BOF1) and 0.9 kg/m2 (BOF2)] varied in terms of the available Pb and As in the paddy soils over four rice-growing cycles (Figure 3). The BOF1 treatment marginally (non-significantly) affected the available Pb and As in the soils; in contrast, the BOF2 treatment resulted in stronger effects on their availability. Compared with the controls, the BOF treatments slightly decreased the concentrations of available soil Pb by 6.3–19.0% in the first cycle but enhanced them by 9.6–21.4% in the last three cycles, particularly for the BOF2 treatment, which generated a significant (p < 0.05) increase. Distinguishing from the trend for Pb, the concentrations of available soil As were elevated by increasing the rate of BOF application. The BOF treatments increased the available soil As by 4.5–26.7% in the former three cycles, with a significant (p < 0.05) increase under the BOF2 treatment in the second cycle, and almost had no impact on available soil As in the fourth cycle.

3.2. BOF Effects on pH, TOC, FDA Hydrolase Activity, and Bulk Density in Soil

The effects of the BOF application on pH, TOC, FDA hydrolase activity, and bulk density in the paddy soils are shown in Table 1. Compared with the controls, the BOF treatments evidently (p < 0.05) increased the soil pH by 0.1–0.37 units in the former two rice-growing cycles. In addition, the BOF treatments improved TOC contents and FDA hydrolase activity by 0.68–11.4% and 1.7–27.7%, respectively, with BOF2 generating significant (p < 0.05) increased in the first cycle, and the BOF1 treatment markedly (p < 0.05) increased the soil FDA hydrolase activity in the first cycle. Meanwhile, the residual effects on the soil pH, TOC contents, and FDA hydrolase activity gradually declined and were not significant in the last two cycles. The soil bulk density was not significantly influenced by the BOF application and marginally decreased by 0.88–5.3% over the four rice-growing cycles. The effects on the soil pH, TOC contents, FDA hydrolase activity, and bulk density were better in the BOF2 treatment than those in the BOF1 treatment.

3.3. BOF Effects on Pb and As Concentrations in Brown Rice

Figure 4 shows the effects of the BOF application on the concentrations of Pb and As in brown rice over four rice-growing cycles. Similar to the results of the available soil Pb and As, the BOF1 treatment barely (non-significantly) altered the Pb and As concentrations in brown rice, in contrast with the BOF2 treatment. Compared with the controls, the BOF treatments reduced the Pb concentrations in brown rice by 14.3–19.0% in the first cycle but increased them by 5.3–56.3% in the last three cycles, and the increases were greater in the BOF2 treatment than those in the BOF1 treatment. And especially, the BOF2 treatment significantly (p < 0.05) increased the rice Pb concentrations in the third cycle and caused the Pb concentrations to exceed the permissible limit of the Food Quality Standard (Pb 0.2 mg/kg in GB2762-2017 of China) in the last three cycles.
Furthermore, the BOF treatments slightly increased the concentrations of As in the brown rice by 5.3–20.0% in the former three cycles, with the biggest increase under the BOF2 treatment in the second cycle, but the rice As concentrations declined slightly in the fourth cycle compared with the controls (Figure 4). Nevertheless, there were no striking differences between the treatments and the controls, and the BOF1 effects on the rice As were negligible over the four cycles.
After the BOF application in the paddy field, the linear regression analysis revealed that significantly positive correlations were found between the available soil Pb and Pb concentrations in brown rice (R = 0.678; p < 0.01) and between the available soil As and As concentrations in brown rice (R = 0.823; p < 0.01) (Figure 5).

3.4. BOF Effects on Rice Yield

The effects of the BOF application on the rice yields over four rice-growing cycles are shown in Figure 6. Compared with the controls, the BOF treatments enhanced the rice grain yields by 7.9–25.5% in the former two cycles, and a significant (p < 0.05) increase was found in the BOF2 treatment in the first cycle. However, the yields were not significantly influenced by the fertilizer amendments in the third and fourth cycles. Furthermore, the yield increases were greater in the BOF2 treatment than that in the BOF1 treatment.

4. Discussion

Bioorganic fertilizer (BOF), which is a mixture of organic fertilizers and functional microorganisms, has been generally employed for agricultural production in some countries, especially in China. This study demonstrated that the application of BOF ameliorated the soil conditions of rice growth and enhanced rice yields in an acidic and contaminated paddy field, whereas the high-dose fertilization generated different effects on Pb and As in rice–soil systems over four rice-growing cycles and increased the Pb and As concentrations in brown rice to different degrees. This signifies a new suggestion for BOF application.
The effects of soil amendments on heavy metal accumulation in crops may be different in field conditions [5]. In the present study, the differences of Pb and As in brown rice might be related to the BOF effects on soil physicochemical behaviors under a paddy field environment. In general, schemes of exogenous organic amendments can influence the bioavailability of Pb and As in soil by altering the soil organic matter, soil pH, and their binding forms [8,33]. The present results indicate the positive correlations of Pb and As concentrations in brown rice with their respective extractable forms in the soils (Figure 5). Previous studies also revealed that the addition of BOF affected rice Pb concentrations by altering the availability of soil Pb in the field experiments [34]. In this study, a one-time application of high-dose BOF decreased the available soil Pb and its concentrations in brown rice in the first rice-growing cycle but increased those in the following three cycles (Figure 3 and Figure 4); meanwhile, this application clearly increased organic carbon contents in the soils (Table 1). Analogously, organic fertilizer additions reduced the Pb concentrations of brown rice in the early rice season but increased it in the late rice season [20,23]. It was reported that the application of organic fertilizers could generate a large amount of organic matter into the soil, causing a reduction in available soil Pb through an initial effective adsorption or complexation capacity, while the breakdown of organic fertilizers could reactivate and remobilize the bound Pb into soils over time, thereby increasing the bioavailability of Pb [8,25]. Organic acids produced by the decomposition of organic matter may activate heavy metals in soil. Bolan [8] reported that the amendments of different organic fertilizers had activation effects on Pb and other metal(loid)s in contaminated soils. Dissolved organic matter can control the solubility of Pb in soil, forming organo-Pb complexes that promote Pb solubility as the soil pH is elevated [33]. Furthermore, here, the BOF contained 9.8 mg/kg Pb, conforming to the national security standard in China, while the high-dosage fertilization and the subsequent decomposition of organic matter could still release a small amount of Pb into the paddy soils, potentially generating an increase in Pb within rice plants.
Regarding As, unlike Pb, this study indicates that the high-dose application of BOF slightly increased the As concentrations in brown rice in the former three cycles (Figure 3). Similarly, Xiao [35] found that the addition of an organic fertilizer increased the concentrations of As in rice plants in a paddy field, which is likely explained by the fact that the rich organic matter in organic fertilizer promoted the release of As adsorbed and increased the availability of As in soil under the condition of paddy field. Another possible explanation is that the soil pH was raised by the BOF application in the present work (Table 1). It is well known that the solubility of soil As tends to increase with an increase in soil pH [33]. Beesley [36] showed that two organic amendments induced considerable solubilization of soil As related to soil pH in a naturally contaminated soil. In addition, the BOF used in this study contained an amount of Bacillus subtilis that may alter the speciation, bioavailability, and mobility of metal(liod)s by different reactions. As reported, B. subtilis coupled with bio-fertilizer influences the heavy metal availability in soils under a laboratory condition [37]. Bai [38] showed that inoculation with B. subtilis could change the availability of soil Pb through adsorption and desorption mechanisms. Altogether, BOF effects on Pb and As in brown rice were due to the changes in available soil Pb and As, respectively, which was likely related to soil variation caused by the decomposition of BOF. The role of BOF in the uptake of Pb and As by crop plants should be understood by more detailed investigations.
Apart from toxic metals, plant growth should be focused on when soil amendments (e.g., organic fertilizers) are applied. Crop growth is difficult to establish in acidic and contaminated soils. In this study, the application of BOF increased the soil pH, organic carbon contents, and FDA hydrolase activity, and slightly decreased the soil bulk density in the acidic and contaminated paddy soils (Table 1). These changes were similar to the increases in soil pH and organic carbon contents and the decreases in soil bulk density found in other studies after BOF application [11,34]. The changes in the soil indicators above imply the improvement in soil quality. BOF has the characteristics of both organic and microbial fertilizers since it contains rich organic matter and beneficial microorganisms. After applying BOF into the soil, the organic matter of BOF is decomposed to humus, which can increase the soil organic matter contents, promote the formation of soil aggregate structure, reduce the soil bulk density, and increase the soil microbial diversity [11,18]. Functional microorganisms in BOF also play a role in loosening the soil and reducing the soil bulk density to a certain extent, which is conducive to the improvement of the soil environment [13]. FDA hydrolase activity, which is widely regarded as one of the soil biological indicators, can well reflect the changes in soil microbial activity and soil quality [39]. Similar to our results (Table 1), Sun [40] found that the addition of BOF significantly increased the activity of FDA hydrolase in a kiwifruit orchard, owing to BOF application that could increase the available contents of nutrients obtained by soil microorganisms and promote the reproduction and activity of microorganisms. After organic fertilizer application, soil organic matter and free enzymes are more likely to form complexes, leading to an increase in soil enzyme contents [41]. Given this perspective, BOFs are not only sources of organic matter, which improve soil fertility and soil quality, but also likely provide nutrition to newly introduced microorganisms for the effective colonization and demonstration. Furthermore, this work showed that BOF treatments increased rice yields to varying degrees over continuous rice-growing cycles (Figure 6). Analogously, Qu [42] found that a one-time application of BOF increased cucumber yields by 3.93–12.9%, 9.73–18.8%, and 10.6–20.2% in the first, second, and third seasons, respectively. Kumar [12] and Wang [18] also reported that the application of BOF could increase the crop yield by the improvement of soil properties. In brief, the application of BOF increased the soil pH, organic carbon, and FDA hydrolase activity, and reduced the soil bulk density in the acidic and contaminated paddy field, thereby improving the physicochemical and ecological environment of rice growth and increasing the rice yields (Table 1).
In addition, the present study found that a one-time application of BOF had significant effects on rice yields and paddy soil properties in the former two growing cycles, but its aftereffects began to decline and were not significant over time (Table 1 and Figure 6), which could be related to the breakdown of organic fertilizers in soil [25]. This phenomenon may be mainly due to the gradual decomposition and utilization of organic compounds, the changes in functional microorganisms, and the uptake of nutrients by rice plants after the application of BOF into the paddy soil, generating a gradual decline in the increasing effect of rice yield over time. Similarly, Bolan [8] have reported that the high compost addition resulted in an initial increase in soil pH, nutrient contents, enzyme activity, and water-holding capacity; however, these attributes decreased gradually over time, and they were analogous at the low fertilizer rates. Nevertheless, the dosage of organic amendments used is an important factor that controls their efficiency in the field condition [5]. Other studies reported that the role of soil amendments on paddy soils and rice plants varied with their dosages, and the amendment impacts on soil heavy metals were stronger with higher dosage treatments [20,28]. In agreement with our results, available contents of heavy metals in soil were elevated by increasing the rate of manure application [10]. In this study, the low-dose application of BOF ameliorated the soil conditions and increased the rice yields basically without altering the concentrations of Pb and As in the brown rice. Consequently, our results might provide a potential estimate for the safe dosage (0.45 kg/m2) of BOF application in the acidic and contaminated paddy field.

5. Conclusions

A two-year field study of four rice-growing cycles indicated that a one-time application of BOF could generate beneficial changes in rice production and soil characteristics (pH, organic carbon content, bulk density, and enzymatic activity) over the former two cycles in an acidic and Pb-As-contaminated paddy field. The alteration of Pb and As in the rice–soil varied with the dosages of BOF. The low-dose fertilization (0.45 kg/m2) hardly affected the concentrations of Pb and As in the brown rice during all cycles, but the high-dose fertilization (0.9 kg/m2) significantly altered the Pb and As in the soil–rice. The possible reason behind the BOF effects on the rice Pb and As was the fertilizer altering the availability of Pb and As in the soil. The Pb concentrations in brown rice under the high-dose fertilization exceeded the Chinese permissible limit of 0.2 mg/kg in three rice-growing cycles, posing a threat to food safety. Therefore, suitable dosages of BOF should be applied to control the risk of heavy metal accumulation in soil and rice. The BOF application at the rate of 0.45 kg/m2 per annum may be a potential strategy for safe rice production in paddy fields slightly contaminated by Pb and As. The effects of bioorganic fertilizer application should be evaluated by further investigations of long-term field trials.

Author Contributions

Conceptualization and methodology, H.H.; investigation, H.H. and A.X.; resources, H.H. and A.X.; formal analysis, H.H. and J.Z.; data curation, H.H.; writing—original draft preparation, H.H. and J.Z.; writing—review and editing, Y.Y., A.C. and B.H.; project administration, H.H.; funding acquisition, H.H. and B.H. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the Natural Science Key Research Project of Universities in Anhui Province (grant no. 2023AH052638), the National Key Research and Development Program of China (grant no. 2023YFC3503804), the Outstanding Youth Research Project of Universities in Anhui Province (grant no. 2023AH030110), and the National Science Foundation of China (grant no. 42301128).

Institutional Review Board Statement

Not applicable.

Data Availability Statement

The data presented in this study are available from the corresponding author upon reasonable request.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Site of the experimental paddy field.
Figure 1. Site of the experimental paddy field.
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Figure 2. Rice plants grown in the experimental plots.
Figure 2. Rice plants grown in the experimental plots.
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Figure 3. Available soil Pb and As in field experiments with and without bioorganic fertilizer (mean ± SE, n = 4). BOF1: bioorganic fertilizer (0.45 kg/m2), BOF2: bioorganic fertilizer (0.9 kg/m2). Different letters within the same parameter and the same cycle indicate a significant difference (p < 0.05) between the treatments.
Figure 3. Available soil Pb and As in field experiments with and without bioorganic fertilizer (mean ± SE, n = 4). BOF1: bioorganic fertilizer (0.45 kg/m2), BOF2: bioorganic fertilizer (0.9 kg/m2). Different letters within the same parameter and the same cycle indicate a significant difference (p < 0.05) between the treatments.
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Figure 4. Concentrations of Pb and As in brown rice in paddy field experiments with and without bioorganic fertilizer (mean ± SE, n = 4). BOF1: bioorganic fertilizer (0.45 kg/m2), BOF2: bioorganic fertilizer (0.9 kg/m2). Different letters within the same parameter and the same cycle indicate a significant difference (p < 0.05) between the treatments.
Figure 4. Concentrations of Pb and As in brown rice in paddy field experiments with and without bioorganic fertilizer (mean ± SE, n = 4). BOF1: bioorganic fertilizer (0.45 kg/m2), BOF2: bioorganic fertilizer (0.9 kg/m2). Different letters within the same parameter and the same cycle indicate a significant difference (p < 0.05) between the treatments.
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Figure 5. Correlations between concentrations of Pb and As in brown rice and concentrations of available soil Pb and As in paddy field experiments, respectively (n = 12).
Figure 5. Correlations between concentrations of Pb and As in brown rice and concentrations of available soil Pb and As in paddy field experiments, respectively (n = 12).
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Figure 6. Rice yields in paddy field experiments with and without bioorganic fertilizer (mean ± SE, n = 4). BOF1: bioorganic fertilizer (0.45 kg/m2), BOF2: bioorganic fertilizer (0.9 kg/m2). Different letters within the same parameter and the same cycle indicate a significant difference (p < 0.05) between the treatments.
Figure 6. Rice yields in paddy field experiments with and without bioorganic fertilizer (mean ± SE, n = 4). BOF1: bioorganic fertilizer (0.45 kg/m2), BOF2: bioorganic fertilizer (0.9 kg/m2). Different letters within the same parameter and the same cycle indicate a significant difference (p < 0.05) between the treatments.
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Table 1. Soil pH, total organic carbon contents, FDA hydrolase activity, and bulk density in paddy field experiments with and without bioorganic fertilizer over four rice-growing cycles (mean ± SE, n = 4).
Table 1. Soil pH, total organic carbon contents, FDA hydrolase activity, and bulk density in paddy field experiments with and without bioorganic fertilizer over four rice-growing cycles (mean ± SE, n = 4).
ParameterTreatmentThe First CycleThe Second CycleThe Third CycleThe Fourth Cycle
pHControl4.33 ± 0.03 c4.35 ± 0.04 b4.38 ± 0.03 a4.36 ± 0.03 a
BOF14.49 ± 0.06 b4.45 ± 0.04 ab4.36 ± 0.04 a4.34 ± 0.09 a
BOF24.70 ± 0.05 a4.59 ± 0.05 a4.42 ± 0.08 a4.38 ± 0.04 a
Total organic carbon (g/kg)Control31.38 ± 0.94 b30.87 ± 0.92 a30.85 ± 1.09 a31.47 ± 0.99 a
BOF133.61 ± 0.76 ab32.40 ± 0.84 a31.06 ± 1.32 a31.39 ± 0.95 a
BOF234.95 ± 0.77 a33.84 ± 0.39 a32.53 ± 0.99 a31.75 ± 0.72 a
FDA hydrolase activity (μg/g h)Control93.8 ± 4.5 b85.0 ± 3.5 a82.2 ± 5.7 a89.1 ± 5.0 a
BOF1117.7 ± 4.5 a90.5 ± 5.2 a83.6 ± 5.9 a86.3 ± 6.9 a
BOF2119.8 ± 5.6 a98.7 ± 3.5 a90.5 ± 4.1 a93.2 ± 5.2 a
Bulk density
(g/cm3)		Control1.14 ± 0.06 a1.13 ± 0.04 a1.15 ± 0.03 a1.14 ± 0.04 a
BOF11.11 ± 0.03 a1.13 ± 0.05 a1.15 ± 0.04 a1.14 ± 0.04 a
BOF21.08 ± 0.03 a1.09 ± 0.04 a1.12 ± 0.03 a1.12 ± 0.03 a
BOF1: bioorganic fertilizer (0.45 kg/m2), BOF2: bioorganic fertilizer (0.9 kg/m2). Different letters within the same parameter and the same cycle indicate a significant difference (p < 0.05) between the treatments.
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MDPI and ACS Style

He, H.; Zhou, J.; Xiao, A.; Yan, Y.; Chen, A.; Han, B. A Two-Year Study of Bioorganic Fertilizer on the Content of Pb and As in Brown Rice and Rice Yield in a Contaminated Paddy Field. Agriculture 2024, 14, 1061. https://doi.org/10.3390/agriculture14071061

AMA Style

He H, Zhou J, Xiao A, Yan Y, Chen A, Han B. A Two-Year Study of Bioorganic Fertilizer on the Content of Pb and As in Brown Rice and Rice Yield in a Contaminated Paddy Field. Agriculture. 2024; 14(7):1061. https://doi.org/10.3390/agriculture14071061

Chicago/Turabian Style

He, Huaidong, Jun Zhou, Anwen Xiao, Yehan Yan, Aimin Chen, and Bangxing Han. 2024. "A Two-Year Study of Bioorganic Fertilizer on the Content of Pb and As in Brown Rice and Rice Yield in a Contaminated Paddy Field" Agriculture 14, no. 7: 1061. https://doi.org/10.3390/agriculture14071061

APA Style

He, H., Zhou, J., Xiao, A., Yan, Y., Chen, A., & Han, B. (2024). A Two-Year Study of Bioorganic Fertilizer on the Content of Pb and As in Brown Rice and Rice Yield in a Contaminated Paddy Field. Agriculture, 14(7), 1061. https://doi.org/10.3390/agriculture14071061

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