Effects of Straw Returning and New Fertilizer Substitution on Rice Growth, Yield, and Soil Properties in the Chaohu Lake Region of China.

Recently, replacing chemical fertilizers with straw returning and new fertilizers has received considerable attention in the agricultural sector, as it is believed to increase rice yield and improve soil properties. However, less is known about rice growth and soil properties in paddy fields with the addition of different fertilizers. Thus, in this paper, we investigated the effects of different fertilizer treatments, including no fertilization (CK), optimized fertilization based on the medium yield recommended fertilizer amount (OF), 4.50 Mg ha-1 straw returning with chemical fertilizers (SF), 0.59 Mg ha-1 slow-release fertilizer with chemical fertilizers (SRF), and 0.60 Mg ha-1 water-soluble fertilizer with chemical fertilizers (WSF), on rice growth, yield, and soil properties through a field experiment. The results show that compared with the OF treatment, the new SF, SRF, and WSF treatments increased plant height, main root length, tiller number, leaf area index, chlorophyll content, and aboveground dry weight. The SF, SRF, and WSF treatments improved rice grain yield by 30.65-32.51% and 0.24-1.66% compared to the CK and OF treatments, respectively. The SRF treatment increased nitrogen (N) and phosphorus (P) uptake by 18.78% and 28.68%, the harvest indexes of N and P by 1.75% and 0.59%, and the partial productivity of N and P by 2.64% and 2.63%, respectively, compared with the OF treatment. However, fertilization did not significantly affect the average yield, harvest indexes of N and P, and partial productivity of N and P. The contents of TN, AN, SOM, TP, AP, and AK across all the treatments decreased significantly with increasing soil depth, while soil pH increased with soil depth. The SF treatment could more effectively increase soil pH and NH4+-N content compared to the SRF and WSF treatments, while the SRF treatment could greatly enhance other soil nutrients and enzyme activities compared to the SF and WSF treatments. A correlation analysis showed that rice yield was significantly positively associated with tiller number, leaf area index, chlorophyll, soil NO3--N, NH4+-N, SOM, TP, AK, and soil enzyme activity. The experimental results indicate that SRF was the best fertilization method to improve rice growth and yield and enhance soil properties, followed by the SF, WSF, and OF treatments. Hence, the results provide useful information for better fertilization management in the Chaohu Lake region of China.

Chemical-microbial effects of acetic acid, oxalic acid and citric acid on arsenic transformation and migration in the rhizosphere of paddy soil.

Low-molecular-weight organic acids (LMWOAs) are essential components of rice roots exudates and an important source of soil organic carbon. The chemical-microbial pathway by which LMWOA affects arsenic (As) cycling in the rhizosphere of paddy soils is still unclear. In this study, three typical LMWOAs (acetic acid (AA), oxalic acid (OA), and citric acid (CA)) in rice root exudates were added to As-contaminated soil at a concentration of 10 mM, mimicking the rhizosphere environment. The results showed that the addition of AA and OA inhibited the mobilization of As in the rhizosphere soil. After 14 days of incubation, the content of As in the porewater of AA and OA decreased by 40% and 22%, respectively, compared with the control. AA hindered the mobilization of As in soil via promoting the formation of secondary minerals. The addition of OA inhibits the mobilization of As via increasing the proportion of As (V) in porewater and promoting the formation of secondary minerals in soil. In addition, OA addition not only significantly increased the aioA gene abundance but also notably enriched the microorganisms containing As (III) methylation functional genes (arsM). The addition of CA greatly expedited the release of As from the soil solid phase through the solubilization of Fe/Mn minerals via the effects of both soil chemistry and microbial action. Furthermore, linear discriminant analysis effect size (LEfSe) revealed the possibility that bacteria such as Burkholderia, Magnetospirillum, and Mycobacterium were involved in the reduction or methylation of As in the rhizosphere of paddy soil. This study revealed the internal causes of LMWOAs regulating As transformation and mobilization in flooded paddy soil and provided theoretical support for reducing As accumulation in rice by breeding rice varieties with high AA and OA secretions.

Construction of Ecological Network of Yangtze Huaihe River Diversion Project (Anhui) Based on Landscape Connectivity Index.

The interbasin water transfer project has realized the optimal allocation of water resources, improved economic benefits, improved people's life and welfare, and had an impact on the ecology. Taking Anhui Jianghuai water transfer project as an example, this study uses morphological spatial pattern analysis (MSPA) to identify the core area, selects the patches in the core area, identifies the source according to the patch importance index, constructs the basic resistance surface according to the resistance factor, modifies the basic resistance surface by using the landscape connectivity index, and constructs the ecological corridor by combining the minimum cumulative resistance (MCR) model and the loop model (curve) to build the ecological network of the completed Huaihe River Water Transfer Project (Anhui). The results show that there are 83 sources, 197 potential ecological corridors, and 80 ecological nodes in the ecological network of Anhui Jianghuai project. Ecological network optimization strategies and protection suggestions are put forward for ecological sources, ecological corridors, and ecological nodes, respectively, so as to provide scientific reference and basis for the ecological environment protection and high-quality development of Anhui Jianghuai water transfer project.

Arsenic and cadmium bioavailability to rice (Oryza sativa L.) plant in paddy soil: Influence of sulfate application.

Arsenic (As) and cadmium (Cd) accumulate easily in rice grains that pose a non-negligible threat to human health worldwide. Sulfur fertilizer has been shown to affect the mobilization of As and Cd in paddy soil, but the effect of co-contamination by As and Cd has not been explored. This study selected three soils co-contaminated with As and Cd from Shangyu (SY), Tongling (TL) and Ma'anshan (MA). Incubation experiments and pot experiments were carried out to explore the effect of sulfate supply (100 mg kg-1) on the bioavailability of As and Cd in soil and the rice growth. The results showed that the exogenous sulfate decreased As concentrations in porewater of SY and TL by 51.1% and 29.2% through forming arsenic-sulfide minerals. The exchangeable Cd in soil also declined by 25.6% and 18.6% and transformed into Fe and Mn oxides-bound Cd. The relative abundance of Desulfotomaculum, Desulfurispora and dsr gene increased remarkably indicated that sulfate addition stimulated the activity of sulfate-reducing bacteria. In MA soil, sulfate addition immobilized Cd but had little effect on As solubility, which was speculated to be related to the high sulfate background of the soil. Further pot experiments showed that sulfate application significantly increased rice tillers, biomass, chlorophyll content in shoots, and decreased electrolyte leakage in root. Finally, sulfate significantly reduced As and Cd in SY rice shoots by 60.2% and 40.8%, respectively, while As decreased by 39.6% in TL rice shoots and Cd decreased by 23.0% in MA rice shoots. These results indicate that the application of sulfate can reduce the bioavailability of As and Cd in the soil-rice system and promote rice growth, and it is possible to reduce the accumulation of As and Cd in rice plants simultaneously.

Biological soil crusts alleviate the stress of arsenic on rice germination and the underlying immobilization mechanisms.

The high concentration of arsenic (As) in paddy soil has seriously threatened the growth of rice and human food safety. Biological soil crusts (BSC), which are ubiquitous in paddy fields, have been shown a high ability to capture trace metal elements. In the present study, we investigated the effectiveness and mechanism of BSC for immobilizing As, and tested their potential to alleviate the stress of As on rice germination. It is found that BSC can remove 77.8% of arsenic in solution with 3.5 mg L-1 initial As concentration. The As content in BSC reached 514.5 mg kg-1 after 216 h exposure, and the entrapped As was mainly distributed in BSC as a non-EDTA-exchangeable fraction, which might be intracellularly accumulated. Proteobacteria and Bacteroidetes were the dominant phyla in BSC after being exposed to As, playing a significant role in tolerating As and As biogeochemical cycling. The presence of BSC notably promoted the germination rate (18.3%) and dry biomass (103.4%) of rice seeds under 3.5 mg L-1 As stress while reducing the As content in plant roots (8.2-34.3%) and shoots (8.7-47.6%). These findings demonstrate that BSC have a great entrapping effect on As and highlight the importance of BSC in alleviating the stress on rice germination by As, providing a potential nature-based and low-cost strategy to decontaminate paddy fields polluted with As.

[Effects of Nano Material on Cadmium Accumulation Capacity and Grain Yield of Indica Hybrid Rice Under Wetting-drying Alternation Irrigation].

Wetting-drying alternation irrigation (WDI) can harvest high grain yield under effective irrigation water saving conditions. However, the kernel cadmium (Cd) content usually exceeds the national standard of 0.20 mg Cd per kg kernel in WDI. Applying a passivating agent with high-efficient repairing capabilities could be a feasible approach to reduce Cd content lower than 0.20 mg·kg-1 in WDI. Therefore, a field experiment was conducted with different irrigation regimes and passivating agents in a mildly Cd-polluted paddy field, of which the irrigation regimes were WDI and traditional flooded irrigation (FI) and the six passivating agents treatments were CK (no passivating agent; T1), slaked lime with 1125 kg·hm-2(T2), 1125 kg slaked lime and 3000 kg biochar per hectare (T3), 1125 kg slaked lime and 3000 kg organic fertilizer per hectare (T4), 1500 kg porous Nano stupalith per hectare (T5), and 1125 kg slaked lime combined with 1500 kg porous Nano stupalith per hectare (T6). Two typical Indica hybrid rice varieties with a high accumulated capacity named cultivar Shenliangyou 1813 and a low accumulated trait named cultivar Liangyou 6206 were utilized. The main reason that Indica hybrid rice cultivars were selected was their higher absorbed and accumulated characteristics than that of Japonica rice. The results indicated that available Cd content of the soil significantly declined with 17.13%-61.01% decreasing amplitude at maturity when compared with pre-transplanting in WDI; however, the reduction was in the range of -43.45%-21.07% for the FI treatment across cultivars and passivating agents treatments. The available Cd content at maturity was significantly greater in FI than in WDI (P<0.05). In contrast, WDI had higher Cd content on stem, leaf, and kernel organs at maturity than with FI treatment of both cultivars and all of the passivating agents (P<0.05). Generally, the T1 treatment had the maximum available Cd content in the soil layer and highest accumulated Cd content on different aboveground organs, followed by the T2, T3, T4, T5, and T6 treatments considering both cultivars and irrigation regimes. The Cd kernel contents were 0.23-0.24 mg·kg-1 and 0.16-0.21 mg·kg-1 for cultivars Shenliangyou 1813 and Liangyou 6206, respectively, in the T6 treatment. The higher Cd kernel content was generally related to a larger Cd content in the stem organ. For the grain yield, no significant differences were observed among cultivars, irrigation regimes, or passivating agents treatments (P>0.05). Under WDI, the kernel Cd content was still slightly higher than 0.20 mg·kg-1 in the T6 treatment (0.24 mg·kg-1 for cultivar Shenliangyou 1813 and 0.21 mg·kg-1 for cultivar Liangyou 6206); however, there is a predictability potential to produce lower than 0.20 mg·kg-1 kernel content in the T6 treatment if a cultivar with low accumulated capacity is used. Thus, the combined mode of the WDI+T6+cultivar with accumulated low Cd content could be considered an optimized cultivation scheme to obtain no Cd contaminated kernels with high grain yield and water-use efficiency in mildly polluted paddy fields.

Plastic pollution in croplands threatens long-term food security.

Plastic pollution is a global concern given its prevalence in aquatic and terrestrial ecosystems. Studies have been conducted on the distribution and impact of plastic pollution in marine ecosystems, but little is known on terrestrial ecosystems. Plastic mulch has been widely used to increase crop yields worldwide, yet the impact of plastic residues in cropland soils to soil health and crop production in the long term remained unclear. In this paper, using a global meta-analysis, we found that the use of plastic mulch can indeed increase crop yields on average by 25%-42% in the immediate season due to the increase of soil temperature (+8%) and moisture (+17%). However, the unabated accumulation of film residues in the field negatively impacts its physicochemical properties linked to healthy soil and threatens food production in the long term. It has multiple negative impacts on plant growth including crop yield (at the mean rate of -3% for every additional 100 kg/ha of film residue), plant height (-2%) and root weight (-5%), and soil properties including soil water evaporation capacity (-2%), soil water infiltration rate (-8%), soil organic matter (-0.8%) and soil available phosphorus (-5%) based on meta-regression. Using a nationwide field survey of China, the largest user of plastic mulch worldwide, we found that plastic residue accumulation in cropland soils has reached 550,800 tonnes, with an estimated 6%-10% reduction in cotton yield in some polluted sites based on current level of plastic residue content. Immediate actions should be taken to ensure the recovery of plastic film mulch and limit further increase in film residue loading to maintain the sustainability of these croplands.

Effects of Vegetable Fields on the Spatial Distribution Patterns of Metal(loid)s in Soils Based on GIS and Moran's I.

Metal(loid) pollution in vegetable field soils has become increasingly severe and affects the safety of vegetable crops. Research in China has mainly focused on greenhouse vegetables (GV), while open field vegetables (OV) and the spatial distribution patterns of metal(loid)s in the surrounding soils have rarely been assessed. In the present study, spatial analysis methods combining Geographic Information Systems (GIS) and Moran's I were applied to analyze the effects of vegetable fields on metal(loid) accumulation in soils. Overall, vegetable fields affected the spatial distribution of metal(loid)s in soils. In long-term vegetable production, the use of large amounts of organic fertilizer led to the bioconcentration of cadmium (Cd) and mercury (Hg), and long-term fertilization resulted in a significant pH decrease and consequent transformation and migration of chromium (Cr), lead (Pb), and arsenic (As). Thus, OV fields with a long history of planting had lower average pH and Cd, and higher average As, Cr, Hg, and Pb than GV fields, reached 0.93%, 10.1%, 5.8%, 3.0%, 80.8%, and 0.43% respectively. Due to the migration and transformation of metal(loid)s in OV soils, these should be further investigated regarding their abilities to reduce the accumulation of metal(loid)s in soils and protect the quality of the cultivated land.

Agronomic Management and Rice Varieties Controlling Cd Bioaccumulation in Rice.

Selection of rice varieties and application of amendments are effective measures to ensure food safety. Here we report that in the non-Cd area, the grain quality of all rice varieties met the Chinese National Grain Safety Standards (CNGSS). In the high-Cd area, rice varieties showed significant different bioaccumulation of Cd with lower rice yields than those in non-Cd area with the average decrease of 31.1%. There was a negative correlation between grain Cd content and yields. A total of 19 rice varieties were selected as low Cd accumulating rice varieties and their Cd content met CNGSS in the low-Cd area. Six of them met CNGSS in the high-Cd area. The application of amendments significantly reduced Cd content in rice grains by 1.0-84.7% with an average of 52.6% and 13 of varieties met CNGSS. The amendments reduced available Cd content in soils by 1.1-75.8% but had no significant effects on rice yields. Therefore, the current study implied that proper agronomic management with selection of rice varieties and soil amendments was essential in controlling Cd accumulation in rice grains.

Electrokinetic-enhanced phytoremediation of uranium-contaminated soil using sunflower and Indian mustard.

Electrokinetic-enhanced phytoremediation is an effective technology to decontaminate heavy metal contaminated soil. In this study, we examined the effects of electrokinetic treatments on plant uptake and bioaccumulation of U from soils with various U sources. Redistribution of uranium in soils as affected by planting and electrokinetic treatments was investigated. The soil was spiked with 100 mg kg-1 UO2, UO3, and UO2(NO3)2. After sunflower and Indian mustard grew for 60 days, 1 voltage of direct-current was applied across the soils for 9 days. The results indicated that U uptake in both plants were significantly enhanced by electrokinetic treatments from soil with UO3 and UO2(NO3)2. U was more accumulated in roots than in shoots. Electrokinetic treatments were effective on lowering soil pH near the anode region. Overall, uranium (U) removal efficiency reached 3.4-4.3% from soils with UO3 and uranyl with both plants while that from soil with UO2 was 0.7-0.8%. Electrokinetic remediation treatment significantly enhanced the U removal efficiency (5-6%) from soils with UO3 and uranyl but it was 0.8-1.3% from soil with UO2, indicating significant effects of U species and electrokinetic enhancement on U bioaccumulation. This study implies the potential feasibility of electrokinetic-enhanced phytoremediation of U soils with sunflower and Indian mustard.

Laboratory spiking process of soil with various uranium and other heavy metals.

Laboratory studies using metal spiked soils are challenging due to soil heterogeneity. This work provides an easy, quick, precise, and accurate technique for the preparation of spiked soils for laboratory research. The process described spiking soil with various uranium species and other heavy metals for laboratory scale pilot experiments under various biogeochemical conditions. The procedure involves grinding both dry soil and metal chemicals into the fine powder. The spiked soil mixture was further homogenized through a modified splitting and combining of the sample by diagonal flipping using plastic sheeting. Comparison of measured concentrations with theoretical values were obtained with <20% precision and accuracy. However, tradition spiking method with metal solution often yielded high heterogeneous spiked soils due to strong metal adsorption in soils. Re-drying and re-grinding of soils were required following the spiking in order to homogenize treated soils, generating inhalable particulates. Thus appropriate personal protective equipment and practices are required for the safety concern. The present method with metal salt powder proved a safe, useful, quick, accurate and precise, and homogenized soil spiking method. •ability to prepare spiked soil with multiple elements•prepared soil at any level of loading•the spiked soil was homogenous for controlled studies.

The remediation potential and kinetics of cadmium in the green alga Cladophora rupestris.

This study determined the subcellular distribution, chemical forms, and effects of metal homeostasis of excess Cd in Cladophora rupestris. Biosorption data were analyzed with Langmuir and Freundlich adsorption models and kinetic equations. Results showed that C. rupestris can accumulate Cd. Cd mainly localized in the cell wall and debris (42.8-68.2%) of C. rupestris, followed by the soluble fraction (22.1-38.4%) observed in C. rupestris. A large quantity of Cd ions existed as insoluble CdHPO4 complexed with organic acids, Cd(H2PO4)2, Cd-phosphate complexes (FHAC) (43.2-56.0%), and pectate and protein-integrated Cd (FNaCl) (30.8-43.2%). The adsorption data were well fitted by the Freundlich model (R2 = 0.933) and could be described by the pseudo-second-order reaction rate (R2 = 0.997) and Elovich (R2 = 0.972) equations. Related parameters indicated that Cd adsorption by C. rupestris is a heterogeneous diffusion. Cd promoted Ca and Zn uptake by C. rupestris. Cu, Fe, Mn, and Mg adsorption was promoted by low Cd concentrations and inhibited by high Cd concentrations. Results suggested that cell wall sequestration, vacuolar compartmentalization, and chemical morphological transformation are important mechanisms of Cd stress tolerance by C. rupestris. This study suggests that C. rupestris has bioremediation potential of Cd.

Absorption, translocation, and detoxification of Cd in two different castor bean (Ricinus communis L.) cultivars.

Cadmium (Cd) is considered to be the most phytotoxic heavy metal pollutant. The selection of castor bean cultivars with Cd tolerance and the exploration of the physiological mechanisms involved in Cd tolerance are critical steps for improving phytoremediation performance. In this study, a hydroponic experiment was used to investigate variations in Cd transportation, chelation, and subcellular distribution in two different castor bean cultivars, namely JX-22 and ZB-9. Both cultivars had high tolerance index scores, indicating that both cultivars were tolerant to Cd. The findings of the present study indicate that Cd is significantly more mobile in JX-22 than in ZB-9 during xylem and phloem transportation, resulting in the accumulation of Cd in the shoots of JX-22 was 7.67 times that in ZB-9. Subcellular distribution assessment verified that more Cd was bound to the biologically detoxified metal fractions than the metal sensitive fractions in JX-22. The contents of the non-protein thiol pool and glutathione in the leaves were higher in JX-22 than ZB-9 when exposed to Cd. These results indicate that JX-22 has a greater ability to accumulate Cd, and well-coordinated physiological changes in JX-22 afford greater Cd tolerance in comparison to ZB-9 under Cd exposure, indicating that JX-22 is suitable for use in the remediation of Cd-contaminated soils.

Effects of fertilizer application schemes and soil environmental factors on nitrous oxide emission fluxes in a rice-wheat cropping system, east China.

Nitrous oxide (N2O) is a potent greenhouse gas (GHG) with agricultural soils representing its largest anthropogenic source. However, the mechanisms involved in the N2O emission and factors affecting N2O emission fluxes in response to various nitrogenous fertilizer applications remain uncertain. We conducted a four-year (2012-2015) field experiment to assess how fertilization scheme impacts N2O emissions from a rice-wheat cropping system in eastern China. The fertilizer treatments included Control (CK), Conventional fertilizer (CF), CF with shallow-irrigation (CF+SI), CF with deep-irrigation system (CF+DI), Optimized fertilizer (OF), OF with Urease inhibitor (OF+UI), OF with conservation tillage (OF+CT) and Slow-release fertilizer (SRF). N2O emissions were measured by a closed static chamber method. N2O emission fluxes ranged from 0.61 µg m-2 h-1 to 1707 µg m-2 h-1, indicating a significant impact of nitrogen fertilizer and cropping type on N2O emissions. The highest crop yields for wheat (3515-3667 kg ha-1) and rice (8633-8990 kg ha-1) were observed under the SRF and OF+UI treatments with significant reduction in N2O emissions by 16.94-21.20% and 5.55-7.93%, respectively. Our findings suggest that the SRF and OF+UI treatments can be effective in achieving maximum crop yield and lowering N2O emissions for the rice-wheat cropping system in eastern China.

Atmospheric emission of nitric oxide and processes involved in its biogeochemical transformation in terrestrial environment.

Nitric oxide (NO) is an intra- and intercellular gaseous signaling molecule with a broad spectrum of regulatory functions in biological system. Its emissions are produced by both natural and anthropogenic sources; however, soils are among the most important sources of NO. Nitric oxide plays a decisive role in environmental-atmospheric chemistry by controlling the tropospheric photochemical production of ozone and regulates formation of various oxidizing agents such as hydroxyl radical (OH), which contributes to the formation of acid of precipitates. Consequently, for developing strategies to overcome the deleterious impact of NO on terrestrial ecosystem, it is mandatory to have reliable information about the exact emission mechanism and processes involved in its transformation in soil-atmospheric system. Although the formation process of NO is a complex phenomenon and depends on many physicochemical characteristics, such as organic matter, soil pH, soil moisture, soil temperature, etc., this review provides comprehensive updates about the emission characteristics and biogeochemical transformation mechanism of NO. Moreover, this article will also be helpful to understand the processes involved in the consumption of NO in soils. Further studies describing the functions of NO in biological system are also discussed.

Effects of cadmium on bioaccumulation and biochemical stress response in rice (Oryza sativa L.).

This study investigated the effects of various Cd concentrations on the bioaccumulation, antioxidative defense, and stress responses of rice (Oryza sativa L.). The distribution characteristics of Cd in rice were in the following order: roots>stems>grains. The bioconcentration factor values of Cd increased at concentrations lower than 3.00 mg Cd/kg and approximately decreased to a constant value at concentrations higher than 3.00 mg Cd/kg. Rice showed a higher Cd accumulation potential at low Cd concentrations than at high Cd concentrations. The Freundlich isotherm model described well the adsorption isotherms of Cd in rice roots. The biosorption mechanism of rice roots was determined to be cooperative adsorption. The malondialdehyde (MDA) content increased at a concentration range of 0.00-5.00 mg/L, indicating the enhancement of lipid peroxidation. By contrast, the MDA content slightly decreased at concentrations higher than 5.00 mg/L. Peroxidase (POD) activity exhibited active response to oxidative stress at concentrations lower than 5.00 mg/L but was inhibited at concentrations higher than 5.00 mg/L. The response to Cd stress of the N-H, O-H and C-O functional groups in rice shoots was observed via Fourier transform infrared spectroscopy.