Paddy Soils In China Research Articles

Crenobacter oryzisoli sp. nov., a novel phosphate-solubilizing bacterium isolated from the paddy soil.

Two Gram-staining-negative, facultative anaerobic, rod-shaped and phosphate-solubilizing strains designated SG2303T and SG2305, were isolated from paddy soil in China. Phylogenetic analysis based on 16S rRNA gene sequences indicated that SG2303T and SG2305 represented a member of the genus Crenobacter within the family Neisseriaceae of the phylum Pseudomonadota. Strain SG2303T displayed higher 16S rRNA gene sequence similarities with members of the genus Crenobacter ranging from 93.5 to 94.0%. Strains C. luteus YIM 78141T and C. cavernae K1W11S-77T were closest related to the isolated strains and were considered as type strains. Growth of strain SG2303T occurred at 10-55°C (optimum 37°C), pH 5.0-9.0 (optimum pH 6.0-7.0) and 0-1% (w/v) NaCl (optimum 0%). The average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between strain SG2303T and its closely related taxa were 76.1-78.2% and 20.5-22.1%, respectively. The genomic DNA G + C content was 62.2%. The quinone of strain SG2303T was Q-8. The major fatty acids (> 10%) of strain SG2303T were C16:0 (30.6%), summed feature 3 (C16:1ω7c and/or C16:1ω6c) (26.0%) and C12:0 3OH (12.1%). The polar lipids were phosphatidylglycerol (PG), diphosphatidylglycerol (DPG), phosphatidylethanolamine (PE), phospholipids (PL), glycolipid (GL) and unidentified lipids (UL). Based on the results of the phylogenetic, physiological, biochemical, and morphological analysis, strain SG2303T is recognized as a novel species of the genus Crenobacter, for which the name Crenobacter oryzisoli sp. nov. is proposed. The type strain is SG2303T (= GDMCC 1.3970T = JCM 36468T). In addition, SG2303T was also able of phosphorus solubilization and promoting the growth of rice seeds. Strain SG2303T exhibited a relatively high dissolvable phosphorus content of 2.52µg·mL- 1.

Research Advances in Barrier Technology of Paddy Soil Co-contaminated with As and Cd

Arsenic (As) and cadmium (Cd) are the most common toxic and harmful heavy metal elements in paddy soils and are easily transferred from the soil to grains. At present, As and Cd and their co-contamination in paddy soils in China are widespread, posing a serious threat to food security and human health. As and Cd have opposite environmental behaviors in soil, and the simultaneous remediation of co-contamination with As and Cd is a current technical difficulty for safe rice production. This review focuses on several practical techniques for simultaneous mitigation of As and Cd uptake and transport in rice in recent years, including water management, passivation, drenching techniques, electrokinetic remediation, phytoremediation, selection of low-accumulation rice varieties, and foliar spraying application. The treatment effects, mechanisms of action, and constraints of various technologies are summarized and analyzed; the development direction of the main barrier control technologies is proposed and the importance of constructing a comprehensive technology model with high regional adaptability is emphasized to provide a reference for the remediation of co-contamination with As and Cd in paddy and safe rice production.

Soil organic carbon dynamics shift by incorporating wheat straw in paddy soil in China.

The objective of this study was to explore the effects of unfertilized control (CK), mineral NPK fertilizer (NPK), NPK plus medium-rate wheat straw (MSNPK), and NPK plus high-rate wheat straw (HSNPK) on soil organic carbon (SOC) fractions and C-cycle enzymes at distinct depths (0-5, 5-10, 10-20, 20-30, and 30-50cm) in paddy soil. The SOC content at 0-50cm depth ranged from 8.50 to 21.15g kg-1 , following the trend HSNPK>MSNPK>NPK>CK. Correspondingly, the content of water-soluble organic carbon (WSOC), microbial biomass carbon (MBC), particulate organic carbon (POC), and easily oxidizable carbon (EOC) ranged from 0.08 to 0.27g kg-1 , 0.11 to 0.53g kg-1 , 1.48 to 8.29g kg-1 , and 3.25 to 7.33g kg-1 , respectively, and HSNPK exhibited the highest values for these parameters among all treatments and soil depths, with significant differences observed compared to NPK and CK (p<0.05). The cellulase activity of HSNPK was significantly (p<0.05) higher by 6.12%-13.30% compared to the CK at 0-30cm depth; while the activity of invertase and β-glucosidase of HSNPK were significantly (p<0.05) higher by 34.09%-433.43% and 26.61%-130.50%, respectively, compared to the CK at 0-50cm depth. Enzyme activities were significantly (p<0.05) correlated with SOC fractions and the dominant factors driving changes in enzyme activities were WSOC, POC, and EOC. HSNPK was associated with the highest SOC fractions and enzyme activities, indicating that it was the most favorable management practice for promoting soil quality in rice paddy fields.

Plastispheres as hotspots of microbially-driven methylmercury production in paddy soils

Microplastics (MPs) as emerging contaminants have accumulated extensively in agricultural ecosystems and are known to exert important effects on biogeochemical processes. However, how MPs in paddy soils influence the conversion of mercury (Hg) to neurotoxic methylmercury (MeHg) remains poorly understood. Here, we evaluated the effects of MPs on Hg methylation and associated microbial communities in microcosms using two typical paddy soils in China (i.e., yellow and red soils). Results showed that the addition of MPs significantly increased MeHg production in both soils, which could be related to higher Hg methylation potential in the plastisphere than in the bulk soil. We found significant divergences in the community composition of Hg methylators between the plastisphere and the bulk soil. In addition, the plastisphere had higher proportions of Geobacterales in the yellow soil and Methanomicrobia in the red soil compared with the bulk soil, respectively; and plastisphere also had more densely connected microbial groups between non-Hg methylators and Hg methylators. These microbiota in the plastisphere are different from those in the bulk soil, which could partially account for their distinct MeHg production ability. Our findings suggest plastisphere as a unique biotope for MeHg production and provide new insights into the environment risks of MP accumulation in agricultural soils.

Iron loss of paddy soil in China and its environmental implications

Iron loss of paddy soil in China and its environmental implications

Genome Analysis and Description of Three Novel Diazotrophs Geomonas Species Isolated From Paddy Soils.

Five strictly anaerobic strains, designated RG2T, RG3, RG10T, RF4T, and RG29, were isolated from paddy soils in China. Strains RG2T, RF4T, RG10T, RG3, and RG29 grew at temperatures ranging 5–42°C and pH ranging 5.5–8.5. Strains RG2T, RF4T, RG3, and RG29 could tolerate NaCl up to 0–0.7% (w/v) while strain RG10T could tolerate NaCl up to 0–0.8% (w/v). The isolated strains showed the highest 16S rRNA gene sequence similarities to the type strains of Geomonas terrae Red111T and Geomonas paludis Red736T. In phylogenetic (based on 16S rRNA gene sequence) and phylogenomic trees, strains clustered with the members of the genus Geomonas. Menaquinone-8 was the predominant quinone present in all strains. The major fatty acid profiles of all strains were C15:1 ω6c, C16:0, iso-C15:0, and Summed Feature 3. The digital DNA–DNA hybridization (dDDH) and average nucleotide identity (ANI) values between the isolated strains and the closely related Geomonas species were lower than the cutoff value (ANI 95–96% and dDDH 70%) for prokaryotic species delineation. Based on physiological, biochemical, and chemotaxonomic properties, strains RG2T, RG10T, and RF4T could easily be differentiated with the members of the genus Geomonas. Additionally, all the isolated strains possessed nifHDK clusters and catalytic compartments of nitrogenase. Based on the above results, the isolated five strains represent three novel species of the genus Geomonas, for which the names Geomonas oryzisoli sp. nov., Geomonas subterranea sp. nov., and Geomonas nitrogeniifigens sp. nov. are proposed. The type strains are RG10T (= GDMCC1.2537T = KCTC 26318T), RG2T (= GDMCC1.2536T = KCTC 25317T), and RF4T (= GDMCC 1.2547T = KCTC 25316T).

Description of two nitrogen-fixing bacteria, Geomonas fuzhouensis sp. nov. and Geomonas agri sp. nov., isolated from paddy soils.

Two strictly anaerobic nitrogen-fixing strains, designated RG17T and RG53T, were isolated from paddy soils in China. Strains RG17T and RG53T showed the highest 16S rRNA gene sequence similarities to the type strain Geomonas paludis (97.9-98.4%). Phylogenetic tree based on 16S rRNA gene sequences showed that two strains clustered with members of the genus Geomonas. Growth of strain RG17T was observed at 20-42°C, pH 5.5-8.5 and 0-0.3% (w/v) NaCl while strain RG53T growth was observed at 20-42°C, pH 5.5-9.5 and 0-0.7% (w/v) NaCl. Strains RG17T and RG53T contained MK-8 as main menaquinone and C15:1 ω6c, iso-C15:0, and Summed Feature 3 as the major fatty acids. The genomic DNA G + C content of strains RG17T and RG53T were 61.6 and 60.7%, respectively. The digital DNA-DNA hybridization (dDDH) and average nucleotide identity (ANI) values between the isolated strains and the closely related Geomonas species were lower than the cut-off value (dDDH 70% and ANI 95-96%) for prokaryotic species delineation. Both strains possessed nif genes nifHDK and nitrogenase activities. Based on the above results, the two strains represent two novel species of the genus Geomonas, for which the names Geomonas fuzhouensis sp. nov. and Geomonas agri sp. nov., are proposed. The type strains are RG17T (= GDMCC 1.2687T = KTCC 25332T) and RG53T (= GDMCC 1.2630T = KCTC 25331T), respectively.

Wheat Straw Incorporation Affecting Soil Carbon and Nitrogen Fractions in Chinese Paddy Soil

Soil organic carbon (SOC) and nitrogen (N) fractions greatly affect soil health and quality. This study explored the effects of wheat straw incorporation on Chinese rice paddy fields with four treatments: (1) a control (CK), (2) a mineral NPK fertilizer (NPK), (3) the moderate wheat straw (3 t ha−1) plus NPK (MSNPK), and (4) the high wheat straw (6 t ha−1) plus NPK (HSNPK). In total, 0–5, 5–10, 10–20, and 20–30 cm soil depths were sampled from paddy soil in China. Compared with the CK, the HSNPK treatment (p &lt; 0.05) increased the C fraction content (from 13.91 to 53.78%), mainly including SOC, microbial biomass C (MBC), water-soluble organic C (WSOC), and labile organic C (LOC) in the soil profile (0–30 cm), and it also (p &lt; 0.05) increased the soil N fraction content (from 10.70 to 55.31%) such as the soil total N (TN) at 0–10 cm depth, microbial biomass N (MBN) at 0–20 cm depth, total water-soluble N (WSTN) at 0–5 and 20–30 cm depths, and total labile N (LTN) at 0–30 cm depth. The primary components of soil LOC and LTN are MBC and MBN. Various soil C and N fractions positively correlated with each other (p &lt; 0.05). The HSNPK treatment promoted the soil MBC, WSOC, and LOC to SOC ratios, and also promoted MBN, WSTN, and LTN to soil TN ratios at a depth of 0–20 cm. To summarize, the application of HSNPK could maintain and improve rice paddy soil quality, which leads to increased rice grain yields.

Comparison of N2O Emissions From Cold Waterlogged and Normal Paddy Fields

Paddy fields are major sources of atmospheric N2O. Soil temperature and moisture strongly affect N2O emissions from rice fields. However, N2O emissions from cold-waterlogged paddy fields (CW), an important kind of paddy soil in China, are not well studied so far. It is unclear whether the N2O emissions from cold-waterlogged paddy fields are the same as normal paddy fields (NW). We investigated the N2O emission characteristics from the CW and NW paddy fields under with (R1) and without (R0) rice in Tuku Village, Baisha Town, Yangxin County (YX site, monitoring in 2013) and Huandiqiao Town, Daye City (DY site, monitoring in 2014); compared the difference and influencing factors between the CW and NW paddy fields at two sites in South China. The results showed that the N2O emissions from NWR0 were 13.4 times higher than from CWR0, and from NWR1 were 10.3 times higher than from CWR1 in the YX site. The N2O emissions from NWR0 were 2.4 times higher than from CWR0, and from NWR1 were 17.3 times higher than from CWR1 in the DY site. The structural equation models (SEMs) showed that the N2O emissions are mainly driven by rice planting and soil moisture in the NW fields at the annual scale, while soil temperature in the CW fields. Overall, N2O emissions from cold waterlogged paddy fields are significantly lower than those of normal paddy fields due to the low temperature and higher water content; however, there are dinitrogen emissions from cold waterlogged paddy fields denitrification should be further examined.

Influence of elemental sulfur on cadmium bioavailability, microbial community in paddy soil and Cd accumulation in rice plants

Cadmium (Cd) is highly toxic to living organisms and the contamination of Cd in paddy soil in China has received much attention. In the present study, by conducting pot experiment, the influence of S fertilizer (S0) on rice growth, iron plaque formation, Cd accumulation in rice plants and bacterial community in rice rhizosphere soil was investigated. The biomass of rice plants was significantly increased by S0 addition (19.5–73.6%). The addition of S0 increased the formation of iron plaque by 24.3–45.8%, meanwhile the amount of Cd sequestered on iron plaque increased. In soil treated with 5 mg/kg Cd, addition of 0.2 g/kg S0 decreased the diffusive gradients in thin films (DGT) extractable Cd by 60.0%. The application of S0 significantly decreased the concentration of Cd in rice grain by 12.1% (0.1 g/kg) and 36.6% (0.2 g/kg) respectively. The addition of S0 significantly increased the ratio of Acidobacteria, Bacteroidetes in rice rhizosphere soil. Meanwhile, the ratio of Planctomycetes and Chloroflexi decreased. The results indicated that promoting Fe- and S-reducing and residue decomposition bacterial in the rhizosphere by S0 may be one biological reason for reducing Cd risk in the soil-rice system.

Mean residence times of active and slow soil organic carbon pools in croplands across China

Using active (Ca) and slow (Cs) soil organic carbon (SOC) pools to simulate changes in SOC stocks has been determined to be a major improvement over treating SOC as a single, homogeneous pool. However, regional patterns and primary controls of the mean residence times of the Ca (MRTa) and Cs (MRTs) pools in China’s croplands are largely unknown. In this study, a total of 373 samples from six regions were analysed based on a 100-d incubation experiment. The data from acid hydrolysis-incubation experiments were fitted to a three-pool first-order kinetics model that estimated MRTa = 1/Ka and MRTs = 1/Ks (Ka and Ks represent the decomposition rate constants of the Ca and Cs pools, respectively). The results showed that significant regional differences were found in the MRTa and MRTs in the surface upland soils (0–20 cm) across China, in which the longest MRTa and MRTs values were 72 d in the north China and 24.0 yr in the northeast China, the shortest MRTa and MRTs values were 12 d and 4.7 yr, respectively, both in the south-central China, while relatively small regional differences were observed in the values of the surface paddy soils (0–20 cm). Both the MRTa and the MRTs in upland soils (average: 30 d and 13.5 yr) were longer than the corresponding values in the paddy soils (average: 11 d and 5.4 yr), especially in the southwest China. Thus, the carbon sequestration potential of paddy soils needs to be revalued. The climate could partly explain the regional distribution of the MRTa and MRTs in the surface upland and paddy soils in China; however, as Chinese agricuture intensified from 1980 to 2010, the regional variabilities of MRTa and MRTs in the surface upland and paddy soils were primarily dominated by the soil texture. Therefore, more attention should be paid to the destruction of mechanical composition caused by land-use change or conventional tillage methods when faced with future carbon sequestration in croplands.

Changes in soil organic carbon fractions in response to wheat straw incorporation in a subtropical paddy field in China

AbstractBackground: Optimal wheat straw management in paddy fields is important for evaluating soil organic carbon (SOC) dynamics and sustaining soil quality.Aims: We investigated the effects of wheat straw incorporation in paddy soil on the total SOC content, soil labile organic C fractions [water soluble organic C (WSOC), hot‐water soluble organic C (HWSOC), easily oxidizable C (EOC), microbial biomass C (MBC), particulate organic C (POC), and light fraction organic C (LFOC)], and C pool management index (CPMI).Methods: Rice (var. Qingjiao 307) was grown from June to November 2019 in a subtropical paddy field, under four different treatments: without any amendments (control; CK); with N, P, and K fertilizers (NPK); with NPK and a moderate rate of wheat straw application (NPKS1); and with NPK and a high rate of wheat straw application (NPKS2). Soil samples were collected from depths of 0–5, 5–10, 10–20, and 20–30 cm after the rice was harvested.Results: In all soil layers, the bulk density was 10.79–51.85% lower and the total SOC, WSOC, HWSOC, EOC, MBC, POC, and LFOC contents were 13.87–145.97% higher in the NPKS2 treatment than in the CK treatment (p &lt; 0.05). The CPMI was highest in the NPKS2 treatment in the top 20 cm soil. SOC correlated positively with labile C fractions and CPMI in the 0–5 and 5–10 cm soil layers (p &lt; 0.05), with the exception of WSOC and LFOC in the 5–10 cm soil layer. The sensitivity of each soil labile organic C fraction to the different treatments varied in the 0–5 cm soil layer. Rice yield was highest in the NPKS2 treatment.Conclusions: Overall, the NPKS2 treatment had a positive effect on SOC stocks and higher soil quality in subtropical paddy soils in China.

Biogeography and diversity patterns of abundant and rare bacterial communities in rice paddy soils across China

Bacteria are critical ecosystem drivers in both aquatic and terrestrial ecosystems. However, our understanding of the mechanisms generating and maintaining biodiversity on large spatial scales remains limited, especially mechanisms involving rare taxa in soil ecosystems. In the present study we took paddy soils in China as model ecosystems and studied the ecological diversity and assembly mechanisms of both the rare and abundant bacterial subcommunities. We collected 339 paddy soil samples from 113 sites across 19 Chinese provinces that span distances of up to 3869 km. The bacterial community was characterized by high-throughput sequencing of the 16S rRNA gene. The α-diversity of rare and abundant subcommunities showed opposite quadratic correlations with the key environmental factor soil pH. Rare taxa exhibited a stronger distance-decay relationship than the abundant subcommunity. Moreover, deterministic selection processes dominated in the assembly of the abundant subcommunity while stochastic processes dominated in that of the rare subcommunity based on both variation partitioning analysis and the phylogenetic null model. Soil pH was also the main deterministic factor driving the geographical distributions of both the rare and abundant subcommunity. Besides, mean annul temperature and soil texture were also found to be important factors affecting the biogeography and diversity patterns of abundant and rare subcommunities. These results indicate that the mechanisms generating and maintaining the diversity of the abundant and rare subcommunities were totally different in paddy soils, suggesting that these two subcommunities may respond differently to future environmental change.

The influence of soil temperature, methanogens and methanotrophs on methane emissions from cold waterlogged paddy fields

Paddy fields are major sources of atmospheric methane (CH4). However, CH4 emissions from cold-waterlogged paddy fields, a major type of paddy soil in China, remain unclear. Here we investigated the CH4 emissions and associated influential factors in cold-waterlogged paddy fields at two sites (Yangxin County and Daye City) in Hubei Province, South China. Normal paddy fields matched with parental material and cropping system were used as the controls. The CH4 emissions from cold-waterlogged fields were significantly higher than those from normal fields with (3.0–4.4-fold) or without (3.5–8.6-fold) rice. Rice planting increased CH4 emissions by 59–78% in cold-waterlogged fields and by 85–247% in normal fields. CH4 instantaneous fluxes were positively correlated with soil temperature and methanogen mcrA (methyl coenzyme M reductase alpha subunit) and methanotroph pmoA (methane monooxygenase) copy numbers at the annual scale. Under rice planting, mcrA copy number was higher in cold-waterlogged fields than in normal fields at both sites, whereas pmoA copy number had the same trend at the Daye site only. Soil temperature and water content influenced mcrA and pmoA copy numbers in the normal paddy fields, whereas soil organic matter content was more influential in the cold-waterlogged paddy fields. These findings suggest that perennial waterlogging is a prerequisite for substantial CH4 emissions from cold-waterlogged paddy fields, and it promotes the proliferation of methanogens and methanotrophs under rice planting. Therefore, CH4 production-oxidation processes are more active in cold-waterlogged paddy fields than in normal paddy fields.

Carbon sequestration of cropland and paddy soils in China: potential, driving factors, and mechanisms

AbstractThe environmental problems caused by global warming have attracted close attention of governments and scientists all over the world. As the source and sink of atmospheric carbon dioxide, cropland soil plays an important role in the global carbon cycle. Paddy soil is a major component of global cropland, and there is growing research on its carbon sequestration potential. Based on the dynamic characteristics of soil carbon sequestration in cropland, this paper reviews and synthesizes the process and mechanism of soil carbon sequestration in cropland, discusses the driving factors of soil carbon sequestration in cropland from the perspective of crop management practices, and emphatically discusses the knowledge of soil carbon sequestration potential in paddy fields in China. The main conclusions are as follows: (1) The organic carbon content of cropland soil in China is obviously lower than the global average, and the current sequestration rate of paddy soil in China is obviously lower than the potential sequestration rate, which has great potential for carbon sequestration. Since the mid‐1980s, China's agricultural soil organic carbon (SOC) has been gradually increasing, especially the carbon sink effect of rice soil in southern China. (2) Soil and crop management practices such as conservation agriculture, irrigation, integrated nutrition management, straw returning, and crop rotation can improve input efficiency, increase SOC content in the soil carbon pool, and reduce greenhouse gas emissions. (3) The research on SOC fixation mechanism has entered the micro level of soil particles. The chemical protection mechanism of clay, the physical protection mechanism of aggregates, and the biological mechanism interact and influence each other. © 2019 Society of Chemical Industry and John Wiley &amp; Sons, Ltd.

Soil aluminum oxides determine biological nitrogen fixation and diazotrophic communities across major types of paddy soils in China

Biological nitrogen fixation (BNF) contributed greatly in maintaining the fertility of paddy soils without the application of chemical fertilizers for thousands of years. However, factors affecting the BNF and composition of diazotrophs in paddy soils across large geographic scales are still largely unknown. In this study, the field-based 15N2 labeling technique and nifH gene high-throughput sequencing were applied to four types of paddy soils collected from northeast to southwest China, representing major rice-growing areas. Results showed that the BNF amount had distinct geographical patterns and ranged from 2.2 ± 0.5 to 20.1 ± 3.7 kg N ha−1 during 42 days 15N2 labeling period, which was positively correlated with the abundance of Nostocales species. Among the soil properties analyzed, the contents of amorphous aluminum oxides may play a key role in determining the BNF amount and major N2-fixers across all paddy soils using a random forest model. Overall, our study demonstrates the potential biotoxic effects of aluminum oxides on the BNF in paddy soils in southern China and may has important implications for the enhancement of BNF in acidic Ultisols and Oxisols.

Long-term fertiliser (organic and inorganic) input effects on soil microbiological characteristics in hydromorphic paddy soils in China

This study investigated long-term fertilisation effects on soil microbiological characteristics of hydromorphic paddy soils. The study was conducted in 30-year-old experimental plots with various treatments involving chemical fertiliser (nitrogen, phosphorus, and potassium) alone or in combination with manure in relation to a control in a rice–rice–fallow system at the farm at Jiangxi Academy of Agricultural Science. The soil microbial biomass carbon (SMBC) and nitrogen (SMBN), microbial enzyme activity, and microbial community structure were analysed. Changes in levels of SMBC and SMBN in response to combinations of organic–inorganic fertilisers were significantly higher than for inorganic fertiliser treatment. Furthermore, activities of microbial enzymes (sucrase, urease, proteinase, acid phosphatase, and catalase) were significantly higher in combined than in inorganic fertiliser and control treatments. Additionally, the richness and evenness of soil bacteria were decreased by long-term fertilisation, especially inorganic, whereas the Shannon–Weiner and richness indexes of soil fungi were higher. Long-term fertilisation with high doses of combined organic–inorganic input significantly increased microbial biomass, enzyme activity, and fungal community diversity. However, the same input decreased bacterial community diversity. This study will be useful for improving fertilisation management in hydromorphic paddy soils.

Long-term effects of biochar on rice production and stabilisation of cadmium and arsenic levels in contaminated paddy soils

ABSTRACTHeavy metal contamination in the paddy soils of China is a serious concern because of its health risk through transfer in food chains. A field experiment was conducted in 2014–2015 to investigate the long-term effects of different biochar amendments on cadmium (Cd) and arsenic (As) immobilisation in a contaminated paddy field in southern China. Two types of biochar, a rice-straw-derived biochar (RB) and a coconut-by-product-derived biochar (CB), were amended separately to determine their impacts on rice yield and their efficacy in reducing Cd and As in rice. The two-year field experiment showed that biochar amendments significantly improved the rice yields and that CB is superior to RB, especially in the first growth season. Using a large amount of biochar amendment (22.5tha–1) significantly increased soil pH and total organic carbon, and concomitantly decreased the Cd content in rice grains over the four growth seasons, regardless of biochar type and application rate. Arsenic levels in rice were similar to the control, and results from this study suggest that there was a sustainable effect of biochar on Cd sequestration in soil and reduction of Cd accumulation in rice for at least two years. Biochar amendment in soil could be considered as a sustainable, reliable and cost-effective option to remediate heavy metal contamination in paddy fields for long periods.

A comparison of CH4 emissions from coastal and inland rice paddy soils in China

To achieve regional CH4 regulation, it is essential to understand the differences in methane (CH4) emissions from inland and coastal rice paddy soils. The aim of this study was to compare the CH4 emissions from coastal and inland rice paddy soils in China. A statistical analysis was conducted using a database compiled from published references, soil property datasets, and field experimental data. The results showed that during the growing seasons, the average CH4 emissions from inland rice paddy soils were significantly higher than those from coastal paddy soils (p < 0.05). For both inland and coastal zones, single and multiple drainage practices greatly decreased CH4 emissions from rice paddy soils (p < 0.05). Organic fertilizer application increased CH4 emissions from Chinese rice paddy soils (p < 0.05). Seasonal CH4 emissions decreased significantly with increases in longitude (p < 0.001) and latitude (p < 0.05). Total nitrogen, available P, soil organic matter, and some exchangeable cations (e.g., Al3+, Mg2+, and Ca2+) greatly affected the CH4 emissions from rice paddy soils. The results of this study can provide information useful to the development of assessment models for CH4 budgets and the best management practices for CH4 mitigation in rice paddy soils at the national scale.

Variations in grain cadmium and arsenic concentrations and screening for stable low-accumulating rice cultivars from multi-environment trials

In order to help mitigate widespread cadmium (Cd) and arsenic (As) co-contamination in paddy soils in China, screening and breeding of low-accumulating rice (Oryza sativa L.) cultivars (excluders) have been widely adopted. However, the performance of rice cultivars for grain Cd and As accumulation may vary in different growing environments. The inability to identify stable low-accumulating cultivars has largely hindered their application. In this study, 51 rice cultivars were evaluated at four Cd- and As-contaminated paddy sites in two crop seasons in northern Guangdong Province, China. The aim was to investigate the effects of cultivar, environment and their interactions in determining grain Cd and As concentrations, and so to identify stable low-accumulating cultivars. Results showed that environment effects dominated the Cd and As concentrations in rice grains, explaining 87% of the total variations. The crop season played a vital role; compared to early season, grain Cd levels increased and As levels lowered significantly in late season. Large variations in grain Cd, total As, inorganic As concentrations and the percentage of inorganic As were observed between different cultivars. Conventional japonica cultivars exhibited lower Cd levels but higher As levels in the grains than did indica cultivars. The cultivar × environment interaction (CEI) was significant, and its importance was comparable to the cultivar effect. By measuring and interpreting such an interaction, stable Cd and As excluder cultivars were identified based upon the yield, grain Cd and As levels as well as the stabilities of cultivars across the trial environments. Two stable Cd and As co-excluders were found among the hybrid indica cultivars. These results demonstrated that the variations in grain Cd and As concentrations could mainly be attributed to the environment effects and cultivar selection practices should include the analysis of CEI to identify stable low-accumulating rice cultivars.