Paddy Field Of Southern China Research Articles

Winter forage crops influence soil properties through establishing different arbuscular mycorrhizal fungi communities in paddy field

Winter planting is promising for improving the utilization rate of fallow paddy fields in southern China by establishing arbuscular mycorrhizal fungi (AMF) communities. However, the effects of different winter forage crops on AMF community construction remain unknown. The AMF community establishment of different winter planting forage crops were conducted in oat, rye, Chinese milk vetch, and ryegrass, with winter fallow as a control. The AMF colonization rate, soil AMF spore density, community structure and diversity, and soil physicochemical properties were determined. The results showed that the total nitrogen and available nitrogen in winter Chinese milk vetch were 11.11% and 16.92% higher than those in winter fallow (P < 0.05). After planting winter forage crops, the AMF spore density in winter oat, rye, Chinese milk vetch, and ryegrass soil were 127.90%, 64.37%, 59.91%, and 73.62% higher than that before planting, respectively (P < 0.05). Claroideoglomus was the dominant AMF genus in the soil of winter planting oat, rye, and ryegrass. The average membership function value of winter Chinese milk vetch was the highest, indicating that it had the best comprehensive effect on soil physicochemical properties, AMF community structure and diversity, and fresh forage yield. Winter forage crops could increase the spore pool of soil AMF and improve the soil AMF community structure and diversity. Winter Chinese milk vetch in paddy field had the best comprehensive effect on soil physicochemical properties and soil AMF community according to the comprehensive evaluation. These findings provide a theoretical basis for sustainable development and utilization of the southern rice paddy ecosystem.

AM-UNet: Field Ridge Segmentation of Paddy Field Images Based on an Improved MultiResUNet Network

In order to solve the problem of image boundary segmentation caused by the irregularity of paddy fields in southern China, a high-precision segmentation method based on the improved MultiResUNet model for paddy field mapping is proposed, combining the characteristics of paddy field scenes. We introduce the attention gate (AG) mechanism at the end of the encoder–decoder skip connections in the MultiResUNet model to generate the weights and highlight the response of the field ridge area, add an atrous spatial pyramid pooling (ASPP) module after the end of the encoder down-sampling, use an appropriate combination of expansion rates to improve the identification of small-scale edge details, use 1 × 1 convolution to improve the range of the sensory field after bilinear interpolation to increase the segmentation accuracy, and, thus, construct the AM-UNet paddy field ridge segmentation model. The experimental results show that the IoU, precision, and F1 value of the AM-UNet model are 88.74%, 93.45%, and 93.95%, respectively, and that inference time for a single image is 168ms, enabling accurate and real-time segmentation of field ridges in a complex paddy field environment. Thus, the AM-UNet model can provide technical support for the development of vision-based automatic navigation systems for agricultural machines.

The dissolved organic matter from the co-decomposition of Chinese milk vetch and rice straw induces the strengthening of Cd remediation by Fe-modified biochar

Fe-modified biochar (FB) and co-using Chinese milk vetch and rice straw (MR) are two effective ways for mitigating the cadmium (Cd) contamination in paddy fields in southern China. Nevertheless, the effects of FB combined with MR on Cd passivation mechanism remain unclear. In the current study, the strengthening effects of FB induced by MR were found and the mechanisms of the extracted dissolved organic matter (DOM) from the co-decomposition of MR on Cd alleviation were investigated through pot experiment and adsorption experiment. Pot experiment demonstrated that co-incorporating FB and MR decreased available Cd by 23.1% and increased iron plaque concentration by 11.8%, resulting in a 34.7% reduction in Cd concentrations in brown rice compared with addition of FB. Furthermore, co-using FB and MR improved available nutrients in the soil. The molecular characteristics of DOM derived from the decomposition of MR (DOM-MR) were analyzed by fluorescence excitation emission matrix spectroscopy-parallel factor analysis (EEM-PARAFAC) and Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS). Results showed that lignin/carboxylic-rich alicyclic molecules and protein/amino sugar were the main compounds, potentially involved in the Cd binding. Adsorption experiments revealed that the addition of DOM-MR improved the functional groups, specific surface area, and negative charges of FB, inducing the strengthening of both physisorption and chemisorption of Cd(II). The maximum adsorption capacity of Fe-modified biochar after adding DOM-MR was 634 mg g−1, 1.30 times that without the addition of DOM-MR. This study suggested that co-incorporating MR, and FB could serve as an innovative practice for simultaneous Cd remediation and soil fertilization in Cd-polluted paddy fields. It also provided valuable insights and basis that DOM-MR could optimize the performances of Fe-modified biochar and enhance its potential for Cd immobilization.Graphical

Microcystis-dominated paddy crusts enhancing the cadmium accumulation in rice plant (Oryza sativa L.)

Paddy crusts (PCs) influence seriously on the heavy metal migration and transformation in the paddy field system. However, their quantitative effect on heavy metal accumulation in rice plant has been rarely reported. In this study, the influence of microcystis-dominated PCs on Cd content and physicochemical properties of the surface soil, water and rice plants (Oryza sativa L.) during PCs' overall life cycle was investigated. During the PC growth period (0–15 d), the Cd content in the surface soil (0–10 cm) and water decreased by 10–20% due to the accumulation effect. However, during the perish period (15–35 d), the Cd content in the surface soil and water increased by 20–30%, as Cd stored in the PCs was re-released. Moreover, the decomposition of PCs produced a large amount of low-molecular-weight organic substances (<500 Da), significantly increasing the bioavailable acid-soluble Cd in the surface soil. Finally, the PCs increase 25–80% and 60–85% Cd content in rice root and shoot, respectively. A structural equation model demonstrated that the contribution to the Cd in rice roots in the sequence: Cd in surface water > PC > surface soil. Potted experiments using sandy, clay, sandy loam soil containing 0.8–3.5 mg/kg of Cd collected from six provinces’ paddy field in southern China confirmed that PCs increased the Cd accumulation in rice plants by as much as 25–80%. Consequently, the presence of PCs can enhance the Cd concentration in rice plants, and the removing PCs could be a potential effectively approach to reducing Cd content in rice plants.

Intercomparison of leaf area index observed by destructive sampling, plant canopy analyzer and tracing radiation and architecture of canopies in paddy fields

ABSTRACT Leaf area index (LAI) is a canopy structure parameter used to characterize vegetation growth. It is increasingly important to obtain continuous and accurate ground LAI measurement data for the validation of remote-sensing products. In this study, direct destructive sampling method and indirect optical measurement including LAI-2200 plant canopy analyser (PCA) and Tracing Radiation and Architecture of Canopies (TRAC) were used for long-term continuous observation of paddy fields in southern China, to explore the variation of LAI during the growth period of paddy, and to quantitatively analyse the errors of indirect optical measurement. The results show that (1) LAI and Plant area index (PAI) increased first and then decreased in the growing period. The proportion of green leaf area gradually decreased at reproductive growth stage (less than 50%). There was a linear relationship between the proportion of green leaf area and PAI at this stage, with a good correlation (R2 = 0.73). This linear relationship can be used to convert PAI into LAI more conveniently. (2) Effective PAI (PAIe) calculated by the two methods (2000 method and Lang method) from PCA showed good consistency between each other in the growing season (the maximum value of R2 is 0.99). With the increase of zenith angle, the consistency between 2000 method and Lang method decreases (R2 = 0.83). Multiple scattering has an effect on PCA measurement, and this effect is more obvious at high zenith angle. Lang method is more sensitive to the change of zenith angle. (3) Compared to the destructive values, both 2000 method and Lang method are able to compute accurate LAI using four ring sensors (4 R), while TRAC underestimates the LAI and PAI from destructive sampling method. This study provided a new idea for reducing the impact of ground reference data errors on LAI product validation.

Tillage with Crop Residue Returning Management Increases Soil Microbial Biomass Turnover in the Double-Cropping Rice Fields of Southern China

The variety of soil microbial biomass carbon (SMBC), soil microbial biomass nitrogen (SMBN) content, and the flux turnover rate of SMBC and SMBN for 0–10 cm and 10–20 cm layers in a paddy field in southern China with different tillage practices were studied. The tillage experiment included conventional tillage and crop residue returning (CT), rotary tillage and crop residue returning (RT), no–tillage and crop residue returning (NT), and rotary tillage with all crop residues removed from the paddy field as a control (RTO). The result showed that the SMBC and SMBN contents at 0–10 cm and 10–20 cm layers in the paddy field with CT, RT, and NT treatments were significantly increased. This result indicates that the flux turnover rate of SMBC and SMBN for 0–10 cm and 10–20 cm layers in the paddy field with CT treatment were increased by 65.49%, 39.61%, and 114.91%, 119.35%, compared with the RTO treatment, respectively. SMBC and SMBN contents and the flux turnover rate of SMBC and SMBN for the 0–10 cm layer were higher than that of the 10–20 cm layer in paddy fields under the same tillage condition. Therefore, applying rotary tillage or conventional tillage and crop residue returning produced beneficial management for increasing soil microbial biomass content and its turnover under a double–cropping rice system in southern China.

Different Rotation and Double Straw Returning Significantly Increase Liable Organic Carbon Content and Yield of Double Cropping Paddy Field in Southern China

Different Rotation and Double Straw Returning Significantly Increase Liable Organic Carbon Content and Yield of Double Cropping Paddy Field in Southern China

Biochar Can Partially Substitute Fertilizer for Rice Production in Acid Paddy Field in Southern China

Biochar application has been confirmed as an efficient way to increase the productivity of the agricultural system. However, the potential of biochar combined with reducing fertilization on the yield, and the fertilizer utilization efficiency of the rice (Oryza sativa) farming system on acidic soil remains to be further studied. Field micro-plot experiments with two factors were performed in 2018 and 2019 to evaluate the responses of the rice yield and nutrient utilization to the combined application of biochar (60, 80, and 100 t/ha) and fertilizer reduction (70%, 85%, and standard doses of N-P-K fertilizer). Taoyouxiangzhan and Taiyou 553 were used in the late growing season of 2018 and 2019, respectively. The results showed that compared with the control without adding biochar under standard fertilization, 70% doses of fertilizer application had no negative effects on the yield and the N, P, and K accumulation of rice after biochar application. K accumulation of rice increased with the increase of biochar application. The partial productivity of N, P, and K fertilizers increased as the fertilizer was decreased. The agronomic efficiency of N, P, and K fertilizers significantly increased after the combined applications of biochar and fertilizer. In both years, micro-plots with 70% doses of fertilizer had the highest N and P physiological efficiency, as well as K physiological efficiency in 2019. Compared with the control under standard fertilization, utilization efficiency of N, P, and K fertilizer under different biochar and fertilizer combinations significantly increased by 34.24~75.48%, 27.44~84.84%, and 78.52~166.70%, respectively. To sum up, biochar can partially substitute fertilizer for rice production in acid paddy fields in southern China. When the amount of biochar added is ≥60 t/ha, 70% doses of fertilizer application can still ensure the nutrient absorption of rice, improve the fertilizer utilization efficiency, and ensure the stable yield of rice.

The effects of organic fertilizer on loss risk of nitrogen and phosphorus in paddy ponded water.

There is a great challenge globally for both achieving high crop yields via fertilization and minimizing environmental pollution from nutrient losses. Organic fertilizer (OF) application has been extensively reported to effectively improve arable soil fertility and mitigate nutrient losses. However, few studies are available that accurately quantified the substitution rates of OF for chemical fertilizers (CF) that affect rice yield, the nitrogen/phosphorus in ponded water, and its loss potential in paddy field. Here, an experiment with 5 levels of CF nitrogen substituted by OF nitrogen was performed during the early stage of rice growth in paddy field of Southern China. The results showed that the first 6days and 3days following fertilization generally were risky period for N losses and for P losses, respectively, due to corresponding high concentrations in ponded water. Compared to CF treatment, over 30% of OF substitution rates significantly decreased the daily mean TN concentrations by 24.5-32.4%, while TP concentrations unaffected and rice yield maintained comparative levels. OF substitution also improved acidic paddy soils, with the increment of 0.33-0.90 unit for ponded water pH compared to CF treatment. Conclusively, the 30-40% of CF substituted by OF based on N amounts can be considered an ecological fertilization practice for rice production to mitigate environmental pollution due to lower N losses and without significant effect of grain yield. However, the attention also must be paid concerning the rise of environmental pollution risk from NH3 volatilization and P runoff after long-term OF application.

Individual and mixed effects of slag and biochar on soil aggregates and their carbon concentration and on fungal community structure in subtropical early‐ and late‐cropping paddy fields

AbstractAggregates are the basis for the formation of a good soil structure. Soil fungi community plays an important role in soil nutrient transformation, soil aggregate formation and ecological balance of the plant–soil system. However, little is known about the multi‐year response of soil aggregates, their carbon concentrations and fungal community structure to different exogenous agents in double cropping paddy fields in southern China. Therefore, we studied the changes of aggregates' carbon concentrations and stability and fungal community structure under the application of slag and biochar individually and mixed in paddy fields in southeastern China for two annual cycles. Geometric mean diameter in the 0–15 cm layer in the early paddy fields was 29.0% lower in the slag + biochar treatment than in the control. The percentage of soil carbon concentrations in aggregates &lt;0.25 mm in the four treatments in the early paddy field was 35.5%, 38.6%, 45.8% and 51.2%, respectively, in the 0–15 cm layer and 36.1%, 33.8%, 54.9% and 50.9%, respectively, in the 15–30 cm layer. Thus, treatments including biochar increase aggregates carbon concentration probably due to carbon retained in the biochar. Amendments with biochar and slag affected the fungal community structure even 2 years after their application. The results of this study reveal the relationship between soil aggregates and their carbon concentration and fungal community structure in paddy fields under slag and biochar application. These findings provide a theoretical basis for sustainable agricultural applications.

Soil nitrogen functional transformation microbial genes response to biochar application in different irrigation paddy field in southern China.

Growing evidence points to the controlled irrigation (CI) and biochar application (BA) having agricultural economic value and ecological benefits, but their synergistic effect and microbial mechanism of nitrogen conversion remain unknown in paddy fields. The effects of different BA (0, 20, 40 t/hm2) on the soil nitrogen functional transformation microbial genes (nifH, AOA-amoA, AOB-amoA) in different irrigation (CI, flooding irrigation) were clarified. After one seasonal growth of paddy, the correlation between the abundance of functional genes OUT and soil nitrogen transformation environment factors during the typical growth period was analyzed. High-throughput sequencing results illustrated that the application of CC (40 t/hm2 biochar) increased the nifH genes bacterial community abundance; the abundance of dominant microorganism increased by 79.68~86.19%. Because biochar can potentially control the rates of N cycling in soil systems by adsorbing ammonia and increasing NH4+ storage, it increased soil NH4+-N and NO3--N content by 60.77% and 26.14%, improving microbial nitrogen fixation. Rare species Nitrosopumilus, Nitrosococcus, and Methylocystis appeared in biochar treatments group, which increased the diversity of microbial in paddy. The combined use of CI and BA affected soil inorganic nitrogen content, temperature (T), pH, Eh, etc., which affected urease, urea hydrolysis, and nitrogen functional transformation microorganism genes. Correlation analysis shows that soil NH4+-N, T, and Eh, respectively, are significant factors for the formation of nifH, AOA-amoA, and AOB-amoA soil bacterial communities, respectively. This study suggests that to maintain the biodiversity of soil and realize the sustainable development of rice cultivation, CI is of great importance in combination with BA.

Improved crop protection and biodiversity of the agroecosystem by reduced tillage in rice paddy fields in southern China

Agricultural sustainability has benefited from the broad adoption of conservation agriculture (CA) practices for decades, in which the reduction of mechanical disturbances to soil (also known as reduced tillage, RT) is one of the most essential principles for CA implementation. Many studies have recommended the advantages of CA practices in the promotion of biodiversity, but the integrated impacts on crop productivity and biodiversity remain unclear. Since CA has been applied in rice production in the subtropical area of southern China for several years, the effects of CA, particularly the RT methods, need to be evaluated for the local and long-term adoption. In this study, we established an integrated network to illustrate how the reduction of tillage intensity influenced organisms including invertebrates (such as rice pests and their predators), pathogens and weeds, and then led to an impact on rice yield. The two-year study demonstrated that major rice pests, such as rice planthoppers, stem borers and apple snails, were effectively controlled by RT practice. Similarly, the occurrence of common diseases declined with less tillage. Compared to the conventional tillage (CT) treatment, the density of weeds in paddy fields deceased significantly in the RT treatment. In addition, the diversity and richness of pest predators increased remarkably in paddy fields where either reduced or no tillage was applied, which highlighted the significance of a CA strategy for the promotion of biodiversity in the agroecosystem. More importantly, the rice yield gradually increased after the two-year reduction of tillage. Taken together, our results suggest that the reduction of tillage intensity is beneficial for the protection of rice crops from various pests, and facilitates the sustainability of the agroecosystem and rice yield, which provides a solid basis and novel insights for the establishment of sustainable agroecosystems by CA-related practices in rice production in southern China.

Effects of different short-term tillage managements on rhizosphere soil autotrophic CO2 -fixing bacteria in a double-cropping rice paddy field.

Soil autotrophic bacteria community plays an important role in carbon (C) cycling process in soil, but there is still limited information about how the rhizosphere soil microbe that drives this process respond to combined application of tillage with crop residue incorporation managements under a double-cropping rice (Oryza sativa L.) paddy field in southern China. Therefore, the 6-years short-term tillage treatment on rhizosphere soil autotrophic bacteria community [RubisCO gene (cbbL)] under the double-cropping rice paddy field in southern China was studied using the high-throughput sequencing method in the present article. The field experiment included four tillage treatments: conventional tillage with crop residue incorporation (CT), rotary tillage with crop residue incorporation (RT), no-tillage with crop residue retention (NT) and rotary tillage with all crop residues removed as a control (RTO). The results showed that abundance, composition and activity of rhizosphere soil cbbL-carrying bacteria were obviously influenced by application of different tillage treatments. The rhizosphere soil abundant cbbL and 16S rRNA genes as well as RubisCO activity with CT, RT and NT treatments were higher than that of RTO treatment. The cbbL sequences in rhizosphere soil with CT, RT andNTtreatments mainly included Azoarcus_sp._KH33C,Ralstonia_pickettii, Thermomonospora_curvata, Variovorax_paradoxus and uncultured_proteobacterium. Meanwhile, the results indicated that cbbL-carrying bacterial composition was significantly affected by soil organic carbon, microbial biomass carbon, dissolved organic carbon contents and soil bulk density. There had an obvious difference in characteristics of rhizosphere soil autotrophic bacteria community between CT, RT, NT treatments and RTO treatment. Therefore, it was a beneficial practice for improving rhizosphere soil autotrophic bacteria community in the double-cropping rice paddy field in southern China by combined application of tillage with crop residue incorporation practices.

Impact of long-term tillage management on utilization of microbial carbon sources in rhizosphere and non-rhizosphere soils under a double-cropping rice paddy field.

In order to reveal the mechanism of microbial carbon (C) sequestration in paddy soil under different tillage management and to provide an important theoretical basis for perfecting the mechanism of C sequestration in paddy soil. C can indicate changes of soil nutrient content and soil microbial community, but more research is needed to study how C sources utilization characteristics respond to different tillage management under a double-cropping rice (Oryza sativa L.) paddy field in southern China. Hence, the impact of long-term (2005-2018) tillage management on utilization of microbial carbon sources in rhizosphere and non-rhizosphere soils under a double-cropping rice paddy field was studied by using 18O-H2O method in this study. The tillage treatments were included: (1) moldboard plow with all crop residue removed as a control (CT), (2) moldboard plow with all crop residue incorporated (CTS), (3) no-tillage with all crop residue retained on the soil surface (NTS), and (4) rotary tillage with all crop residue incorporated (RTS). The results indicated that Richness, Shannon, and McIntosh indices were increased by application of crop residue management, compared with treatment without crop residue, and soil microbial growth rate, soil microbial biomass C content, and soil microbial basal respiration with CT treatment were significantly lower (p < 0.05) than that of NTS, RTS, and CTS treatments. And the soil C utilization efficiency in rhizosphere soil with NTS, RTS, and CTS treatments was significantly lower (p < 0.05) than that of CT treatment. Compared with CT and CTS treatments, the metabolic capacity of soil microorganisms to exogenous C sources with NTS and RTS treatments was increased, and the different types of exogenous C sources were showed as following: complex compounds < carbohydrate < amino acid < carboxylic acids. The redundancy analysis results showed that utilization characteristics of soil microorganisms to exogenous C sources were significantly changed under tillage and crop residue incorporated conditions. Hence, this result indicated that characteristics of soil C sources utilization were significantly increased combined applied with tillage and crop residue incorporated management.

Effects of different tillage management on rhizosphere soil nitrogen mineralization and its extracellular enzyme activity in a double‐cropping rice paddy field of southern China

AbstractSoil extracellular enzyme activity plays an important role in regulating the process of nitrogen (N) mineralization in the paddy field. However, there is still limited information about how rhizosphere N mineralization and its extracellular enzyme activities respond to different tillage treatments in a double‐cropping rice paddy fields of southern China. Therefore, the effects of 6‐year (short‐term) tillage management on rhizosphere soil acid hydrolysable N and its fractions, N mineralization, and its extracellular enzyme activities in a double‐cropping rice paddy fields of southern China were studied and reported in this article. The field experiment included four tillage treatments: conventional tillage with crop residue incorporation (CT), rotary tillage with crop residue incorporation (RT), no‐tillage with crop residue retention (NT), and rotary tillage with crop residue removed as a control (RTO). The results showed that rhizosphere soil total acid hydrolysable N and its fractions with CT, RT and NT treatments were higher than those with RTO treatment. Compared to RTO treatment, the rhizosphere soil total acid hydrolysable N content with CT and RT treatments was increased by 19.17% and 17.74%, respectively. Compared to RTO treatment, the rhizosphere soil aerobic and anaerobic N mineralization rates with CT and RT treatments were increased by 100.00% and 80.65%, and 43.02% and 33.72%, respectively. Rhizosphere soil extracellular enzyme activities with CT and RT treatments were higher than those with NT and RTO treatments. There was a positive correlation between rhizosphere soil amino sugar N, amino acid N, total acid hydrolysable N contents, L‐glutaminase activity and N mineralization rate. The principal component analysis results indicated that rhizosphere soil organic carbon, amino sugar N, amino acid N and total acid hydrolysable N contents, soil β‐glucosaminidase, β‐glucosidase and L‐glutaminase activities were the main factors affecting rhizosphere soil aerobic and anaerobic N mineralization rates. As a result, rhizosphere soil acid hydrolysable N and its fractions, N mineralization, and its extracellular enzyme activities were significantly increased under the combined application of conventional tillage and rotary tillage with the crop residue incorporation condition.

CO2 fluxes over two paddy fields with different management practices in Southern China

Management practices in paddy fields are changing in the Poyang Lake basin, southern China. Investigating CO2 fluxes in paddy fields under different management practices is essential for understanding regional carbon cycles affected by human activities. Two-year CO2 fluxes were collected from paired eddy covariance (EC) towers at two paddy fields in southern China. One site is under the traditional farmers' management (direct-seeded early rice and transplanted late rice with continuous flooding (CF) irrigation, FM site), while the other site is under the promotion of milk vetch rotation and alternate wetting and drying (AWD) irrigation (PM site). The results showed both sites were CO2 sink with annual cumulative net ecosystem exchange of CO2 (NEE) of -744±21 and -645±22 g C m−2 in 2017, and -794±22 and -766±20 g C m−2 in 2018 at the PM and FM site, respectively. After considering the grain carbon, the CO2 budgets were -142±21 and -59±22 g C m−2 in 2017, and -170±22 and -173±20 g C m−2 in 2018 at the PM and FM site, respectively. The partitioning of NEE into gross primary productivity (GPP) and ecosystem respiration (Reco) showed that the PM site had higher GPP and Reco, which was mainly caused by the milk vetch growth. The AWD irrigation did not affect the field water conditions of the early rice season, but resulted in 16 more drying days and 5.6% more Reco for the late rice season compared to the FM site. Overall, our results imply that the field with milk vetch rotation and AWD irrigation was able to fix more CO2 in 2017, while it had similar CO2 budgets to the traditional farmers’ field when the light and heat conditions during the direct seeded early rice were affluent in 2018.

Effect of different long-term fertilizer managements on soil nitrogen fixing bacteria community in a double-cropping rice paddy field of southern China.

Soil microorganism plays an important role in nitrogen (N) fixation process of paddy field, but the related information about how soil microorganism that drive N fixation process response to change of soil phy-chemical characteristics under the double-cropping rice (Oryza sativa L.) paddy field in southern of China is need to further study. Therefore, the impacts of 34-years different long-term fertilization system on soil N-fixing bacteria community under the double-cropping rice paddy field in southern of China were investigated by taken chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) method in this paper. The field experiment were set up four different fertilizer treatments: chemical fertilizer alone (MF), rice straw and chemical fertilizer (RF), 30% organic manure and 70% chemical fertilizer (OM), and unfertilized as a control (CK). This results showed that compared with CK treatment, the diversity index of cbbLR and nifH genes with OM and RF treatments were significantly increased (p<0.05), respectively. Meanwhile, the abundance of cbbLR gene with OM, RF and MF treatments were increased by 23.94, 12.19 and 6.70×107 copies g-1 compared to CK treatment, respectively. Compared with CK treatment, the abundance of nifH gene with OM, RF and MF treatments were increased by 23.90, 8.82 and 5.40×109 copies g-1, respectively. This results indicated that compared with CK treatment, the soil autotrophic azotobacter and nitrogenase activities with OM and RF treatments were also significantly increased (p<0.05), respectively. There were an obvious difference in features of soil N-fixing bacteria community between application of inorganic fertilizer and organic manure treatments. Therefore, this results demonstrated that abundance of soil N-fixing bacteria community in the double-cropping rice paddy field were increased by long-term applied with organic manure and crop residue managements.

Integrated Life Cycle Assessment for Sustainable Remediation of Contaminated Agricultural Soil in China.

Agricultural land degradation is posing a serious threat to global food security. Restoration of the degraded land has traditionally been viewed as an inherently sustainable practice; however, restoration processes render consequential environmental impacts which could potentially exceed the benefit of restoration itself. In the present study, an integrated life cycle assessment analysis was conducted to evaluate life cycle primary, secondary, and tertiary impacts associated with the restoration of the contaminated agricultural land. The results demonstrated the importance of including spatially differentiated impacts associated with managing the land and growing crops. Comparing four risk management scenarios at a contaminated field in Southern China, it was found that the primary and secondary impacts followed the order of no action > chemical stabilization > phytoextraction > alternative planting. However, when tertiary impacts were taken into account, alternative planting rendered much higher footprint in comparison with phytoextraction and chemical stabilization, which provides evidence against an emerging notion held by some policy makers. Furthermore, assuming that the loss of the rice paddy field in Southern China is compensated by the deforested land in the Amazon rainforest, the total global environmental impact would far exceed that of no action, resulting in 687 ton CO2-e ha-1 of climate change impact. Overall, the present study provides new research findings to support more holistic policy making and also sheds lights on the future development of various restoration technologies.

Variations and Drivers of Methane Fluxes from Double-Cropping Paddy Fields in Southern China at Diurnal, Seasonal and Inter-Seasonal Timescales

Methane (CH4) is the second most important anthropogenic greenhouse gas (GHG) after carbon dioxide (CO2), and paddy fields are among the largest sources of CH4 emissions. Owing to the scarcity of observational data, the characteristics and influencing factors of CH4 fluxes in paddy fields at different timescales need to be further investigated. Observations of CH4 fluxes via eddy covariance (EC) data were performed over four seasons in two paddy fields in Nanchang, Jiangxi Province, China. The pattern, magnitude and biophysical controls of CH4 emissions were explored by wavelet analysis and stepwise multiplicative modelling. The results revealed a distinct, single-peak diurnal pattern in CH4 fluxes during the vegetative stage in all four rice growing seasons and the reproductive stage of early rice. Large seasonal variations in daily CH4 emissions were observed in the two double-cropping paddy fields, and the soil temperature at a depth of 5 cm (Ts5) explained most of the seasonality of the CH4 fluxes. At the inter-seasonal scale, under local farms’ traditional field management method, reducing the amount and frequency of irrigation during the vegetative stage could decrease CH4 emissions in southern China. This study improves the understanding of CH4 emissions and helps in developing GHG management strategies for paddy fields.

Reduced colloidal phosphorus loss potential and enhanced phosphorus availability by manure-derived biochar addition to paddy soils

Colloidal phosphorus (Pcoll) and available phosphorus (AP) are of fundamental importance in the nutrient cycle in soil solutions and subsurface drainage of ecosystems. Although many studies have been conducted on soil P loss and P availability, there remains limited focus on the relationship between Pcoll and AP. In this regional-scale study, soils with loam texture were collected from 63 paddy fields in southern China to explore the relationships between Pcoll and AP as well as other soil parameters. Subsequently, three typical paddy soils (sandy loam, silt loam, and clay loam) were incubated to study the effect of cattle manure biochar (CMB) amendment on Pcoll and AP at three application rates (0, 1, and 2%, w/w) for 30 d. The results showed that Pcoll was closely related to AP (R2 = 0.453, P < 0.05) and pH (R2 = 0. 487; P < 0.05) on a regional scale. In addition, clay loam soils contained higher Pcoll than the other soil types. The CMB amendment increased the AP by 129.0–872.0% but reduced the Pcoll by 9.65–22.95%, in which colloidal molybdenum-nonreactive phosphorus (MUPcoll) was reduced by 7.69–34.15% and colloidal molybdenum-reactive phosphorus (MRPcoll) was reduced by 5.13–22.73%. Multiple linear regression revealed that the release potentials of Pcoll (R2 = 0.735), MRPcoll (R2 = 0.543), and MUPcoll (R2 = 0.512) could be predicted by the dissolved organic carbon, total carbon, pH, and AP. Overall, this study confirmed that the application of CMB reduced the loss of Pcoll from paddy soils and enhanced the soil AP content.