Recycled Household Ash in Rice Paddies of Bangladesh for Sustainable Production of Rice Without Altering Grain Arsenic and Cadmium.

In Bangladesh most agronomic biomass (straw, husk, dried dung) is burnt for domestic cooking use. Consequently, the soil is continuously stripped of mineral nutrients and carbon (C) substrate. Here we investigate if recycling of household ash (ash) as fertilizer can sustainably improve soil fertility as well as minimise accumulation of toxic elements (As, Cd) in rice grain. Large scale field trials across two geographic regions (Barind, Madhupur) and two seasons (wet, dry) and with application of 3 fertiliser treatments (NPKS, ash, NPKS + ash) were conducted. At the end of each season, the impact of region*season*treatment on soil microbial comunities, rice yield, and grain quality (As, Cd, nutrient elements) was assessed. When compared to conventional field application rates of NPKS (control), application of ash boosted rice yield by circa. 20% in both regions during wet and dry season, with no effect on rice grain carcinogenic inorganic arsenic (iAs), dimethylarsonic acid (DMA) or cadmium (Cd), but with potential to increase zinc (Zn). For soil microbial communities, a significant region and season effect as well as correlation with elements in rice grain was observed, amongst these Cd, Zn, iAs and DMA. This study illustrates that application of ash can reduce the requirement for expensive chemical fertiliser, whilst at the same time increasing rice yield and maintaining grain quality, making farming in Bangladesh more sustainable and productive. The study also implies that the combined impact of region, season, and soil microbes determines accumulation of elements in rice grain. Supplementary Information: The online version contains supplementary material available at 10.1007/s12403-023-00539-y.

Treatment of nitrogen and phosphorus from sewage tailwater in paddy rice wetlands: concept and environmental benefits.

Domestic sewage tailwater (DSTW) reuse for crop irrigation is considered a promising practice to reduce water demand, mitigate water pollution, and substitute chemical fertilization. The level of the above environmental benefits of this water reuse strategy, especially when applied to paddy wetlands, remains unclear. In this study, soil column experiments were conducted to investigate the nitrogen and phosphorus fate in paddy wetlands subjected to different tailwater irrigation and drainage strategies, specifically, (i) TW1 and TW2 for regular or enhanced irrigation-drainage without N fertilization, (ii) TW3 and TW4 for regular irrigation with base or tillering N fertilizer, (iii) conventional fertilization N210, and (iv) no-fertilization controls N0. The results showed that the total nitrogen (TN), nitrate (NO3-), and total phosphorus (TP) removal rates from the paddies irrigated by DSTW ranged between 51.92 and 59.34%, 68.1 and 83.42%, and 85.69 and 86.98% respectively. Ammonia emissions from the DSTW-irrigated treatments were reduced by 14.6~47.2% compared to those paddies subjected to conventional fertilization (N210), similarly for TN emissions, with the exception of the TW2 treatment. Overall, it is established that the paddy wetland could effectively remove residual N and P from surface water runoffs, while the partial substitution of chemical fertilization by DSTW could be confirmed. The outcome of this study demonstrates that DSTW irrigation is a promising strategy for sustainable rice production with a minimized environmental impact.

Effects of selenium on biogeochemical cycles of cadmium in rice from flooded paddy soil systems in the alluvial Indus Valley of Pakistan.

This study delves into the pollution status, assesses the effects of Se on Cd biogeochemical pathways, and explores their interactions in nutrient-rich paddy soil-rice ecosystems through 500 soil-rice samples in Pakistan. The results showed that 99.6 % and 12.8 % of soil samples exceeded the World Health Organization (WHO) allowable Se and Cd levels (7 and 0.35 mg/kg). In comparison, 23 % and 6 % of the grain samples exceeded WHO's allowable Se and Cd levels (0.3 and 0.2 mg/kg), respectively. Geographically Weighted Regression (GWR) model results further revealed spatial nonstationarity, confirming diverse associations between dependent variables (Se and Cd in rice grain) and independent variables from paddy soil and plant tissues (root and shoot), such as Soil Organic Matter (SOM), pH, Se, and Cd concentrations. High Se:Cd molar ratios (>1) and a negative correlation (r = -0.16, p < 0.01) between the Cd translocation factor (Cd in rice grain/Cd in root) and Se in roots suggest that increased root Se levels inhibit the transfer of Cd from roots to grains. The inverse correlation between Se and Cd in paddy grains was further characterized as Se deficiency, no risk, high Cd risk, Se risk, Cd risk, and Se-Cd co-exposure risk. There was no apparent risk for human co-consumption in 42.6 % of grain samples with moderate Se and low Cd. The remaining categories indicate differing degrees of risk. In the study area, 31 % and 20 % of grain samples with low Se and Cd indicate Se deficiency and risk, respectively. High Se and low Cd levels in rice samples suggest a potential hazard for severe Se exposure due to frequent rice consumption. This study not only systematically evaluates the pollution status of paddy-soil systems in Pakistan but also provides a reference to thoroughly contemplate the development of a scientific approach for evaluating human risks and the potential dangers associated with paddy soils and rice, specifically in regions characterized by low Se and low Cd concentrations, as well as those with moderate Se and high Cd concentrations. SYNOPSIS: This study is significant for understanding the effects of Se on Cd geochemical cycles and their interactions in paddy soil systems in Pakistan.

Impacts, causes and biofortification strategy of rice selenium deficiency based on publication collection.

Selenium (Se) deficiency in rice will result in a Se hidden hunger threat to the general public's human health, particularly in areas where rice consumption is high. Nevertheless, the impact scope and coping strategies have not been given sufficient focus on a worldwide scale. In order to evaluate the impacts, causes and biofortification strategies of Se-deficient rice, this study collected data from the publications on three themes: market survey, field sampling and controlled experiments. According to the market survey, global rice Se concentrations were 0.079 mg/kg on mean and 0.062 mg/kg on median. East Asia has a human Se intake gap due to the region's high rice consumption and the lowest rice Se concentration in markets globally. Total Se concentrations in East Asian paddy soils were found to be adequate based on the field sampling. However, over 70 % of East Asian paddy fields were inadequate to yield rice that met the global mean for rice Se concentration. The Se-deficient rice was probably caused by widespread low Se bioavailability in East Asian paddy fields. There were two important factors influencing rice Se enrichment including root Se uptake and iron oxide in soils. Concentrating on these processes is beneficial to rice Se biofortification. Since Se is adequate in the paddy soils of East Asia. Rather of adding Se exogenously, activating the native Se in paddy soil is probably a more appropriate strategy for rice Se biofortification in East Asia. Meta-analysis revealed water management had the greatest impact on rice Se biofortification. The risks and solutions for rice Se deficiency were discussed in our farmland-to-table survey, which will be a valuable information in addressing the global challenge of Se hidden hunger. This study also provided new perspectives and their justifications, critically analyzing both present and future strategies to address Se hidden hunger.

Selenium- and chitosan-modified biochars reduce methylmercury contents in rice seeds with recruiting Bacillus to inhibit methylmercury production.

Biochar could reshape microbial communities, thereby altering methylmercury (MeHg) concentrations in rice rhizosphere and seeds. However, it remains unclear whether and how biochar amendment perturbs microbe-mediated MeHg production in mercury (Hg) contaminated paddy soil. Here, we used pinecone-derived biochar and its six modified biochars to reveal the disturbance. Results showed that selenium- and chitosan-modified biochar significantly reduced MeHg concentrations in the rhizosphere by 85.83% and 63.90%, thereby decreasing MeHg contents in seeds by 86.37% and 75.50%. The two modified bicohars increased the abundance of putative Hg-resistant microorganisms Bacillus, the dominant microbe in rhizosphere. These reductions about MeHg could be facilitated by biochar sensitive microbes such as Oxalobacteraceae and Subgroup_7. Pinecone-derived biochar increased MeHg concentration in rhizosphere but unimpacted MeHg content in seeds was observed. This biochar decreased the abundance in Bacillus but enhanced in putative Hg methylator Desulfovibrio. The increasing MeHg concentration in rhizosphere could be improved by biochar sensitive microbes such as Saccharimonadales and Clostridia. Network analysis showed that Saccharimonadales and Clostridia were the most prominent keystone taxa in rhizosphere, and the three biochars manipulated abundances of the microbes related to MeHg production in rhizosphere by those biochar sensitive microbes. Therefore, selenium- and chitosan-modified biochar could reduce soil MeHg production by these microorganisms, and is helpful in controlling MeHg contamination in rice.

Biochar amendment reassembles microbial community in a long-term phosphorus fertilization paddy soil.

This study investigates the effect of biochar amendment on microbial community structure and soil nutrient status in paddy soil that has been fertilized for an extended period of time, shedding light on sustainable agricultural practices. A 90-day incubation period revealed that biochar amendment, as opposed to long-term fertilization, significantly influenced the physicochemical properties and microbial composition of the soil. The microcosm experiment conducted using six treatments analyzed soil samples from a long-term rice ecosystem. We employed microbial biomarkers (phospholipid fatty acids, PLFAs; isoprenoid and branched glycerol dialkyl glycerol tetraethers, iGDGTs and brGDGTs; DNA) to assess microbial biomass and community structure. Biochar addition led to a decrease in PLFA biomass (15-32%) and archaeal iGDGT abundance (14-43%), while enhancing bacterial brGDGT abundance by 15-77%. Intact biochar increased archaeal and bacterial diversity, though fungal diversity remained unchanged. However, acid-washed biochar did not result in a uniform microbial diversity response. The abundance of various microbial taxa was changed by biochar amendment, including Crenarchaeota, Proteobacteria, Nitrospira, Basidiomycota, Halobacterota, Chloroflexi, Planctomycetota, and Ascomycota. Soil NH4+-N was found as the primary environmental factor impacting the composition of archaea, bacteria, and fungus in this study. These findings imply that the addition of biochar has a quick influence on the structure and activity of microbial communities, with fungi possibly having a critical role in acid paddy soil. This study contributes valuable knowledge for developing sustainable agricultural practices that promote healthy soil ecosystems. KEY POINTS: • Biochar type and phosphorus fertilization demonstrated an interactive effect on the diversity of archaea, but no such effect was observed for bacteria and fungi. • Soil fungi contribute to approximately 20% of the total phospholipid fatty acid (PLFA) content. • Biochar, especially acid-washed rice straw biochar, increases glucose metabolism in bacteria and archaea and decreases saprophytic fungi.

Nano hydroxyapatite pre-treatment effectively reduces Cd accumulation in rice (Oryza sativa L.) and its impact on paddy microbial communities.

Cadmium (Cd) contamination in paddy soil has become a worldwide concern and severely endangered human health. Nano hydroxyapatite (n-HAP) is a practical material to manage paddy Cd pollution, but its dosage should not be excessive. Based on previous studies, we validated the effect of n-HAP pre-treatment on rice Cd uptake in pot and field experiments. The results indicated that n-HAP pre-treatment effectively restricted Cd translocation in the soil-rice system. In pot experiment, when soil n-HAP concentration was 5000 mg/kg, the Cd content in the grains of n-HAP pre-treated rice was 0.171 mg/kg, decreased by 29.3% compared with normal rice (0.242 mg/kg). In field experiment, when soil n-HAP concentration was 20,000 mg/kg, the Cd content in the grains of n-HAP pre-treated rice was 0.156 mg/kg, decreased by 35.3% compared with normal rice (0.241 mg/kg). The primary mechanism was that n-HAP pre-treatment altered the formation and composition of iron plaque and therefore enhanced the Cd binding ability of iron plaque. The available N and P content and urease activity in paddy field were increased. We further investigated the impact of n-HAP on the diversity and structure of paddy microbial communities. The Chao1 and Shannon diversity indices showed no significant difference. The relative abundance of Actinobacteria and Proteobacteria was significantly decreased by n-HAP, indicating that Cd pollution might be alleviated. Desulfobacterota, Gemmatimonadota, and Geobacteraceae were significantly enriched by n-HAP. The declining relative abundance of Basidiomycota and the increasing relative abundance of other fungal taxa also suggested that n-HAP could alleviate Cd toxicity in soil.

[Effects of Combined Application of Fungal Residue and Chemical Fertilizer on Soil Microbial Community Composition and Diversity in Paddy Soil].

Fungal residue is a unique abundant organic material undervalued in agricultural production. The application of chemical fertilizer combined with fungal residue can not only improve soil quality but also regulate the microbial community. However, it is unclear whether the response of soil bacteria and fungi to the combined application of fungal residue and chemical fertilizer is consistent. Therefore, a long-term positioning experiment in a rice field was conducted with a total of nine treatments. Chemical fertilizer (C) and fungal residue (F) were applied at 0, 50%, and 100% to evaluate 1 the change in soil fertility properties and microbial community structure and 2 the main driving factors of soil microbial diversity and species composition. The results showed that soil total nitrogen (TN) was highest after treatment C0F100 (55.56% higher than in the control), and the carbon to nitrogen ratio (C/N), total phosphorus (TP), dissolved organic carbon (DOC), and available phosphorus (AP) contents were highest after treatment with C100F100(26.18%, 26.46%, 17.13%, and 279.54% higher than in the control, respectively). The amounts of soil organic carbon (SOC), available nitrogen (AN), available potassium (AK), and pH were highest after treatment with C50F100 (85.57%, 41.61%, 29.33%, and 4.62% higher than in the control, respectively). Following the application of fungal residue with chemical fertilizer, there were significant changes in the α-diversity of bacteria and fungi in each treatment. Compared with that of the control (C0F0), different long-term applications of fungal residue with chemical fertilizer did not significantly change soil bacterial ß-diversity but resulted in significant differences in fungal ß-diversity, and the relative abundance of soil fungal Ascomycota and Sordariomycetes significantly decreased after the application of C50F100. The random forest prediction model indicated that AP and C/N were the main driving factors of bacterial and fungal α-diversity, respectively, and AN, pH, SOC, and DOC were the main driving factors of bacterial ß-diversity, whereas AP and DOC were the main driving factors of fungal ß-diversity. Correlation analysis suggested that the relative abundance of soil fungal Ascomycota and Sordariomycetes had a significantly negative correlation with SOC, TN, TP, AN, AP, AK, and C/N. PERMANOVA showed that variation in soil fertility properties, dominant species of soil bacteria at the phylum and class level, and dominant species of soil fungi at the phylum and class level were all best explained by fungal residue (46.35%, 18.47%, and 41.57%, respectively), and variation in bacterial diversity was best explained by fungal residue (23.84%) and to a lesser extent by the interaction between fungal residue and chemical fertilizer (9.90%). In contrast, the variation in fungal diversity was best explained by the interaction between fungal residue and chemical fertilizer (35.00%) and to a lesser extent by fungal residue (10.42%). In conclusion, the application of fungal residue has more advantages than chemical fertilizer in influencing soil fertility properties and microbial community structure changes.

Calcium enhances phosphorus reclamation during biochar formation: Mechanisms and potential application as a phosphorus fertilizer in a paddy soil.

Transformation of phosphorus (P) species during pyrolytic production of biochar from P-rich biowastes with a subsequent soil amendment is important to P reclamation. Aiming at increasing the content of plant-available P and restraining the formation of easily mobile P in pyrolysis product, this study used exogenous calcium ions (20 wt% CaCl2) addition prior to pyrolysis to regulate the pyrolytic transformation of P chemical fractions from sewage sludge and bone dreg. Results showed that active Ca catalyzed the decomposition of organic P to transform into inorganic orthophosphate. Based on Hedley's sequential extraction method, this study found that addition of Ca ions remarkably reduced the content of soluble P, exchange P, Fe/Al bound P, and occluded P in biochar, while increased Ca bound P from 78 to 85% to 85-96%. Liquid 31P NMR indicated that exogenous Ca induced the crack of the P-O-P bond in pyrophosphate to become orthophosphates. It also explained why new orthophosphates including chlorapatite (Ca5(PO4)3Cl) and calcium hydroxyapatite (Ca10(PO4)6(OH)2) appeared in the Ca-composite biochar compared to pristine biochar. Combined with rapid P-release test in paddy soil (pH 6.27) and 30-days rice seedling growth test under flooded condition (10 wt% biochar addition ratio), it was confirmed that compared to pristine biochar, Ca-composite biochar released more P in paddy soil, but also promoted more P to be taken in by rice root and stalk. These results suggested that pretreating biowaste with Ca ion was a friendly approach to enhance P reclamation during biochar formation, making it a promising P fertilizer.

Impact of long-term fertilization on phosphorus fractions and manganese oxide with their interactions in paddy soil aggregates.

One under-studied microelement, manganese (Mn), due to its potential to considerably interact, and limit labile, and moderately-labile soil phosphorus (P) pools, was studied in Nanchang (NC), and Qiyang (QY) under paddy conditions. The Hedley's P sequential fractionation procedure was utilized to extract, and quantify various P fractions at both surface (0-20 cm) and subsurface (20-40 cm) layers. Unfertilized control (CK), nitrogen, phosphorus, and potassium (NPK), and NPK amended with animal manure (NPKM) were used as treatments. From both sites, the manure amended fertilizer (NPKM) compared to chemical NPK formed higher proportions of macro-aggregates (>2 and 2-0.25 mm) in both layers. Total P (TP) values of 842.1 (>2 mm), and 744.4 mg kg-1 (2-0.25 mm) from NC, and QY, respectively were accumulated by NPKM compared to NPK, and CK. Total P values of 806.4, and 350.4 mg kg-1 in the >2 mm aggregate size, respectively for NC, and QY were observed in the subsurface layer. Inorganic moderately labile P (NaOH-Pi) was the dominant fraction under all fertilizer treatments. Concentrations of 232.3 (<0.053 mm), and 202.1 mg kg-1 (0.25-0.053 mm) of NaOH-Pi were accumulated by NPKM, respectively for NC, and QY in the surface layer. In the subsurface layer, concentrations of NaOH-Pi (217.5 mg kg-1; <0.053 mm) from NC, and residual-P (57.3 mg kg-1; >2 mm) from QY were accumulated by NPKM. Similarly, NPKM in contrast to NPK contributed higher Mehlich-3 manganese (M3-Mn) oxide in all aggregate sizes from both sites. Generally, macro-aggregates contributed higher TP, fractions of P, and M3-Mn oxide than micro-aggregates. There was a positive relationship between P pools and M3-Mn oxide at both sites. Additions of animal manure were associated with increased P fractions, and Mn oxides in the paddy soil aggregates, which raises environmental concern.

Application of phosphorus amendments reduces metal uptake and increases yield of Oryza saliva L. (rice) in Cd/Cu-contaminated paddy field.

To alleviate worldwide food safety issues caused by metal contamination, an easily available material is urgently needed for extensive application. In this study, calcium magnesium phosphate fertiliser (Pcm) was applied to a Cd/Cu co-contaminated paddy field in comparison with limestone and organic fertiliser. The results showed that only Pcm is effective in simultaneously reducing Cd uptake by 56.7% and Cu uptake by 36.2% in Oryza saliva L. (rice). The rice yield, reduced mainly by Cu, also increased by 30.1% with respect to the enhancement of soil pH, cation exchange capacity and availability of phosphorus, as well as the reduction in availabilities of Cd and Cu. Additionally, Pcm dramatically shaped the bacterial community structure, with Proteobacteria and Firmicutes predominant in the soils. The beneficial genera Exiguobacterium, Citrobacter, and Acinetobacter, which are vital for phosphate dissolution and Cd/Cu immobilisation, were also enriched. The results demonstrated that the application of Pcm at 0.4% (w:w) was able to enhance both crop quantity and quality in Cd/Cu co-contaminated paddy fields by reducing Cu/Cd availability, promoting rice yield, and reshaping bacterial community structures.

Biochar reduces colloidal phosphorus in soil aggregates: The role of microbial communities.

Colloidal phosphorus (Pcoll) in paddy soils can pose a serious threat to the water environment. Biochar amendment not only directly absorb Pcoll to reduce the runoff loss, but also create hotspots for microbial communities which simultaneously affects soil Pcoll. However, despite the crucial role of microorganisms, it remains elusive regarding how biochar and its feedstock types affect the relationships of soil microbial communities and Pcoll in soil matrix (such as at soil aggregate level). To address the knowledge gap, we explored the (in)direct effects of biochar on the soil Pcoll in physically separated fractions including micro- (53-250 µm) and macroaggregates (250-2000 µm). Results showed that straw and manure biochars decreased the soil Pcoll content by 55.2-56.7% in microaggregates and 41.2-48.4% in macroaggregates after 120 days of incubation, compared to the respective control. The fungal communities showed a significantly correlation (0.34, p < 0.05) with Pcoll content in the macroaggregates, whereas the bacterial communities were extremely significantly correlated (0.66, p < 0.001) with Pcoll content in the microaggregates. Furthermore, the partial least squares path model analysis indicated that biochar amendments directly increased Pcoll content (0.76 and 0.61) in micro- and macroaggregates, but the reduced Pcoll content by biochar was mainly derived from indirect effects, such as changed soil biological characteristics carbon (C)/P (-0.69), microbial biomass C (-0.63), microbial biomass P (-0.68), keystone taxa Proteobacteria (-0.63), and Ascomycota (-0.59), particularly for the macroaggregates. This study highlights that to some extent, biochar addition can reduce soil Pcoll content by affecting microbial communities (some keystone taxa), and soil biological characteristics at soil aggregate level.

Mechanisms and influencing factors of yttrium sorption on paddy soil: Experiments and modeling.

High-technology rare earth elements (REEs) as emerging contaminants have potentially hazardous risks for human health and the environment. Investigating the sorption of REEs on soils is crucial for understanding their migration and transformation. This study evaluated the sorption mechanisms and influencing factors of the rare earth element yttrium (Y) on paddy soil via integrated batch sorption experiments and theoretical modeling analysis. Site energy distribution theory (SEDT) combined with kinetics, thermodynamics, and isotherm sorption models were applied to illustrate the sorption mechanism. In addition, the effects of phosphorus (P), solution pH, particle size of soil microaggregates, and initial Y content on the sorption processes were evaluated by self-organizing map (SOM) and Boruta algorithm. The sorption kinetic behavior of Y on paddy soil was more consistent with the pseudo-second-order model. Thermodynamic results showed that the Y sorption was a spontaneous endothermic reaction. The generalized Langmuir model well described the isotherm data of Y sorption on heterogeneous paddy soil and soil microaggregates surface. The maximum sorption capacity of Y decreased with increasing soil particle size, which may be related to the number of sorption sites for Y on paddy soil and soil microaggregates, as confirmed by SEDT. The heterogeneity of sorption site energy for Y was the highest in the original paddy soil compared with the separated soil microaggregates. The SOM technique and Boruta algorithm highlighted that the initial concentration of Y and coexisting phosphorus played essential roles in the sorption process of Y, indicating that the addition of phosphate fertilizer may be an effective way to reduce the Y bioavailability in paddy soil in practice. These results can provide a scientific basis for the sustainable management of soil REEs and a theoretical foundation for the remediation of REEs-contaminated soils.

How different nitrogen fertilizers affect arsenic mobility in paddy soil after straw incorporation?

In straw return fields, nitrogen-fertilizers are added to mitigate microbial competition for nitrogen with plants. However, in arsenic (As)-contaminated paddy fields, the specific effects of different nitrogen fertilizers on As mobility after straw incorporation and the interactions among iron(Fe)/carbon(C)/nitrogen(N)/As are not well understood. In the reported microcosm experiment we monitored As-mobility as a function of different dosages of KNO3, NH4Cl and rice straw incorporation. Addition of both KNO3 and NH4Cl significantly inhibited the As mobilization induced by straw incorporation. Following the KNO3 addition, the As concentration in porewater dropped by 51-66% after 2 days of the incubation by restraining Fe reduction and enhancing Fe oxidation. High-dose NH4Cl addition reduced As in porewater by 22-43% throughout the incubation by decreasing porewater pH. High-throughput sequencing results demonstrated that KNO3 addition enriches both the denitrifying and Fe-oxidizing bacteria, while diminishing Fe-reducing bacteria; NH4Cl addition has the opposite effect on Fe-reducing bacteria. Network analysis revealed that As and Fe concentrations in porewater were positively correlated with the abundance of denitrifying and Fe-reducing bacteria. This study broadens our insight into the As biogeochemistry associated with the N/C/Fe balance in soil, which are of great significance for agronomic management and mitigation the risk of As-contaminated paddy fields.

The effectiveness of reed-biochar in mitigating phosphorus losses and enhancing microbially-driven phosphorus dynamics in paddy soil.

Biochar is a promising novel material for mitigating phosphorus (P) loss and enhancing P retention in chemical-amended agricultural soils. However, the optimal application rate for aforesaid effectiveness and potential drivers of the process are not well understood. Herein, a column-based pot experiment was carried out to investigate how and to what extent reed-biochar is effective in positively triggering P loss and availability in paddy soils treated by chemical fertilizer. Compared with chemical-only treatment, the accumulated leakage of total P, dissoluble P, and particulate P in chemical fertilizer coupled with 1-4% reed-biochar treatment decreased by 5.3-13.3%, 8.3-10.4%, and 3.0-15.4%, respectively. The accumulated leakage of total P and dissoluble P in 6-8% rate treatments was increased by 5.6-7.5% and 18.3-32.9%, respectively. Increasing reed-biochar rate from 1% to 8% caused an enhancement in soil total P and available P content and P activation coefficient, and the 4% rate achieved a similar effectiveness to the higher rate. Reed-biochar application increased the abundance and diversty of soil phoD-harboring microbes (P < 0.05), while the increment had little to do with the application rate. Soil phoD-harboring community composition and total C content were the main predictors of the P leaching losses, and meanwhile, the total C content was the dominated predictor of soil P retention and availability. These results suggest that adding 1-4% reed-biochar was more beneficial to mitigate paddy P loss and to enhance soil P availability. This study highlights the importance of understanding how microbial populations mediate P transformation to decipher the biochar-driven improvement of soil P utilization.

Animal manures promoted soil phosphorus transformation via affecting soil microbial community in paddy soil.

Animal manures are reported as good substitutes for chemical fertilizers to mobilize soil phosphorus (P). However, the mechanisms on how different types of manures regulate microbial biomass involved in P mobilization remain unclear. In this study, we conducted a two-year field experiment to investigate variations in soil microbial biomass carbon (MBC) and P (MBP) and P fractions after 30% animal manures substitution (pig manure (PM), chicken manure (CM), and dairy manure (DM)) in paddy soil. Furthermore, a 30-day incubation experiment was used to explore the mechanisms of soil P transformation induced by 100% manures addition. Two-year field experiment results showed that, compared to the chemical NPK fertilizer, 30% manure substitution didn't influence rice and wheat yields significantly but decreased soil total P loss from runoff by 3.2%. However, 30% manure substitution significantly enhanced MBC and MBP by 11.3-18.4% and 57.1-81.2%, respectively, which also promoted the transformation of moderately labile P (M-P) to labile P (L-P). Moreover, the incubation experiment also convinced that all manures caused higher MBC than chemical P fertilizer. Meanwhile, compared to the no P fertilizer, manures increased L-P and organic P by 2.7%-14.7% and 6.4%-20.0%, respectively. Redundancy analysis indicated that soil MBC/MBP ratio was the main factor to soil L-P and M-P, indicating that animal manures can improve soil microbial abundance and thus promote M-P to L-P in soil. Among three animal manures, PM could improve the mobilization potential of P mostly, due to the highest C source activity by 13C NMR analysis. Our study indicated that animal manures especially PM can be considered as a good candidate for agricultural P management in paddy soils because of their capacity to promote soil P transformation.

Yield Variation Characteristics of Red Paddy Soil under Long-Term Green Manure Cultivation and Its Influencing Factors.

Rice is an important food crop in China, fertilization measures significantly affect soil properties and ultimately change rice yield. Thus, examining the effects of long-term green manure cultivation on the rice yield and the driving factors on rice yield, plays a crucial role in maintaining food security. Based on the long-term green manure cultivation, the treatments included no fertilizer (CK), chemical fertilizer (NPK), chemical fertilizer + Chinese milk vetch (NPK + GM), chemical fertilizer + Chinese milk vetch + rice straws (NPK + GM + S), and chemical fertilizer + Chinese milk vetch + pig manure (NPK + GM + M) treatments. One-way repeated ANOVA was used to determine the effects of diverse fertilizer modes on temporal variations in rice yields. The redundancy analysis (RDA) was used to calculate the magnitudes of the effects of soil properties on rice yield. Compared with the CK treatment, four fertilizer treatments led to significantly increased double-season rice yields (116.40−124.49%), with no significant difference between four fertilizer treatments (p> 0.05). There were five soil properties accounting for 66.3% variation in rice yield (p< 0.05), with available potassium (AK) being the most influential factor (32.2% variation), whereas potential of hydrogen (pH), total nitrogen (TN), total phosphorus (TP), and soil organic carbon (SOC) accounted for 15.3%, 10.5%, 5.1%, and 3.2% variation in rice yield (p< 0.05), respectively. Thus, SOC, TN, TP, AK, and pH were major factors affecting the double-season rice yield of red paddy soil under long-term green manure cultivation. However, the results suggested that the effect of green manure on soil fertility is limited by the relatively large amount of chemical fertilizer. The results reported herein can not only increase soil fertility and improve the soil ecological environment, but also enhance and stabilize the yields of double-season rice grown in the red paddy soil of southern China.

Goethite modified biochar simultaneously mitigates the arsenic and cadmium accumulation in paddy rice (Oryza sativa) L.

Cadmium (Cd) and arsenic (As) contamination of paddy soils is a serious global issue because of the opposite geochemical behavior of Cd and As in paddy soils. Rice plant (Oryza sativa L.) cultivation in Cd- and As- contaminated paddy soil is regarded as one of the main dietary cause of Cd and As entry in human beings. This study aimed to determine the impact of goethite-modified biochar (GB) on bioavailability of both Cd and As in Cd- and As- polluted paddy soil. Contrary to control and biochar (BC) amendments, the application of GB amendments significantly impeded the accumulation of both Cd and As in rice plants. The results confirmed an obvious reduction in Cd and As content of rice grains by 85% and 77%, respectively after soil supplementation with GB 2% amendment. BC 3% application minimized the Cd uptake by 59% in the rice grains as compared to the control but exhibited a little impact on As accumulation in rice grains. Sequential extraction results displayed an increase in immobile Cd and As fractions of the soil by decreasing the bioavailable fractions of both elements after GB treatments. Fe-plaque formation on the root surfaces was significantly variable (P Ë‚ 0.05) among all the amendments. GB 2% treatment significantly increased the Fe content (10 g kg-1) of root Fe-plaque by 48%, which ultimately enhanced the sequestration of Cd and As by Fe-plaque and minimized the transport of Cd and As in rice plants. Moreover, GB treatments significantly changed the relative abundance of the microbial community in the rice rhizosphere and minimized the metal(loid)s mobility in the soil. The relative abundance of Acidobacteria, Firmicutes and Verrucomicrobia increased with GB 2% treatment while those of Bacteroidetes and Choloroflexi decreased. Our findings confirmed improvement in the rice grains quality regarding enhanced amino acid contents with GB application. Overall, the results of this study demonstrated that GB amendment simultaneously alleviated the Cd and As concentrations in edible parts of rice plant and provided a new valuable method to protect the public health by effectively remediating the co-occurrence of Cd and As in paddy soils.

Flooding and straw returning regulates the partitioning of soil phosphorus fractions and phoD-harboring bacterial community in paddy soils.

Flooding and straw returning are effective agricultural practices in promoting phosphorus (P) availability in paddy soils. However, little is known about the effects of these practices and their interaction on the soil P pools and functional microbes responsible for soil P mobilization. Our 4-year paddy field experiment aimed to analyze the responses of soil P fractions and phoD-harboring bacterial communities in a double-rice cropping system to intermittent flooding (IF) and continuous flooding (CF), in plots with (+ S) and without (-S) straw return. Compared to IF, CF significantly increased soil citrate-P and marginally decreased the HCl-P fractions, suggesting that the stable inorganic P pools are transferred to labile inorganic P at lower redox potentials. Compared to the -S treatments, + S treatments significantly increased the labile organic fractions (enzyme-P). Correspondingly, a decreased soil total organic P concentration was observed in + S treatment. Additionally, + S treatment significantly increased the activity of acid phosphomonoesterase and alkaline phosphomonoesterase and the abundance of phoD-harboring bacteria. These results indicated that straw promoted organic P minimization to release orthophosphate. The diversity of the phoD-harboring bacteria and complexity of the co-occurrence network decreased under the CF + S treatment; however, all keystone species of the phoD-harboring bacteria were retained in this oxygen-deficient environment. This study highlights that irrigation regimes mediate the processes of inorganic P mobilization, while straw returns regulate the processes of organic P mineralization. Additionally, flooding could be a more effective agricultural practice than straw returning to promote soil P availability in paddy soils. KEY POINTS: •Soil P pools and phoD-harboring bacteria communities were assessed. •Straw return mainly affects the mineralization of organic P. •Continuous flooding mainly affects the mobilization of inorganic P.

[Effects of long-term straw returning on distribution of aggregates and nitrogen, phosphorus, and potassium in paddy]. / é•¿æœŸç§¸ç§†è¿˜ç”°å¯¹æ°´ç¨»åœŸå›¢èšä½“åŠæ°®ç£·é’¾åˆ†é çš„å½±å“.

In order to understand the composition and stability of soil aggregate in paddy filed, as well as the changes of soil aggregate-associated nitrogen (N), phosphorus (P) and potassium (K) after straw addition combined with chemical fertilization, soil samples were collected from a 34-year positioning experiment with three treatments, including no chemical fertilizer (CK), chemical fertilizer only (NPK), and straw addition plus chemical fertilizer (NPKS). The composition of water-stable aggregates at the soil layers of 0-20 cm and 20-40 cm were analyzed with the wet sieving method, as well as the distribution characteristics, contribution rate and activation rate of soil aggregate-associated N, P, and K. Results showed that the fractions of >2 mm and 0.25-1 mm aggregates dominated the soil water-stable aggregates in paddy field, while the contribution of <0.053 mm aggregates was lowest. Compared with CK, NPKS treatment increased the contents of >2 mm and 1-2 mm aggregates at the layers of 0-20 and 20-40 cm, and reduced the contents of 0.053-0.25 mm and <0.053 mm. Similar result in NPK treatment was observed at the layer of 0-20 cm. Compared with tat under the NPK treatment, mean weight diameter (MWD) and geometric mean diameter (GMD) increased by 3.9%-15.5% and 6.3%-41.7% in NPKS treatment, respectively. However, the unstable aggregate index (ELT) reduced by 5.7%-28.7% in the NPKS treatment. NPKS significantly increased the contents of total N (TN), available P (AP), and available K (AK) in soil aggregates, especially in the >0.25 mm aggregates. There were no significant diffe-rences about alkali-hydrolysable N (AN) and total K (TK) between NPK and NPKS treatments. The nutrient contribution of soil aggregates in paddy field was affected by aggregate composition. NPKS significantly increased the contribution of AN, AP, and AK within >1 mm aggregates. In all, straw addition combined with chemical fertilizer could increase the stability of soil aggregates at the layers of 0-20 cm and 20-40 cm, and increase the contents of soil aggregate-associated N, P and K, especially for the >1 mm aggregates. Our results provided insights into ensuring soil quality and sustainable development of resources in paddy field by adjusting the ratio of soil C to N.