Enhancing the management of saline-alkali lands can expand the area of crop cultivation. Gypsum application and straw retention are widely adopted practices to mitigate soil salinization and boost soil fertility in saline-alkali lands worldwide, but their combined effects on methane (CH4) emissions remain unclear. We conducted a pot experiment to investigate how the application of flue gas desulfurization gypsum and wheat straw incorporation affects CH4 emissions in coastal saline-alkali paddies. There were 4 treatments including no straw incorporation or gypsum application, gypsum application without straw incorporation, straw incorporation without gypsum application, and straw incorporation combined with gypsum application. Straw incorporation significantly increased seasonal CH4 emissions by an average of 9.7 times compared to straw absence, through the increase in the dissolved organic carbon and abundance of mcrA gene. However, gypsum application substantially decreased CH4 emissions by 74.8

This study conducted a two-year field artificial intelligence (AI) greenhouse rice planting experiment with different canopy humidity (normal humidity, NH; high humidity, and HH) and irrigation regimes (continuous flooding, CF; drought cultivation, DC; alternate wetting-drying, AWD) to test whether high canopy humidity from heading to maturity deteriorates rice grain quality, whether appropriate water management can alleviate these adverse effects, and the related mechanisms. The results showed that compared with NH, HH significantly decreased the head rice rate while increasing the protein, amino acid, amylopectin, amylose, and chalkiness. Moreover, HH significantly decreased the peak viscosity, breakdown, and number of small starch granules, while increasing the setback, number of large starch granules, relative crystallinity, gelatinization temperature, and enthalpy. Under NH and HH, AWD treatment resulted in a higher head rice rate, peak viscosity, breakdown, key enzyme activities of starch synthesis, amylose, amylopecan, relative crystallinity, small starch granules, gelatinization temperature, and enthalpy than DC and CF treatments, while lower chalkiness, setback, protein, amino acid, and large starch granules were observed. HH increased the chalkiness by promoting the formation of large starch granules, thus reducing the milling quality. The increase in amylose and relative crystallinity further causes HH to deteriorate the cooking and eating quality. AWD could alleviate the deterioration of rice grain milling, appearance, and eating quality caused by HH by improving starch granules.

Biochar exhibits a good adsorption ability for heavy metals in soil and has been widely used as a remediation material in Cd-contaminated soil. However, the status of Cd uptake by rice driven by soil physicochemical properties and rhizosphere microbial communities after years of biochar application is not well understood. In this study, the relationship between the rhizosphere microbial community and soil physicochemical properties and rice Cd accumulation were investigated during the main rice growth stages. The results showed that in comparison to the non-biochar treatment (control), a noticeable reduction in Cd content in rice stem sheaths, leaves, rice husks and milled rice with different growth stages were observed in the biochar treatment after four years, which decreased by 38.76–66.18%, 40.93–70.27%, 43.64–47.92% and 31.91–34.38%, respectively. Compared to non-biochar treatment (control), the properties of the soil in different growth stages by biochar treatment of the soil pH, soil organic matter (SOM), total nitrogen (TN) and available phosphorus (AP) were significantly increased, which increased by 10.5–16.13%, 8–25%, 75–130.13% and 132.95–191.43%, respectively. The content of available Cd (ACd) concentration in different stages by biochar treatment was significantly decreased, which decreased by 26.57–44.24%. Biochar application after four years changed the rhizosphere bacterial community structure composition (phyla level) in all stages. The relative abundance of Proteobacteria, Bacteroidetes and Nitrospirae was increased, while the relative abundance of Chloroflexi, Acidobacteria and Actinobacteria was decreased. Meanwhile, the biochar application enriched Rhodocyclaceae, Burkholderiaceae, Nitrosomonadaceae, Anaerolineaceae, Ignavibacteriales and Bacteroidales, which may contribute to the reduction of Cd uptake and accumulation in rice. These results suggest that biochar treatment after four years changed the rhizosphere microbial community structure and soil physicochemical properties and promoted the colonization of specific microbial populations in the rice rhizosphere to form a special protective system in the rice rhizosphere, which reduced Cd uptake by rice.

BACKGROUNDBiochar can play a key role in improving paddy soil and productivity. However, there is limited information on the effects of biochar on rice quality and starch gelatinization. In this study, four rice straw biochar dosage treatments (0, 20, 40 and 60 g kg(-1); CK, C20, C40 and C60, respectively) were set up to investigate rice yield components, rice processing, appearance and cooking quality, and starch gelatinization. RESULTSAddition of biochar increased the effective panicle, grain number per panicle and seed setting rate. However, it decreased the 1000-grain weight, resulting in an increase in yield. In 2019, all the biochar treatments improved the head rice rate (9.13-11.42%), whereas in 2020 only the C20 treatment improved. Low biochar dosage had little effect on grain appearance. High biochar dosage significantly decreased the chalky rice rate by 21.47% and chalkiness by 19.44% in 2019. However, it significantly increased the chalky rice rate and chalkiness by 118.95% and 85.45% in 2020, respectively. Biochar significantly lowered the amylose content except for the C20 and C40 treatments in 2020, and the gel consistency. The C40 and C60 treatments significantly increased the peak and breakdown viscosities and decreased the setback viscosity compared with CK. Correlation analysis showed that starch gelatinization characteristics were significantly correlated with the head rice rate, chalky rate and amylose content. CONCLUSIONA lower biochar dosage can improve the yield and milled rice rate and maintain a higher quality of appearance, whereas a higher biochar dosage can significantly improve starch gelatinization. (c) 2023 Society of Chemical Industry.

Biochar has become a research hotspot in soil heavy metal pollution remediation. However, there are few studies on the effect of biochar on the heavy metal accumulation in rice under different irrigation regimes, and there is very limited information on the soil heavy metal speciation changes during whole rice growth period. This study aims to clarify the effect and mechanism of biochar on Cd and Cu accumulation in rice grains under different irrigation regimes. The rice straw biochar (0 g kg−1 (CK), 20 g kg−1 (BC20), 40 g kg−1 (BC40), and 60 g kg−1 (BC60)) was applied to the paddy soil (contaminated with Cd and Cu) under three irrigation regimes (flooding irrigation (FI), intermittent irrigation (II), and wet irrigation (WI)), and a rice pot experiment was carried out for two consecutive years. The speciation changes of Cd and Cu in the soil during the key stage of rice growth and the metal content of each part of the rice were analyzed. Biochar promoted the formation of reducible and oxidizable Cd throughout the rice growth period, while the acid-extractable and residual forms were dynamic and affected by irrigation regimes. A significant reduction in acid-extractable Cu content was observed, and biochar mainly converted the acid-extractable Cu to oxidizable Cu, while reducible Cu was sensitive to soil water conditions. As biochar reduced soil available Cd content, BC60 decreased Cd content in brown rice by 50.41%, 70.32%, and 81.52% under FI, II, and WI, respectively, but the Cd content in brown rice was the lowest in FI. Biochar decreased the Cu content in brown rice under FI (maximum 31.2%), while significantly increased Cu content under II (maximum 74.33%) and WI (maximum 49.3%) because biochar increased soil available Cu content after rice heading stage and encouraged its transport from root to shoot. Rice straw biochar can be used to control Cd pollution in rice under various irrigation regimes, and the effect is better when combined with flooding irrigation. The application of rice straw biochar to control crop Cu pollution is not suitable for water-saving irrigation.

Exogenous application of methyl jasmonate (MeJA) improves rice drought tolerance, but its effects on rice yield and quality under drought stress during the reproductive phase remain unclear. A pot experiment was conducted to measure rice yield, grain quality, and starch physicochemical properties under three treatments: continuous flooding irrigation throughout the whole growth season (CF), ten days of −40 kPa drought stress at the heading stage (DS), and foliar spraying 100 μmol L−1 MeJA on the first three days of the ten-day −40 kPa heading stage drought stress (DM). An inbred japonica rice variety, Huaidao 5, was the experimental material, and each treatment had 11 replicates for sampling. The results indicated that DS significantly reduced rice yield and quality compared to CF. With increases in superoxide dismutase (+22.2%), peroxidase activities (+10.5%), catalase (+5.0%), and proline content (+5.7%), DM significantly increased 1000-grain weight (+8.6%), filled grain percentage (+3.6%), and yield (+11.1%) compared with DS. Regarding grain quality, DM significantly decreased the chalkiness degree (−12.3%) and protein content (−3.9%) but increased the amylose content (+17.2%) and taste value (+7.3%) relative to DS. In addition, DM improved breakdown viscosity (+17.8%), gelatinization enthalpy (+17.2%), retrogradation enthalpy (+28.0%), 1045/1022 cm−1 ratio (+3.0%), and starch granule morphology compared to DS. In conclusion, exogenous application of 100 μmol L−1 MeJA enhanced the antioxidant capacity of rice leaves, and thus improved starch physicochemical properties to increase grain yield and quality under terminal drought stress.

This study aimed to investigate the effects of biochar on soil nutrient dynamics and rice productivity under different irrigation regimes. A pot experiment of rice straw biochar application (0, CK; 2

Smart agronomic management practices (e.g., employing lodging-resistant cultivars, appropriate fertilization, and applying plant growth regulators (PGRs)) can reduce crop lodging risk. However, their integrated effects on grain yield and lodging risk in rice paddies remain poorly defined. Here, we conducted a meta-analysis to examine the effects of agronomic practices on rice yield and lodging risk, synthesizing data from 68 published studies with 475 observations. Our results showed that compared with inbred varieties, hybrid rice increased grain yield by an average of 8.9%, and enhanced lodging index (LI) (increasing lodging risk with a higher LI) at the 1st (+23%) and 3rd (+17%) internodes with no significant effect at the 2nd internode. Inorganic nitrogen (N) fertilization increased both rice yield (+42%) and LI at the 2nd (+31%) and 3rd (+23%) internodes, but did not significantly affect LI at the 1st internode. The application of silicon (Si) and potassium (K) fertilizers increased rice yield by 7.2% and 18%, respectively, while simultaneously reducing LI by 14% and 19% at the 1st internode, by 15% and 21% at the 2nd internode, and by 4.5% and 18% at the 3rd internode. Prohexadione calcium and uniconazole increased rice yield by 6.7% and 8.3%, respectively, while paclobutrazol had no significant effect on rice yield. Prohexadione calcium and uniconazole reduced LI by 14% and 21% at the 1st internode, by 26% and 31% at the 2nd internode, and by 16% and 54% at the 3rd internode, respectively, whereas paclobutrazol only reduced LI at the 3rd internode by 12%. In conclusion, the application of Si, K, prohexadione calcium, and uniconazole is a promising strategy for improving rice yield and reducing lodging risk. In addition, we suggest that high-yielding practices (e.g., hybrid rice and inorganic N fertilization) and lodging-resistant practices (e.g., the application of Si, K, and PGRs) should be combined to increase grain yield and simultaneously reduce lodging risk in rice paddies.

To ascertain the effect of biochar on remediation of paddy soil contaminated by heavy metals under different irrigation regimes (flooding irrigation (FI), intermittent irrigation (II) and wet irrigation (WI)), rice straw biochar (RSB) and rice husk biochar (RHB) were applied into soil contaminated by Cd and Cu. The concentrations of available Cd and Cu were significantly reduced by RSB, and decreased by 6.8-15.9%, 11.1-20.0% and 6.8-18.2%, and 6.2-12.9%, 7.0-14.8% and 5.6-17.7% under FI, II and WI regimes, respectively. The application of RHB generally reduced the content of acid extractable and reducible Cd under FI and II regimes, and promoted its transformation to oxidizable and residual form. Similarly, both biochars reduced the acid extractable Cu in paddy soil and promoted its transformation to reducible and oxidizable form under three irrigation regimes (especially in II). This is significantly related to the increase of soil pH, organic matter content and cation exchange capacity by biochar. The preliminary results of this study indicate that biochar application combined with intermittent irrigation could be an effective measure to enhance the paddy soil quality. However, future studies are still needed to evaluate the long-term impact of biochar on heavy metal bioavailability under different water conditions.

Biochar can change the availability and morphology of soil Cd. However, the influence of biochar on Cd chemical form and subcellular fraction in rice is poorly understood, particularly under different irrigation methods. A pot experiment of biochar application combined with two irrigation methods (continuous flooding and intermittent irrigation, CF and II) was conducted. The Cd accumulation, chemical form and subcellular fraction in rice organs and the associated physiological responses were examined. Biochar significantly reduced soil available Cd (30.85–47.26% and 32.35–52.35%) under CF and II but increased the Cd content (30.4–63.88% and 13.03–18.59%) in brown rice. Additionally, the Cd content in shoots/grains under II was higher than that under CF. Biochar elevated the Cd soluble fraction in roots while lowered the cell wall fraction under both irrigation methods, whereas the opposite result was observed in leaves. Biochar increased water-, ethanol-, and NaCl-extractable Cd in roots meanwhile increased ethanol-extractable Cd in leaves under both irrigation methods. Moreover, the total amount of water-, ethanol-, and NaCl-extractable Cd in rice roots was higher under II than under CF. Related hormones and antioxidant enzymes may also be involved in biochar-mediated Cd accumulation in rice grains. Thus, changes in Cd chemical form and subcellular fraction in the root and leaf are the main mechanisms of biochar-induced rice grains Cd accumulation. Graphical Abstract

Abrupt drought-flood alternation is a frequent meteorological disaster that occurs during the summer in southern China. This study sought to clarify the composition of the bacterial community in the rhizosphere soil of rice under nitrogen (N) application after abrupt drought-flood alternation and to provide more basic data for understanding N absorption by the roots system under N application after abrupt drought-flood alternation. The activity of N metabolism enzymes and the N content and N accumulation in various organs improved under N application after abrupt drought-flood alternation. Between the T1_N and T1 comparison groups, 1758 differentially expressed genes were identified, including 1027 upregulated and 731 downregulated genes. Transcriptomic GO and KEGG analyses indicated that nitrate assimilation, response to bacterium, defence response to bacterium, and N compound metabolic processes were enriched. At the phylum level, Proteobacteria, Acidobacteria, Nitrospirota, and Gemmatimonadota were the dominant flora. The root glutamine synthetase activity was significantly negatively correlated with Nitrospirota. Nitrospirota is a key taxon regulating rice root N absorption under N application after abrupt drought-flood alternation. N application after abrupt drought-flood alternation promoted the rapid recovery ability of plants and improved the microbial environment in rice. This study preliminarily clarified the role of microorganisms in the root uptake of rice under N application after abrupt drought-flood alternation.

The aim of this study was to investigate the effect of biochar on Cd and Cu immobilization and bioavailability in soils with different acidity levels. Four dosages (0, 20, 40 and 60 g kg(-1); namely CK, C1, C2 and C3) of biochar produced from rice straw were applied into the soils with four acidity levels (pH 4.5, 5.0, 5.5 and 6.0; namely L1, L2, L3 and L4), the uptake and transport of Cd and Cu by rice and metal speciation dynamics in soil were investigated through the two-year pot experiment. The soil pH and organic matter under all the four acidity levels were significantly increased during the rice maturity stage in the second year after biochar application. Biochar mainly promoted the formation of oxidizable Cd, followed by reducible Cd, and decreased residual Cd content (except for the first-year in the jointing period) during the two consecutive years of rice growth. Biochar reduced the acid extractable Cu content (especially in L2 and L3), increased the oxidizable Cu content, and interconverted Cu between reducible and residual status. The content of Cd in different rice organs were reduced by biochar, and compared with CK, the two-year average reduction in brown rice was 38.12%, 58.07%, 50.99% and 36.45% under L1, L2, L3 and L4. The reduction effect of Cu content in brown rice by biochar was mainly reflected in the second year, which decreased by 17.52%, 20.17%, 20.63% and 9.74% respectively under the four acidity levels. Rice straw biochar can be used for Cd pollution control of rice grain in paddy soil with varied acidity levels. However, further studies are needed on how biochar promotes Cu transport from rice root to shoot.

Rice agriculture is both an important source of the potent greenhouse gas methane (CH4) and a bioaccumulator of cadmium (Cd), which is hazardous to human health. Avoiding flooding during rice production is effective for reducing CH4 emissions, but it increases rice Cd uptake. Although lime application decreases Cd concentration in rice grains, it is not clear whether combining appropriate water management with liming can simultaneously reduce CH4 emissions and Cd uptake in rice paddies. Thus, a pot experiment was performed to investigate the interactive effects of water management (F: continuous flooding, FDF: flooding - midseason drainage - flooding, FDI: flooding - midseason drainage - intermittent irrigation) and lime application on CH4 emissions and rice Cd uptake in an acid paddy soil spiked with Cd. Results showed that neither water management nor liming significantly affected grain yield. Overall, liming reduced CH4 emissions by 42.2%. Compared to F, the FDF and FDI treatments reduced CH4 emissions by 43.5% and 54.2%, respectively. Liming reduced CH4 emissions by 32.6% under F, but with a greater decrease of 48.6% and 52.7% under FDF and FDI, respectively. Overall, liming reduced rice Cd uptake by an average of 47.3%. Compared to FDI, F and FDF significantly reduced Cd uptake by 84.0% and 75.1%, respectively, but there was no significant difference between F and FDF. Liming did not significantly affect Cd uptake under F and FDF, whereas liming reduced Cd uptake by 55.9% under FDI. These results suggest that maintaining flooding following midseason drainage can help in reducing rice Cd uptake, though slightly promoting CH4 emissions. Therefore, we recommend FDF combined with liming to mitigate CH4 emissions without increasing rice Cd uptake in acid paddy soils.

Potted-seedling machine transplantation (PSMT) is an innovative method of mechanical rice transplanting to improve seedling quality and reduce mechanical injury relative to blanket-seedling machine transplantation (BSMT). However, the responses of yield, grain quality, and risk of lodging in rice to PSMT have not yet been comprehensively defined. Here, we present a meta-analysis of 67 peer-reviewed studies with 382 field observations to investigate the impacts of PSMT on rice yield, grain quality, and lodging resistance in mainland China. The results indicated that compared to BSMT, PSMT increased grain yield, aboveground biomass, and nitrogen uptake by an average of 8.4%, 6.2%, and 7.2%, respectively. PSMT boosted grain yield with hybrid rice (+10.2%) more strongly than with inbred rice (+6.9%). PSMT improved the brown rice rate (+0.74%), milled rice rate (+1.1%), head rice rate (+2.3%), and gel consistency (+4.4%) while reducing the amylose content by 3.7% with no significant effects on the chalky grain rate, chalkiness, length/width ratio, or protein content. The increase in the milled rice rate under PSMT was greater with hybrid rice than with inbred rice. PSMT reduced the lodging index at the first (−5.1%), second (−9.4%), and third (−8.0%) internodes. In conclusion, PSMT is a promising practice for simultaneously improving rice yield, milling quality, cooking and eating quality, and lodging resistance in paddies. In addition, the grain yield and milling quality of hybrid rice under PSMT are higher than those of inbred rice.

【Objective】Compared with continuous flooding, the water-saving irrigation can increase water use efficiency. However, the effects of water-saving irrigation on yield and quality in rice paddies have not been clearly defined. The objective of this study was to identify the systematic effects of water-saving irrigation on rice yield and quality through Meta-analysis techniques.【Method】In the present study, a total of 34 studies that adapted a water-saving treatment and continuous flooding as the control involving 263 paired observations were included across this dataset. The meta-analysis was conducted to identify the responses of yield and quality to water-saving irrigation as affected by experimental type, water-saving irrigation type, cropping system, rice type, the period of water-saving irrigation, soil total nitrogen (N), soil texture, N rate, and the number of N application.【Result】Overall, the water-saving irrigation did not significantly affect grain yield and quality relative to continuous flooding. In terms of water-saving irrigation type, the moderate water-saving irrigation increased brown rice rate (+0.9%), milled rice rate (+1.5%), and head milled rice rate (+2.3%), but did not affect grain yield, chalkiness percentage, chalkiness degree, length/width ratio, amylose content, gel consistency, and protein content relative to continuous flooding. However, the severe water-saving irrigation significantly decreased grain yield (-22.1%), brown rice rate (-2.7%), milled rice rate (-2.7%), and head milled rice rate (-3.6%), and increased chalkiness percentage (+28.0%) and chalkiness degree (+46.7%), while no marked differences were observed on length/width ratio, amylose content, gel consistency, and protein content. Furthermore, compared with continuous flooding, the water-saving irrigation reduced protein content (-9.8%) of late rice, but did not affect that of early rice, middle rice, and single rice.【Conclusion】Compared with continuous flooding, the moderate water-saving irrigation could improve rice milling quality, and did not affect grain yield, appearance quality, cooking and eating quality, and nutrition quality. The severe water-saving irrigation significantly reduced rice yield, milling quality, and appearance quality, while no significant effects were found on cooking and eating quality and nutrition quality. The results provided an insight to evaluate the responses of grain yield and quality to water-saving irrigation.

The activation of toxic heavy metals caused by soil acidification has shown detrimental effect on rice safety and quality in paddy soil of southern China. Previous reports have shown that biochar had great potential in controlling heavy metal pollution in soil, but the effect of biochar on soil fertility and heavy metal availability in different soil acidity levels remains unknown. In our study, rice straw (RSBC) and rice husk (RHBC) were selected to produce biochar. An incubation experiment with three biochar application rates, namely 0 (CK), 20 g kg−1 (C1), and 50 g kg−1 (C2) combined with four soil acidification levels, pH value 4.09 (L1), 4.48 (L2), 4.68 (L3), and 5.04 (L4), was conducted in this study. The soil pH, total nitrogen (N), soil organic matter (SOM), available phosphorus (P), available potassium (K), available Cu and Cd concentrations were determined after incubation for 60 days. Results showed that the RSBC is greater in improving the pH and nutrients in acidified soil than RHBC, and the increase depends on biochar dosage. Compared with RHBC, the RSBC showed greater performance in decreasing the availability of Cu and Cd in four soil acidity levels (L1, L2, L3, and L4); the available Cu reduced by 41.32, 25.09, 21.42, and 5.80%, and available Cd by 15.69, 13.73, 17.65, and 17.65%, respectively. In addition, higher soil acidification degree induced smaller increase range of soil pH and available P concentration by biochar. We suggest that biochar can be applied in acidified paddy field to remediate heavy metal pollution in Southern China rice production. At the same time, we need to further ascertain the impact of these two biochars on the bioavailability of heavy metals in different soil acidity levels.

In order to ascertain the effects of biochar on paddy soil fertility under different water management modes, two types of biochar as rice straw biochar (RSC) and rice husk biochar (RHC) were applied into two types of paddy soils, sandy loam (soil I) and silty loam (soil II). Five biochar application rates as 0 (CK), 5 (C1), 10 (C2), 20 (C3), and 50 (C4) g kg−1 were used under three water management modes, i.e., flooded irrigation (FI), intermittent irrigation (II), and wet irrigation (WI); all treatments are incubated for 60 days. The biochar application increased soil water holding capacity (WHC) (0.88–47.93%), pH (− 0.03–1.61 units), cation exchange capacity (CEC) (0.1–3.4 cmol kg−1), soil organic matter (SOM) (2.35–229.31%), total nitrogen (TN) (4.88–86.84%), available phosphorus (P) (0–171.74%), and potassium (K) (0.25–14.47 times). The increased nutrient content of soil I was higher than that of soil II, and the increase by RSC was significantly greater than that by RHC. In addition, the II mode or WI mode was more beneficial to increase soil pH, available P, and CEC. The water management modes, biochar types, and its dosage, as well as soil type and their interaction, had remarkable effects on soil improvement of paddy soil fertility. The study showed that biochar applied under intermittent and wet irrigation modes offers a good potential for the improvement of paddy soil fertility than flooding irrigation mode.