Rice-growing Season Research Articles

Enhanced As extraction from paddy soils with high As contamination risk by rice plant upon Si fertilization

Owing to flooded growing conditions and specific physiological characteristics, rice plant is more efficient in As uptake and accumulation, which provides a cost-effective and time-efficient pathway to deplete bioavailable As from paddy soils. In the present study, the enhancing effect of silicon (Si) fertilization on As extraction from heavily contaminated paddy soils by rice was explored Upon incorporation of one weak acid Si fertilizer (AcSF), soil As solubility was significantly promoted by 1.3–1.4-fold, while a slightly increase in porewater As was observed with alkaline soluble Si fertilizer Na2SiO3 (AlSF). With both Si fertilizers applied before transplanting, a relatively low Si/As molar ratio (<100) in soil porewater was obtained, As a result, soil As uptake by rice plant with Si fertilizers was enhanced by 37.2%–171.7% compared to control (CK). Notably, up to 91.6% of the total As in rice plant retained in root with Si fertilization, suggesting the importance of root removal. By harvesting the whole rice plant including roots, soil bioavailable As measured by diffusive gradients in thin films (DGT) declined by 26.9%–31.3% in AlSF treatments relative to CK. Total soil As depletion by the whole rice plant was significantly enhanced from 2.8% in CK to 7.0%–11.2% in Si fertilizer treatments. In this way, 197.5 mg As m−2-232.5 mg As m−2 could be eliminated from soil following one rice-growth season, which was 2.3–2.7-fold higher compared to CK. These results identified the effectiveness of soluble Si fertilizer in enhancing soil As depletion by rice from paddy soils with high As contamination risk, which could serve as a cost-effective strategy with little technical-restriction.

Comammox plays a functionally important role in the nitrification of rice paddy soil with different nitrogen fertilization levels

Chemoautotrophic ammonia-oxidizing bacteria (AOB), ammonia-oxidizing archaea (AOA), and the recently discovered complete ammonia oxidizers (comammox) catalyze ammonia oxidation; however, quantifying their individual gross ammonia oxidation activities in complex soil ecosystems remains elusive. In this study, we investigated the nitrifying population and community dynamics in response to fertilization in paddy soil under long-term treatment with different urea concentrations (0, 100, 200, and 300 kg N ha−1; designated N0, N100, N200, and N300, respectively). The community structure of nitrifiers, including comammox, was changed by long-term N fertilizers input, which also enhanced AOB abundance and comammox clade A/B abundance ratio, whereas it did not affect AOA abundance. Nevertheless, the microbial population sizes and community compositions remained largely similar following short-term fertilization throughout one rice-growing season. Furthermore, by employing a 15NO3− pool dilution technique in combination with chlorate and 1-octyne inhibition, we conducted a soil microcosm incubation without substrate supplementation to distinguish the relative contribution of comammox to gross ammonia oxidation from those of AOA and AOB. Comammox exhibited higher nitrification activity in soils treated with more N fertilizers, with the contribution increasing from 34 % (N0) to 75 % (N300), although its abundance was not dominant. This could be attributed to the repeated N-based fertilization, which reduced the soil pH, thereby decreasing the soil-free ammonia concentration. In contrast, the contribution of AOA declined from 57 % (N0) to 19 % (N300), while that of AOB only accounted for a minor fraction (<25 %) despite being in high abundance. Altogether, our findings provide evidence that the activity of nitrifying guilds is more valuable than their abundance and provide insights into the potential functional significance of comammox in the nitrification process in rice paddy systems.

N-loaded clinoptilolite under water-saving irrigation mitigates ammonia volatilization while increasing grain yield and water-nitrogen use efficiency

Minimizing ammonia volatilization (AV) in paddy fields can not only reduce nitrogen (N) loss but also prevent environmental pollution. While clinoptilolite has been shown to effectively decrease AV, it is important to note that natural clinoptilolite contains non-desorption active sites that can hinder soil N effectiveness, ultimately leading to decreased N utilization. Therefore, we proposed modifying clinoptilolite with a weakly acidic NH4Cl solution (N-loaded clinoptilolite, NZ) to replenish exogenous N while continuously reducing AV. A lysimeter experiment was conducted under two irrigation regimes (ICF: continuous flooding irrigation; IAWD: alternate wet-dry irrigation) to examine the effect of N-loaded clinoptilolite on soil N, water-N use, AV loss and grain yield over two rice-growing seasons in Northeast China. The results show that AWD significantly reduced AV during the basal fertilization period and the first top-dressing period in 2020 and 2021. Compared with the control (without N-loaded clinoptilolite), N-loaded clinoptilolite at 10 t·ha−1 (NZ10) significantly reduced the total AV by 29% and 33% in the two years, respectively, with the most significant reduction impact (30% and 36%) occurring in the first top-dressing period. NZ10 coupled with AWD regime reduced AV more significantly and compared with conventional management (ICFNZ0), IAWDNZ10 decreased the total amount of AV by 36% and 42% in two years, respectively. N-loaded clinoptilolite also increased the soil NH4+-N and NO3--N content during the tillering and grain-filling stages of rice, which in turn increased the rate of maximum N accumulation, shortened the duration, promoted N accumulation and translocation in rice plants, and finally reduced AV. Additionally, when compared to the control, the utilization of NZ10 under the AWD irrigation regime resulted in an average 29% reduction in irrigation water usage and a yield increase of 5% over two years. Thus, IAWDNZ10 was not only highly productive and water-efficient but also significantly reduced AV, making it an environmentally friendly and effective management model for on-farm practices.

Nutrient runoff loss from saline-alkali paddy fields in Songnen Plain of Northeast China via different runoff pathways: effects of nitrogen fertilizer types.

The application of nitrogen (N) fertilizer aggravates the nutrient runoff loss from paddy, causing serious agricultural non-point source pollution, and leading to a serious decline in water quality. The global area of saline-alkali paddy has expanded, but the response of nutrient loss via runoff to N-fertilizer applications in saline-alkali paddy is still unclear. This study conducted a 147-day field experiment to evaluate the nutrient runoff loss from saline-alkali paddy with different N-fertilizer application strategies in Songnen Plain of Northeast China. Regardless of N-fertilizer types, the nutrient loss via rainfall runoff in the entire rice-growing season was significantly (p < 0.05) higher than that via artificial drainage. The N and phosphorus (P) concentrations in runoff water were correlated with salinity and alkalinity. Especially, pH had a significant positive correlation with total-P (TP) (r = 0.658, p < 0.01). In the entire rice-growing season, the TN runoff losses in urea (U), microbial fertilizer (MF), and inorganic compound fertilizer (ICF) treatments were significantly (p < 0.05) lower compared with carbon-based slow-release fertilizer (CSF) and organic-inorganic compound fertilizer (OCF), respectively. Meanwhile, the TP runoff losses in OCF and ICF treatments were significantly (p < 0.05) lower than U and MF, respectively. Overall, the application of ICF is a better choice to avoid N and P losses via runoff from saline-alkali paddy fields.

Irrigation schedule impact on greenhouse gas mitigation, carbon sequestration, and yield improvement of double rice-cropping systems in southern China

The development of water-saving irrigation in paddy soils is crucial because of the increasing demand for water resources. There is a need to improve the understanding of water use strategies that save water and reduce greenhouse gas (GHG) emissions without causing yield losses in double rice-cropping systems. The current study was conducted to examine the net global warming potential (NGWP) and net greenhouse gas intensity (NGHGI) based on the net GHG emissions, including soil organic carbon (SOC) change and indirect emissions (IEs). An experiment was conducted under flood irrigation (FI), shallow irrigation (SI), and intermittent irrigation (II) conditions. The average double rice yields under the SI and II treatments were significantly higher than those under FI by 4.7% and 12.1%, respectively. The SI and II treatments could save 44% and 67% of irrigation water in the entire double-cropping rice-growing season, respectively. However, the SOC sequestration rate over 4 years was not significantly different among the three irrigation regimes. Compared to FI, the annual methane (CH4) emissions decreased by 34% and 45% under SI and II, respectively. In contrast, nitrous oxide (N2O) emissions under SI and II increased by 27% and 50%, respectively. IEs were nearly the same among the three irrigation regimes, with fertilizer use as the top contributor, and followed the order FI > SI > II. The NGWP and NGHGI decreased by 37% and 44%, respectively, under II compared to FI. In conclusion, water-saving irrigation strategies, especially the II practice, are an effective method that can simultaneously achieve great success in saving water, increasing rice production, and reducing GHG emissions.

Exogenous TiO2 Nanoparticles Alleviate Cd Toxicity by Reducing Cd Uptake and Regulating Plant Physiological Activity and Antioxidant Defense Systems in Rice (Oryza sativa L.)

Cadmium (Cd) is a potentially hazardous element with significant biological toxicity, negatively affecting plant growth and physio-biochemical metabolism. Thus, it is necessary to examine practical and eco-friendly approaches to reduce Cd toxicity. Titanium dioxide nanoparticles (TiO2-NPs) are growth regulators that help in nutrient uptake and improve plant defense systems against abiotic and biological stress. A pot experiment was performed in the late rice-growing season (July—November) 2022 to explore the role of TiO2-NPs in relieving Cd toxicity on leaf physiological activity, biochemical attributes, and plant antioxidant defense systems of two different fragrant rice cultivars, i.e., Xiangyaxiangzhan (XGZ) and Meixiangzhan-2 (MXZ-2). Both cultivars were cultivated under normal and Cd-stress conditions. Different doses of TiO2-NPs with and without Cd-stress conditions were studied. The treatment combinations were: Cd−, 0 mg/kg CdCl2·2.5 H2O; Cd+, 50 mg/kg CdCl2·2.5 H2O; Cd + NP1, 50 mg/kg Cd + 50 TiO2-NPs mg/L; Cd + NP2, 50 mg/kg Cd + 100 TiO2-NPs mg/L; Cd + NP3, 50 mg/kg Cd + 200 TiO2-NPs mg/L; Cd + NP4, 50 mg/kg Cd + 400 TiO2-NPs mg/L. Our results showed that the Cd stress significantly (p &lt; 0.05) decreased leaf photosynthetic efficiency, stomatal traits, antioxidant enzyme activities, and the expression of their encoding genes and protein content. Moreover, Cd toxicity destabilized plant metabolism owing to greater accretion of hydrogen peroxide (H2O2) and malondialdehyde (MDA) levels at vegetative and reproductive stages. However, TiO2-NPs application improved leaf photosynthetic efficacy, stomatal traits, and protein and antioxidant enzyme activities under Cd toxicity. Application of TiO2-NPs decreased the uptake and accumulation of Cd in plants and levels of H2O2 and MDA, thereby helping to relieve Cd-induced peroxidation damage of leaf membrane lipids by enhancing the activities of different enzymes like ascorbate peroxidase (APX), catalase (CAT), peroxidase (POS), and superoxide dismutase (SOD). Average increases in SOD, APX, CAT, and POS activities of 120.5 and 110.4%, 116.2 and 123.4%, 41.4 and 43.8%, and 36.6 and 34.2% in MXZ-2 and XGZ, respectively, were noted in Cd + NP3 treatment across the growth stages as compared with Cd-stressed plants without NPs. Moreover, the correlation analysis revealed that the leaf net photosynthetic rate is strongly associated with leaf proline and soluble protein content, suggesting that a higher net photosynthetic rate results in higher leaf proline and soluble protein content. Of the treatments, the Cd + NP3 (50 mg/kg Cd + 200 mg/L TiO2-NPs) performed the best for both fragrant rice cultivars under Cd toxicity. Our results showed that TiO2-NPs strengthened rice metabolism through an enhanced antioxidant defense system across the growth stages, thereby improving plant physiological activity and biochemical characteristics under Cd toxicity.

Effect of Irrigation Management and Transplanting Date on the Rice Production and Water Productivity

ABSTRACT Water supply via irrigation and other water sources during the rice-growing season is vital for obtaining reasonable yield. The present study was carried out to investigate the dual-interacted effects of different irrigation intervals and transplanting dates on the yield, yield components, and water productivity of rice (Hashemi cultivar). The study was conducted in a three replicated randomized complete block design (RCBD) with the split-plot arrangement in two growing seasons (spring and summer) of 2016 and 2017 at Rice Research Institute of Iran, Rasht. The main factor was irrigation at four levels (full flooding, 5-, 10-, and 15-day irrigation intervals), and the second factor was three transplanting dates (April 21st, May 11th, and May 31st). The productivity of irrigation water (WPI) and irrigation water + precipitation (WPI+R) was reported in terms of grain yield and biomass. The highest paddy yield was observed in flooding treatment (4271 kg per hectare) and the irrigation intervals of 5, 10, and 15 days with 3844, 3196, and 3264 kg/ha were in the next rank, respectively. According to the biomass yield, 15-day irrigation interval and flooding irrigation had the highest and lowest water irrigation productivity, respectively. In the study of different transplanting dates, the highest paddy yield (3795 and 3820 kg/ha, respectively) was observed on the May 11th, and May 31st transplanting dates, and the highest water productivity based on paddy and biomass yield was obtained in the April 21st transplanting date. Regarding grain and biomass yield of rice, water productivity, and water use, the five-day irrigation treatment resulted in the best crop grain and biomass yield on April 21st transplanting date.

The effects of no-tillage and conventional tillage on greenhouse gas emissions from paddy fields with various rice varieties

Rice (Oryza sativa L.) production worldwide strives to meet the challenges of the millennium and ensure food for the overgrown population. Improving traditional rice-growing techniques could effectively increase productivity, reduce water and fertilizer consumption, and mitigate greenhouse gas (GHG) emissions. The current study attempts to examine the effect of two rice cultivation (RC) methods, viz. conventional tillage (CT) and no-tillage (NT) and “rice varieties (RV), namely var. MTU 1010, var. IET 4786, var. IET 17430 and var. IET 9947″, on methane (CH4), nitrous oxide (N2O) and carbon dioxide (CO2) emissions during the rice-growing season (Kharif) in India. The results showed CH4 and CO2 fluxes were higher under the CT plots than under the NT plots. There was a trade-off between CH4 and N2O production in paddy fields (PF), with CT plots showing lower N2O flux than NT. The “CO2-eq emission (pGWP)” and “yield-scaled CO2-eq emission (YpGWP)” in NT were significantly lower compared to CT with increased rice yields (p < 0.05). Analysis of the energy budget showed that energy use was reduced to 41.67% when replaced with the NT method. When compared to CT cultivation, the energy saved through the NT cultivation was around 2.33 MJ for every kilogram of rice produced. The study showed that the NT is one of the promising methods that should be encouraged among farmers to curb GHG emissions and increase rice production.

Content Variation and Potential Runoff Loss Risk of Nutrients in Surface Water of Saline-Alkali Paddy in Response to the Application of Different Nitrogen Fertilizer Types

As the saline-alkali paddy area continues to grow, the nutrient (e.g., nitrogen (N) and phosphorus (P)) runoff loss is becoming more serious in the world. The N-fertilizer application affects the nutrient runoff loss risk in paddy. Selecting suitable fertilizer types to reduce nutrient loss is beneficial to agricultural sustainability. However, the effects of N-fertilizer application in saline-alkali paddy are not clear. This study measured the N and P concentration of surface water in saline-alkali paddy, using various N—fertilizer treatments (i.e., urea (U), urea with urease—nitrification inhibitors (UI), organic–inorganic compound fertilizer (OCF), carbon—based slow—release fertilizer (CSF), and no N fertilization (CK)). Based on the structural equation model, both phosphate (PO43−-P) and total−P (TP) concentrations had a positive influence on total-N (TN) concentration regardless of N−fertilizer types applied. Potential risks of ammonia—N (NH4+—N) and nitrate—N (NO3−—N) runoff losses were reduced in UI treatment, but the TN and TP losses were increased. At the panicle-initiation fertilizer stage, the NO3−−N, TN, and TP concentrations in CSF and OCF treatments were lower than U. The CSF application can control the TP runoff loss risk during the rice-growing season. UI should not be suggested for the control of nutrient runoff loss in saline-alkali paddy.

Ammonia volatilization, greenhouse gas emissions and microbiological mechanisms following the application of nitrogen fertilizers in a saline-alkali paddy ecosystem

The application of nitrogen (N) fertilizer can promote rice yield, but is accompanied by considerable quantities of ammonia (NH3) volatilization and greenhouse gas (GHG) emissions. The effect of N-fertilization to these gas emissions in saline-alkali paddy ecosystems is unclear. A 137-day mesocosm-scale experiment was carried out to clarify the effect of different N-fertilizer application strategies on NH3 volatilization and GHG emissions in saline-alkali paddy ecosystems and to determine the microbiological mechanisms. Five N-fertilizer treatments consisting of control without N-fertilizer (CK), urea (U), urea with urease-nitrification inhibitors (UI), organic–inorganic compound fertilizer (OCF) and carbon-based slow-release fertilizer (CSF) were established. During the entire rice-growing season, the cumulative NH3 emissions of UI, OCF and CSF treatments were 22.60–25.55 % significantly (p < 0.05) higher than U, respectively. The cumulative methane emissions in all N-fertilizer treatments were decreased by 9.23–28.24 % compared with CK. The cumulative carbon dioxide emissions were U > CSF > OCF > CK > UI, and the cumulative nitrous oxide (N2O) emissions were U > CSF > UI > CK > OCF. The global warming potential of UI was 5.39–32.35 % lower than all the other treatments. Compared with the other N-fertilizer treatments, the relative abundance of N-related functional bacteria (e.g., Sphingomonas and Alphaproteobacteria) in OCF treatment was increased, and the (nirS + nirK)/nosZ ratio was reduced, thereby decreasing the N2O emission. Overall, U is a better choice for controlling NH3 volatilization in saline-alkali paddy ecosystems, whereas UI and OCF are more beneficial for reducing GHG emissions.

Three years of biochar and straw application could reduce greenhouse gas and improve rice productivity

ABSTRACT Applying soil amendments such as biochar has been proposed as a means to improve soil properties and reduce greenhouse gas emission from agricultural soils. The objective of this study was to evaluate and compare the effects of biochar and straw application on rice yield, select soil properties, global warming potential (GWP), and greenhouse gas intensity (GHGI) over the 3-year period. The study treatments included control (CN), barley straw biochar (BC, 2,000 kg ha−1), barley straw (BS, 2,000 kg ha−1), and BC+BS (each 1,000 kg ha−1). During the rice-growing season, significant interactive effects of BC and BS treatment were observed in major soil properties. The average rice yields in BC, BS, and BC+BS treatments increased by 4.6%, 4.7%, and 18.7%, compared with CN treatment, respectively. Also, BC+BS treatment produced relatively stable yield during the 3-year study. Both BC and BS applications, either alone or in combination, lowered soil bulk density values compared to the CN treatment. Further, BC application produced a low total CH4 flux than other treatments. The total produced GWP over the 3 years occurred in the order: BS ≧ CN > BC+BS > BC treatment. These results clearly demonstrate the advantages of biochar and straw applications in improving rice yield and soil fertility while reducing GWP and GHGI.

Nitrogen migration and transformation in a saline-alkali paddy ecosystem with application of different nitrogen fertilizers.

With the increasing transformation of saline-alkali land into paddy, the nitrogen (N) loss in saline-alkali paddy fields becomes an urgent agricultural-environmental problem. However, N migration and transformation following the application of different N fertilizers in saline-alkali paddy fields remains unclear. In this study, four types of N fertilizers were tested to explore the N migration and transformation among water-soil-gas-plant media in saline-alkali paddy ecosystems. Based on the structural equation models, N fertilizer types can change the effects of electrical conductivity (EC), pH, and ammonia-N (NH4+-N) of surface water and/or soil on ammonia (NH3) volatilization and nitrous oxide (N2O) emission. Compared with urea (U), the application of urea with urease-nitrification inhibitors (UI) can reduce the potential risk of NH4+-N and nitrate-N (NO3--N) loss via runoff, and significantly (p < 0.05) reduce the N2O emission. However, the expected effectiveness of UI on NH3 volatilization control and total N (TN) uptake capacity of rice was not achieved. For organic-inorganic compound fertilizer (OCF) and carbon-based slow-release fertilizer (CSF), the average TN concentrations in surface water at panicle initiation fertilizer (PIF) stage were reduced by 45.97% and 38.63%, respectively, and the TN contents in aboveground crops were increased by 15.62% and 23.91%. The cumulative N2O emissions by the end of the entire rice-growing season were also decreased by 103.62% and 36.69%, respectively. Overall, both OCF and CSF are beneficial for controlling N2O emission and the potential risks of N loss via runoff caused by surface water discharge, and improving the TN uptake capacity of rice in saline-alkali paddy fields.

Changes in planting methods will change the potential distribution of rice in South China under climate warming

Evaluation of and adaptation to climate warming have become major challenges, given the profound impacts of climate warming and technical advances in rice cropping systems. However, the dual influences of climate warming and planting methods on rice production remain unclear. Here, we developed a methodological framework based on temperature-based rice growth season determination and GIS spatial analysis to quantify the effect of climate warming and improvements in planting methods (transplanting to direct seeding) on the potential distribution of rice cropping systems in South China from 1960 to 2017. The accumulated temperature during the potential growing period of rice increased significantly, and the safe season for rice production extended substantially, which resulted in northward and westward expansions of the planting boundaries for rice cropping systems over the past few decades. Significant changes in planting boundaries and potential planting areas were observed for early maturity double rice (DR_Early) because of climate warming. Since transplanting requires less thermal time compared to direct seeding in the main field, the planting boundaries of DR would shift southward because of planting methods change. The planting boundaries of DR_Early and medium maturity double rice (DR_Medium) changed significantly, moving on average 267 and 159 km southward, resulting in a 13.3% decrease in the study area. The dual analysis showed that the change in planting methods would shift the rice planting boundaries southward, offset the impact of climate warming, and reduce the rice planting areas by 4.0%. Therefore, improvements in planting methods should be considered when evaluating the effects of climate warming on agricultural systems. This research provides new insights that could be used to optimize rice cropping systems, improve the utilization efficiency of thermal resources and adapt to climate warming.

Real-Time Measurement of Atmospheric CO2, CH4 and N2O above Rice Fields Based on Laser Heterodyne Radiometers (LHR)

High-precision observations provide an efficient way to calculate greenhouse gas emissions from agricultural fields and their spatial and temporal distributions. Two high-resolution laser heterodyne radiometers (LHRs) were deployed in the suburb of Hefei (31.9°N 117.16°E) for the remote sensing of atmospheric CO2, CH4 and N2O above rice paddy fields. The atmospheric transmittance spectra of CO2, CH4 and N2O were measured simultaneously in real time, and the atmospheric total column abundance was retrieved from the measured data based on the optimal estimation algorithm, with errors of 0.7 ppm, 4 ppb and 2 ppb, respectively. From July to October, the abundance of CO2 in the atmospheric column that was influenced by emissions from rice fields increased by 0.7 ppm CH4 by 30 ppb, and by 4 ppb N2O. During the rice growth season, rice paddy fields play a role in carbon sequestration. CH4 and N2O emissions from paddy fields are negatively correlated. The method of baking rice paddy fields reduces CH4 emissions from rice fields, but N2O emissions from rice fields are usually subsequently increased. The measurement results showed that LHRs are highly accurate in monitoring atmospheric concentrations and have promising applications in monitoring emissions from rice paddy fields. In the observation period, rice paddy fields can sequester carbon, and CH4 and N2O emissions from rice fields are negatively correlated. The LHRs have strong application prospects for monitoring emissions from agricultural fields.

Methane emission under straw return is mitigated by tillage types depending on crop growth stages in a wheat-rotated rice farming system

Straw return (SR) is a recommended management practice to improve soil fertility, but often increases methane (CH4) emissions from rice paddies. Tillage type (before or after irrigation) will change the contact surface between soil and straw, as well as soil structure, but little is known about how tillage type affects CH4 emission under SR from rice fields. A field experiment using split-plot design (straw as main plot and tillage type as subplot) was conducted to quantify the interactive effects of SR and tillage type on CH4 emission from transplanting to jointing, jointing to booting, and booting to maturity stages of rice in 2018 and 2019 and its underlying mechanisms. The results showed that SR significantly increased CH4 emission throughout the rice growing season by 58.8% due to enhanced methanogenic activity compared with straw removal (S0). Cumulative CH4 emission from transplanting to booting stage accounts for 95% of that from the whole rice growth season. Dry tillage (tillage before irrigation, -W) mitigates CH4 emission under SR from transplanting to jointing stage due to lower mcrA abundance compared with wet tillage (tillage after irrigation, +W). However, +W mitigates CH4 emission from jointing to booting stage in the absence of significant interaction between straw and tillage type through improved soil aggregation and higher carbon accumulation compared with -W. Overall, S0 +W had lower CH4 emission by 18.3%− 36.5%, 42.9%− 52.7%, and 44.0%− 48.6% than S0-W, SR-W, and SR+W, respectively (P < 0.0.5). Our results emphasize the importance of adjusting paddy tillage method in mitigating CH4 emission boosted by straw incorporation.

Combining Controlled-Release Urea and Normal Urea to Improve the Yield, Nitrogen Use Efficiency, and Grain Quality of Single Season Late japonica Rice

Controlled-release urea (CRU) is widely adopted to improve yields and nitrogen use efficiencies (NUEs) in rice. However, there are few studies on the effects of the mixed application of CRU and normal urea (at different N ratios) on rice yield, nitrogen efficiency, and grain quality. A series of simplified fertilization modes (SFMs) were set up in 2018–2019. CRU with release periods of 80 days and 120 days were mixed with urea at N ratios of 7:3, 6:4, 5:5, 4:6, and 3:7 and applied during the rice-growing season. We determined the rice yield, dry matter accumulation, NUEs, and grain quality. The yields of SFM_80_6/4 (CRU with release periods of 80 days were mixed with urea at N ratios of 6:4) and SFM_120_5/5 (CRU with release periods of 120 days were mixed with urea at N ratios of 5:5) were 3.69% and 4.39% higher than that of fractionated urea (FU), respectively, across 2018 and 2019. Combining the application of controlled-release urea and normal urea improved the dry matter accumulation, nitrogen accumulation, and nitrogen uptake rate when compared with FU. SFMs improved the processing quality and appearance quality of rice grains and did not reduce the cooking and eating quality. SFM_80_6/4 and SFM_120_5/5 are a one-time fertilization mode with high yield, high efficiency, and good grain quality, which is worthy of further promotion and application.

Nutrient dynamics in water and soil under conventional rice cultivation in the Vietnamese Mekong Delta.

Background The evaluation of nutrient variability plays a crucial role in accessing soil potentials and practical intervention responses in rice production systems. Synthetic fertilizer applications and cultivation practices are considered key factors affecting nutrient dynamics and availability. Here, we assessed the nutrient dynamics in surface, subsurface water and soil under local water management and conventional rice cultivation practices in the Vietnamese Mekong Delta. Methods We implemented a field experiment (200 m 2) in the 2018 wet season and the 2019 dry season in a triple rice-cropping field. Eight samples of surface water, subsurface water (30-45 cm), and topsoil (0-20 cm) were collected and analysed during the rice-growing seasons. Results The results showed that N-NH 4 +, P-PO 4 3- and total P peaks were achieved after fertilizing. Irrespective of seasons, the nutrient content in surface water was always greater than that of subsurface water ( P < 0.001), with the exception of N-NO 3 -, which was insignificant ( P > 0.05). When comparing the wet and dry seasons, nutrient concentrations exhibited minor differences ( P > 0.05). Under conventional rice cultivation, the effects of synthetic fertilizer topdressing on the total N, soil organic matter (SOM), and total P were negligible in the soil. Higher rates of N fertilizer application did not significantly increase soil N-NH 4 +, total N, yet larger P fertilizer amounts substantially enhanced soil total P ( P < 0.001). Conclusions Under conventional rice cultivation, N-NH 4 +, P-PO 4 3- and total P losses mainly occur through runoff rather than leaching. While N-NO 3 - loss is similar in surface water and subsurface water. Notably, nutrient content in soil was high; whilst SOM was seen to be low-to-medium between seasons. Future work should consider the nutrient balance and dynamic simulation in the lowland soil of the Vietnamese Mekong Delta's paddy fields.

Interaction of lime application and straw retention on ammonia emissions from a double-cropped rice field

Ammonia (NH3) emissions are an important pathway of nitrogen (N) losses in rice paddies. Lime application and straw retention are common practices to enhance soil fertility in acidic soils. However, the interaction of lime and straw application on NH3 emissions from paddies remain unclear. Here, a factorial experiment was employed to examine the interactive effects of slaked lime (i.e., Ca(OH)2) and straw retention on NH3 emissions and NH3 emission factors (EFs) in a double-cropped rice field. The results showed that compared to unlimed treatments, liming promoted NH3 emissions and EFs by 98.6% and 90.2% in the early rice growth season, respectively, with increases of 16.3% and 15.7% in the late rice growth season. Relative to straw removal, straw retention increased NH3 emissions by 52.8% in the early rice growth season but did not alter EFs, while reducing NH3 emissions by 9.9% and EFs by 25.7% in the late rice growth season. Liming interacted with straw retention to increase NH3 emissions and EFs in the early rice growth season. Under straw retention, liming promoted NH3 emissions by 147.7% and EFs by 148.3%, whereas liming raised NH3 emissions and EFs only by 45.3% and 45.5% under straw removal, respectively. Liming had no significant interactions with straw retention on NH3 emissions and EFs in the late rice growth season. It is likely that the decomposition extent of straw can alter the response of NH3 emissions to liming. Thus, NH3 emission inventories should take into account the interaction of liming and straw retention and its dependence on rice growth seasons in double-cropped rice systems with acidic soils.

Direct and Indirect Effects of Planting Density, Nitrogenous Fertilizer and Host Plant Resistance on Rice Herbivores and Their Natural Enemies

In rice ecosystems, seeding densities can be adjusted to compensate for lower nitrogen levels that reduce GHG emissions, or to increase farm profitability. However, density-induced changes to plant anatomy could affect herbivore-rice interactions, and alter arthropod community dynamics. We conducted an experiment that varied transplanting density (low or high), nitrogenous fertilizer (0, 60 or 150 kg added ha−1) and rice variety (resistant or susceptible to phloem-feeding insects) over two rice-growing seasons. Yields per plot increased with added nitrogen, but were not affected by variety or transplanting density. Planthopper and leafhopper densities were lower on resistant rice and in high-density field plots. Nitrogen was associated with higher densities of planthoppers, but lower densities of leafhoppers per plot. High planting densities and high nitrogen also increased rodent damage. The structure of arthropod herbivore communities was largely determined by season and transplanting density. Furthermore, two abundant planthoppers (Sogatella furcifera (Horváth) and Nilaparvata lugens (Stål)) segregated to low and high-density plots, respectively. The structure of decomposer communities was determined by season and fertilizer regime; total decomposer abundance increased in high-nitrogen plots during the dry season. Predator community structure was determined by season and total prey abundance (including decomposers) with several spider species dominating in plots with high prey abundance during the wet season. Our results indicate how rice plasticity and arthropod biodiversity promote stability and resilience in rice ecosystems. We recommend that conservation biological control, which includes a reduction or elimination of insecticides, could be promoted to attain sustainable rice production systems.

Polymer-coated urea application can increase both grain yield and nitrogen use efficiency injaponica-indicahybrid rice

AbstractWe investigated whether the one-time application of polymer-coated urea (PCU) before transplanting could simultaneously improve the grain yield and nitrogen use efficiency (NUE) ofjaponica-indicahybrid rice (JIHR) through a field experiment. The local high-yield JIHR cultivar Chunyou-927 was field grown during the rice-growing seasons in 2019 and 2020. The experiment consisted of three treatments: no nitrogen application (0N), application of conventional urea (CU), and the one-time application of PCU. Grain yield was 1.0–1.3 t/ha higher, and agronomic NUE (kg grain yield increase per kg N applied) was 5.2–5.9 kg/kg higher, respectively, under the PCU treatment compared with the CU treatment across the two study years. When compared with the CU treatment, the PCU treatment could (1) improve root morphological trait, (2) reduce redundant vegetative growth during the early growth period, (3) increase matter production during the mid and late growth period, and (4) increase plant activity during the grain-filling period. Overall, our findings indicate that one-time PCU application before transplanting of the JIHR cultivar holds great promise for increasing grain yield and NUE.