Search Results (92)

Sustainable rice production requires management strategies that reduce drainage-related nitrogen export while maintaining grain yield under increasingly constrained water and labor conditions. This study evaluated a controlled-irrigation-based integrated management regime in direct-seeded and mechanically transplanted rice under production-field conditions in the lower Yangtze River region, China. The optimized regime combined threshold-based controlled irrigation, functional basal fertilizer, and key-stage foliar regulation, whereas the traditional treatments followed local conventional flooding and fertilization practices. Drainage-related total nitrogen (TN) export was mainly associated with rainfall or irrigation-overflow events after fertilization. Compared with the corresponding traditional treatments, optimized management reduced irrigation input by 28.5% and 26.4%, cumulative drainage volume by 54.8% and 46.5%, and monitored-event TN export load by 63.6% and 60.0% in mechanically transplanted and direct-seeded rice, respectively. Grain yields reached 10,088 and 9870 kg ha⁻¹ in Opt-MT and Opt-DS, increasing by 6.5% and 7.2%, respectively. The optimized treatments also reduced chalky grain rate and chalkiness degree, although head rice rate did not improve synchronously. These findings provide field-based evidence that integrated management may help coordinate monitored drainage-related nitrogen-export mitigation, water-saving irrigation, and yield maintenance under similar production-field conditions. Full article

The persistence of cadmium (Cd) immobilization in acidic paddy soils is exacerbated by acidification and fluctuating redox conditions that promote Cd re-mobilization. While biochar is a promising amendment, its long-term efficacy in Cd immobilization relative to conventional lime and the underlying mechanisms remain incompletely resolved. This study tested the hypothesis that biochar’s superior effect lies in its durable enhancement of soil pH buffering capacity (pHBC), not merely in increasing initial pH. Using six acidic paddy soils amended with three biochars (corn straw, peanut straw, and seeded sunflower plate) and pH-matched lime [Ca(OH)₂] controls, we quantified pHBC changes, resistance to simulated acidification, and Cd dynamics during a flooding-drying cycle. Results showed that biochar amendments increased pHBC by 24.7–110%, significantly more than lime. Under acid stress, biochar-treated soils maintained higher pH and released 40–85% less soluble and extractable Cd than lime controls at equivalent pH range. Correlation and regression analyses established that the biochar-induced change in pHBC (ΔpHBC) was the strongest predictor of reduced Cd availability, exerting twice the influence of native soil pHBC. During the redox cycle, enhanced pHBC directly attenuated soil re-acidification upon drainage, minimizing Cd re-mobilization. Thus, the durable enhancement of soil pHBC is the central mechanism for biochar’s sustained Cd immobilization, advocating a strategic shift from transient pH adjustment to building inherent soil buffering resilience for long-term remediation security. Full article

Chieng Hac in northern Vietnam is expanding maize cultivation, intensifying water competition and soil erosion. This study mapped regional water balance and erosion using remote sensing and GISs by coupling the Thornthwaite–Mather (TM) water balance model with the Revised Universal Soil Loss Equation (RUSLE) at 12.5 m resolution. Land cover was classified into maize, tree crops, paddy, forest, and other types using Random Forest. The TM model used 2021 precipitation and temperature measurements to estimate evapotranspiration, surplus, and deficit, while the RUSLE quantified soil loss. Two scenarios were evaluated: a baseline reflecting existing land use and an adjusted case applying strip cropping on 10–20° maize slopes and converting maize to tree crops on slopes > 20°. Tree crop conversion increased evapotranspiration and prolonged seasonal deficits relative to maize, increasing water deficit from 1013.6 to 1022.2 mm/year. In contrast, the interventions reduced mean soil loss from 15.52 to 11.51 t/ha/year, with the largest decline in the 5–25 t/ha/year class. Residual hotspots persisted on steep slopes and near drainage lines. The integrated framework highlights trade-offs between erosion control and seasonal water availability, supporting slope-based land-use planning in upland agricultural systems. These findings offer guidance for slope-based land-use planning by indicating that intervention priorities should vary depending on slope conditions and local water availability. Full article

To address the challenge of optimizing hydrological parameters for nitrogen pollution control in paddy polders, this study coupled the Stella eco-dynamics model with an external optimization algorithm and developed a nonlinear programming framework using the water surface ratio and inflow rate as decision variables and the maximum nitrogen removal rate as the objective function. The simulation and optimization conducted for the Hongze Lake polder area indicated that the model exhibited strong robustness, as verified through Monte Carlo uncertainty analysis, with coefficients of variation (CV) of nitrogen outlet concentrations all below 3%. Under the optimal regulation scheme, the maximum nitrogen removal rates (${\eta }_1$, ${\eta }_2$, and ${\eta }_4$) during the soaking, tillering, and grain-filling periods reached 98.86%, 98.74%, and 96.26%, respectively. The corresponding optimal inflow rates ($Q^{*}$) were aligned with the lower threshold limits of each growth period (1.20, 0.80, and 0.50 m³/s). The optimal channel water surface ratios ($A_1^{*}$) were 3.81%, 3.51%, and 3.34%, respectively, while the optimal pond water surface ratios ($A_2^{*}$) were 19.94%, 16.30%, and 17.54%, respectively. Owing to the agronomic conflict between “water retention without drainage” and concentrated fertilization during the heading period, the maximum nitrogen removal rate (${\eta }_3$) during this stage was only 37.34%. The optimal channel water surface ratio ($A_1^{*}$) was 2.37%, the pond water surface ratio ($A_2^{*}$) was 19.04%, and the outlet total nitrogen load increased to 8.39 mg/L. Morphological analysis demonstrated that nitrate nitrogen and organic nitrogen dominated the outlet water body. The “simulation–optimization” coupled framework established in this study can provides quantifiable decision-making tools and methodological support for the precise control and sustainable management of agricultural non-point source pollution in the floodplain area. Full article

Electron transfer (ET) is a foundational biogeochemical process in paddy soils, distinctively molded by alternating anaerobic-aerobic conditions from flooding-drainage cycles. Despite extensive research on heavy metal(loid) (denoted as “HM”, e.g., As, Cd, Cr, Hg) dynamics in paddies, ET has not been systematically synthesized as a unifying regulatory mechanism, and the trade-offs of ET-based mitigation strategies remain unclear. These critical gaps have drastically controlled HMs’ mobility, which further modulates bioavailability and subsequent accumulation in rice (Oryza sativa L., a staple sustaining half the global population), posing substantial food safety risks. Alongside progress in electroactive microorganism (EAM) research, extracellular electron transfer (EET) mechanism delineation, and soil electrochemical monitoring, ET’s role in orchestrating paddy soil HM dynamics has garnered unparalleled attention. This review explicitly focuses on the linkage between ET processes and HM biogeochemistry in paddy ecosystems: (1) elucidates core ET mechanisms in paddy soils (microbial EET, Fe/Mn/S redox cycling, organic matter-mediated electron shuttling, rice root-associated electron exchange) and their acclimation to flooded conditions; (2) systematically unravels how ET drives HM valence transformation (e.g., As(V) to As(III), Cr(VI) to Cr(III)), speciation shifts (e.g., exchangeable Cd to oxide-bound Cd), and mobility changes; (3) expounds on ET-regulated HM bioavailability by modulating soil retention capacity and iron plaque formation; (4) synopsizes ET-modulated HM accumulation pathways in rice (root uptake, xylem/phloem translocation, grain sequestration); (5) evaluates key factors (water management, fertilization, straw return) impacting ET efficiency and associated HM risks. Ultimately, we put forward future avenues for ET-based mitigation strategies to uphold rice safety and paddy soil sustainability. Full article

The intensification of extreme rainfall events under changing climate regimes has heightened concerns over nutrient losses from paddy agriculture, particularly nitrogen (N), a primary contributor to non-point source pollution. Despite advances in drainage management, limited studies have integrated probabilistic rainfall modeling with N transport simulation to evaluate mitigation strategies in rice-based systems. This study addresses this critical gap by coupling the Log-Pearson Type III (LP-III) distribution with the DRAINMOD-N II model to simulate N dynamics under varying rainfall exceedance probabilities and drainage design configurations in the Kunshan region of eastern China. The DRAINMOD-N II showed good performance, with R² values of 0.70 and 0.69, AAD of 0.05 and 0.39 mg L⁻¹, and RMSE of 0.14 and 0.91 mg L⁻¹ for NO₃⁻-N and NH₄⁺-N during calibration, and R² values of 0.88 and 0.72, AAD of 0.06 and 0.21 mg L⁻¹, and RMSE of 0.10 and 0.34 mg L⁻¹ during validation. Using around 50 years of historical precipitation data, we developed intensity–duration–frequency (IDF) curves via LP-III to derive return-period rainfall scenarios (2%, 5%, 10%, and 20%). These scenarios were then input into a validated DRAINMOD-N II model to assess nitrate-nitrogen (NO₃⁻-N) and ammonium-nitrogen (NH₄⁺-N) losses across multiple drain spacing (1000–2000 cm) and depth (80–120 cm) treatments. Results demonstrated that NO₃⁻-N and NH₄⁺-N losses increase with rainfall intensity, with up to 57.9% and 45.1% greater leaching, respectively, under 2% exceedance events compared to 20%. However, wider drain spacing substantially mitigated N losses, reducing NO₃⁻-N and NH₄⁺-N loads by up to 18% and 12%, respectively, across extreme rainfall scenarios. The integrated framework developed in this study highlights the efficacy of drainage design optimization in reducing nutrient losses while maintaining hydrological resilience under extreme weather conditions. Full article

Climate change is expected to increase the frequency of extreme soil moisture events, such as winter waterlogging followed by spring drought, particularly in temperate regions of Europe, North America and Northeast China. While N₂O emissions from paddy soils under waterlogging and subsequent drainage have been widely studied, knowledge of upland arable soils under wheat cultivation remains limited. We hypothesized that: (1) in upland soils, combined waterlogging and drought reduces N₂O emissions compared to continuous waterlogging, and (2) plant presence mitigates soil nitrate accumulation and N₂O emissions across different moisture regimes. A greenhouse experiment was conducted using intact upland soil cores with and without wheat under four moisture treatments: control (60% water-holding capacity, WHC), drought (30% WHC), waterlogging, and waterlogging followed by drought. Daily and cumulative N₂O fluxes, soil mineral nitrogen (NH₄⁺-002DN and NO₃⁻-N), and total nitrogen uptake by wheat shoots were measured. Prolonged waterlogging resulted in the highest cumulative N₂O emissions, whereas the transition from waterlogging to drought triggered a sharp but transient N₂O peak, particularly in soils without plants. Wheat presence consistently reduced N₂O emissions, likely through nitrate uptake, which limited substrate availability for incomplete denitrification. Moisture regimes strongly affected nitrate dynamics, with drought promoting nitrate accumulation and waterlogging enhancing nitrate loss. These findings highlight the vulnerability of upland soils in regions prone to seasonal moisture extremes. Effective management of soil moisture and nitrogen, including the promotion of plant growth, is essential to mitigate N₂O emissions and improve nitrogen use efficiency under future climate scenarios. Full article

This study evaluated the growth characteristics and yield of rice under various water management strategies in an environmentally friendly paddy field in Korea from 2022 to 2024. The water management treatments included mid-season drainage (MD) lasting for 2, 3, or 4 weeks, followed by either low-level water management (maintaining a 4 cm water depth, denoted as “1”) or alternate wetting and drying irrigation (4 cm irrigation followed by drying, denoted as “2”) until harvest. The conventional treatment consisted of continuous flooding (CF). Treatments with poor yields (4MD1 and 4MD2) were discontinued in subsequent years. The rice cultivar Saecheongmu was transplanted in June, and water management began in July. Among the treatments, CF produced the highest number of mean panicles, whereas the 2MD2 treatment showed the most favorable yield components. The highest mean grain yield was recorded in 2MD2, with values of 5.85, 5.74-, and 5.38-tons ha⁻¹ over the three years—representing a 7.8–15.0% increase compared to CF. Across all treatments, MD1 consistently produced higher yields than MD2. Water use was lowest in 2MD2, achieving a 61.8% reduction compared to CF. Overall, the 2MD2 treatment emerged as the most promising strategy, effectively reducing water use by 61.8% while maintaining high yields comparable to those under continuous flooding. Full article

To investigate differences in water and salt transport during irrigation, freezing, and thawing periods in typical saline-affected paddy fields and saline-affected upland fields, field-based automated in situ monitoring was conducted in both types of saline-affected farmland (May 2023 to May 2024). Correlation analysis identified seasonal drivers of water–salt migration, while the HYDRUS-3D model simulated transport and equilibrium processes. The HYDRUS-3D model, equipped with a freeze–thaw module, accurately simulated complex water–salt transport in cold arid regions. Key findings include: (1) During freeze–thaw periods, soil moisture content and electrical conductivity (Ec) increased with the retreating frost front in both upland and paddy soils. During the irrigation period, maximum soil moisture content and Ec values occurred at 80 cm depth in dryland soils and 60 cm depth in paddy soils, primarily influenced by irrigation and capillary rise. (2) Groundwater salt ions significantly affected soil salinization in both farmland types. During the freeze–thaw period, Ec positively correlated with soil temperature. During the irrigation period, Ec positively correlated with evapotranspiration and negatively correlated with precipitation. (3) Salt changes during the irrigation, freezing, and thawing periods were −565.4, 326.85, and 376.55 kg/ha for upland fields, respectively; corresponding changes for paddy fields were −1217.0, 280.07, and 299.35 kg/ha. (4) Both land types exhibited reduced salinity during the irrigation period, with paddy fields showing a reduction 3.36 times greater than dryland fields. During the freezing and thawing periods, both land types experienced salinity accumulation, with dryland fields accumulating higher salinity levels than paddy fields. These results indicate that paddy field irrigation and drainage systems help mitigate salinization, while dryland fields are more prone to springtime salt accumulation. These findings provide a basis for developing targeted management strategies for saline–alkali soils. Full article

Rice is a major dietary component for more than half of the world’s population, and its cultivation requires a careful balance of nutrients to ensure high yields and sustainable practices. Soil-derived N₂O fluxes represent a major environmental challenge with global implications. While agriculture is a necessary activity to feed a growing population, it must evolve to minimize its ecological footprint. This review provides an update on the effects of nitrogen fertilizer application, such as ammonium nitrate (NH₄NO₃), urea (CO(NH₂)₂), ammonium sulfate ((NH₄)₂SO₄), and calcium ammonium nitrate (CAN), on N₂O emissions from rice cultivation. The role of various nitrification inhibitors (e.g., dicyandiamide (DCD), 2-chloro-6-(trichloromethyl) pyridine (nitrapyrin) and 3,4-dimethylpyrazole phosphate (DMPP)) in minimizing the release of N₂O from soils to the atmosphere was also discussed. Here, we described N₂O production by nitrification and denitrification processes in the paddy rice field, and then summarized the strategies, such as optimized fertilizer use, improved drainage and water management, and the use of organic amendments, that can enhance crop productivity while promoting sustainable reductions in N₂O emissions. Full article

This study developed an efficient cultivation strategy for cabbage production in paddy fields. To address poor drainage, discarded coir substrates (CS) were reused and compared with conventional paddy soil (PS). Four irrigation levels (ETc140, ETc100, ETc60, and ETc0) were applied to both CS and PS to evaluate their interactive effects. An automated irrigation system was deployed, integrating a weather sensor and solenoid valves via a LoRa-based IoT network. Hourly ET₀ was calculated based on Penman–Monteith in real time, and an irrigation event was triggered when cumulative ET₀ reached 1 mm (CS) or 3 mm (PS). The automated irrigation system showed stable performance. Hourly ET₀ estimates were 97% consistent with Korea Meteorological Administration data. The actual total irrigation depth (ID_actual) remained within 2% of the calculated depth (ID). Under moderate irrigation depths (ETc60 and ETc100), the reuse of CS significantly improved cabbage photosynthetic efficiency. Both CS-ETc60 and CS-ETc100 treatments maintained superior yield performance compared with other treatments. This integrated strategy not only offers a practical solution for improving water use efficiency but also enhances the multifunctional utilization of paddy fields, supporting the transition toward more sustainable agricultural practices. Full article

Cadmium (Cd) mobilization in paddy soils during redox fluctuations poses significant risks to rice safety. This study investigated the efficacy of nano-calcium carbonate (NCC), nano-hydroxyapatite (NHAP), and their composite (C+P) in immobilizing Cd under simulated flooding–drainage cycles. Soil treatments (0.5% and 1.0% w/w) were subjected to 40 day anaerobic and 20 day aerobic incubation. The results demonstrated that NCC and C+P elevated the soil pH by 1.35–1.39 and 0.72–1.01 units during the anaerobic and aerobic phases, respectively. These amendments suppressed Fe(II) and Mn(II) release by 41–75%, correlating with reduced Cd bioavailability. While nanomaterials minimally influenced Cd speciation during flooding, aerobic conditions triggered a marked shift: residual Cd fractions increased by 80.8–116.4% under NCC, driven by CdCO₃ precipitation and phosphate complexation. Cd release rates decreased by 53.6–66.8% in NCC and C+P treatments during oxidation. Microbial analysis revealed diminished bacterial diversity but enriched Firmicutes (up to 58.9%), which positively correlated with pH and residual Cd. Redundancy analysis identified pH and Fe/Mn dynamics as key regulators of the microbial community structure. NCC emerged as the most effective amendment. This study highlights the potential of NCC-based strategies for mitigating Cd risks in acidic paddy soils, particularly during post-flooding drainage. Full article

This study aimed to reveal the characteristics of returned water in paddy fields at different scales and the rules of its reuse in China’s Ganfu Plain Irrigation District through multiscale (field, lateral canal, main canal, small watershed) observations, thereby optimizing water resource management and improving water use efficiency. Subsequent investigations during the 2021–2022 double-cropping rice seasons revealed that the tillering stage emerged as a critical drainage period, with 49.5% and 52.2% of total drainage occurring during this phase in early and late rice, respectively. Multiscale drainage heterogeneity displayed distinct patterns, with early rice following a “decrease-increase” trend while late rice exhibited “decrease-peak-decline” dynamics. Smaller scales (field and lateral canal) produced 37.1% higher drainage than larger scales (main canal and small watershed) during the reviving stage. In contrast, post-jointing-booting stages showed 103.6% higher drainage at larger scales. Return flow utilization peaked at the field-lateral canal scales, while dynamic regulation of Fangxi Lake’s storage capacity achieved 60% reuse efficiency at the watershed scale. We propose an integrated optimization strategy combining tillering-stage irrigation/drainage control, multiscale hydraulic interception (control gates and pond weirs), and dynamic watershed storage scheduling. This framework provides theoretical and practical insights for enhancing water use efficiency and mitigating non-point source pollution in plain irrigation districts. Full article

Non-point source (NPS) pollution from agriculture accounts for more than 20% of the total pollution load in the Republic of Korea, with the highest nutrient balance among OECD countries. Rice paddy fields are among the most important NPSs because of their large area, intensive fertilizer use, intensive use of irrigation water, and subsequent drainage. Therefore, the use of controlled drainage in paddy fields (Test) was evaluated for reduction in the discharged volumes and pollutant loads in drainage and stormwater runoff in comparison to plots using traditional drainages (Control). The results show that the loads were highly variable and that the reductions in the annual load of biochemical oxygen demand (BOD), suspended solid (SS), total nitrogen (T-N), total phosphorus (T-P), and total organic carbon (TOC) in the Test compared to that of the Control were 31.0 ± 28.9%, 83.5 ± 11.8%, 65.4 ± 12.2%, 69.1 ± 21.7%, and 64.9 ± 12.9%, respectively. It was shown that discharge in the post-harrowing and transplanting drainage (HD) was predominantly responsible for the total loads; therefore, the load reduction in HD was evaluated further at additional sites. The reduction at all studied sites was highly variable and as follows: 30.0 ± 33.6%, 70.9 ± 24.6%, 32.2 ± 45.5%, 45.7 ± 37.0%, and 27.0 ± 71.5%, for BOD, SS, T-N, T-P, and TOC, respectively. It was also demonstrated that controlled drainage contributed significantly to reducing the loads and volume of stormwater runoff from paddy fields. Correlations between paddy field conditions and multiple regression showed that the loads were significantly related to paddy water quality. The results of this study strongly suggest that controlled drainage is an excellent alternative for reducing the discharge of NPS pollutants from paddy fields. It is also suggested that the best discharge control would be achieved by combinations of various discharge mitigation alternatives, such as the management of irrigation, drainage, and fertilization, as well as drainage treatment, supported by more field tests, identification of the fates of pollutants, effects of rainfall, and climate changes. Full article

This study investigated the impact of the response mechanism of tillage construction on paddy yield in black soil fields by adopting four mechanical tillage techniques, namely, rotary tillage (RT), shallow plowing (SP), deep plowing (DP), and culvert pipe drainage (CD), to solve the problems associated with the reduction in the effective tillage layer in black soil paddy fields, as well as the poor quality and low yield of paddy rice. The results showed that SP, DP, and CD techniques were able to increase the rice yield and improve the effective tillage layer of the soil and the soil structure. Among them, DP had the most obvious effect, compared with traditional RT; the fast-acting N was 37.27 mg/kg higher in the 20–30 cm soil layer, and the soil solid phase decreased by 1.86–3.90% in the soil tripartite ratio. The soil bulk density of DP in the 10–20 cm soil layer decreased by 0.08 g/cm³, and, in the 20–30 cm soil layer, it decreased by 0.03 g/cm³. These physicochemical properties promoted the development and growth of roots and increased the growth of the root system by 6.53–16.33%, with the yield also increased by up to 9.81%. The CD technique could improve paddy field drainage and increase crop yields. This study combines four mechanical tillage techniques and proposes a mechanism of tillage construction from soil structure improvement to soil physicochemical property enhancement, and then to root system and yield enhancement. This mechanism may help to guide the implementation of mechanical tillage methods in paddy fields, which will provide important insights for future agricultural practices. Full article