Rice-wheat Rotation Research Articles

Optimizing nitrogen application and sowing date can improve environmental sustainability and economic benefit in wheat-rice rotation

CONTEXTIn wheat-rice rotation, late sowing and excessive nitrogen (N) application lead to low annual yield and additional fertilizer waste. A comprehensive assessment of yield sustainability, N use efficiency, N balancing mechanism, and economic benefit is urgent. OBJECTIVETo explore the feasibility of optimizing N application and sowing date to improve yield, N use efficiency, and economic benefit in wheat-rice rotation. METHODSA two-year experiment of wheat-rice rotation was conducted in China, involving four N application rates (0, 180, 240, and 300 kg ha−1), three sowing dates (normal, delayed, and late sowing), three planting density (1.2 × 104, 1.8 × 104, and 2.4 × 104 seeds ha−1) for wheat (Yangmai-23), and four N application rates (0, 135, 270, and 405 kg ha−1), three sowing dates (normal, delayed, and late sowing), and three varieties (Yongyou-2640, Wuyunjing-32, and Nanjing-9108) for rice. Treatments were imposed in a split-plot experiment design with three replications (except N0). Soil information, N uptake, and yield were obtained through field survey and sampling. In addition, N balance was studied based on measured data and Denitrification-Decomposition (DNDC) model. Reactive N emissions (NH3, N2O, and NO) simulated by DNDC were converted into environmental damage costs for annual economic analysis. RESULTS AND CONCLUSIONSDelaying sowing could reduce annual yield from 6.14% to 13.72%, while appropriate N application can mitigate this trend. However, delaying sowing promoted soil N accumulation and yield sustainability. N fertilizer addition and late sowing would reduce annual N physiologic efficiency by 45.98%, N recovery efficiency by 42.02%, and N agronomic efficiency by 68.10%, leading to N surplus. Applying more N not only increased annual yield (24.85%–39.44%) and profit (74.27%–162.16%) but also brought more reactive N damage cost (7.40%–25.14%). In this study, the appropriate N application rate for delayed sowing (WR-S2) and late sowing (WR-S3) were 510–705 kg N ha−1 and 315–510 kg N ha−1, respectively. SIGNIFICANCEOptimizing N fertilizer and sowing date is an easy-followed strategy for improving yield, N use efficiency, and economic benefit in wheat-rice rotation, which is highly-consistent with United Nations Sustainable Development Goals. This strategy is simple to implement for policy formulation on precision agriculture and highly-effective to manage.

STUDY OF SURFACE CH4 FLUX EMISSION FROM GOSAT SATELLITE DATA OVER SELECTED AGRO-ECOSYSTEMS IN INDIA

The present study was carried out to characterize and quantify the seasonal behaviour of surface CH4 emissions from L4A product over two selected irrigated agro-ecosystems in India over sub-humid region of Indo-Gangetic Plain (IGP) and semi-arid region of Gujarat Plain and Hills Region (GPHR). Satellite data of Greenhouse Gases Observing SATllite (GOSAT) with L4A data product has been used with a cluster of contiguous grids of 3 x 3 within the Region of Interest (ROI) representing agricultural land uses spread over trans, upper, middle and lower part of IGP for analysis. The seasonal behaviour was studied for three agricultural years of June 2009 to May 2012 through time series plots of monthly means of each ROI. The annual CH4 emission from agricultural region using GOSAT data was found to be about 8-9 Mt CH4 which was about three times higher than reported over rice system in India using sparse ground samplings. The IGP showed the highest annual mean (88.11 mg CH4 d-1m-2) of surface emission in Lower Gangetic Plain Region (LGPR) and the lowest annual mean (7.01 mg CH4 d-1m-2) in Trans-Gangetic Plain Region (TGPR). These sub-humid irrigated agricultural regions with rice-wheat rotation showed substantially higher emissions than those in semi-arid irrigated agriculture (10.38 mg CH4 d-1m-2 to 11.32 mg CH4 d-1m-2) in GPHR. In IGP for an agricultural growing year (June 2009 to May 2010), the mean of CH4 emissions for kharif (June to October) season showed higher emission flux with 51.04 mg CH4 d-1m-2 than in rabi (November to April) Season (14.31 mg CH4 d-1m-2), but coefficient of variation was found to be more in rabi season (77.8%) than in kharif (39.3%) season. In GPHR region for same year, the annual mean of CH4 emissions for kharif and rabi season were 14.26 mgCH4 d-1m-2 and 7.03 mg CH4 d-1m-2, respectively but the coefficient of variation (CV) during kharif are more (30.37%) than in rabi (29.29%).

Optimization Design and Simulation Experiment of a Press Roller Based on a Lemniscate-Shaped Curve in Rice–Wheat Rotation Region of China

In order to solve the problems of high forward-resistance and serious soil adhesion in a rice–wheat rotation area, the smooth press roller of a wheat planter in a rice–wheat rotation area was selected as the research object. The low resistance and the adhesion structure of the press roller on a lemniscate-shaped curve were considered, and the geometric design method was adopted to modify the geometric structure of the smooth press roller. A simulation model of the roller–soil interaction was designed using the EDEM2020 software (DEM Solutions Ltd., Edinburgh, Scotland, UK), to investigate the behavior of soil adhering to the surface of the press roller, as well as the effects of the structure and the working parameters on soil adhesion and forward resistance. In addition, the numerical simulation method was combined with the central-plane composite response test scheme to perform the simulation test, using Design-Expert 10.0.4 software (Stat-Ease Inc., Minneapolis, MN, USA). In this test, the forward speed, the axial spacing, and the bulge height were taken as the test factors. On this basis, the working performance of the lemniscate curve type of the press roller was evaluated by establishing a response surface for soil adhesion and forward resistance. With the reduction in soil adhesion and the working resistance as constraints, the optimization was carried out under the condition of a forward speed of 7 km/h. Under a forward speed of 7 km/h, an axial spacing of 40.7–46.8 mm, and a bulge height of 9.3–11.5 mm, the soil adhesion was less than 70 g and the forward resistance was less than 50 N, meaning that the working performance of the lemniscate curve type of the press roller meets the requirements for actual production. In short, this research provides a new idea and reference for the application of a press roller in a rice–wheat rotation area.

Promotion of Natural Resource Management Technologies Through Frontline Demonstrations in Rice-Wheat Rotation in Punjab

Promotion of Natural Resource Management Technologies Through Frontline Demonstrations in Rice-Wheat Rotation in Punjab

Land use intensification significantly reduced CH4 emissions while increasing N2O emissions: Taihu Lake region, China

Land use intensification is becoming increasingly common in China’s Taihu Lake region because of economic interests. Frequent intensification is the conversion from natural wetlands (NW) to conventional rice-wheat rotation fields (RW), and from conventional RW to greenhouse vegetable fields (GH). However, the impact of land use intensification on greenhouse gas emissions in this area is still unknown. In our study, we chose typical NW, RW, and GH to compare and measure methane (CH4) and nitrous oxide (N2O) emissions from the three land use types through two-year in-situ field experiments. The results showed that land use intensification significantly reduced CH4 emissions, and NW, RW, and GH emissions were 970.66 ± 100.09, 896.71 ± 300.44, and −71.23 ± 63.62 kg C ha-1. Land use intensification significantly increased N2O emissions, and NW, RW, and GH emissions were 3.35 ± 0.44, 14.38 ± 4.09, and 81.62 ± 4.89 kg N ha-1. The global warming potential of CH4 and N2O under different land use types was in the order of RW (28,137.98 ± 9077.12 kg eq-CO2 ha-1) > NW (27,123.76 ± 2703.34 kg eq-CO2 ha-1) > GH (20,360.44 ± 2651.51 kg eq-CO2 ha-1). Overall, we observed that the comprehensive greenhouse effect of CH4 and N2O was enhanced by conversion from NW to RW and weakened by conversion from RW to GH. Our study provides a predictive understanding of how land use intensification changes greenhouse gas emissions in the Taihu Lake region and in regions with similar land use types.

Soil Bacteria Mediate Soil Organic Carbon Sequestration under Different Tillage and Straw Management in Rice-Wheat Cropping Systems

Soil organic carbon (SOC) largely influences soil quality and sustainability. The effects of no-till (NT) and crop straw return practices (SR) on soil organic carbon sequestration have been well documented. However, the mechanism of soil bacterial community in regulating soil organic carbon under NT and SR remains unclear. In this study, we investigated the impacts of tillage (conventional tillage (CT) and NT) and crop straw return practices (crop straw removal (NS) and SR) on topsoil layer (0–5 cm) bacterial community, CH4 and CO2 emissions and SOC fractions in rice-wheat cropping system. Overall, in the wheat season following the annual rice-wheat rotation in two cycles, NT significantly increased SOC by 4.4% for 1–2 mm aggregates in the 0–5 cm soil layer, but decreased CO2 emissions by 7.4%. Compared with NS, SR notably increased the contents of SOC in the topsoil layer by 6.5% and in macro-aggregate by 17.4% in 0–5 cm soil layer, and promoted CH4 emissions (by 22.3%) and CO2 emissions (by 22.4%). The combination of NT and NS resulted in relatively high SOC and low CH4 emissions along with high bacterial community abundance. The most abundant genus under different treatments was Gp6, which significant impacted SOC and MBC. Bacterial communities like Subdivision3 had the most impact on CH4 emissions. Structural equation modeling further suggested that the soil bacterial community indirectly mediated the SOC through balancing SOC in 1–2 mm aggregates and CH4 emissions. This study provides a new idea to reveal the mechanism of short-term tillage and straw return on SOC.

Soil bacterial communities and co-occurrence changes associated with multi-nutrient cycling under rice-wheat rotation reclamation in coastal wetland

Coastal reclamation is a global threat to coastal wetland ecosystems, but the impacts of coastal reclamation on belowground biodiversity and their consequences for ecosystem nutrient cycling remain poorly understood. In this study, we examined soil bacterial communities, bacterial co-occurrence pattern and soil multi-nutrient cycling index after natural vegetated coastal wetlands were converted for 6-year and 30-year rice-wheat rotation fields. The soil multi-nutrient cycling index was higher in 6-year and 30-year rice-wheat rotation fields than natural vegetated coastal wetlands. For bacterial community, rice-wheat rotation reclamation increased soil bacterial alpha diversity but decreased beta diversity and co-occurrence network complexity than those in the vegetated coastal wetland. Rice-wheat rotation reclamation also changed soil bacterial community assemblages by increasing the relative abundance of Actinobacteriota and Desulfobacterota while decreasing the relative abundance of Alphaproteobacteria and Gammproteobacteria. Changes in the relative importance of dispersal limitation and homogenizing dispersal mainly controlled the variations in soil bacterial community assemblages. Soil bacterial community variations induced by rice-wheat reclamation were strongly related to soil multi-nutrient cycling, especially bacterial connection complexity. Our results provide experimental support that belowground microbial interactions are crucial for maintaining ecosystem functioning.

Optimization and Experiment of Fertilizer-Spreading Device for Wheat Wide-Boundary Sowing Planter under Full Rice Straw Retention

When sowing with a wide boundary under full rice straw retention in the rice–wheat rotation area of China, conventional fertilization methods have some problems, such as a low fertilizer utilization rate, heap soil around a buried fertilizer device, or blocked fertilizing orifice. Firstly, combined with theoretical analysis, discrete element numerical simulation technology, and central composite test method, the wide-boundary fertilization device for wheat wide-boundary sowing was designed. Then, with the coefficient of variation for particle uniformity (CVPU) as the response value, the central composite experiment was carried out on the key structural parameters (focal length coefficient, lateral span, tilt angle, and ground clearance) of the wide-boundary fertilization device by EDEM software. Finally, the influential rules of core factors of the device on the CVPU were analyzed by Design-Expert software; then, the optimal parameter combination was determined and verified by a field test. The results showed that all factors had significant effects on the CVPU. The primary and secondary factors affecting the CVPU were the tilt angle, lateral span, focal length coefficient, ground clearance, tilt angle × ground clearance, and lateral span × ground clearance, in which there were certain interactions between the tilt angle and ground clearance and lateral span and ground clearance. When the focal length coefficient, lateral span, tilt angle, and ground clearance were 1.5, 60 mm, 30°, and 192 mm, respectively, the lateral was minimum. In this case, the theoretical value and field test value were 14.11% and 17.63%, respectively. The field test value is consistent with the theoretical calculation value. This study could provide references for the design of a fertilizer-spreading device with a wide boundary.

Analysis and Evaluation of Influencing Factors on Uniform Sowing of Wheat with Wide Seed Belt after Sowing and Soil Throwing Device

The uneven sowing of wheat on ground covered with rice straw in the rice–wheat rotation area in the middle and lower reaches of the Yangtze River has become a serious problem. Therefore, a test bed for throwing soil after sowing with a wide wheat seed belt was designed, which could complete the functions of straw crushing, straw lateral concentration and uniform sowing at one time. The discrete element simulation model of throwing soil after sowing with a wide wheat seed belt was established with rotary blade shaft speed, soil guide plate angle and soil retaining plate angle as variables. Taking the variation coefficient of wheat sowing depth and variation coefficient of sowing lateral uniformity as evaluation indexes, the effects of three variables on sowing uniformity were analyzed by single factor test and Box–Behnken test. The results of single factor test observed that when the rotating speed of rotary blade shaft was 260–300 rpm, the angle of soil guide plate was 36°–48°, the angle of soil retaining plate was 58°–74° and the experiment of utilizing a soil throwing and covering device with a wide seed belt after sowing revealed a good consistency of sowing depth and lateral uniformity effect. The Box–Behnken simulation experiment showed that the primary and secondary factors affecting the variation coefficient of wheat sowing lateral uniformity were the angle of soil guide plate, the rotation speed of rotary blade shaft, the angle of soil retaining plate and the angle of soil guide plate. When the rotation speed of rotary blade shaft, the angle of soil guide plate and the angle of soil retaining plate were 282.1 rpm, 42.4° and 65.5°, respectively, the soil throwing and covering device after sowing has the best seed-homogenizing effect. At this time, the variation coefficients of sowing depth and lateral uniformity in simulation test and field verification test were 4.35% and 4.57%, respectively, and 12.46% and 12.73%, respectively. The results of field verification test were basically consistent with those of the simulation test, which proved that the results of applying discrete element methods to optimize the soil-throwing device after sowing with a wide seed belt were credible. This study could provide a theoretical reference for the structure optimization of a soil-throwing device after sowing with a wide seed belt.

Effects of Tillage Methods on Crop Root Growth Trend Based on 3D Modeling Technology

Strip rotary tillage seeding technology has been widely used in rice–wheat rotation system, benefiting the economy greatly. The purpose of farming is to create a comfortable seedbed environment for crop growth. Therefore, it is necessary to consider the effects of tillage methods on wheat root configuration and growth trend in the research of strip tillage, instead of just focusing on optimizing the shape of tillage tools, sowing methods, and soil fragmentation. To clarify the effects of different tillage methods on crop root growth trends, a two-year wheat planting experiment was carried out. Strip tillage (ST1 and ST2) and full width tillage treatment (FT) were designed, 3D models of root structure and soil on the surface of the seedbed wall were established, and four quantitative indexes were proposed: soil surface roughness of seedbed wall (SR), difference coefficient of root soil space occupation (P), difference coefficient of root angle expansion trend (PA), and difference coefficient of root length expansion trend (PL). The results showed that the cultivation method directly affects the growth trend of wheat roots. The wheat roots tended to grow along the inter-specific direction under ST treatment on the 14th day, and the average P, PA, and PL were as high as 38, 43, and 55, respectively. The SR produced by ST1 treatment was 70% lower than that of ST2 treatment, suggesting ST1 treatment had more serious restrictions on root growth. P, PA, and PL in ST1 treatment were 38.5%, 14%, and 43% higher than those in ST2 treatment within 14 days, respectively. This paper briefly explains the effects of tillage methods on the growth trend of wheat roots, provides new methods and technologies for the rapid and effective acquisition of soil surface information, solved the problem of the trend of root expansion being difficult to quantify, and provided a new direction for the optimization of tillage methods.

Effects of Nitrogen Reduction and Optimized Fertilization Combined with Straw Return on Greenhouse Gas Emissions and Crop Yields of a Rice–Wheat Rotation System

Effects of Nitrogen Reduction and Optimized Fertilization Combined with Straw Return on Greenhouse Gas Emissions and Crop Yields of a Rice–Wheat Rotation System

Potential Application of Alternate Tillage (AT) in a Rice–Wheat Rotation System—Based on Soil Physical Properties, Wheat Growth and Yield

Alternate tillage (AT) has the potential to reduce inputs and improve soil quality and crop yield, but there has been no research on the effect of AT on soil and wheat in a rice–wheat rotation system. In this study, field experiments were conducted to examine the effects of four tillage management methods (conventional tilling (CT) in each crop (RCT–WCT), no tilling (NT) in rice and conventional tilling in wheat (RNT–WCT, AT1), conventional tilling in rice and no tilling in wheat (RCT–WNT, AT2), and no tilling in each crop (RNT–WNT)) on the physical properties of soil, wheat growth, and yield. At the 0–5 cm soil layer, CT in the wheat season increased bulk density (BD) and decreased total properties, but it decreased BD at the 5–40 cm soil layer, and the effect of RCT–WCT was significantly greater than that of RNT–WCT. CT in the wheat season increased the root activity, root dry weight, net photosynthetic rate, leaf area index, antioxidant enzyme activities, and yield, and there was no significant effect between RCT–WCT and RNT–WCT. RNT-WCT has the potential to reduce inputs and maintain wheat yields.

Improvement of the DRAINMOD model's performance under time-variable surface storage capacities using neural network models

DRINAMOD is a superior model being used globally to assess the impacts of different agricultural drainage layouts and practices on farmlands' water balance. But the model considers a fixed value of surface storage capacity (SSC) for the whole simulation period, which causes the model to predict improper water distribution patterns in farmlands where SSC varies with time due to agricultural practices. The present study presents a novel artificial neural network model (ANNM) that mimics the DRAINMOD model and overcomes such a shortage of considering a fixed SSC value when predicting farmlands' water balance. After training the ANNM by sets of data, which were generated by the DRAINMOD model after being calibrated and validated in rice-wheat rotation farmland at the lower reaches of the Yangtze River basin, China, groundwater tables in the study area were predicted by both models under different scenarios of drainage layouts and management practices. Results show that there were excellent agreements between these predictions, which validates the applicability of the developed ANNM in predicting the water balance in artificial-drained farmlands. The developed ANNM enhances water fate predictions in artificial-drained farmlands characterized by time-variable surface storage capacities, thus resulting in a better assessment of the available water resources alongside high agricultural productivity. Findings from the present study point also to the potential role of neural network models as a tool to enhance the performance of hydrologic models without modifying their source code.

Brown manuring and sorghum allelopathy affects weeds, soil health, and paddy yield

AbstractThis 5‐yr study (2012–2017) aimed to evaluate the effects of sesbania (Sesbania rostrata Bremek. & Oberm) brown manure (SBM) and sorghum [Sorghum bicolor (L.) Moench] in rice (Oryza sativa L.)‐based rotations on weeds, soil properties, and rice yield. Four rice production systems were used: (a) wheat (Triticum aestivum L.)–rice (control), (b) wheat–rice + SBM, (c) wheat–sorghum–rice, and (d) wheat–sorghum–rice + SBM. Compared with control, allelochemicals accumulated in the rhizospheric soil of all other cropping systems over time and were the highest in the sorghum‐based rotations. Allelochemical accumulation in the soil reduced the densities and aboveground biomass of sedges and grassy and broad‐leaved weeds. Weed suppression was more evident when SBM in rice was included in the postsorghum field vs. the control. The use of SBM also enhanced soil organic matter (SOM), soil microbial biomass nitrogen (SMBN), and soil microbial biomass carbon (SMBC), and reduced the soil bulk density compared with the control. There was an improvement in SOM by 6.82, 0.57, and 9.09%, SMBC by 3.92, 0.86, and 6.29%, and SMBN by 3.12, 0.97, and 4.43% with wheat–rice + SBM, wheat–sorghum–rice, and wheat–sorghum–rice + SBM rotation, respectively, compared with the control. The highest paddy yield was recorded in the wheat–sorghum–rice–SBM, which was attributed to improved weed suppression in this system vs. wheat–rice rotation. The improved paddy yield in SBM‐based rotations was a direct outcome of better soil health and the built up of allelochemicals in the soil profile, which suppressed weeds and improved rice yield.

Climate Change Impact on Yield and Water Use of Rice-Wheat Rotation System in the Huang-Huai-Hai Plain, China.

Simple SummaryQuantitatively exploring the impact of climate change on crop production and water consumption (i.e., crop evapotranspiration during crop growth period, ET) is very important to achieve sustainable regional agricultural development. In this study, based on daily downscaled climate data from 22 Global Climate Models (GCMs), we applied the Agricultural Production Systems sIMulator (APSIM) to investigate the possible impact of climate change (e.g., temperature (Temp), solar radiation (Rad), precipitation (Prec) and CO2) on crop phenology, yield and water consumption for the rice (Oryza sativa L.) -wheat (Triticum aestivum L.) rotation. Due to the increase in Temp, the key phenological periods (flowering and maturity) of wheat in the future mainly tend to advance, while the phenological changes of rice show different trends at different sites. Both rice and wheat yields were negatively correlated with Temp, but positively correlated with Rad, Prec, and CO2 concentration ([CO2]). However, crop ET was positively correlated with Rad, but negatively correlated with [CO2], as elevated [CO2] decreased stomatal conductance. Moreover, the water use efficiency (WUE) of rice and wheat was negatively correlated with Temp, but positively correlated with [CO2]. Overall, climate change will have a significant impact on the crop growth process, yield and water consumption.Global climate change has had a significant impact on crop production and agricultural water use. Investigating different future climate scenarios and their possible impacts on crop production and water consumption is critical for proposing effective responses to climate change. In this study, based on daily downscaled climate data from 22 Global Climate Models (GCMs) provided by Coupled Model Intercomparison Project Phase 6 (CMIP6), we applied the well-validated Agricultural Production Systems sIMulator (APSIM) to simulate crop phenology, yield, and water use of the rice–wheat rotation at four representative stations (including Hefei and Shouxian stations in Anhui province and Kunshan and Xuzhou stations in Jiangsu province) across the Huang-Huai-Hai Plain, China during the 2041–2070 period (2050s) under four Shared Socioeconomic Pathways (i.e., SSP126, SSP245, SSP370, and SSP585). The results showed a significant increase in annual mean temperature (Temp) and solar radiation (Rad), and annual total precipitation (Prec) at four investigated stations, except Rad under SSP370. Climate change mainly leads to a consistent advance in wheat phenology, but inconsistent trends in rice phenology across four stations. Moreover, the reproductive growth period (RGP) of wheat was prolonged while that of rice was shorted at three of four stations. Both rice and wheat yields were negatively correlated with Temp, but positively correlated with Rad, Prec, and CO2 concentration ([CO2]). However, crop ET was positively correlated with Rad, but negatively correlated with [CO2], as elevated [CO2] decreased stomatal conductance. Moreover, the water use efficiency (WUE) of rice and wheat was negatively correlated with Temp, but positively correlated with [CO2]. Overall, our study indicated that the change in Temp, Rad, Prec, and [CO2] have different impacts on different crops and at different stations. Therefore, in the impact assessment for climate change, it is necessary to explore and analyze different crops in different regions. Additionally, our study helps to improve understanding of the impacts of climate change on crop production and water consumption and provides data support for the sustainable development of agriculture.

Increasing the Contents of Paddy Soil Available Nutrients and Crop Yield via Optimization of Nitrogen Management in a Wheat-Rice Rotation System.

To explore the impact of nitrogen (N) rate during the wheat season and N fertilizer management during the rice season on carbon and soil nutrient pools in paddy soil, a wheat–rice rotation system for 2 successive years was implemented. In the rotation system, a conventional N rate (Nc; 150 kg/ha) and a reduced N rate (Nr; 120 kg/ha) were applied in the wheat season. Based on an application rate of 150 kg/hm2 N in the rice season, three N management models were applied, in which the application ratio of base:tiller:panicle fertilizer was 20%:20%:60% in treatment M1, 30%:30%:40% in treatment M2, and 40%:40%:20% in treatment M3. Zero N was used as the control (M0). Experimental results indicate that, under Nc, the M2 management model during the rice season, improvements were seen in paddy soil urease, organic carbon, and annual yield relative to other conditions. The average organic matter and total N associated with the M2 rice management model and conventional N application during the wheat season were 5.13% and 4.95% higher, respectively, relative to the use of a reduced N application rate during the wheat season. Similarly, the average total carbon content and annual yields were 6.61% and 5.56% higher under the model M2 with conventional N application during the wheat season, respectively, relative to reduced N application after the two-year study period. These findings indicate that production and carbon fixation in paddy fields can be optimized through a conventional N application rate during the wheat season, and an M2 N management model during the rice season in southern China under a wheat–rice rotation system.

Grain yield and soil potassium fertility changes arising from different potassium-bearing materials in rice–wheat rotation

Grain yield and soil potassium fertility changes arising from different potassium-bearing materials in rice–wheat rotation

Effects of Drainage on Greenhouse Gas Emissions and Yields of Lowland Rice—Wheat Rotation System in East China

The subtropical region of East China is characterized by abundant water and temperature resources conducive to crop cultivation, and large areas of lowland have been widely used for agricultural planting. The objectives of the study were to explore feasible methods of greenhouse gas (GHG) reduction for rice–wheat rotation systems and to explain the mechanism underlying the effect of drainage on GHG reduction. Shallow ditch (SD) and deep ditch (DD) treatments in the wheat season were set up for drainage to control the paddy soil water content, with conventional non-ditching as the control group (CG). CH4 and N2O emission fluxes were continuously measured, and related soil physical and chemical properties were also measured in this study. The results showed that CH4 emissions from paddy soil accounted for most of the global warming potential (GWP) in the rice–wheat rotation system. Drainage led to a significant reduction in cumulative soil CH4 emissions during the rice and wheat seasons; however, the overall cumulative N2O flux increased significantly. The total GWP produced by SD and DD in the three years was reduced by 58.21% and 54.87%, respectively. The GHG emission intensity (GHGI) of SD and DD declined by 60.13% and 56.40%, respectively. The CH4 emission flux was significantly positively correlated with the 5 cm ground temperature but negatively correlated with the soil redox potential (soil Eh). The drainage decreased the soil water and soil organic matter contents and increased soil pH, which were the mechanisms that reduced the CH4 emissions. The drainage increased the soil nitrogen content, which is the main reason for regulating N2O. The findings indicate that SD and DD not only ensured a stable increase in production but also effectively reduced GHG emissions, and we recommend SD treatment for agricultural production.

Long-Term Successive Biochar Amendments Alter the Composition and α-Diversity of Bacterial Community of Paddy Soil in Rice-Wheat Rotation

The specific effect of long-term successive biochar application on soil fertility, α-diversity, and composition of bacterial community and their correlations remain unclear. A field experiment was conducted to investigate the effects of straw biochar application on soil physical and chemical properties and the diversity and composition of the bacterial communities in 12 consecutive crop seasons. Four treatments: BC1 (2.25 Mgha−1 biochar), BC5 (11.25 Mgha−1 biochar), RS (2.25 Mgha−1 rice straw), and blank control (CK, without biochar or rice straw) were set up. The results indicated that biochar and rice straw reduced the richness indexes of the soil bacterial community (Chao1 and ACE by 10.3%–27.4% and 12.2%–26.4%, respectively). High-throughput sequencing results showed that the relative abundance of Cyanobacteria, Bacteroidetes, and Actinobacteria increased as the amount of biochar increased, while those of norank_c__Acidobacteria and norank_f__Anaerolineaceae Proteobacteria, Acidobacteria and Nitrospirae decreased. Long-term successive biochar application significantly increased soil pH, available potassium, total organic carbon, total nitrogen, and cation exchange capacity by 5.7%–25.9%, 40.0%–680.0%, 48.0%–217.1%, 51.0%–109.5%, and 5.4%–24.0%, respectively. Soil dissolved organic carbon was slightly decreased by 1.4%–4.0%. Soil pH and C/N were the two major environmental factors affecting the composition of the soil bacterial community according to redundancy analysis. Furthermore, the phylogenetic investigation of communities by reconstruction of unobserved states showed that biochar significantly increased the relative abundance of information on the functions of the metabolism of other amino acids, metabolism of terpenoids and polyketides, and biosynthesis of other secondary metabolites (p < 0.05). Therefore, long-term successive biochar amendment in rice-wheat rotation systems improved soil fertility, altered the structure of the soil bacterial community, and increased the functions of soil bacteria, but decreased the α-diversity of the bacterial community. This study will provide technical and theoretical support for rice-straw carbonization and long-term soil remediation from the perspective of microorganisms.

Increasing the appropriate seedling density for higher yield in dry direct-seeded rice sown by a multifunctional seeder after wheat-straw return

Dry direct-seeded rice (DDR) sown using a multifunctional seeder that performs synchronous rotary tillage and sowing has received increased attention because it is highly efficient, relatively cheap, and environmentally friendly. However, this method of rice production may produce lower yields in a rice–wheat rotation system because of its poor seedling establishment. To address this problem, we performed field experiments to determine the rice yield at five seedling density levels (B1, B2, B3, B4, and B5=100, 190, 280, 370, and 460 seedlings m−2, respectively) and clarify the physiological basis of yield formation. We selected a representative high-quality rice variety and a multifunctional seeder that used in a typical rice–wheat rotation area in 2016 and 2018. The proportion of main stem panicle increased with increasing seedling density. There was a parabolic relationship between yield and seedling density, and the maximum yield (9.34−9.47 t ha−1) was obtained under B3. The maximum yield was associated with a higher total spikelet number m−2 and greater biomass accumulation from heading to maturity. The higher total spikelet number m−2 under B3 was attributed to an increase in panicle number m−2 compared with B1 and B2. Although the panicle numbers also increased under B4 and B5, these increases were insufficient to compensate for the reduced spikelet numbers per panicle. Lower biomass, smaller leaf area, and lower N uptake per plant from the stem elongation stage to the heading stage were partially responsible for the smaller panicle size at higher seedling density levels such as B5. The higher biomass accumulation under B3 was ascribed to the increases in the photosynthetic rate of the top three leaves m−2 of land, crop growth rate, net assimilation rate, and leaf area index. Furthermore, the B3 rice population was marked by a higher grain–leaf ratio, as well as a lower export ratio and transport ratio of biomass per stem-sheath. A quadratic function predicted that 260−290 seedlings m−2 is the optimum seedling density for achieving maximum yield. Together, these results suggested that appropriately increasing the seedling density, and thereby increasing the proportion of panicles formed by the main stem, is an effective approach for obtaining a higher yield in DDR sown using a multifunctional seeder in a rice–wheat rotation system.