Rice-wheat Rotation Research Articles

Straw return in paddy field alters photodegradation of organic contaminants by changing the quantity rather than the quality of water-soluble soil organic matter

Straw return, an important agricultural management practice, is worldwide adopted to enhance soil carbon sequestration and soil fertility. Although water-soluble soil organic matter (WSOM) in paddy field is known to affect the photodegradation of organic contaminants, how straw return regulates the photosensitization of WSOM by changing its properties remain unclear. Here, we determined the temporal variations in the content, chemical characteristics, and photosensitizing ability of WSOM after wheat straw return in a wheat-rice rotation system using optical spectroscopy and steady-state photodegradation tests. After straw return, the WSOM content first increased to a maximum and then gradually decreased to pre-return level at day 90. Nevertheless, the relative abundance of humic-like components in WSOM was not shifted by straw return, and protein-like component in WSOM just showed a slight decrease at day 45. All the WSOM samples inhibited sulfamethoxazole (SMX) photodegradation by light filtering, reactive species quenching and other mechanisms, while promoted diuron (DIU) degradation via reacting with •OH, 1O2 and excited triplet WSOM. The photodegradation of SMX and DIU was little affected by straw return changing WSOM composition and photochemical activity. However, straw return could decelerate SMX and DIU photodegradation by elevating WSOM content in a relatively short-term. This study emphasizes that straw return may reduce the photodegradation of organic contaminants by increasing WSOM concentration instead of altering WSOM chemical characteristics.

The Classification of Farming Progress in Rice–Wheat Rotation Fields Based on UAV RGB Images and the Regional Mean Model

Extraction of farming progress information in rice–wheat rotation regions is an important topic in smart field research. In this study, a new method for the classification of farming progress types using unmanned aerial vehicle (UAV) RGB images and the proposed regional mean (RM) model is presented. First, RGB information was extracted from the images to create and select the optimal color indices. After index classification, we compared the brightness reflection of the corresponding grayscale map, the classification interval, and the standard deviation of each farming progress type. These comparisons showed that the optimal classification color indices were the normalized red–blue difference index (NRBDI), the normalized green–blue difference index (NGBDI), and the modified red–blue difference index (MRBDI). Second, the RM model was built according to the whole-field farming progress classification requirements to achieve the final classification. We verified the model accuracy, and the Kappa coefficients obtained by combining the NRBDI, NGBDI, and MRBDI with the RM model were 0.86, 0.82, and 0.88, respectively. The proposed method was then applied to predict UAV RGB images of unharvested wheat, harvested wheat, and tilled and irrigated fields. The results were compared with those obtained with traditional machine learning methods, that is, the support vector machine, maximum likelihood classification, and random forest methods. The NRBDI, NGBDI, and MRBDI were combined with the RM model to monitor farming progress of ground truth ROIs, and the Kappa coefficients obtained were 0.9134, 0.8738, and 0.9179, respectively, while traditional machine learning methods all produced a Kappa coefficient less than 0.7. The results indicate a significantly higher accuracy of the proposed method than those of the traditional machine learning classification methods for the identification of farming progress type. The proposed work provides an important reference for the application of UAV to the field classification of progress types.

Crop rotation stage has a greater effect than fertilisation on soil microbiome assembly and enzymatic stoichiometry

Agronomic practises, such as fertilisation and crop rotation, affect soil microbial communities and functions. However, limited information is available regarding the relative importance of fertilisation and crop rotation stages in determining the soil microbiome and assembly processes. In addition, insights into the connections between the soil microbiome and enzymatic stoichiometry are scarce. In this study, soil samples were collected from a wheat–rice rotation system that received mineral and organic fertiliser inputs for 6 years to investigate soil microbiome assembly, and the relationship between the soil microbiome and enzymatic stoichiometry. Our results revealed that the crop rotation stage strongly affected the soil microbial community structure, assembly, and enzymatic functions compared to that of the fertilisation regime. Enzymatic stoichiometry results and vector analysis implied that mineral and organic fertilisation could alleviate the microbial N limitation. However, no-manure fertilisation led to microbial P limitation during the wheat stage. The decreases in soil pH mainly drove microbial P limitation due to the acidification induced by the mineral fertilisers. Microbial N/P limitation correlated more strongly with the bacterial assembly than with fungal assembly. Moreover, co-occurrence network analysis showed that ecological relationships between microbial taxa and enzymes were more complex during the wheat stage than that during the rice stage. Microbial nodes linked to acid phosphomonoesterase correlated significantly with the soil pH. Our study highlights the distinct responses of the soil microbiome to fertilisation in different crop-rotation stages, and provides novel insights into connections between microbial assembly and enzymatic stoichiometry.

Short-term legacy effects of rice season irrigation and fertilization on the soil bacterial community of the subsequent wheat season in a rice-wheat rotation system

Soil properties and microbial diversity are markedly enhanced by the long-term effects of organic fertilizers. However, the short-term impacts of inorganic and organic fertilizers vary in different agroecosystems, especially when combined with different irrigation conditions. Here, we examined the influence of different fertilizer types (NPK: mineral fertilizer, NPKM: mineral fertilizer plus organic fertilizer, NPKWS: mineral fertilizer plus straw) combined with different irrigation regimes (AWMID: shallow water layer, AWMOD: alternate wetting and moderate drying, AWSD: alternate wetting and severe drying) on the soil properties and bacterial communities at the wheat harvest stage of a one-year rice-wheat rotation system (RWRS), in the rice zone along the Yellow River of China. Our results revealed that the irrigation mode had a stronger impact on the soil properties, and bacterial community than the fertilizer regime, although most indicators did not differ significantly, probably owing to the short duration of the trial. Several low-abundance bacteria were recognized to be strongly (P < 0.05) influenced by different irrigation and fertilizer regimes in the RWRS using LEfSe analysis, but no definite trends were observed among the treatments. A co-occurrence network uncovered the modular clustering patterns of bacteria, which were significantly correlated with the available phosphorus content and some soil enzyme activities. Moreover, the denitrification, nitrite respiration, and sulfur respiration capacities of soil microbes were significantly improved in the mineral fertilizer combined with the alternate wetting and moderate drying treatment. In addition, the wheat yield did not significantly (P < 0.05) decrease after water-saving irrigation regime during the previous rice season. Further research is warranted to elucidate the long-term effects of partial substitution of chemical nitrogen with organic nitrogen and water-saving irrigation regimes on an RWRS.

Long-term straw return influenced ammonium ion retention at the soil aggregate scale in an Anthrosol with rice-wheat rotations in China

Soil aggregates are an important controlling factor for the physico-chemical and biological processes such as ammonium (NH4+) retention. Straw return to the field is increasingly recommended to promote soil carbon (C) sequestration and improve crop yields. However, the effects of straw return on NH4+ retention at soil aggregate level in agricultural soils have seldom been investigated. This study aimed to evaluate the influences of long-term straw return on NH4+ adsorption and fixation in microaggregates (<0.25 mm) with or without soil organic carbon (SOC) oxidization. Soil samples were collected from plots of three treatments, i.e., no fertilizer (CK), inorganic NPK fertilizers (NPK), and inorganic NPK fertilizers with rice straw return (NPKS), from a 20-year-old field trial with rice-wheat rotations in Taihu Lake Region, China. Soil aggregates were separated using wet-sieving method. The SOC of microaggregates was oxidized by H2O2. The results showed that long-term straw return significantly increased SOC and NH4+ adsorption, but inhibited NH4+ fixation in microaggregates. NH4+ adsorption potential and strength - obtained from adsorption isotherms - increased, but NH4+ fixation decreased along with increasing SOC in microaggregates, indicating the important role of SOC in NH4+ adsorption and fixation. This was verified by the SOC oxidization test that showed a relative decrease in NH4+ adsorption potential for the NPKS treatment and an increase in NH4+ fixation in all three treatments. Therefore, long-term straw return influences NH4+ adsorption and fixation by enhancing SOC content and could improve N availability for crop uptake and minimize applied N fertilizer losses in rice-wheat cropping systems.

Optimization Design of a Pneumatic Wheat-Shooting Device Based on Numerical Simulation and Field Test in Rice–Wheat Rotation Areas

In rice–wheat rotation areas of China, traditional wheat seeders have severe blockage, low working efficiency and poor seeding quality. In this study, a pneumatic shooting technology was designed, consisting mainly of a nozzle, shell and acceleration tube. To improve the sowing depth of the pneumatic shooting device, the response-surface methodology of structure parameters and CFD simulation technology was adopted in this work. The effects of working pressure, acceleration-tube diameter and throat distance on the steady airflow length (SAL) and steady airflow velocity (SAV) were studied by airflow field analysis, and the response-surface method was introduced to obtain the optimal parameter combination of the pneumatic shooting device for wheat. The optimal parameter combination was working pressure 686 kPa, acceleration tube diameter 8 mm and throat distance 20 mm. The simulation result showed that the optimized device of pneumatic shooting performs faster and has more stable airflow field characteristics in comparison to the initial device. The field test demonstrated that the optimized device has about 68% higher seeding depth than the initial device. The average field-seeding depth of the optimized device was 19.95 mm, which is about 68% higher than the initial device. The emergence rate for the optimized device was about 88.7% without obvious reduction. CFD and response-surface methods positively affect the optimization of pneumatic wheat-shooting devices, and the significance was also confirmed.

Effects of tillage on soil nitrogen and its components from rice-wheat fields in subtropical regions of China

It is of great significance to explore the effects of different tillage practices on total nitrogen and its components in rice-wheat rotation farmland. The experiment was carried out in Jiangyan County, Jiangsu Province of China, and a total of four treatments were set up: minimum tillage (MT), rotary tillage (RT), conventional tillage (CT), and conventional tillage without straw retention (CT0). The total nitrogen (TN), light fraction nitrogen (LFN), heavy fraction nitrogen (HFN), particulate nitrogen (PN), and mineral-associated nitrogen (MN) in 0-20 cm soil were determined. The results show that MT increased TN concentration by2.26%-27.57% compared with the other treatments in 0-5 cm soil, but it lost this advantage in 5-10 cm and 10-20 cm soil. MT altered the concentration of LFN by 6.03%-95.86%, of HFN by 1.68%-20.75%, of PN by 12.58%-96.83%, and of MN by −1.73%-9.83% as compared to RT, CT, and CT0 in 0-5 cm soil, respectively. With the deepened of soil depth, the concentration of TN, LFN, HFN, PN, and MN decreased quickly in MT, which was lower than that in RT and CT at 10-20 cm soil depth. Straw return increased the concentration of TN and its components in 0-20 cm soil. The concentration of TN was extremely significantly positively correlated with that of LFN, HFN, PN, and MN (p<0.01). The variation of TN was significantly positively correlated with that of LFN, HFN, PN, and MN (p<0.01), and LFN showed the highest sensitivity to tillage practice. In general, minimum tillage combined with straw retention increased the concentration of soil TN and its components in topsoil. LFN was the best indicator to indicate the change in soil total nitrogen affected by tillage practice. Keywords: rice-wheat rotation, soil active nitrogen components, light fraction nitrogen, heavy fraction nitrogen, particulate nitrogen, mineral-associated nitrogen DOI: 10.25165/j.ijabe.20221503.5661 Citation: Cui S Y, Zhu X K, Cao G Q. Effects of tillage on soil nitrogen and its components from rice-wheat fields in subtropical regions of China. Int J Agric & Biol Eng, 2022; 15(3): 146–152.

Soil Bacterial Communities and Co-Occurrence Changes Associated with Multi-Nutrient Cycling Under Rice-Wheat Rotation Reclamation in Coastal Wetland

Soil Bacterial Communities and Co-Occurrence Changes Associated with Multi-Nutrient Cycling Under Rice-Wheat Rotation Reclamation in Coastal Wetland

Overexpression of a Glycosyltransferase Gene from a Metabolically Poly-Resistant Beckmannia syzigachne Population Alters Growth and Confers Herbicide Resistance to Brachypodium distachyon

Beckmannia syzigachne is a noxious weed for rice-wheat rotations in China. The B. syzigachne (AH-02) population evolved metabolic resistance to fenoxaprop-P-ethyl and mesosulfuron-methyl. To investigate the function of GT73C1 in this population, the GT73C1 gene was amplified by reverse transcription-polymerase chain reaction, and the sequence was 100% consistent with the transcriptome data. Its phylogenetic tree was displayed and annotated using FigTree v1.4.4. The plant overexpression vector of GT73C1 gene was constructed and used to transform Brachypodium distachyon plants. Furthermore, the expression of GT73C1 was significantly induced by fenoxaprop-P-ethyl and mesosulfuron-methyl, which was consistent with the findings from the whole plant bioassay. These results indicate that GT73C1 is closely related to the metabolic resistance of B. distachyon.

Partial substitution of chemical fertilizer with organic fertilizer over seven years increases yields and restores soil bacterial community diversity in wheat–rice rotation

Substituting chemical fertilizer with organic fertilizer is an important agricultural practice that improves crop yields but also affects soil biogeochemical cycling. To explore the effects of organic fertilizer on soil properties and bacterial community structure and diversity, a long-term field experiment (2011–2017) was conducted in a wheat–rice rotation system with four treatments: control (CK, no fertilizer), chemical fertilizer only (NPK), substitution of 50% of chemical nitrogen (N) fertilizer with organic fertilizer (NPKM), and substitution of 100% of chemical N fertilizer with organic fertilizer (OM). Results showed that, crop yields (wheat and rice) from 2011–2017 were highest in NPKM. Combined with α-diversity analysis, long-term application of NPK led to a decrease in soil bacterial diversity. However, soil bacterial community richness (Ace and Chao1 indices) increased in NPKM in the wheat season, as well as in OM in the rice season. Compared with NPK, organic fertilizer inputs (NPKM and OM) increased microbial biomass carbon and abundance of dominant bacteria (Acidobacteria, Anaerolineaceae, and Nitrospira) in both crop seasons. In NPK, relative abundance of Rhodanobacter increased significantly in the wheat season because of low soil pH. Bacterial community composition and structure were similar between NPKM and OM in the wheat season. Redundancy analysis further found that soil pH (R2 = 0.735, P = 0.013) co-varied with the bacterial community structure in the wheat season. In the rice season, relative abundance of Nitrospira increased significantly in NPKM, which could generate large amounts of nitrate nitrogen (NO3−-N), and then increase risks of N2O emissions and NO3−-N leaching in paddies. Overall, partial substitution of chemical fertilizer with organic fertilizer was optimal to increase crop yields and recover soil bacterial diversity in the wheat–rice rotation, and greater substitution with organic fertilizer in combination with chemical fertilizer is recommended only for rice seasons.

Combined Fertilization Could Increase Crop Productivity and Reduce Greenhouse Gas Intensity through Carbon Sequestration under Rice-Wheat Rotation

Quantifying greenhouse gas intensity (GHGI) and soil carbon sequestration is a method to assess the mitigation potential of agricultural activities. However, the effects of different fertilizer amendments on soil carbon sequestration and net GHGI in a rice-wheat cropping system are poorly understood. Here, fertilizer treatments including PK (P and K fertilizers); NPK (N, P and K fertilizers), NPK + OM (NPK plus manure), NPK + SR (NPK plus straw returning), and NPK + CR (NPK plus controlled-release fertilizer) with equal N input were conducted to gain insight into the change of soil organic carbon (SOC) derived from the net ecosystem carbon budget (NECB), net global warming potential (GWP), and GHGI under rice-wheat rotation. Results showed that compared with NPK treatment, NPK + OM significantly increased wheat yield and NPK + SR caused significant increase in rice yield. Meanwhile, NPK + SR and NPK + CR treatments reduced net GWP by 30.80% and 21.83%, GHGI by 36.84% and 28.07%, respectively, which suggested that improved grain production could be achieved without sacrificing the environment. With the greatest C sequestration, lowest GHGI, the NPK plus straw returning practices (NPK + SR) might be the best strategy to mitigate net GWP and improve grain yield and NUE in the current rice-wheat rotation system.

Effects of biochar on water quality and rice productivity under straw returning condition in a rice-wheat rotation region

Straw returning is helpful to improve soil properties and realize the reutilization of agricultural waste. However, wheat straw returning may result in paddy water quality deterioration in rice-wheat rotation regions. This study conducted pot experiments of rice planting with different biochar application rates (0, 5, 20, and 40 t/hm2) under wheat straw returning conditions. The purposes are to investigate the applicability of biochar mixed with wheat straw returning to paddy fields and explore the effects of biochar on water quality, leaching losses of nitrogen (N) and phosphorus (P), and rice yield components. Results indicated that total straw returning reduced the water quality in paddy surface water and aggravated the leaching losses of N and P. Fortunately, the biochar application improved the negative effects caused by straw returning. 40 t/hm2 biochar mixed with straw returning significantly reduced the concentrations of COD and N in paddy surface water and N leaching loss than straw returning treatment (ST), decreased by 48.33%, 41.01%, and 45.73%, respectively. Meanwhile, applying biochar at a rate of 20 t/hm2 with straw returning is suitable to control the diffusion of P. In addition, the ST treatment had no significant effect on rice yield, while the proper application rate of biochar under straw returning condition can improve rice yield and promote N utilization. 20 t/hm2 biochar treatment is more effective to improving rice yield (16.89%) and N use efficiency (NUE) (10.14%). These findings can provide a new method to solve the negative effects of total straw returning on the water environment and rice growth and guide the utilization of straw resources in the rice-wheat rotation regions.

Differences in responses of ammonia volatilization and greenhouse gas emissions to straw return and paddy-upland rotations.

Paddy-upland rotation and/or straw return could improve soil structure and soil nutrient availability. Different previous crops (wheat and/or oilseed rape) and straw return methods (straw mulching and/or returning) might increase soil organic carbon (C) and total nitrogen (N) content, and further affected the ammonia (NH3) volatilization, nitrous oxide (N2O), and methane (CH4) emissions. A comparison study was carried out in a located field experiment started from 2014 in Central China, aiming to exam seasonal and annual NH3, N2O, and CH4 emissions under the wheat-rice (WR) and oilseed rape-rice (OR) rotations. Three treatments were chosen, i.e., (i) no chemical N fertilizer application (PK), (ii) chemical nitrogen-phosphorus-potassium combination (NPK), and (iii) chemical NPK with straw returning (NPK+St). We found that after 3years of cultivation, treatment with straw return increased soil total N content and organic C by 15.57% and 17.11% on average as compared with the NPK treatment, respectively. Straw return did not generate additional NH3 and N2O losses during the rice season after improving soil fertility. However, CH4 emissions increased by 45.35% on average after straw return in summer. In winter, straw return increased NH3, N2O, and CH4 emissions by 70.12-85.23%, 16.93-22.97%, and 7.18-9.17%, respectively. The stimulation of NH3 volatilization mainly occurred in the topdressing stage. Compared with WR rotation, OR rotation had no significant effect on NH3 and CH4 emissions, and the change of N2O emission might be related to the increase of soil C and N pools. The retention of residues in the process of straw decomposition may be the main factor leading to the difference of gas emission between the paddy-upland rotation and straw return.

Impacts of long-term composted manure and straw amendments on rice-associated weeds in a rice–wheat rotation system

AbstractAs part of a long-term experiment to determine the impacts of composted manure and straw amendments (replacing 50% of chemical fertilizer with composted pig manure, wheat straw return combined with chemical fertilizer, and setting no fertilizer and chemical fertilizer-only as controls) on rice-associated weeds in a rice (Oryza sativaL.)–wheat (Triticum aestivumL.) rotation system, species richness, abundance, density, and biomass of weeds were assessed during years 8 and 9. Fertilization decreased the species richness and total density of rice-associated weeds but increased their total biomass. The species richness and densities of broadleaf and sedge weeds decreased with fertilization, while species richness of grass weeds increased only with straw return and density was not significantly affected. The shoot biomass per square meter of grass and broadleaf weeds was significantly higher with fertilization treatments than with the no-fertilizer control, while that of sedge weeds declined with fertilizer application. With fertilization, the densities of monarch redstem (Ammannia bacciferaL.) and smallflower umbrella sedge (Cyperus difformisL.) decreased, that of Chinese sprangletop [Leptochloa chinensis(L.) Nees] increased, and those of barnyardgrass [Echinochloa crus-galli(L.) P. Beauv.] and monochoria [Monochoria vaginalis(Burm. f.) C. Presl ex Kunth] were not significantly affected.Ammannia bacciferawas the most abundant weed species in all treatments. Whereas composted pig manure plus fertilizer resulted in higher density ofA. bacciferaand lower shoot biomass per plant than chemical fertilizer only, wheat straw return plus chemical fertilizer caused lower density and shoot biomass ofA. baccifera. Therefore, it may be possible that fertilization strategies that suppress specific weeds could be used as improved weed management program components in rice production systems.

Spatiotemporal Variation Characteristics and Driving Factors of Nitrogen Use Efficiency of Wheat–Rice Rotation Systems in the Taihu Lake Region

During the past three decades, a large amount of nitrogen (N) fertilizers has been applied in the rice and wheat rotation system in the Taihu Lake region of southern China to achieve high yield, resulting in low N use efficiency (NUE). China is implementing the national strategy “fertilizer reduction with efficiency increase” to solve the serious ecological problems caused by excessive fertilization. However, the effects of N fertilizer reduction on soil fertility and their integrated effect on NUE of rice–wheat rotation systems in the Taihu Lake region are not fully understood. In this study, test fields with different soil-fertility qualities were selected in typical rice–wheat areas in the Taihu Lake region to perform a 2-year rice–wheat N fertilizer effect test to obtain the comprehensive quantitative relationship among the integrated fertility index (IFI), nitrogen application level (NA), and NUE. Through the investigation and spatial analysis of NA and IFI in the study area in 2003 and 2017, the spatial and temporal variation characteristics of NA and IFI in the study area in the past 15-year period were obtained, and this information was spatially coupled with the comprehensive quantitative relationship model of NUE to reveal the variation characteristics and driving factors of NUE in the study area. The result shows that the wheat and rice NA in the study area in 2017 increased by 35.5 and 8.4%, respectively, compared with 2003. Due to excessive fertilization, the soil nitrogen, phosphorus, and potassium content of cultivated land in the study area in 2017 was greater than that in 2003, especially soil-available phosphorus and potassium contents, whereas soil organic matter (SOM) content was reduced. The cultivated land IFI of the study area as a whole increased by 7.2% in the 15-year period. The NUE of rice and wheat rotation increased by 5.8% in 2017 compared with that of 2003 due to the improvement in crop varieties and N fertilizer yield benefits. The increases of NA and IFI both have negative correlations with the NUE improvement, and the NA increase has a greater impact. In addition, the terrain, soil type, texture, and parent material also affect the soil nutrient-preserving capability and, thus, affect the spatial variation of IFI and NUE improvement. These factors have greater influence on NUE improvement of wheat than rice. This study provides a novel and effective method for analyzing the spatial-temporal variation characteristics of NUE in the rice–wheat system and is conducive to guide precise fertilization and N fertilizer reduction based on the spatial analysis of NA with IFI and NUE.

Gross Ecosystem Productivity Dominates the Control of Ecosystem Methane Flux in Rice Paddies

Although rice paddy fields are one of the world’s largest anthropogenic sources of methane CH4, the budget of ecosystem CH4 and its’ controls in rice paddies remain unclear. Here, we analyze seasonal dynamics of direct ecosystem-scale measurements of CH4 flux in a rice-wheat rotation agroecosystem over 3 consecutive years. Results showed that the averaged CO2 uptakes and CH4 emissions in rice seasons were 2.2 and 20.9 folds of the wheat seasons, respectively. In sum, the wheat-rice rotation agroecosystem acted as a large net C sink (averaged 460.79 g C m−2) and a GHG (averaged 174.38 g CO2eq m−2) source except for a GHG sink in one year (2016) with a very high rice seeding density. While the linear correlation between daily CH4 fluxes and gross ecosystem productivity (GEP) was not significant for the whole rice season, daily CH4 fluxes were significantly correlated to daily GEP both before (R2: 0.52–0.83) and after the mid-season drainage (R2: 0.71–0.79). Furthermore, the F partial test showed that GEP was much greater than that of any other variable including soil temperature for the rice season in each year. Meanwhile, the parameters of the best-fit functions between daily CH4 fluxes and GEP shifted between rice growth stages. This study highlights that GEP is a good predictor of daily CH4 fluxes in rice paddies.

Application of enhanced-efficiency nitrogen fertilizers reduces mineral nitrogen usage and emissions of both N2O and NH3 while sustaining yields in a wheat-rice rotation system

The application of nitrification and urease inhibitors with urea can increase the residence time of ammonium (NH4+) in soils and thus reduce nitrogen (N) losses to the environment. We therefore hypothesized that these inhibitors would perform better in enhancing crop yield and lowering nitrous oxide (N2O) and ammonia (NH3) emissions in rice preferring NH4+ than in wheat preferring nitrate (NO3–). Additionally, a biostimulant (BS) when co-applied with urea would improve N uptake and thus reduce N loss as well. Thereby, the objective of this two-year field experiment was to evaluate the effects of urease inhibitor (UI) N-(n-butyl) thiophosphorictriamide (NBPT), the new nitrification inhibitor (NI) 3,4-dimethylpyrazole succinic acid (DMPSA), dual inhibitors (UI + NI) (NBPT + DMPSA), and a BS on crop yield and soil N2O and NH3 emissions in a wheat-rice rotation system. Treatments comprised no N fertilizer (Zero-N), urea under conventional practice (CN), and urea at a reduced rate by 20% either alone (RN) or combined with UI, NI, UI + NI, or BS. Averagely, RN treatment decreased N2O and NH3 emissions by 29.9% and 21.7%, respectively, but reduced grain yield and N use efficiency by 13.1% and 16.3%, respectively, compared with the CN treatment, although not always significantly. However, the combined use of RN and UI, NI, UI + NI, or BS resulted in comparable grain yield and N use efficiency but with lesser N2O and NH3 emissions by 56.4% and 36.1%, respectively averaged across treatments compared with CN treatment. We demonstrated that both inhibitors performed better in reducing N2O and NH3 emissions in rice than in wheat. Overall, we propose that the application of NBPT, DMPSA, and BS could be an effective strategy to mitigate gaseous N pollution while sustaining crop yields in the wheat-rice rotation system.

The Distribution of Fusarium graminearum and Fusarium asiaticum Causing Fusarium Head Blight of Wheat in Relation to Climate and Cropping System

In the main wheat production area of China (the Huang Huai Plain [HHP]), both Fusarium graminearum and Fusarium asiaticum, the causal agents of Fusarium head blight (FHB), are present. We investigated whether the relative prevalence of F. graminearum and F. asiaticum is related to cropping systems and/or climate factors. A total of 1,844 Fusarium isolates were obtained from 103 fields of two cropping systems: maize-wheat and rice-wheat rotations. To maximize the differences in climatic conditions, isolates were sampled from the north and south HHP regions. Based on the phylogenetic analysis of EF-1α and Tri101 sequences, 1,207 of the 1,844 isolates belonged to F. graminearum, and the remaining 637 isolates belonged to F. asiaticum. The former was predominant in the northern region: 1,022 of the 1,078 Fusarium isolates in the north were F. graminearum. The latter was predominant in the southern region: 581 of the 766 Fusarium isolates belonged to F. asiaticum. Using an analysis based on generalized linear modeling, the relative prevalence of the two species was associated more with climatic conditions than with the cropping system. F. graminearum was associated with drier conditions and cooler conditions during the winter but also with warmer conditions in the infection and grain-colonization period as well as with maize-wheat rotation. The opposite was true for F. asiaticum. Except for the 15-acetyldeoxynvalenol genotype, the trichothecene chemotype composition of F. asiaticum differed between the two cropping systems. The 3-acetyldeoxynivalenol genotype was more prevalent in the maize-wheat rotation, whereas the nivalenol genotype was more prevalent in the rice-wheat rotation. The results also suggested that environmental conditions in the overwintering period appeared to be more important than those in the infection, grain-colonization, and preanthesis sporulation periods in affecting the relative prevalence of F. graminearum and F. asiaticum. More research is needed to study the effect of overwintering conditions on subsequent epidemic in the following spring.

Effects of elevated air CO2 concentrations on the carbon and nitrogen contents of rice and winter wheat

Investigating the effects of different air CO2 concentrations on the carbon (C) and nitrogen (N) contents of straw and roots of different generations of crops is crucial to predict crop responses to elevated CO2. We performed a field experiment with open-top chambers (OTCs) and applied consecutively elevating CO2 concentrations (120 ppm and 160 ppm during the investigated 2018 rice and 2018–2019 winter wheat seasons, respectively, with a consecutive increase of 40 ppm per year beginning from the first winter wheat–rice rotation season in November 2015) and a continuously elevated CO2 concentration of 200 ppm during each season. The results indicated that elevated CO2 concentrations generally increased the root C content of both rice and winter wheat. The most obvious effects between the treatments appeared in the crops grown from seeds harvested in the OTCs each season. An elevated CO2 concentration increased the rice root N content, with more obvious effects over multiple generations that had been planted in the OTCs for three or four growing seasons than on a single generation that was planted in the OTCs for only one growing season. An elevated CO2 concentration also induced an increase in the ratio of C to N (C/N) in the roots of rice and in the straw and roots of winter wheat. The C content of the rice and winter wheat roots increased significantly with increasing root N content. The enhancement effect of an elevated CO2 concentration on the C and N content and the C/N ratios in rice and winter wheat is more significant for multiple generations than for one generation.

Effects of organic fertilizer application on crop yield and soil properties in rice-wheat rotation system: A meta-analysis

To clarify the effects of organic fertilizer application on crop yield and soil properties in rice-wheat rotation system in China, we carried out a meta-analysis to quantitatively evaluate the effects of organic fertilizer types (ordinary organic fertilizer, biochar, and straw), fertilization regimes (organic fertilizer alone, organic fertilizer + partial chemical fertilizer, and organic fertilizer + full amount of chemical fertilizer), and experiment duration (short term, medium term, and long term) on soil properties and the yield of rice and wheat, as well as their responses to soil conditions (acid, neutral, basic). Results showed that the application of organic fertilizer had similar yield-increase effect on rice yield (3.1%) and wheat yield (3.0%) compared to chemical fertilizer application alone. The effect of organic fertilizer application on soil quality was more obvious, significantly reducing soil bulk density by 5.7%, and increasing the concentrations of soil organic matter, total nitrogen, total phosphorus, alkali-hydrolyzable nitrogen, available phosphorus, available potassium, microbial biomass carbon, and microbial biomass nitrogen by 11.7%-38.4%. Among different types of organic fertilizer, the effects of ordinary organic fertilizer and biochar on soil properties improvement were better than straw. Compared to the organic fertilizer application alone, the effects of organic fertilizer combined with chemical fertilizer on crop yield was better, but poorer on soil property improvement. With the increasing duration of organic fertilizer application, crop yield and soil fertility gradually increased. Under the condition of acid soil, the effect of organic fertilizer application on crop yield was the best. The annual yield of rice and wheat showed significant negative correlation with soil bulk density, but a significant positive correlation with the concentrations of soil total nitrogen, available phosphorus, available potassium, and microbial biomass nitrogen.