Rice Yield Reduction Research Articles

Upland rice intercropping with Solanum nigrum inoculated with arbuscular mycorrhizal fungi reduces grain Cd while promoting phytoremediation of Cd-contaminated soil

Intercropping of hyperaccumulators with crops is a promising measure to enhance phytoremediation without impeding agricultural production. A Cd-hyperaccumulator, Solanum nigrum L. (S. nigrum), was intercropped with upland rice in a pot and rhizo-box experiment with Cd-contaminated soil to evaluate the combined effects of intercropping and arbuscular mycorrhizal fungi on plant growth and Cd accumulation. The results showed that, compared with monoculture, the combined treatments markedly decreased Cd concentration in rice parts, with the lowest Cd concentration in brown rice (reducing by 64.5%). The spatial distribution of root surface area and DTPA-Cd in the rhizo-box indicated competitive Cd uptake by neighbouring S. nigrum. Moreover, the combined treatments reduced Nramp5 expression but increased HMA3 levels in rice roots, leading to lower bioaccumulation and transfer coefficients. Additionally, fewer secreted organic acids and a higher rhizosphere pH were observed in rice. Conversely, the combined treatments promoted biomass, root length, root surface area, and decreased the rhizosphere pH in S. nigrum, thus increasing the Cd accumulation. Although the intercropping system with AMF inoculation notably reduced rice yield, the land-use efficiency was higher. These results provided insights into the role of AMF in the upland rice/S. nigrum system and demonstrated an alternative system for Cd phytoremediation.

Rice cultivar response to sublethal concentrations of glyphosate and paraquat late in the season

AbstractDifferential tolerance may be observed among rice cultivars with desiccant exposure events during rice reproduction and ripening. Five field studies were established at the Mississippi State University Delta Research and Extension Center in Stoneville, MS, to determine the effects of exposure to sublethal concentrations of common desiccants across multiple rice cultivars. Rice cultivars in the study were ‘CLXL745’, ‘XL753’, ‘CL163’, ‘Rex’, and ‘Jupiter’. Desiccant treatments included no desiccant, paraquat, or glyphosate and were applied at the 50% heading growth stage respective to cultivar. Differential injury estimates among cultivars and desiccant treatments was observed when glyphosate or paraquat was applied at 50% heading. Injury from glyphosate at 50% heading was nondetectable across all cultivars. However, injury following paraquat applications was >7% across all rating intervals and cultivars. Hybrid cultivars exhibited less injury with paraquat applications than the inbred cultivars in the study. Rice following exposure to glyphosate or paraquat at 50% heading growth stage produced rough rice grain yield decreases ranging from 0% to 20% and 9% to 21%, respectively. Rough rice grain yield decreases were observed across all cultivars following paraquat exposure, and all inbred cultivars following glyphosate exposure. Across desiccant treatment, head rice yield was reduced in three of five cultivars in the study. When pooled across cultivar, paraquat applications cause a head rice yield reduction of 10%, whereas rice yield following glyphosate application remained >95%. Although differential tolerance among cultivars to paraquat or glyphosate exposure was observed, impacts on grain quality coupled with yield reductions suggests extreme rice sensitivity to exposure to sublethal concentrations of these desiccants at the 50% heading growth stage.

Allelic variation in rice Fertilization Independent Endosperm 1 contributes to grain width under high night temperature stress.

Summary A higher minimum (night‐time) temperature is considered a greater limiting factor for reduced rice yield than a similar increase in maximum (daytime) temperature. While the physiological impact of high night temperature (HNT) has been studied, the genetic and molecular basis of HNT stress response remains unexplored.We examined the phenotypic variation for mature grain size (length and width) in a diverse set of rice accessions under HNT stress. Genome‐wide association analysis identified several HNT‐specific loci regulating grain size as well as loci that are common for optimal and HNT stress conditions.A novel locus contributing to grain width under HNT conditions colocalized with Fie1, a component of the FIS‐PRC2 complex. Our results suggest that the allelic difference controlling grain width under HNT is a result of differential transcript‐level response of Fie1 in grains developing under HNT stress.We present evidence to support the role of Fie1 in grain size regulation by testing overexpression (OE) and knockout mutants under heat stress. The OE mutants were either unaltered or had a positive impact on mature grain size under HNT, while the knockouts exhibited significant grain size reduction under these conditions.

Allelopathic effect of Sphenoclea zeylanica Gaertn. on rice (Oryza sativa L.) germination and seedling growth

The allelopathic effect of Sphenoclea zeylanica Gaertn., a broadleaf paddy weed that hinders rice production in Thailand, was investigated. Different parts of S. zeylanica were used to determine their inhibitory effect on seed germination, and shoot and root length of rice in a laboratory. Aqueous extracts of leaves and stems had an inhibitory effect on rice germination and seedling growth more than 50% that of control at concentrations higher than 50 g L-1, whereas all concentrations of root extracts had no effect on rice seeds. At the concentration of 100 g L-1, leaf and stem extracts completely (100%) inhibited rice seed germination. The inhibitory effect was increased with increasing concentrations. Additionally, leaf extracts contained higher total phenolics (7.36 mg GE g-1 DW) and total flavonoids (254.19 µg QE g-1 DW) than extracts of other parts. In glasshouse conditions, soil incorporation with dried whole plant residue had a significant inhibitory effect on rice emergence, seedling height, and dry weight when compared with extracted residue at an equal concentration. The decomposition of S. zeylanica in the soil was also evaluated regarding rice seedling growth. The maximum inhibition was achieved 1-3 days after the application of plant residues. At the 30th day, the inhibition disappeared, suggesting that residue decomposition in the soil has been finished. These results support that S. zeylanica has an allelopathic effect on paddy fields, which may cause a reduction in rice growth and yield.

Assessment of rice leaf blast severity using hyperspectral imaging during late vegetative growth

Rice blast (Magnaporthe grisea) is an epidemic rice disease that reduces rice yield and quality worldwide. The objective of this study was to present and evaluate a data reconstruction method for assessment of rice leaf blast severity using hyperspectral imaging technology at the late vegetative growth stage. Experiments were carried out on Mongolian rice, which is susceptible to the disease. To carry out the study under natural conditions, rice was cultivated without any disease control measures. We obtained hyperspectral images of rice leaves and extracted average spectral reflectance data for entire leaves and undiseased leaf regions. To analyze the hyperspectral data, we presented a spectral reflectance ratio (SRR) data reconstruction method. A support vector machine model was constructed to identify five infection severities based on the transformed data. The classification accuracy of the model at jointing, booting and heading stages was 83.33%, 97.06% and 83.87%, respectively. According to our results, the SRR data reconstruction method presented here can be used to assess rice leaf blast severity during late vegetative growth.

An endophytic strain JK of genus bacillus isolated from the seeds of super hybrid rice (Oryza sativa L., Shenliangyou 5814) has antagonistic activity against rice blast pathogen

Rice is an important food crop in the world, and rice blast is one of the major fungal diseases that cause large-scale rice yield reduction. This study aimed to investigate the antagonistic activity and its molecular mechanism of bacterial strain JK isolated from seeds of super hybrid rice ‘Shenliangyou 5814’ (Oryza sativa L.) against rice blast pathogen Magnaporthe oryzae ACCC 36020. Through plate confrontation experiment, strain JK showed obvious and highly effective antagonistic activity against M. oryzae. And strain JK was identified as Bacillus velezensis by molecular biological identification basing on 16S rRNA gene and gyrA gene phylogenetic analysis. The draft genome of strain JK was sequenced by Illumina NextSeq500, and 1 CDS for beta-1,4-glucanase (cellulase), 1 CDS for endo-beta-1,3-1,4 glucanase (licheninase), 2 CDS for 3-hydroxybutyrate dehydrogenase, 4 CDS for surfactin synthase, 28 CDS for polyketide biosynthesis were annotated and correlated to antagonistic activity. The present study provides a theoretical basis and microbial strain resources for further study on the biological control of rice blast.

Spatiotemporal rice yield variations and potential agro-adaptation strategies in Bangladesh: A biophysical modeling approach

Rice (Oryza sativa) is the major cereal crop in the Southeast Asian region, and its yield variations are highly sensitive to climate change. Climate change will not only threaten regional food security but also affect the global economy. Considering the fact, this study intends to assess the spatiotemporal variations of rice yield and to evaluate the effectiveness of agro-adaptive measures under future climate change in the five rice-growing regions of Bangladesh. We simulated rice yield of the 21st century by driving the rice crop model (ORYZA2000) with downscaling climate data from the outputs of two General Circulation Models (GCMs) using the A1B scenario. The simulation results indicated the substantial rice yield reduction in the two future periods ignoring the carbon dioxide (CO2) effect, while the CO2 fertilization effect was considered, it could mitigate but still not fully compensate for the rice yield reduction. The significant reductions in yields were spatially greater in the northwest region than the southeast region but marginally from central to northeast regions of Bangladesh. Four global agro-adaptation strategies, e.g., shifting transplanting dates, introducing supplemental irrigation, transplanting date delaying, and extra irrigation would decrease rice yield losses significantly by the future periods of various extents. Based on the findings, it is found that a combination of transplanting dates delaying and supplementary irrigation has proved a more effective strategy for increasing rice yield than other adaptive measures. These agro-adaptation measures can be beneficial for sustainable future rice production in Bangladesh and other parts of the world.

Reproductive tissues-specific meta-QTLs and candidate genes for development of heat-tolerant rice cultivars.

By integrating genetics and genomics data, reproductive tissues-specific and heat stress responsive 35 meta-QTLs and 45 candidate genes were identified, which could be exploited through marker-assisted breeding for fast-track development of heat-tolerant rice cultivars. Rice holds the key to future food security. In rice-growing areas, temperature has already reached an optimum level for growth, hence, any further increase due to global climate change could significantly reduce rice yield. Several mapping studies have identified a plethora of reproductive tissue-specific and heat stress associated inconsistent quantitative trait loci (QTL), which could be exploited for improvement of heat tolerance. In this study, we performed a meta-analysis on previously reported QTLs and identified 35 most consistent meta-QTLs (MQTLs) across diverse genetic backgrounds and environments. Genetic and physical intervals of nearly 66% MQTLs were narrower than 5cM and 2Mb respectively, indicating hotspot genomic regions for heat tolerance. Comparative analyses of MQTLs underlying genes with microarray and RNA-seq based transcriptomic data sets revealed a core set of 45 heat-responsive genes, among which 24 were reproductive tissue-specific and have not been studied in detail before. Remarkably, all these genes corresponded to various stress associated functions, ranging from abiotic stress sensing to regulating plant stress responses, and included heat-shock genes (OsBiP2, OsMed37_1), transcription factors (OsNAS3, OsTEF1, OsWRKY10, OsWRKY21), transmembrane transporters (OsAAP7A, OsAMT2;1), sugar metabolizing (OsSUS4, α-Gal III) and abiotic stress (OsRCI2-7, SRWD1) genes. Functional data evidences from Arabidopsis heat-shock genes also suggest that OsBIP2 may be associated with thermotolerance of pollen tubes under heat stress conditions. Furthermore, promoters of identified genes were enriched with heat, dehydration, pollen and sugar responsive cis-acting regulatory elements, proposing a common regulatory mechanism might exist in rice for mitigating reproductive stage heat stress. These findings strongly support our results and provide new candidate genes for fast-track development of heat-tolerant rice cultivars.

Application of Chinese milk vetch affects rice yield and soil productivity in a subtropical double-rice cropping system

Green manure can be used as a substitute for chemical fertilizer without reducing rice yield. We studied the responses of soil fertility and rice yield to different combinations of Chinese milk vetch (CMV; Astragalus sinicus L.) and chemical fertilizer in a subtropical double-rice cropping system. Our goal is to reduce chemical fertilizer use and decrease environmental contamination. Compared with the recommended rate of chemical fertilizer (CF), both early- and late-rice yields in the two treatments supplied with 15 and 22.5 Mg CMV ha−1 plus 60% CF (represented as 60A and 60B, respectively) showed no significant differences while the two treatments supplied with 30 and 37.5 Mg CMV ha−1 plus 60% CF (represented as 60C and 60D, respectively) showed significantly higher values. The sustainable yield index (SYI) values in the 60C and 60D treatments with double-rice croppong system were significantly higher than those in other treatments (P<0.05). Early-rice yield showed a significant positive relationship with the Chinese milk vetch incorporation rate. The coefficients increased annually from 2009 to 2013 and then decreased in 2014. Soil organic matter increased over time by the end of the experiment in all of the treatment groups. Soil organic matter in 60A, 60B and 60C showed no significant difference compared with that in CF, while soil organic matter in 60D was significantly higher than that in CF. The slopes of soil organic matter and total nitrogen over six years were the highest in 60C and 60D. The soil total nitrogen content in 60A, 60B, 60C and 60D was higher than that in CF, but the differences were not significant (P>0.05). Therefore, a relatively high Chinese milk vetch incorporation rate (≥30 Mg ha−1) was more effective in improving the productivity and sustainability of paddy soil. The decreased coefficients of early-rice yield and the Chinese milk vetch incorporation rate in 2014 implied that the benefits of soil fertility and rice yield created by Chinese milk vetch input may decline after five years under a continuously high rate of Chinese milk vetch incorporation.

Spatiotemporal changes of surface solar radiation: Implication for air pollution and rice yield in East China

The changes of surface solar radiation (SSR) have significant implication for air pollution and rice yield. In this study, gridded SSR data, derived from multi-platform datasets and radiation model, were used to analyze its spatiotemporal changes over East China during 2000–2016. The results show SSR experiences dimming during 2000–2005, then turns into brightening till 2016. Both aerosol optical depth (AOD) and single scattering albedo (SSA) contribute to SSR trend. AOD dominates the spatiotemporal changes of SSR in East China, and this impact is higher in the North than the South. SSA has little impact on SSR with low AOD, but its contribution to SSR becomes important as AOD increases. Moreover, gridded planet boundary layer (PBL) was simulated by the Weather Research and Forecasting Model (WRF) and SSR-PBL relationship was also explored. Long-term evidence indicates PBL has a regulatory effect on SSR in the air pollution. Additionally, aerosol-induced radiation reduction can influence rice yield in East China, and it can result in about mean 6.74% reduction in rice yield over East China. Province-level changes of aerosol-induced reduction in rice production were also evaluated and it suggests the impact of aerosols on rice production is non-negligible, especially in Jiangsu and Anhui Province. Our study underscores the importance of aerosol pollution on surface radiation and the mitigation of aerosols is beneficial for crop production under climate change.

Seasonal variation and vertical distribution of nematode communities and their relation to soil chemical property and rice productivity under triple rice cultivation in the Mekong Delta, Vietnam

Summary Rice is an important agricultural crop in Vietnam. Nematodes are diverse in soil agroecosystems. However, little is known about their seasonal variation in extremely intensive rice cultivation in tropical regions. The objectives of this study were to investigate the seasonal variation and spatial distribution of the nematode community, and to assess its relationship with the soil chemical property and rice yield. Soils (0-10 cm and 10-20 cm deep) were collected at harvest in spring-summer (S-S), summer-autumn (S-A), and winter-spring (W-S) cultivation in 2017 and 2018. Plant-parasitic nematodes were the largest group and accounted for 47-80 and 79-92% of total nematode abundance in the topsoil and subsoil, respectively. Hirschmanniella was the most dominant taxon whose abundance in topsoil varied from 275-739 in W-S to 1010-1270 indiv. (100 g soil)−1 in the S-S season. Nematode assemblages differed between topsoil and subsoil, and those of topsoil had clear seasonal distribution patterns. Bacterivore nematodes were the predominant group of free-living nematodes, with increasing relative abundance in the topsoil of S-S (average 23.2% of total free-living nematodes) &lt; S-A (average 41.9%) &lt; W-S (average 57.3%). Furthermore, soil in the W-S season had the highest microbial activity in 2018. Soil pH, EC and abundance of Hirschmanniella spp. were significantly negatively related with rice yield. The present results suggest that the presence of Hirschmanniella spp. in soil may be involved in a reduction of rice yield in the triple rice system.

Bio-Economics of Different Dry Direct Seeded Winter Rice Based Intercropping Systems Under Varying Fertilizer Management

The experiment was conducted at the Agronomy Field Laboratory, Bangladesh Agricultural University, Mymensingh during February to June 2017 to study the feasibility of different direct seeded rice based intercropping systems under varying fertilizer management. The experiment was conducted in afactorialrandomized complete block design with three replications. Four leafy vegetables viz., gimakalmi, Indian spinach, red amaranth andjute were intercropped with dry direct seeded boro rice (cv. BRRI dhan28) following three fertilizer dose such as 100, 75 and 125% of recommended fertilizer, and sole rice was also maintained as control. Rice yield was the highest (3.87t ha-1) in sole cropping, and intercroppingresulted insignificant rice yield reduction. Although inintercropping rice yielddecreased, but increased both gross margin and benefit cost ratio (BCR) as compared to rice sole cropping. Among the vegetables, gimakalmi performed the best followed by red amaranth in terms of yield and 125% recommended fertilizer was the best fertilizer dose. Gimakalmi intercropped with rice following 125% recommended fertilizer showed the highest gross return and BCR (2.53). Therefore, vegetables like gimakalmi and red amaranth couldbe recommended as intercrop with dry direct seeded winter rice with 125% recommended fertilizer for better productivity and higher economicreturn.&#x0D; Bangladesh Agron. J. 2019, 22(2): 103-112

Responses of Lowland, Upland and Aerobic Rice Genotypes to Water Limitation During Different Phases

Rice yield reduction due to water limitation depends on its severity and duration and on the phenological stage of its occurrence. We exposed three contrasting rice genotypes, IR64, UPLRi7 and Apo (adapted to lowland, upland and aerobic conditions, respectively), to three water regimes (puddle, 100% and 60% field capacity) in pots during the vegetative (GSI), flowering (GSII) and grain filling (GSIII) stages. Stress at all the three stages significantly reduced yield especially in lowland genotype IR64. Effect of water limitation was more severe at GSII than at the other two stages. Stress at GSI stage reduced both source activity (leaf area and photosynthetic rate) and sink capacity (tiller number or panicle number per pot). When stress was imposed at GSII, spikelet fertility was most affected in all the three genotypes. In both GSII and GSIII, although leaf area was constant in all the three water regimes, estimated relative whole-plant photosynthesis was strongly associated with yield reduction. Reduced photosynthesis due to stress at any given stage was found to have direct impact on yield. Compared to the other genotypes, Apo had deeper roots and maintained a better water relation, thus, higher carbon gain and spikelet viability, and ultimately, higher biomass and productivity under water-limited conditions. Therefore, screening for these stage-dependent adaptive mechanisms is crucial in breeding for sustained rice production under water limitation.

UJI KETAHANAN PADI LOKAL POTENSIAL ASAL BARAT-SELATAN ACEH TERHADAP PENYAKIT HAWAR DAUN BAKTERI

Aceh Province has many local varieties that are still cultivated by farmers, especially in the South-West Region of Aceh, the local rice needs to be identified and used as a source of genes in the assembly of new improved varieties to support food security and sustainable agriculture. Bacterial leaf blight (HDB) is one of the limiting factors in rice production. HDB disease is caused by Xanthomonas oryzae pv. oryzae (Xoo), which can reduce rice yield by 30-40%. However, the potential of these varieties as sources of resistance genes against HDB has not been evaluated. This study aims to determine and obtain the potential genotypes of local rice in the West-South Region of Aceh that are resistant to Bacterial Leaves Disease. The research was carried out at the Experimental Garden of the Faculty of Agriculture, Teuku Umar University, Meulaboh, West Aceh from January to completion. The research was carried out starting from the treatment and seeding, preparation of planting media, planting, observation variables: Plant height and number of tillers per age 60 HST, incubation period and length of the observed lesio: 21 HSI: Test results of potential local rice resistance in the West- South Aceh obtained 9 genotypes that are resistant to bacterial leaf blight. The genotypes are used as genetic sources for assembling new high yielding varieties Keywords : Bacterial, Bacterial leaf blight, rice of local varieties,

Improvement of the CERES-Rice model using controlled experiments and a Meta-analysis

Extreme heat has occurred more frequently in recent years and will intensify in the future, and this change has serious impacts on rice (Oryza sativa L.) yields. Thus, it was crucial to evaluate its influence on rice yield reductions. Recent papers have shown that a lack of experimental data makes it difficult for most crop models to capture the impacts of heat stress. Therefore, this paper explored how to improve the performance of crop models under extreme heat stress based on the Decision Support System for Agrotechnology Transfer (DSSAT) CERES-Rice model. This study primarily focused on (i) quantifying spikelet fertility based on daily temperature and durations derived from controlled experiments, (ii) improving the performance of the CERES-Rice model under extreme heat stress, and (iii) simulating historical and future rice yields using the improved model. Specifically, a meta-analysis method was utilized to build a new heat stress function between spikelet fertility and temperature and heat day duration with high realization. Subsequently, independent artificial controlled experiments at two sites were proposed to calibrate and validate the CERES-Rice model. The results showed a higher R2 (> 0.739) and a lower RMSE that was reduced by 38~68% after incorporating the new heat stress function in the CERES-Rice model compared with that of the original model. Furthermore, a historical simulation (1980–2010) demonstrated that an improved CERES-Rice model could better capture rice yield in response to extreme heat. Using an ensemble of five climate model datasets and four Representative Concentration Pathways (RCPs), the analysis of the projected future (2020–2099) rice yield showed that the rice yield reduction caused by high temperature was considerable; however, the rice yields were overestimated by 34% and 18%, respectively, at the two sites. Some regions rarely affected by heat are likely to experience yield reductions in the future due to climate change.

Influence of integrated nutrient management and spacing on growth and yield of rice (BIRRI dhan69)

With the development of high yielding rice varieties, use of chemical fertilizers increased rapidly in Bangladesh. Depending on chemical fertilizer solely is not wise and maintaining soil health becomes a great concern worldwide. The purpose of the study is to know about the effect of organic and inorganic fertilizer on growth and yield of rice. The experiment was laid out in a split-plot design with four nutrient managements (N1= BRRI recommended fertilizer dose (N-P-K-S-Z = 117-19-58-15-4 kg ha-1), N2= 75% of BRRI recommended dose, N3= 75% of BRRI recommended dose + Decomposed poultry litter (DPL) (2.5 t ha-1) and N4= No fertilizer) in the main plots and three spacing(S1= 20 cm × 20 cm, S2= 20 cm × 15 cm and S3= 25 cm × 15 cm) in the subplots with three replications. In growth and yield characteristics, insignificant difference was found for different spacing but significant difference was found for different nutrient managements. N1 and N3 performed better than N2 and N4 in all observed characteristics. N1 and N3 gave statistically similar result in yield. The result revealed that, with the application of 2.5 t ha-1 DPL we can reduce 25% chemical fertilizer without yield reduction in rice.&#x0D; Res. Agric., Livest. Fish.7(1): 25-32, April 2020

PENGELOLAAN LINGKUNGAN CEKAMAN SALIN UNTUK MENINGKATKAN HASIL PADI

Management of the environment which is gripped by saline is very necessary to increase the yield of rice. The research was carried out in the farmers' land of Indramayu-West Java district in February - July 2019 using a split plot design with 3 replications. The variety used is Inpari 34. The treatment is gypsum dossage and organic matter. The results showed that the management of saline environmental stress by giving gypsum and organic matter did not affect plant growth including the number of tillers, leaf greenness value and yield on rice. Gypsum 1 ton/ha will provide maximum results 2,375 tons/ha dried grain if accompanied by the provision of 4 tons of organic matter/ha. Gypsum 1 ton/ha with organic matter more than 4 tons/ha will reduce rice yield. Gypsum application of 3 tons / ha reaches 2,6792 tons ha without the provision of organic matter.

Understanding sheath blight resistance in rice: the road behind and the road ahead.

SummaryRice sheath blight disease, caused by the basidiomycetous necrotroph Rhizoctonia solani, became one of the major threats to the rice cultivation worldwide, especially after the adoption of high‐yielding varieties. The pathogen is challenging to manage because of its extensively broad host range and high genetic variability and also due to the inability to find any satisfactory level of natural resistance from the available rice germplasm. It is high time to find remedies to combat the pathogen for reducing rice yield losses and subsequently to minimize the threat to global food security. The development of genetic resistance is one of the alternative means to avoid the use of hazardous chemical fungicides. This review mainly focuses on the effort of better understanding the host–pathogen relationship, finding the gene loci/markers imparting resistance response and modifying the host genome through transgenic development. The latest development and trend in the R. solani–rice pathosystem research with gap analysis are provided.

Ozone-induced reduction in rice yield is closely related to the response of spikelet density under ozone stress

Six modern rice cultivars, including three indica and three japonica cultivars were exposed to 100 ppb ozone (8 h per day) and control conditions throughout cropping season in 2016 to 2017 at Yangzhou, China. Ozone decreased plant height and inhibited tillering development as well as panicle number per plant of all cultivars, but had no effect on the productive tiller ratio. Ozone significantly decreased spikelet number per panicle, spikelet number per plant, fully-filled grain percentage and fully-filled grain weight, resulting in yield decrease by 39.3% on average for all cultivars and by 42.6 and 34.4% in the indica and the japonica groups, respectively. The response of aboveground biomass to ozone was similar to that of yield, albeit with a lower decrease, which led to a 7.6% decrease in harvest index. In terms of grain positions (grains attached to the upper primary rachis: superior spikelet (SS); grains attached to the lower secondary rachis: inferior spikelet (IS), and the remaining grains: medium spikelet (MS)), the ozone-induced change in yield traits (yield, spikelet number per panicle, spikelet number per plant, fully-filled grain percentage, and empty grain percentage) followed the order IS > MS > SS, as indicated by the significant interaction between ozone and grain position. Although ozone had negative effects on all yield traits, only ozone-induced reduction in spikelet density (spikelet number per panicle and or spikelet number per plant) was significantly correlated to yield loss. Grain yield showed significant ozone by cultivar and ozone by year interactions, indicating ozone impacts on rice yield varied with meteorological conditions and cultivars.

Yield reduction of direct-seeded rice under returned straw can be mitigated by appropriate water management improving soil phosphorus availability

The yield of direct-seeded rice has been shown to decrease after straw amendment. However, the reasons for the yield decrease, and any measures to alleviate it, are currently unknown. We hypothesised that straw return exerts negative effects on soil fertility and on root growth of direct-seeded rice, which subsequently reduces the remobilisation of reserves to grains under continuous flooding (CF); and that alternate wetting and drying (AWD) irrigation can alleviate these negative impacts. Field and greenhouse experiments were conducted to test the hypotheses, by comparing CF and AWD in combination with two wheat-straw treatments (incorporation and mulching). Under CF, wheat-straw incorporation decreased soil available phosphorus by 23–79%, root biomass by 10%, leaf biomass by 13%, and leaf area by 15% compared with the control with no straw incorporation; negative effects on these characteristics were lessened if the straw was mulched. The AWD treatment alleviated the negative effects of straw incorporation compared with CF, and straw mulching with AWD had no negative effects or resulted in positive effects. The results suggest that CF along with straw incorporation limits soil phosphorus availability, root growth and grain yield by affecting photosynthate accumulation and remobilisation. AWD irrigation mitigates these undesirable effects by decreasing soil total reductants, which subsequently increases soil pH and plant-available phosphorus. The proposed AWD treatment could be a promising strategy for the sustainable production of direct-seeded rice.