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    水稻耕作栽培合辑Rice Physiology · Biochemistry · Cultivation · Tillage

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    Photosynthetic properties of the mid-vein and leaf lamina of field-grown, high-yield hybrid rice during senescence
    GAO Zhi-ping, XU Min-li, ZHANG Hai-zi, LÜ Chuan-gen, CHEN Guo-xiang
    2022, 21 (7): 1913-1926.   DOI: 10.1016/S2095-3119(21)63676-6
    Abstract146)      PDF in ScienceDirect      
    Previous studies with rice (Oryza sativa L.) have shown that the different components of the photosynthetic apparatus are not uniformly synthesized or degraded during senescence.  However, while most of those studies have focused on the leaf lamina, few have addressed senescence-associated chloroplast function or leaf physiology.  Here, we investigated the photosynthetic properties of the mid-vein and leaf lamina in a high-yield hybrid rice cultivar (Liangyoupei 9, LYP9) during the senescence stage.  Assimilation and transpiration decreased more slowly in the mid-vein than in the lamina during senescence, suggesting more sustained photosynthesis in the mid-vein, as well as stronger heat dissipation.  Two-dimensional gel electrophoresis suggested that photosynthesis and energy metabolism were less affected by senescence in the mid-vein than in the leaf lamina.  During late senescence, the excess energy dissipation in the mid-vein through the xanthophyll cycle had a higher active photosynthetic capacity than in the leaf lamina, and we inferred that the mid-vein and leaf lamina of LYP9 rice differed in terms of their maturation.  Taken together, these results provide new insights into the underlying mechanisms of senescence of the rice mid-vein and associated physiology.
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    Optimization of nitrogen fertilization improves rice quality by affecting the structure and physicochemical properties of starch at high yield levels
    ZHOU Tian-yang, LI Zhi-kang, LI En-peng, WANG Wei-lu, YUAN Li-min, ZHANG Hao, LIU Li-jun, WANG Zhi-qin, GU Jun-fei, YANG Jian-chang
    2022, 21 (6): 1576-1592.   DOI: 10.1016/S2095-3119(21)63678-X
    Abstract220)      PDF in ScienceDirect      
    A major challenge in modern rice production is to achieve the dual goals of high yield and good quality with low environmental costs.  This study was designed to determine whether optimized nitrogen (N) fertilization could fulfill these multiple goals.  In two-year experiments, two high yielding ‘super’ rice cultivars were grown with different N fertilization management regimes, including zero N input, local farmers’ practice (LFP) with heavy N inputs, and optimized N fertilization (ONF).  In ONF, by reducing N input, increasing planting density, and optimizing the ratio of urea application at different stages, N use efficiency and the physicochemical and textural properties of milled rice were improved at higher yield levels.  Compared with LFP, yield and partial factor productivity of applied N (PFP) under ONF were increased (on average) by 1.70 and 13.06%, respectively.  ONF increased starch and amylose content, and significantly decreased protein content.  The contents of the short chains of A chain (degree of polymerization (DP) 6–12) and B1 chain (DP 13–25) of amylopectin were significantly increased under ONF, which resulted in a decrease in the stability of rice starch crystals.  ONF increased viscosity values and improved the thermodynamic properties of starch, which resulted in better eating and cooking quality of the rice.  Thus, ONF could substantially compensate the negative effects caused by N fertilizer and achieve the multiple goals of higher grain quality and nitrogen use efficiency (NUE) at high yield levels.  These results will be useful for applications of high quality rice production at high yield levels.
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    Growth characteristics and grain yield of machine-transplanted medium indica hybrid rice with high daily yield
    DENG Fei, HE Lian-hua, CHEN Duo, ZHANG Chi, TIAN Qing-lan, WU Zhen-yuan, LI Qiu-ping, ZENG Yu-ling, ZHONG Xiao-yuan, CHEN Hong, WANG Li, REN Wan-jun
    2022, 21 (9): 2547-2558.   DOI: 10.1016/j.jia.2022.07.030
    Abstract158)      PDF in ScienceDirect      
    High-yield rice varieties with a suitable growth duration are required for mechanical transplanting in multiple cropping systems.  Daily yield is an appropriate criterion for the selection of machine-transplanted rice varieties.  The aim of this study was to investigate the growth characteristics and grain production in machine-transplanted medium indica hybrid rice with a high daily yield.  We conducted a field experiment on 20 medium indica hybrid rice varieties in 2017 and 2018.  Grain yield decreased significantly with growth duration between jointing and heading, but it increased with dry matter accumulation, growth rate between jointing and heading, dry matter partitioning to the stem plus sheath at heading, daily yield, and number of spikelets per panicle.  Compared with the medium and low daily yield variety types, the high daily yield variety type increased shoot biomass by improving crop growth rate and dry matter accumulation amount between jointing and heading and after heading.  The high daily yield variety type decreased the growth duration pre-heading and the proportions of dry matter partitioned to the leaf lamina at heading and maturity, but it also increased the post-heading accumulated dry matter in the grain and the remobilization of dry matter stored in the vegetative organs.  Furthermore, the high daily yield variety type significantly increased the occurrence rate of tillers, which is beneficial for the formation of a larger panicle size and an increase in the grain-filling rate.  These changes contributed to a 6.51–23.16% relative increase in grain yield of the high daily yield variety type.  In conclusion, the selection of high daily yield indica hybrid rice varieties with shorter pre-heading growth duration, greater tiller occurrence rate and spikelet numbers per panicle, higher post-jointing growth rates and stem plus sheath dry matter accumulation at heading is suitable for machine-transplanted rice.
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    Moderate drought alleviate the damage of high temperature to grain quality by improving the starch synthesis of inferior grain in japonica rice
    TONG Hui, DUAN Hua, WANG Sheng-jun, SU Jing-ping, SUN Yue, LIU Yan-qing, TANG Liang, LIU Xue-jun, CHEN Wen-fu
    2022, 21 (10): 3094-3101.   DOI: 10.1016/j.jia.2022.07.012
    Abstract175)      PDF in ScienceDirect      

    In agricultural production, temperature and moisture are important factors affecting grain yield and quality.  Although moderate drought at the grain-filling stage can effectively alleviate the damage caused by high temperature, the specific regulatory mechanism driving the effect of moderate drought at the high temperature on starch synthesis is still unclear.  To explore the effects and mechanisms of high temperature and moderate drought on rice starch synthesis at the grain-filling stage, the activities of enzymes and expression levels of the genes involved in starch synthesis under four different treatments involving high temperature and/or water stress (CK, HT, WS, and HT+WS) were investigated in this study.  The starch synthesis of a japonica inbred rice was measured under the four treatments during the grain filling.  The results show that the effects of high temperature and moderate drought on grain filling mainly occur in the inferior grains of rice.  Through the regulation of enzymes involved in starch synthesis and the expression levels of their main genes, the synthesis of rice starch can be affected.  Therefore, the high temperature and moderate drought were antagonistic, and moderate drought can alleviate the damage to grain quality at a high temperature by improving the starch synthesis of inferior grains in japonica rice.  This study provides a basis for stress-resistance cultivation and breeding strategies of rice with high temperature tolerance.

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    Grain yield and lodging-related traits of ultrashort-duration varieties for direct-seeded and double-season rice in Central China
    WANG Xin-yu, XU Le, LI Xiao-xiao, YANG Guo-dong, WANG Fei, PENG Shao-bing
    2022, 21 (10): 2888-2899.   DOI: 10.1016/j.jia.2022.07.035
    Abstract160)      PDF in ScienceDirect      
    Lodging is the most common constraint on grain yield of direct-seeded rice.  There is limited information about lodging resistance and its related plant traits in direct-seeded and double-season rice (DDR) in Central China.  This study aims  to identify the plant traits that achieve high lodging resistance in ultrashort-duration varieties (about 95 days) of DDR.  Field experiments were conducted in 2017 and 2018 in Wuxue County, Hubei Province, China, with four ultrashort-duration varieties grown under two nitrogen (N) rates.  Lodging-related traits were measured on the 15th day after heading, and yield and yield attributes were measured at maturity.  The grain yield of the four varieties ranged from 4.59 to 7.61 t ha–1 across the two N rates, with a total growth duration of 85 to 97 days.  Varietal differences in lodging index were mainly explained by the bending moment, which was closely related to plant height.  Breaking resistance did not affect the lodging index significantly.  Shortening plant height from 95.4 to 80.5 cm decreased the lodging index by 22.4% but did not reduce grain yield.  Our results suggested that reducing plant height was effective in improving the lodging resistance of ultrashort-duration varieties of DDR.  Lodging resistance should be enhanced by improving breaking resistance rather than reducing plant height to increase DDR grain yield further.
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    Deciphering the morpho–physiological traits for high yield potential in nitrogen efficient varieties (NEVs): A japonica rice case study
    ZHU Kuan-yu, YAN Jia-qian, SHEN Yong, ZHANG Wei-yang, XU Yun-ji, WANG Zhi-qin, YANG Jian-chang
    2022, 21 (4): 947-963.   DOI: 10.1016/S2095-3119(20)63600-0
    Abstract172)      PDF in ScienceDirect      
    The use of nitrogen (N)-efficient rice (Oryza sativa L.) varieties could reduce excessive N input without sacrificing yields. However, the plant traits associated with N-efficient rice varieties have not been fully defined or comprehensively explored.  Here, three japonica N-efficient varieties (NEVs) and three japonica N-inefficient varieties (NIVs) of rice were grown in a paddy field under N omission (0 N, 0 kg N ha–1) and normal N (NN, 180 or 200 kg N ha−1) treatments.  Results showed that NEVs exhibited higher grain yield and nitrogen use efficiency (NUE) than NIVs under both treatments, due to improved sink size and filled-grains percentage in the former which had higher root oxidation activity and greater root dry weight, root length and root diameter at panicle initiation (PI), as well as higher spikelet–leaf ratio and more productive tillers during the grain-filling stage.  Compared with NIVs, NEVs also exhibited enhanced N translocation and dry matter accumulation after heading and improved flag leaf morpho–physiological traits, including greater leaf thickness and specific leaf weight and higher contents of ribulose-1,5-bisphosphate carboxylase/oxygenase, chlorophyll, nitrogen, and soluble sugars, leading to better photosynthetic performance.  Additionally, NEVs had a better canopy structure, as reflected by a higher ratio of the extinction coefficient for effective leaf N to the light extinction coefficient, leading to enhanced canopy photosynthesis and dry matter accumulation.  These improved agronomic and physiological traits were positively and significantly correlated with grain yield and internal NUE, which could be used to select and breed N-efficient rice varieties.

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    Root characteristics and yield of rice as affected by the cultivation pattern of strong seedlings with increased planting density and reduced nitrogen application
    GUAN Xian-jiao, CHEN Jin, CHEN Xian-mao, XIE Jiang, DENG Guo-qiang, HU Li-zhen, LI Yao, QIAN Yin-fei, QIU Cai-fei, PENG Chun-rui
    2022, 21 (5): 1278-1289.   DOI: 10.1016/S2095-3119(20)63595-X
    Abstract145)      PDF in ScienceDirect      
    To address the relationships between the amount of nitrogen fertilizer application and the yield of double cropping rice systems, we investigated the effects of a cultivation pattern of strong seedlings with increased planting density and reduced nitrogen application (SDN) on the morphological and physiological characteristics of double cropping rice.  Our results indicated that the effects of SDN on the morphological characteristics of the single plant roots of double cropping rice were not significant, but the morphological characteristics of the population roots were largely different.  Specifically, SDN significantly increased the morphological indexes of the root population such as root fresh weight, root volume, root number, root length and root dry weight.  The effects of SDN on the total root absorption areas and root active absorption areas of the single plants were non-significant, but it dramatically enhanced the total root absorption areas and root active absorption areas of the plant population during the tillering, heading and mature stages.  In addition, SDN significantly increased the root bleeding intensity and elevated the soluble sugar and free amino acid contents of root bleeding sap.  Compared to the traditional cultivation pattern (CK), SDN significantly increased root bleeding intensity at the heading stage by 4.37 and 8.90% for early and late rice, respectively.  Meanwhile, SDN profoundly enhanced the soluble sugar contents of root bleeding sap by 12.85 and 10.41% for early and late rice, respectively.  In addition, SDN also significantly enhanced free amino acid content of root bleeding sap by 43.25% for early rice and by 37.50% for late rice systems compared to CK.  Furthermore, SDN increased the actual yield of double cropping rice mainly due to the higher effective panicle number and the larger seed-setting rate.  The actual yields of early rice under SDN were higher than CK by 9.37 and 5.98% in 2016 and 2017, and the actual yields of late rice under SDN were higher than CK by 0.20 and 1.41% in 2016 and 2017, respectively.  Correlation analysis indicated that the significant positive correlations were observed between the majority of the root indexes and the actual yield across the four different growth stages.

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    Higher leaf area through leaf width and lower leaf angle were the primary morphological traits for yield advantage of japonica/indica hybrids
    WEI Huan-he, YANG Yu-lin, SHAO Xing-yu, SHI Tian-yi, MENG Tian-yao, LU Yu, TAO Yuan, LI Xin-yue, DING En-hao, CHEN Ying-long, DAI Qi-gen
    2020, 19 (2): 483-494.   DOI: 10.1016/S2095-3119(19)62628-6
    Abstract117)      PDF in ScienceDirect      
    The yield potential of japonica/indica hybrids (JIH) has been achieved over 13.5 t ha–1 in large-scale rice fields, and some physiological traits for yield advantage of JIH over japonica inbred rice (JI) and indica hybrid rice (IH) were also identified.  To date, little attention has been paid to morphological traits for yield advantage of JIH over JI and IH.  For this reason, three JIH, three JI, and three IH were field-grown at East China (Ningbo, Zhejiang Province) in 2015 and 2016.  Compared with JI and IH, JIH had 14.3 and 20.8% higher grain yield, respectively, attributed to its more spikelets per panicle and relatively high percentage of filled grains.  The advantage in spikelets per panicle of JIH over JI and IH was shown in number of grains on the upper, middle, and lower branches.  Compared with JI and IH, JIH had higher leaf area through leaf width and lower leaf angle of upper three leaves, higher leaf area index and leaf area per tiller at heading and maturity stages, higher stem weight per tiller and K and Si concentrations of stem at maturity, higher dry matter weight in leaf, stem, and panicle at heading and maturity stages, and higher biomass accumulation after heading and lower biomass translocation from stem during ripening.  Leaf width of upper three leaves were correlated positively, while leaf angle of upper three leaves were correlated negatively with biomass accumulation after heading, stem weight per tiller, and per unit length.  Our results indicated that the grain yield advantage of JIH was ascribed mainly to the more spikelets per panicle and relatively high percentage of filled grains.  Higher leaf area through leaf width and more erect leaves were associated with improved biomass accumulation and stem weighing during ripening, and were the primary morphological traits underlying higher grain yield of JIH.
     
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    Putrescine, spermidine, and spermine play distinct roles in rice salt tolerance
    Md Azizul ISlam, PANG Jin-huan, MENG Fan-wei, LI Ya-wen, XU Ning, YANG Chao, LIU Jun
    2020, 19 (3): 643-655.   DOI: 10.1016/S2095-3119(19)62705-X
    Abstract77)      PDF in ScienceDirect      
    Polyamines (PAs) play diverse roles in plant growth and development, as well as responses to environmental stimuli.  In this study, the effects of PAs on rice salt tolerance were investigated.  Salt stress resulted in the alteration of endogenous PAs levels in rice roots and leaves, where spermidine (Spd) and spermine (Spm) contents were increased, and putrescine (Put) content was decreased.  RT-qPCR analysis revealed that PAs biosynthesis-related genes ADC1, ODC, and Arginase were significantly downregulated by salt treatment; however, SAMDC transcription was significantly upregulated.  Exogenous Spm enhanced rice salt tolerance remarkably; however, exogenous Put and Spd undermined rice salt tolerance.  Transgenic rice plants overexpressing SAMDC display a higher ratio of Spm/(Put+Spd) and enhanced salt tolerance.  Salt stress also increased polyamine oxidase activities in rice, resulting in elevated reactive oxygen species (ROS) production.  Our findings revealed that accumulation of Put and Spd substantially reduced salt tolerance in rice, likely by facilitating ROS production; whereas, conversion of Put and Spd to Spm contributes to rice salt tolerance.
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    Application of brassinolide alleviates cold stress at the booting stage of rice
    WANG Shi-qiang, ZHAO Hai-hong, ZHAO Li-ming, GU Chun-mei, NA Yong-guang, XIE Bao-sheng, CHENG Shi-hua, PAN Guo-jun
    2020, 19 (4): 975-987.   DOI: 10.1016/S2095-3119(19)62639-0
    Abstract125)      PDF in ScienceDirect      
    The objective of the study was to determine the physiological mechanisms of plants in response to brassinolide (BR) alleviating cold water stress on rice.  In this study, physiological responses of rice to exogenous BR and cold water submergence were investigated using the chilling-tolerant cultivar Kongyu 131 (KY131) and the chilling-sensitive cultivar Kenjiandao 6 (KJD6).  A total of 2 mg L–1 BR increased activities of superoxide dismutase (SOD) and peroxidase (POD) and the contents of soluble sugar, soluble protein, and chlorophyll, but decreased the malondialdehyde (MDA) content in KY131 and KJD6 under cold water stress.  The observed decreases in SOD and POD activities and MDA content recovered quickly after plants were returned to irrigation with water at temperatures of about 23.0°C in 2014.  Additionally, the contents of nitrogen (N), phosphorous (P), and potassium (K) were increased by BR treatment under cold water stress.  Exposure to BR also raised the percentage of high effective leaf area and leaf area index at the heading stage.  Furthermore, it promoted soluble sugar synthesis, increased the rate of dry matter accumulation, and enhanced the export and translocation rates of the stem-sheath.  The yield in KJD6 was significantly (P≤0.01 and P≤0.05) higher than that of the control in 2013 and 2014, respectively.  The effect of BR treatment on rice leaf SOD and POD activities, MDA, chlorophyll, P, and stem-sheath K contents were more significant in KJD6 than in KY131.  In conclusion, exogenous BR effectively reduced the physiological and metabolic damage in rice due to cold stress at the booting stage, promoted functional recovery in plants that received irrigation with water at a normal temperature following cold stress, and mitigated the effects of cold water stress on yield.  The two varieties exhibited differential responses to BR; the weaker cold-resistant variety was more sensitive to BR and displayed stronger responses to exogenous BR.
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    Characterization of eating quality and starch properties of two Wx alleles japonica rice cultivars under different nitrogen treatments
    HUANG Shuang-jie, ZHAO Chun-fang, ZHU Zhen, ZHOU Li-hui, ZHENG Qing-huan, WANG Cai-lin
    2020, 19 (4): 988-998.   DOI: 10.1016/S2095-3119(19)62672-9
    Abstract116)      PDF in ScienceDirect      
    To understand the effect of nitrogen (N) fertilizer on rice (Oryza sativa L.) eating and cooking quality (ECQ).  Here, we investigated the ECQ attributes, physicochemical foundation of ECQ, and amylopectin fine structure of two Waxy (Wx) alleles japonica rice cultivars Nanjing 9108 (NJ9108) and Huaidao 5 (HD5) under four N rates (0, 150, 300, and 450 kg ha–1).  Sensory and pasting properties of the two cultivars varied depending on N rates.  Compared with the control (0 kg ha–1), the overall eating quality and sensory value were significantly decreased under the N rates of 300 and 450 kg ha–1.  Further, conventional descriptive analysis showed that the stickiness and retrogradation of cooked rice were significantly decreased.  These results indicated that application of N fertilizer seems to affect the texture of cooked rice, causing it to be less sticky, lowering its retrogradation, and consequently reducing its palatability.  Results from rapid visco analyzer (RVA) revealed that the peak and breakdown viscosities significantly decreased, while the setback viscosity and peak time increased under the N rates of 300 and 450 kg ha–1.  However, no significant difference was observed when the N rate was 150 kg ha–1, indicating that less N fertilization can maintain rice ECQ.  As the N rate increasing, protein content increased, whereas apparent amylose content, starch content, and gel consistency almost unchanged.  Interestingly, compared with the control, under N treatments, the percentage of short amylopectin branches in NJ9108 was decreased, but increased in HD5, as controlled by amylopectin synthesis-related genes.  Notably, SSI and BEIIb were down-regulated in NJ9108, whereas BEIIb was up-regulated in HD5.  Thus, the palatability of both rice cultivars was significantly decreased under excessive N fertilization as a consequence of reduced stickiness and retrogradation of the cooked rice, which might have resulted from an elevated protein content and altered amylopectin fine structure.  In addition, amylopectin synthesis appeared to be affected by N fertilizer and the genotype of the rice cultivar.
     
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    Comparative analysis on grain quality and yield of different panicle weight indica-japonica hybrid rice (Oryza sativa L.) cultivars
    BIAN Jin-long, REN Gao-lei, HAN Chao, XU Fang-fu, QIU Shi, TANG Jia-hua, ZHANG Hong-cheng, WEI Hai-yan, GAO Hui
    2020, 19 (4): 999-1009.   DOI: 10.1016/S2095-3119(19)62798-X
    Abstract86)      PDF in ScienceDirect      
    Indica-japonica hybrid rice (Oryza sativa L.) cultivars showed high yield potential and poor tasting quality when compared with common japonica rice cultivars.  Large panicle is a prominent factor of high yield for indica-japonica hybrid rice cultivars, and the panicle weight varies greatly among different indica-japonica hybrid rice cultivars.  It is important to research on yield and grain quality of different panicle weight indica-japonica hybrid rice cultivars.  In this study, two different panicle types indica-japonica hybrid cultivars were used to research on the relation of yield and grain quality.  The yields of two heavy panicle weights indica-japonica hybrid cultivars were significantly higher than that of two medium panicle weight rice cultivars.  The cooking and eating quality and starch properties of different panicle type cultivars were evaluated.  Yongyou 6715 (medium panicle) and Yongyou 1852 (heavy panicle) got the relatively higher cooking and eating quality.  Rice cultivars with medium panicle weight had more large starch granules and higher relative crystallinity than cultivars with heavy panicle weight.  Transition temperature and retrogradation enthalpy (ΔHret) of medium panicle type cultivars were significantly higher than that of heavy panicle type cultivars.  There was no significant difference in amylose content among different panicle type cultivars.  Protein content of heavy panicle type cultivar was higher than that of medium panicle type cultivar, and protein content is the main factor affect cooking and eating quality in this study.  The cultivar Yongyou 6715 got the highest taste value with the lowest protein content.  Thus, it is suggested that the emphasis on improving rice cooking and eating quality of indica-japonica hybrid rice cultivars is how to reduce the protein content in rice grain.  According to the results of this study, medium panicle type with high grain weight is the desired panicle type for high quality indica-japonica hybrid rice breeding.
     
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    Effect of wide-narrow row arrangement in mechanical pot-seedling transplanting and plant density on yield formation and grain quality of japonica rice
    HU Qun, JIANG Wei-qin, QIU Shi, XING Zhi-peng, HU Ya-jie, GUO Bao-wei, LIU Guo-dong, GAO Hui, ZHANG Hong-cheng, WEI Hai-yan
    2020, 19 (5): 1197-1214.   DOI: 10.1016/S2095-3119(19)62800-5
    Abstract85)      PDF in ScienceDirect      
    Mechanical pot-seedling transplanting is an innovatively developed transplanting method that has the potential to replace mechanical carpet-seedling transplanting.  However, the initial pot-seedling transplanting machine lacked optimized density spacing and limited yield potential for japonica rice.  Therefore, ascertaining the optimized density by wide-narrow rows and the appropriate transplanting method for yield formation and grain quality of japonica rice is of great importance for high-quality rice production.  Field experiments were conducted using two japonica rice cultivars Nanjing 9108 and Nanjing 5055 under three transplanting methods in 2016 and 2017: mechanical pot-seedling transplanting with wide-narrow row (K, average row spacing of 30 cm); equidistant row (D, 33 cm×12 cm); and mechanical carpet-seedling transplanting (T, 30 cm×12.4 cm).  In addition, five different density treatments were set in K (K1–K5, from 18.62×104 to 28.49×104 hills ha–1).  The results showed that the highest yield was produced by a planting density of 26.88×104 hills ha–1 in mechanical pot-seedling transplanting with wide-narrow row with a greater number of total spikelets that resulted from significantly more panicles per area and slightly more grain number per panicle, as compared with equidistant row, and yield among density in wide-narrow row showed a parabolic trend.  Compared with mechanical carpet-seedling transplanting, the treatment of the highest yield increased yield significantly, which was mainly attributed to the larger sink size with improved filled-grain percentage and grain weight, higher harvest index, and increased total dry matter accumulation, especially the larger amount accumulated from heading stage to maturity stage.  With the density in wide-narrow row decreasing, processing quality, appearance quality, and nutrition quality were all improved, whereas amylose content and the taste value were decreased.  Compared with mechanical carpet-seedling transplanting, mechanical pot-seedling transplanting improved processing quality and nutrition quality, but decreased amylose content and deteriorated appearance quality.  These results suggested that mechanical pot-seedling transplanting with wide-narrow row coupling produced a suitable planting density of 26.88×104 hills ha–1 and may be an alternative approach to improving grain yield and quality for japonica rice.
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    Effects of light-emitting diodes on tissue culture plantlets and seedlings of rice (Oryza sativa L.)
    YU Lan-lan, SONG Chang-mei, SUN Lin-jing, LI Li-li, XU Zhi-gang, TANG Can-ming
    2020, 19 (7): 1743-1754.   DOI: 10.1016/S2095-3119(19)62793-0
    Abstract114)      PDF in ScienceDirect      
    Light-emitting diodes (LEDs) are a new light source with low energy consumption and high photoelectric conversion efficiency, and they can satisfy the energy-saving needs of plant culture systems.  However, the effects of LED light sources on rice tissue culture and rice seedling cultivation are poorly understood.  This study aimed to evaluate the effects of LEDs on the growth of tissue culture plantlets and seedlings of the rice (Oryza sativa L.) cultivar Nipponbare.  The best light source for rice tissue culture was different from that for rice seedling cultivation.  Blue (B) LED light was the most appropriate light for rice tissue culture.  Under a B LED light, the time required for callus proliferation, differentiation and regeneration was the shortest, and the frequency of plantlet initiation, differentiation and regeneration was the highest.  A blue:red (B:R)=1:1 LED light facilitated the growth of rice seedlings and produced the highest chlorophyll and carotenoid contents and photosynthetic rates in the rice seedlings.  Abundant photosynthetic products were more effectively generated in the rice seedlings under the B:R=1:1 LED and R LED lights than under the B LED light.  B LED light is the most appropriate light for rice tissue culture plantlets and can be used as an alternative light source for rice tissue culture, and B:R=1:1 LED light facilitated the cultivation of robust rice seedlings and can be used as the primary light source for rice factory seedling cultivation.
     
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    Effects of seedling age on the growth stage and yield formation of hydroponically grown long-mat rice seedlings
    LI Yu-xiang, LIU Yang, WANG Yu-hui, DING Yan-feng, WANG Shao-hua, LIU Zheng-hui, LI Gang-hua
    2020, 19 (7): 1755-1767.   DOI: 10.1016/S2095-3119(19)62756-5
    Abstract126)      PDF in ScienceDirect      
    Understanding the characteristics of rice productivity is of great importance for achieving high yield formation.  However, such traits have not yet been studied for different ages of hydroponically grown long-mat rice seedlings (HLMS), which constitutes a new method of seedling cultivation.  Field experiments were conducted to evaluate the effects of seedling age on the growth stage, photosynthesis characteristics, dry matter production, and yield of HLMS.  A conventional japonica rice cultivar (Wuyunjing 24) and an indica hybrid rice cultivar (6 Liangyou 9368) were used as test materials.  The results showed that the whole phase was shortened by 13–15 days for young seedlings (13-day-old) compared with old seedlings (27-day-old), which occurred because the growth process accelerated with the transplantation of young seedlings.  As seedling age increased, the dry matter weight of stems of individual plants and of the population increased at the transplanting stage but decreased at the maturity stage (MS).  Compared with that of 27-day-old seedlings, the average ratio of panicle weight to total plant dry weight of 13-day-old seedlings during a 2-year period increased by 3.71% for Wuyunjing 24 and by 3.78% for 6 Liangyou 9368 at the MS.  Moreover, as seedling age increased, the leaf area index and photosynthetic potential decreased for both cultivars, and the photosynthetic rate markedly decreased at the heading stage (HS).  With the exception of that of Wuyunjing 24 from the jointing stage to the HS in 2014, the crop growth rate was higher for young seedlings than for old seedlings.  Grain yield significantly decreased with seedling age, but no significant difference was detected between the 13- and 20-day-old seedlings for either cultivar.  Therefore, equilibrious and high biological yield formation, vigorous growth in the late stages, and high photosynthetic production capacity are important characteristics and causes of the efficient and sustainable output of photosynthetic systems and for achieving high yield formation in young transplanted seedlings (13–20-day-old).
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    Effects of water application uniformity using a center pivot on winter wheat yield, water and nitrogen use efficiency in the North China Plain
    CAI Dong-yu, YAN Hai-jun, LI Lian-hao
    2020, 19 (9): 2326-2339.   DOI: 10.1016/S2095-3119(19)62877-7
    Abstract113)      PDF in ScienceDirect      
    In recent years, the use of fertigation technology with center pivot irrigation systems has increased rapidly in the North China Plain (NCP).  The combined effects of water and nitrogen application uniformity on the grain yield, water use efficiency (WUE) and nitrogen use efficiency (NUE) have become a research hotspot.  In this study, a two-year field experiment was conducted during the winter wheat growing season in 2016–2018 to evaluate the water application uniformity of a center pivot with two low pressure sprinklers (the R3000 sprinklers were installed in the first span, the corresponding treatment was RS; the D3000 sprinklers were installed in the second span, the corresponding treatment was DS) and a P85A impact sprinkler as the end gun (the corresponding treatment was EG), and to analyze its effects on grain yield, WUE and NUE.  The results showed that the water application uniformity coefficients of R3000, D3000 and P85A along the radial direction of the pivot (CUH) were 87.5, 79.5 and 65%, respectively.  While the uniformity coefficients along the traveling direction of the pivot (CUC) were all higher than 85%.  The effects of water application uniformity of the R3000 and D3000 sprinklers on grain yield were not significant (P>0.05); however, the average grain yield of EG was significantly lower (P<0.05) than those of RS and DS, by 9.4 and 11.1% during two growing seasons, respectively.  The coefficients of variation (CV) of the grain yield had a negative correlation with the uniformity coefficient.  The CV of WUE was more strongly affected by the water application uniformity, compared with the WUE value, among the three treatments.  The NUE of RS was higher than those of DS and EG by about 6.1 and 4.8%, respectively, but there were no significant differences in NUE among the three treatments during the two growing seasons.  Although the CUH of the D3000 sprinklers was lower than that of the R3000, it had only limited effects on the grain yield, WUE and NUE.  However, the cost of D3000 sprinklers is lower than that of R3000 sprinklers.  Therefore, the D3000 sprinklers are recommended for winter wheat irrigation and fertigation in the NCP. 
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    Yield characteristics of japonica/indica hybrids rice in the middle and lower reaches of the Yangtze River in China
    XU Dong, ZHU Ying, CHEN Zhi-feng, HAN Chao, HU Lei, QIU Shi, WU Pei, LIU Guo-dong, WEI Hai-yan, ZHANG Hong-cheng
    2020, 19 (10): 2394-2406.   DOI: 10.1016/S2095-3119(19)62872-8
    Abstract78)      PDF in ScienceDirect      
    Although a lot of researches have been done on yield characteristics of japonica/indica hybrid rice, there is little information on differences of yield characteristics between different types of hybrid.  To determine common characteristics of japonica/indica hybrid rice (JIHR) and identify the differences between different types of JIHR, the present study assessed yield characteristics, such as panicle trait, leaf area index (LAI), above-ground biomass accumulation, and nitrogen absorption and utilization, among three types of cultivar of JIHR.  In our field experiments, three types of JIHR, e.g., Yongyou, Chunyou and Jiayouzhongke, were divided, and each of them has two cultivars, which were used as materials, meanwhile, using conventional japonica rice (CJR) Wuyingjing 31 and Sujing 9 were as controls.  The results showed that the mean yield of those JIHR was above 12 t ha–1 in 2017 and 2018, and was 31.9 and 32.2%, respectively higher than that of CJR in the two years.  Spikelet number per panicle of JIHR resulted in high yield.  Higher yield of JIHR was likely contributed to greater panicle number and more spikelets per panicle.  Higher yielding JIHR showed stronger tillering capacity, larger LAI and above-ground biomass accumulation from jointing to heading stages, which likely contributed to the higher number of spikelets per panicle.  The long duration from heading to maturity stages allowed more nitrogen accumulation of higher yielding JIHR.
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    Morpho-physiological traits contributing to better yield performance of japonica/indica hybrids over indica hybrids under input-reduced practices
    WEI Huan-he, MENG Tian-yao, GE Jia-lin, ZHANG Xu-bin, LU Yu, LI Xin-yue, TAO Yuan, DING En-hao, CHEN Ying-long, DAI Qi-gen
    2020, 19 (11): 2643-2655.   DOI: 10.1016/S2095-3119(20)63251-8
    Abstract101)      PDF in ScienceDirect      
    It is widely reported that japonica/indica hybrids (JIH) have superior grain yield over other main varietal groups such as indica hybrids (IH) under sufficient resource inputs.  To date, little attention has been paid to yield performance of JIH under input-reduced practices, and whether JIH could have better grain yield performance over IH under input-reduced practices.  In this study, three JIH varieties and three IH varieties were compared in grain yield and their related morpho-physiological traits under two cultivation modes, i.e., conventional high-yielding method (CHYM) and double reductions in nitrogen rate and planting density (DRNP).  Our results showed that JIH had 8.3 and 13.3% higher grain yield over IH under CHYM and DRNP, respectively.  The superior grain yield of JIH over IH under DRNP was mainly attributed to larger sink size and improved sink filling efficiency.  Three main morpho-physiological traits were concluded for better yield performance of JIH over IH under DRNP.  Firstly, JIH had the reduced unproductive tillers growth, indicated by a higher percentage of productive tillers and the percentage of effective leaf area index (LAI) to total LAI at heading stage.  Secondly, a synergistic increase in biomass accumulation and harvest index were achieved of JIH, supported by higher biomass accumulation and leaf area duration during the main growth periods, and improved non-structural carbohydrate (NSC) remobilization after heading.  Thirdly, JIH had an improved canopy structure, showing as higher leaf area of upper three leaves and lower light extinction coefficient.  Our results suggested that improved morpho-physiological traits of JIH could lead to better grain yield performance over IH under input-reduced practices.
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    Growth, yield and water productivity of dry direct seeded rice and transplanted aromatic rice under different irrigation management regimes
    Muhammad ISHFAQ, Nadeem AKBAR, shakeel Ahmed ANJUM, Muhammad ANWAR-UL-HAQ
    2020, 19 (11): 2656-2673.   DOI: 10.1016/S2095-3119(19)62876-5
    Abstract109)      PDF in ScienceDirect      
    Sustainability of traditionally cultivated rice in the rice-wheat cropping zone (RWCZ) of Pakistan is dwindling due to the high cost of production, declining water resources and escalating labour availability.  Thus, farmers and researchers are compelled to find promising alternatives to traditional transplanted rice (TPR).  A field study was conducted in Punjab, Pakistan, in 2017 and 2018 to explore the trade-offs between water saving and paddy yield, water productivity and economics of two aromatic rice varieties under dry direct seeded rice (DDSR) and TPR.  The experiment was comprised of three irrigation regimes on the basis of soil moisture tension (SMT) viz., continuous flooded (>–10 kPa SMT), alternate wetting and drying (AWD) (–20 kPa SMT) and aerobic rice (–40 kPa SMT), maintained under TPR and DDSR systems.   Two aromatic rice verities: Basmati-515 and Chenab Basmati-2016 were used during both years of study.  In both years, DDSR produced higher yields (13–18%) and reduced the total water inputs (8–12%) in comparison to TPR.  In comparison to traditional continuous flooded (CF), AWD under DDSR reduced total water input by 27–29% and improved the leaf area index (LAI), tillering, yield (7–9%), and water productivity (44–50%).  The performance of AWD with regard to water savings and increased productivity was much higher in DDSR system as compared to AWD in TPR system.  Cultivation of DDSR with aerobic irrigation improved water savings (49–55%) and water productivity (22–30%) at the expense of paddy yield reduction (36–39%) and spikelet sterility.  With regard to variety, the highest paddy yield (6.6 and 6.7 t ha–1) was recorded in DDSR using Chenab Basmati-2016 under AWD irrigation threshold that attributed to high tiller density and LAI.  The economic analysis showed DDSR as more beneficial rice establishment method than TPR with a high benefit-cost ratio (BCR) when the crop was irrigated with AWD irrigation threshold.  Our results highlighted that with the use of short duration varieties, DDSR cultivation in conjunction with AWD irrigation can be more beneficial for higher productivity and crop yield.
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    Changes in starch quality of mid-season indica rice varieties in the lower reaches of the Yangtze River in last 80 years
    ZHANG Hao, JING Wen-jiang, XU Jing-ju, MA Bing-ju, WANG Wei-lu, ZHANG Wei-yang, GU Jun-fei, LIU Li-jun, WANG Zhi-qin, YANG Jian-chang
    2020, 19 (12): 2983-2996.   DOI: 10.1016/S2095-3119(20)63431-1
    Abstract108)      PDF in ScienceDirect      
    Rice (Oryza sativa L.) quality depends mainly on the characteristics of starch stored in kernels.  Understanding the changes in starch characteristics in kernels during variety improvement would have great significance to improve rice quality.  This study was designed to investigate the starch characteristics in the kernels and associated physiological traits of indica rice varieties in the lower reaches of the Yangtze River in China in last 80 years.  Eight representative mid-season indica rice varieties were grown in the field.  The results showed that the grain yield was significantly increased with the improvement of varieties and such an increase was mainly attributed to the increase in total number of spikelets.  The tall varieties applied in the 1940s–1950s had higher protein content, relative crystallinity and infrared (IR) ratio of 1 045/1 022 cm–1.  The semi-dwarf varieties applied in the 1980s–1990s had higher gel consistency, amylopectin content, IR ratio of 1 022/995 cm–1, and breakdown value.  With the improvement of varieties, the amylose content, large-sized starch granule number and volume distribution, onset and peak of gelatinization temperature, gelatinization and retrogradation enthalpy, setback value, pasting temperature, viscosity of peak, hot and final, and 1-aminocycopropane-1-carboxylic acid (ACC) concentrations in panicles and root bleeding were gradually decreased, whereas the medium-sized starch granule number and volume distribution, activities of key enzymes in grains, and zeatin (Z)+zeatin riboside (ZR) contents in panicles and root bleeding at grain filling stage were gradually increased.  Correlation analysis showed that starch thermodynamic characteristics were closely related to starch structure and components, key enzymes and hormones.  The results suggest that starch quality was enhanced through the optimization of starch components, structure, thermodynamics, and the regulation of key enzymes in grains and hormones in panicles and root bleedings at grain filling stage during the improvement of mid-season indica rice.
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    Compact plant type rice has higher lodging and N resistance under machine transplanting
    DING Chao, LUO Xi-kun, WU Qiong, LU Bo, DING Yan-feng, WANG Shao-hua, LI Gang-hua
    2021, 20 (1): 65-77.   DOI: 10.1016/S2095-3119(20)63229-4
    Abstract109)      PDF in ScienceDirect      
    To identify the major factors that contribute to the difference in lodging among different rice varieties under machine transplanting and their responses to nitrogen (N), field experiments were conducted at Danyang County (a representative eco-site of the Lower Yangtze River) in Jiangsu Province, China in 2017 and 2018, 22 hybrid indica varieties (HIs), 22 inbred japonica varieties (IJs) and two indica japonica hybrid varieties (IJHs) were transplanted by machine with three N rates (N0, N150 and N300, 0, 150 and 300 kg ha–1, respectively).  Lodging-related physical parameters, morphological characteristics and apparent transport rates of dry matter were examined.  Significant difference in yield was observed among different types of rice, and followed by IJs<HIs<IJHs.  The average lodging index (LI) of hybrid varieties (HIs and IJHs) was higher than that of the inbred varieties (IJs) with higher plant height; moreover, lower apparent export rate of dry matter resulted lower LI in IJHs than in HIs.  The HIs had a large difference in the LI, which came from the difference in bending stress (BS) induced by the difference in the apparent export rate of dry matter, varieties with lower leaf angle of upper three leaves possess strong lodging resistance capacity; however, the gap among the IJs was due to the difference in the cross section modulus (Z).  The LI in the IJs or IJHs increased slightly with the increased N application, and there was no lodging incidence under the high N level, which was due to the low leaf angle and barely changed under high N; there was a significant interaction between varieties (HIs) and N rates in lodging rate and LI, varieties with lower leaf angle of upper three leaves were resistant to high N.  These results suggest that compact plant type rice has higher lodging and N resistance at machine-transplanting method. 
     
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    Effects of different mechanical direct seeding methods on grain yield and lodging resistance of early indica rice in South China
    WANG Wen-xia, DU Jie, ZHOU Yan-zhi, ZENG Yong-jun, TAN Xue-ming, PAN Xiao-hua, SHI Qing-hua, WU Zi-ming, ZENG Yan-hua
    2021, 20 (5): 1204-1215.   DOI: 10.1016/S2095-3119(20)63191-4
    Abstract122)      PDF in ScienceDirect      
    Direct seeding of rice has become a main planting method due to the low labor input and high economic benefit in South China.  Dry direct seeding (DDS) has been widely used for single-season rice planting establishment.  However, few studies have examined the performance of early-season indica rice under mechanical dry direct seeding.  A two-year field experiment was conducted with two indica rice cultivars (i.e., Zhongjiazao 17 and Zhuliangyou 819) to study lodging characteristics and grain yield formation under DDS, flooded direct seeding (FDS) and wet direct seeding (WDS) patterns.  The results showed that the annual grain yield in DDS was higher by 14.42–26.34% for cultivar ZLY819 and 6.64–24.58% for cultivar ZJZ17 than in WDS and FDS, respectively, and these increases were mainly attributed to the improvement of the panicles.  The DDS pattern significantly increased the seedling emergence rate of early indica rice cultivars, and increased total dry weight and crop growth rate.  Meanwhile, shorter basal internodes, better stem diameter and stem wall thickness and lower lodging index were found in DDS in contrast to FDS and WDS.  In particular, DDS improved the stem lodging resistance.  Our results suggested that the appropriate direct seeding method was beneficial for improving the grain yield and lodging resistance of early indica rice.
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    Effects of temperature and solar radiation on yield of good eating-quality rice in the lower reaches of the Huai River Basin, China
    ZHOU Nian-bing, ZHANG jun, FANG Shu-liang, WEI Hai-yan, ZHANG Hong-cheng
    2021, 20 (7): 1762-1774.   DOI: 10.1016/S2095-3119(20)63561-4
    Abstract129)      PDF in ScienceDirect      
    We studied the effects of temperature and solar radiation on rice yield with the aim of understanding the temperature and solar radiation requirements for high yield rice production in the lower reaches of the Huai River, China.  Field experiments were conducted with two medium-maturing japonica rice (MMJR) varieties and four late-maturing japonica rice (LMJR) varieties in 2017 and 2018.  Seeds were sown on May 10 (T1), May 17 (T2), May 24 (T3), May 31 (T4), June 7 (T5), June 14 (T6), and June 21 (T7).  The whole growth duration (WGD) of rice was shortened when sowing date was delayed, especially for the duration from sowing to heading (S–H).  The effective accumulated temperature (EAT), mean daily temperature (Tmean), cumulative solar radiation (CSR), and mean daily solar radiation (Rmean) over the WGD decreased when sowing date was delayed.  Compared with T1, yields in T2, T3, T4, T5, T6, and T7 decreased by 0.12–0.35, 0.45–0.89, 0.74–1.56, 1.41–2.24, 2.16–2.90, and 2.69–3.64 t ha−1, respectively.  There was a significant positive correlation between rice yield and EAT in different growth stages.  Temperature was the main factor that affected the yield of good eating-quality rice in the lower reaches of the Huai River.  We found that a relatively high yield can be obtained when the optimal Tmean for medium-maturing japonica rice (MMJR) and late-maturing japonica rice (LMJR) was 25.8–27.0°C and 26.6–27.1°C in the stages from sowing to heading (S–H), and 20.3–23.3°C and 20.3–22.1°C in the stages from heading to maturity (H–M), respectively.  The optimal sowing dates for MMJR and LMJR in the lower reaches of the Huai River were May 15–31 and May 15–18, respectively.
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    Comparison of grain yield and quality of different types of japonica rice cultivars in the northern Jiangsu plain, China
    BIAN Jin-long, REN Gao-lei, XU Fang-fu, ZHANG Hong-cheng, WEI Hai-yan
    2021, 20 (8): 2065-2076.   DOI: 10.1016/S2095-3119(20)63348-2
    Abstract129)      PDF in ScienceDirect      
    In recent years, an increasing number of different types of japonica rice cultivars have been released in the southern rice region of China.  The grain yield and quality of these new cultivars showed significant differences in large scale planting.  However, the causes of the differences remain little known.  Therefore, three typical types of japonica rice cultivars were used in this study to investigate their grain yield and quality.  A scanning calorimeter (DSC), X-ray powder diffractometer (XRD), rapid viscosity analyzer (RVA) and taste analyzer were used to evaluate the cooking and eating properties.  The results showed that the yield of non-soft hybrid japonica rice cultivars was significantly higher than that of non-soft inbred japonica rice cultivars and soft inbred japonica rice cultivars.  Soft inbred japonica rice cultivars had a low amylose content and moderate protein content, which are the main reasons for the superior cooking and eating quality.  In addition, the relative crystallinity of soft inbred japonica rice cultivars was significantly higher than that of non-soft inbred and non-soft hybrid japonica rice cultivars, which is considered the major factor resulting in higher transition temperature and gelatinization enthalpy (ΔHgel).  Non-soft hybrid japonica rice cultivars had a higher number of large starch granules than soft inbred and non-soft inbred japonica rice cultivars.  The setback value (SB) and breakdown value (BD), indirectly reflecting the cooking and eating quality of the three types of japonica rice cultivars, also confirmed that soft inbred japonica rice cultivars with a low SB value and a high BD value had better palatability than the other two types.  This study provides guidance for future plantation of different types of japonica rice cultivars in large rice-producing areas.
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    Effect of various combinations of temperature during different phenolgical stages on indica rice yield and quality in Yangtze River Basin in China
    TU De-bao JIANG Yang, ZHANG Li-juan, CAI Ming-li, LI Cheng-fang, CAO Cou-gui
    2022, 21 (10): 2900-2909.   DOI: 10.1016/j.jia.2022.07.056
    Abstract137)      PDF in ScienceDirect      
    Rice grain yield and quality declines are due to unsuitable temperatures from wide regions and various sowing dates.  This study aimed to evaluate the effects of temperature on rice yield and quality at different phenological periods and obtain suitable temperatures for phenological periods in the Yangtze River Basin, China.  This study conducted experiments on different sowing dates under different areas in the Yangtze River Basin to observe and compare the differences in rice growth, yield, and quality, controlling for regional varieties.  The results showed significant differences in rice growth, yield, and quality among sowing dates and areas, which were related to the average daily temperature during the vegetative period (VT) and the first 20 days of the grain-filling period (GT20).  In addition, there was a smaller variation in the average daily temperature in the reproductive period (RT) than in the two phenological periods.  Therefore, according to the VT and GT20 thresholds of different yields and qualities, the experimental results were divided into four scenarios (I, II, III, and IV) in this study.  In Scenario I, high head rice production (rice grain yield multiplied by head rice rate) and rice quality could be obtained.  The head rice production of Scenarios III and IV was lower than that of Scenario I, by 30.1 and 27.6%, respectively.  In Scenario II, the head rice production increased insignificantly while the chalky grain rate and chalkiness were 50.6 and 56.3% higher than those of Scenario I.  In conclusion, the Scenario I combination with VT ranges of 22.8–23.9°C and GT20 ranges of 24.2–27.0°C or the combination with VT ranges of 23.9–25.3°C and GT20 ranges of 24.2–24.9°C, which can be obtained by adjusting sowing date and selecting rice varieties with suitable growth periods, is recommended to achieve high levels of rice grain yield and quality in the Yangtze River Basin. 
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    Border effects of the main and ratoon crops in rice ratooning system
    ZHENG Chang, WANG Yue-chao, XU Wen-ba, YANG De-sheng, YANG Guo-dong, YANG Chen, HUANG Jian-liang, PENG Shao-bing
    2023, 22 (1): 80-91.   DOI: 10.1016/j.jia.2022.08.048
    Abstract462)      PDF in ScienceDirect      

    The border effect (BE) is widely observed in crop field experiments, and it has been extensively studied in many crops.  However, only limited attention has been paid to the BE of ratoon rice.  We conducted field experiments on ratoon rice in Qichun County, Hubei Province, Central China in 2018 and 2019 to compare the BE in the main and ratoon crops, and to quantify the contribution of BE in the main crop to that in the ratoon crop.  The BE of two hybrid varieties was measured for the outermost, second outermost, and third outermost rows in each plot of both crops.  To determine the contribution of BE between the two crops, portions of hills in the outermost and second outermost rows were uprooted during the harvest of the main crop so that the second and third outermost rows then became the outermost rows in the ratoon crop.  Overall, the BE on grain yield was greater in the main crop than in the ratoon crop.  In the main crop, the BE on grain yield was 98.3% in the outermost row, which was explained by the BE on panicles m–2, spikelets/panicle, spikelets m–2, and total dry weight.  In the ratoon crop, the BE on grain yield was reduced to 60.9 and 27.6% with and without the contribution of the BE in the main crop, respectively.  Consequently, 55.1% of the BE on grain yield in the ratoon crop was contributed from the main crop.  High stubble dry weight and non-structural carbohydrate (NSC) accumulation at the harvest of the main crop were responsible for the contribution of BE in the main crop to that in the ratoon crop.  Our results suggest that increases in stubble dry weight and NSC accumulation at the harvest of the main crop could be important strategies for developing high-yielding cropping practices in the rice ratooning system.

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    Increasing the appropriate seedling density for higher yield in dry direct-seeded rice sown by a multifunctional seeder after wheat-straw return
    TIAN Jin-yu, LI Shao-ping, CHENG Shuang, LIU Qiu-yuan, ZHOU Lei, TAO Yu, XING Zhi-peng, HU Ya-jie, GUO Bao-wei, WEI Hai-yan, ZHANG Hong-cheng
    2023, 22 (2): 400-416.   DOI: 10.1016/j.jia.2022.08.064
    Abstract216)      PDF in ScienceDirect      
    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.

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    Optimal management of nitrogen fertilizer in the main rice crop and its carrying-over effect on ratoon rice under mechanized cultivation in Southeast China
    HUANG Jin-wen, WU Jia-yi, CHEN Hong-fei, ZHANG Zhi-xing, FANG Chang-xun, SHAO Cai-hong, LIN Wei-wei, WENG Pei-ying, Muhammad Umar KHAN, LIN Wen-xiong
    2022, 21 (2): 351-364.   DOI: 10.1016/S2095-3119(21)63668-7
    Abstract207)      PDF in ScienceDirect      
    This study attempted to clarify the carrying-over effect of different nitrogen treatments applied to the main crop on the crop population growth and yield formation of ratoon rice under mechanized cultivation in Southeast China.  Based on the constant total nitrogen application amounts (225.00 kg ha–1) in the main crop, an experiment with different ratios of basal and topdressing nitrogen fertilizer (the ratio of basal fertilizer:primary tillering fertilizer:secondary tillering fertilizer:booting fertilizer at 3:1:2:4 (N1), 3:2:1:4 (N2), 3:3:0:4 (N3), and 4:3:0:3 (N4), respectively, and a control without nitrogen treatment (N0)) was set up across two consecutive years in field using hybrid rice variety Yongyou 1540 as the test materials.  The results showed that the total tiller number and effective tillering percentage increased in the main crop under the N1 treatment, more nitrogen fertilizer applied in late growth stage of the main crop, and its effective tillering percentage of the main crop was the highest at up to 70.18%, which was 9.15% higher than that of conventional fertilization treatment (N4), more nitrogen fertilizer applied in early growth stage of the main crop.  The same tendency was observed in leaf area index (LAI) value of the main crop and its subsequent ratoon rice, which were 16.52 and 29.87% higher, respectively, in the N1 treatment than that in the N4 treatment at the full heading stage.  The same was true in the case of the transport rates of stem and sheath dry mater and the canopy light interception rates in both the main and its ratoon crops.  The transport rate of stem and sheath in main crop rice under N1 treatment increased by 50.57% compared with N4 treatment.  The canopy light interception rate of N1 treatment increased by 5.07% compared with N4 treatment at the full heading stage of the ratoon crop.  Therefore, the total actual yield was the highest in the main and its ratoon crops under N1 treatment, averaging 17 351.23 kg ha–1 in two-year trials, which was 23.00% higher than that in the conventional fertilization treatment (N4).  The results showed that appropriate nitrogen treatment was able to produce a good crop stand in the main crop, which was essential for producing a good ratoon crop population and high yield especially under mechanized cultivation with low stubble height of the main crop.  The study suggested that shifting the proper nitrogen application amounts to the late growth stage of the main crop, such as N1 treatment, not only had a higher productive effect on ensuring the yield of the main crop, but also had a positive effect on the axillary bud sprouts from the stubbles for ratoon rice, resulting in an increased percentage of productive panicles and achieving the goal of one planting with two good harvests under the conditions of our study.

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    Grain yield, nitrogen use efficiency and physiological performance of indica/japonica hybrid rice in response to various nitrogen rates
    ZHOU Qun, YUAN Rui, ZHANG Wei-yang, GU Jun-fei, LIU Li-jun, ZHANG Hao, WANG Zhi-qin, YANG Jian-chang
    2023, 22 (1): 63-79.   DOI: 10.1016/j.jia.2022.08.076
    Abstract374)      PDF in ScienceDirect      

    Utilizing the heterosis of indica/japonica hybrid rice (IJHR) is an effective way to further increase rice grain yield.  Rational application of nitrogen (N) fertilizer plays a very important role in using the heterosis of IJHR to achieve its great yield potential.  However, the responses of the grain yield and N utilization of IJHR to N application rates and the underlying physiological mechanism remain elusive.  The purpose of this study was to clarify these issues.  Three rice cultivars currently used in rice production, an IJHR cultivar Yongyou 2640 (YY2640), a japonica cultivar Lianjing 7 (LJ-7) and an indica cultivar Yangdao 6 (YD-6), were grown in the field with six N rates (0, 100, 200, 300, 400, and 500 kg ha–1) in 2018 and 2019.  The results showed that with the increase in N application rates, the grain yield of each test cultivar increased at first and then decreased, and the highest grain yield was at the N rate of 400 kg ha–1 for YY2640, with a grain yield of 13.4 t ha–1, and at 300 kg ha–1 for LJ-7 and YD-6, with grain yields of 9.4–10.6 t ha–1.  The grain yield and N use efficiency (NUE) of YY2640 were higher than those of LJ-7 or YD-6 at the same N rate, especially at the higher N rates.  When compared with LJ-7 or YD-6, YY2640 exhibited better physiological traits, including greater root oxidation activity and leaf photosynthetic rate, higher cytokinin content in the roots and leaves, and more remobilization of assimilates from the stem to the grain during grain filling.  The results suggest that IJHR could attain both higher grain yield and higher NUE than inbred rice at either low or high N application rates.  Improved shoot and root traits of the IJHR contribute to its higher grain yield and NUE, and a higher content of cytokinins in the IJHR plants plays a vital role in their responses to N application rates and also benefits other physiological processes. 

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