Nitrogen (N) and seeding rates are important factors affecting grain yield and N use efficiency (NUE) in direct-seeded rice.  However, these factors have not been adequately investigated on direct-seeded and double-season rice (DDR) in Central China.  The objective of this study was to evaluate the effects of various N and seeding rates on the grain yield and NUE of an ultrashort-duration variety grown under DDR.  Field experiments were conducted in 2018 in Wuxue County and 2019 in Qichun County, Hubei Province, China with four N rates and three seeding rates.  The results showed that the grain yield of the ultrashort-duration variety ranged from 6.32 to 8.23 t ha^–1 with a total growth duration of 85 to 97 days across all treatments with N application.  Grain yield was increased significantly by N application in most cases, but seeding rate had an inconsistent effect on grain yield.  Furthermore, the response of grain yield to the N rates was much higher than the response to seeding rates.  The moderate N rates of 100–150 and 70–120 kg N ha^–1 in the early and late seasons, respectively, could fully express the yield potential of the ultrashort-duration variety grown under DDR.  Remarkably higher N responses and agronomic NUE levels were achieved in the early-season rice compared with the late-season rice due to the difference in indigenous soil N supply capacity (INS) between the two seasons.  Seasonal differences in INS and N response should be considered when crop management practices are optimized for achieving high grain yield and NUE in ultrashort-duration variety grown under DDR.

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.

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.

Rice research has always been the top priority in China and China produces the highest number of scientific journal papers on rice, particularly on rice genetics and breeding.  In this study, we used a bibliometric approach to analyze the trends of papers published by Chinese researchers on rice physiology and management.  Data were collected from three major agronomic journals (i.e., Agronomy Journal, Crop Science, and Field Crops Research) by searching in the Web of Science on September 8, 2017.  A total of 186 rice papers were published by Chinese researchers on crop physiology and management in the three journals since their establishment.  Yearly average number of such papers was 1.6, 6.5, and 21.0 for the periods of 1993–2005, 2006–2011, and 2012–2017, respectively.  Their quality in terms of citation performance has also improved significantly in the recent decade.  Huazhong Agricultural University, Yangzhou University, and Nanjing Agricultural University were leading organizations and published 54.4% of all 186 papers.  Huang Min of Hunan Agricultural University and Peng Shaobing of Huazhong Agricultural University published the most number of rice papers on crop physiology and management as the first and corresponding authors, respectively.  Yield potential and nitrogen-related research such as nitrogen use efficiency, nitrogen management, and plant nitrogen diagnosis have been the research focuses for rice crop.  In recent years, research on global warming including high temperature stress, direct seeding, zero tillage, Bt rice, and critical nitrogen dilution curve were becoming popular.  New research is emerging on yield gap, rice ratooning, and simplified and reduced-input practices in rice production.

In 1996, a mega project that aimed to develop rice varieties with super-high yield potential (super rice) was launched by the Ministry of Agriculture (MOA) in China using a combination of the ideotype approach and intersubspecific heterosis.  Significant progress has been made in the last two decades, with a large number of super rice varieties being approved by the MOA and the national average grain yield being increased from 6.21 t ha⁻¹ in 1996 to 6.89 t ha⁻¹ in 2015.  The increase in yield potential of super rice was mainly due to the larger sink size which resulted from larger panicles.  Moreover, higher photosynthetic capacity and improved root physiological traits before heading contributed to the increase in sink size.  However, the poor grain filling of the later-flowering inferior spikelets and the quickly decreased root activity of super rice during grain filling period restrict the achievement of high yield potential of super rice.  Furthermore, it is widely accepted that the high yield potential of super rice requires a large amount of N fertilizer input, which has resulted in an increase in N consumption and a decrease in nitrogen use efficiency (NUE), although it remains unclear whether super rice per se is responsible for the latter.  In the present paper, we review the history and success of China’s Super Rice Breeding Program, summarize the advances in agronomic and physiological mechanisms underlying the high yield potential of super rice, and examine NUE differences between super rice and ordinary rice varieties.  We also provide a brief introduction to the Green Super Rice Project, which aims to diversify breeding targets beyond yield improvement alone to address global concerns around resource use and environmental change.  It is hoped that this review will facilitate further improvement of rice production into the future.

The ecosystem services value (ESV) of rice system has received increasing attention in agricultural policy decision. Over the last three decades, China’s rice production presented an obviously trend that moving towards north locations. However, the impacts of this migration on the ESV of rice production have not been well documented. In this paper, we analyzed the change of the ESV of rice production in China under “north migration” and “no migration” scenarios during 1980–2014 based on long-term historical data. The results showed that both the positive and negative ESVs of rice production were lower under “north migration” than under “no migration” scenarios. The total ESV during 1980–2014 was reduced by 15.8%. “North migration” significantly reduced the area-scaled ESV since the early 1990s; while its impact on yield-scaled ESV was not significant. The effects of “north migration” on ESV showed great spatial variation. The greatest reduction in total and area-scaled ESV was observed in south locations. While the yield-scaled ESVs of most south locations were enhanced under “north migration” scenario. These results indicated that “north migration” has generated adverse effects on the ESV of rice production. An adjustment in the spatial distribution is essential to protecting the non-production benefits of rice ecosystem.

To compare the grain yield and growth behaviors of hybrid rice, field experiments were conducted in a subtropical environment in Changsha, Hunan Province, China, and in two tropical environments in Gazipur and Habiganj in Bangladesh during 2009 to 2011. Three hybrid rice cultivars were grown under three nitrogen (N) management treatments in each experiment. The results showed that grain yield was significantly affected by locations, N treatments and their interaction but not by cultivars. Changsha produced 8-58% higher grain yields than Bangladesh locations. Sink size (spikelet number per unit land area) was responsible for these yield differences. Larger panicle size (spikelet number per panicle) contributed to greater sink size in Changsha. Aboveground total biomass was greater in Changsha than in Bangladesh locations, whereas harvest index was higher in Bangladesh locations than in Changsha. Crop growth rate (CGR) was greater at Changsha than Bangladesh locations during vegetative phase, while the difference was relatively small and not consistent during the later growth phases. Higher leaf area index and leaf area duration were partly responsible for the greater CGR in Changsha. Real-time N management (RTNM) produced lower grain yields than fixed-time N management in more than half of the experiments. Our study suggested that further improvement in rice yield in the tropical environments similar to those of Bangladesh will depend mainly on the ability to increase panicle size as well as CGR during vegetative phase, and the chlorophyll meter threshold value used in RTNM needs to be modified according to environmental conditions and cultivar characteristics to achieve a desirable grain yield.

Poor nitrogen use efficiency in rice production is a critical issue in China. Site-specific N managements (SSNM) such as real-time N management (RTNM) and fixed-time adjustable-dose N management (FTNM) improve fertilizer-N use efficiency of irrigated rice. This study was aimed to compare the different nitrogen (N) rates and application methods (FFP, SSNM, and RTNM methods) under with- and without-fungicide application conditions on grain yield, yield components, solar radiation use efficiency (RUE), agronomic-nitrogen use efficiency (AEN), and sheath blight disease intensity. Field experiments were carried out at Liuyang County, Hunan Province, China, during 2006 and 2007. A super hybrid rice Liangyou 293 (LY293) was used as experimental material. The results showed that RTNM and SSNM have great potential for improving agronomic-nitrogen use efficiency without sacrificing the grain yield. There were significant differences in light interception rate, sheath blight disease incidence (DI) and the disease index (ShBI), and total dry matter among the different nitrogen management methods. The radiation use efficiency was increased in a certain level of applied N. But, the harvest index (HI) decreased with the increase in applied N. There is a quadratic curve relationship between grain yield and applied N rates. With the same N fertilizer rate, different fertilizer-N application methods affected the RUE and grain yield. The fungicide application not only improved the canopy light interception rate, RUE, grain filling, and harvest index, but also reduced the degree of sheath blight disease. The treatment of RTNM under the SPAD threshold value 40 obtained the highest yield. While the treatment of SSNM led to the highest nitrogen agronomic efficiency and higher rice yield, and decreased the infestation of sheath blight disease dramatically as well. Nitrogen application regimes and diseases control in rice caused obvious effects on light interception rate, RUE, and HI. Optimal N rate is helpful to get higher light interception rate, RUE, and HI. Disease control with fungicide application decreased and delayed the negative effects of the high N on rice yield formation. SSNM and RTNM under the proper SPAD threshold value obtained highyield with high efficiency and could alleviate environmental pollution in rice production.

Behaviours of urediospore germtube in Melampsora larici-populina on the leaf surface of Populus purdomii were studied by light microscope, scanning electron microscope (SEM), transmission electron microscope (TEM), and fluorescence microscope. Crab-like fusion cells on leaf surface, intercellular hyphal cells in leaf tissues, as well as nucleus states, were observed and counted up in this study. Under unsaturated humidity, 32% of germinated tubes fused into a distinguishable swollen crab-shaped cell at the merging site, and 10.5% of observed crab-like cells had more than three nuclei. Wedge-shaped mycelia developed and then penetrated the leaf surface directly, or indirectly through stomata. Tips of germtube passed through the intercellular cells of poplar leaves directly were found in TEM. Aniline blue dyeing also showed that the infecting hyphae could invade into the cuticle and epidemic cell wall directly. For the case of infection through stomata, there were two different situations. Short branches and wedge hyphae usually penetrated the leaf surface via opened stomata, whereas, some germtube branches and wedge hyphae penetrated leaves through the guard cell walls or stoma lips. In the latter case, the stomata were always closed. The samples from wild forestlands had the same fused cells and wedge hyphae, but the occurrence rate was much higher than that in the chamber. Even under the saturated air humidity, germtubes could roll back and formed fusion structure, or merged together with their tips. The fusion cells might centralize the plasma of merged germtubes and have a strong survival capacity to protect germtubes from dying under arid circumstances, and provide a chance of genetic variation as well.