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The carbon and nitrogen (N) metabolism of rice under different mid-stage N compensation timings is unclear. Two Japonica super rice cultivars were examined under four N compensation timings (N1-N3: N compensation at mid-tillering, panicle initiation, and spikelet differentiation. N0: no N compensation) and CK with no N application. Mid-stage N compensation increased the N concentrations of various tissues, and N2 showed the highest plant N uptake at both the heading stage, maturity, and the grain filling period. Among the treatments, N2 showed the highest N utilization efficiency. With delayed compensation timing, there was a gradual decrease in soluble sugar and starch concentrations in each tissue, accompanied by a decline in the non-structural carbohydrate (NSC) concentration. Specifically, N2 treatment exhibited the highest NSC accumulation and the remobilized NSC reserve, but NSCs per spikelet decreased with delayed compensation timing. The highest yield was also obtained with N2, exhibiting a 4.5% increase compared to the N0 treatment, primarily due to an improvement in spikelets per panicle. Conclusively, N compensation at the panicle initiation stage is a reasonable N management strategy that can coordinate the improvement of carbon and N metabolism, enhance N accumulation with efficient utilization and NSC accumulation, and ultimately increase the yield. [ABSTRACT FROM AUTHOR]

Unmanned aerial seeding (UAS) is an efficient unmanned rice planting method with broad application prospects. But its optimum basic seedling number and yield and quality characteristics remain unclear. Field experiments were conducted to compare UAS, unmanned dry direct seeding (UDDS), and unmanned carpet transplanting (UCT) methods using inbred japonica rice variety Nanjing 5718. The UAS method was subdivided into four planting density treatments (UAS105, UAS150, UAS195, and UAS240 = 105, 150, 195, and 240 seedlings/m2, respectively). The results showed that increasing the basic seedling density first increased the yield but then it decreased, and UAS195 produced a significantly higher yield. On the other hand, the grain processing, appearance, and taste quality deteriorated with improved nutritional quality. Among the three planting methods, UAS (UAS195) yielded less than UCT due to there being fewer spikelets per panicle, a lower grain-filling rate, and less photosynthetic activity after heading. However, UAS (UAS195) produced more yields than UDDS by having more panicles, more spikelets per panicle, and more biomass accumulation. Both UAS195 and UDDS had poorer grain processing, appearance, and nutritional quality than UCT, but increased amylose content and taste values. Therefore, UAS195 could be an alternative planting method for inbred japonica rice with coordinated yield, quality, and production efficiency. [ABSTRACT FROM AUTHOR]

Exogenous application of methyl jasmonate (MeJA) improves rice drought tolerance, but its effects on rice yield and quality under drought stress during the reproductive phase remain unclear. A pot experiment was conducted to measure rice yield, grain quality, and starch physicochemical properties under three treatments: continuous flooding irrigation throughout the whole growth season (CF), ten days of −40 kPa drought stress at the heading stage (DS), and foliar spraying 100 μmol L−1 MeJA on the first three days of the ten-day −40 kPa heading stage drought stress (DM). An inbred japonica rice variety, Huaidao 5, was the experimental material, and each treatment had 11 replicates for sampling. The results indicated that DS significantly reduced rice yield and quality compared to CF. With increases in superoxide dismutase (+22.2%), peroxidase activities (+10.5%), catalase (+5.0%), and proline content (+5.7%), DM significantly increased 1000-grain weight (+8.6%), filled grain percentage (+3.6%), and yield (+11.1%) compared with DS. Regarding grain quality, DM significantly decreased the chalkiness degree (−12.3%) and protein content (−3.9%) but increased the amylose content (+17.2%) and taste value (+7.3%) relative to DS. In addition, DM improved breakdown viscosity (+17.8%), gelatinization enthalpy (+17.2%), retrogradation enthalpy (+28.0%), 1045/1022 cm−1 ratio (+3.0%), and starch granule morphology compared to DS. In conclusion, exogenous application of 100 μmol L−1 MeJA enhanced the antioxidant capacity of rice leaves, and thus improved starch physicochemical properties to increase grain yield and quality under terminal drought stress. [ABSTRACT FROM AUTHOR]

Direct-seeding methods have received growing interest from rice growers. Wheat straw return is an important measure in rice-wheat rotation system. This study aimed to investigate the influence of wheat straw return on the yield and grain quality in different direct-seeding rice production systems. A split-plot design was adopted for the on-farm trial. The main plots were treated with and without wheat straw return. Dry and wet direct-seeding rice production systems were used in the split plots. The results showed that the yield of direct-seeding rice was reduced by 4.2–7.3% due to wheat straw return, which may be related to a negative effect of wheat straw return on the tiller number (p < 0.05) and biomass accumulation (p < 0.05). Additionally, the content of the amylose and protein of the grain of direct-seeding rice decreased by 4.3–5.5% and 6.0–6.8%, respectively, due to wheat straw return. Furthermore, wheat straw return increased the chalkiness area and the chalkiness degree of the grain of direct-seeding rice, which may be related to the reduced protein content of the grain. However, wheat straw return improved the taste score of the cooked rice (p < 0.05) and the breakdown of the rapid viscosity analyzer (RVA) parameters (p < 0.05), and reduced the setback of the RVA parameters, probably related to an increase in the stickness of the cooked rice (p < 0.05) caused by the reduced amylose content of the grain. When compared to a dry direct-seeding rice production system, a wet direct-seeding rice production system has advantages in the tiller number (p < 0.05) and biomass accumulation, thus increasing the yield and resulting in a lower content of protein and protein components, which reduces both the chalkiness area and chalkiness degree of the grain. However, by using the wet direct-seeding method, the amylose content of the grain improved; hence, the stickness of the cooked rice (p < 0.05) and the breakdown of the RVA parameters decreased, and the setback of the RVA parameters increased. The above results indicated that wheat straw return reduced the yield, nutritional quality, and appearance quality of direct-seeding rice but improved the cooking quality of the grain. Although using the wet direct-seeding method is beneficial to improving the yield, it negatively impacts the grain quality of direct-seeding rice. [ABSTRACT FROM AUTHOR]

Field experiments were performed in 2019 and 2020 to explore yield performance and biomass accumulation dynamics for different direct‐seeded rice methods after wheat straw return. The experimental treatments included two direct‐seeded rice methods (dry direct‐seeded rice and wet direct‐seeded rice) and two wheat straw return treatments (with and without wheat straw return). Wheat straw return had a negative impact on the yield and biomass of direct‐seeded rice. Compared with wet direct‐seeded rice, dry direct‐seeded rice was more negatively affected, with yield and biomass reduced by 6.7%–7.6% and 5.4%–6.5%, respectively. The yield loss was mainly associated with insufficient total spikelet numbers caused by reduced panicle numbers. A lower maximum tiller number caused by the restricted seedling tillering capacity was partly responsible for the inadequate panicle numbers in direct‐seeded rice after wheat straw return. Wheat straw return reduced the maximum and average rate of biomass accumulation, shortened the duration of effective biomass accumulation, and delayed the days to achieve the maximum rate of biomass accumulation for direct‐seeded rice. The negative effect of wheat straw return on direct‐seeded rice was concentrated mainly in the early stage; reduction in the average biomass accumulation rate in the early stage accounted for 61.1%–75.3% of the reduction in total average rate. Wet direct‐seeded rice had a higher average rate and amount of biomass accumulation at the early stage, a greater maximum tiller number, as well as a stronger photosynthetic ability and grain filling ability after heading, which contributed to improving panicle number and total spikelet number, ultimately increasing yield and biomass compared with dry direct‐seeded rice. These results demonstrate that wheat straw return reduced yield and biomass, mainly by inhibiting growth in the early stage of direct‐seeded rice. However, the wet direct‐seeding method decreased the losses in yield and biomass after wheat straw return. [ABSTRACT FROM AUTHOR]

Currently, the information about different characteristics of high yield formation between inbred japonica super rice cultivars (IJSRC) and inter-sub-specific hybrid super rice cultivars (IHSRC) is quite limited. In this present study, the different characteristics of high yield formation between IJSRC (Nanjing 44 and Ningjing 3) and IHSRC (Yongyou 12 and Yongyou 15) were further investigated. Our results indicated that compared with IJSRC, IHSRC displayed a significant increase of the total spikelet numbers per square meter and had higher yields (exceeding 13.18%), which might be related to IHSRC’s more efficient use of temperature and light during the stage from elongating to heading. Moreover, with the strong ability to tiller, the leaf area indexes of IHSRC at elongating, heading and maturity stages were larger than those of IJSRC. Leaf area durations of IHSRC were also higher, in particular during the periods from elongating to heading and from heading to maturity. Although the percentages of above-ground biomass accumulation in IJSRC and IHSRC were similar, IHSRC accumulated more above-ground biomass during the periods from elongating to heading and from heading to maturity. At 30 days after heading, the photosynthetic rate, chlorophyll content and the root oxidation activity of IHSRC were significantly higher. In addition, the photosynthetic functions of IHSRC flag leaves were 6–8 days longer than those of IJSRC flag leaves. Although the yields of IHSRC were significantly higher than those of IJSRC, no differences in yield per day between two types of super rice were observed because of more days from sowing to maturity in IHSRC. Therefore, we concluded that both IJSRC and IHSRC had high yield per day, and the final yield depended on not only the characters of rice related to high yield formation but also the utilization of temperature and light resources in the ecological environment during their growth duration. [ABSTRACT FROM AUTHOR]

This study was conducted to investigate the effects of seeding date and variety type on yield, growth period and utilization of temperature and sunshine under the rice-wheat cropping system in different ecological regions of Henan Province. Taking conventional medium-maturing medium Japonica rice variety, conventional and hybrid late-maturing medium Japonica rice varieties, conventional early-maturing late Japonica rice variety and hybrid late-maturing medium indica rice variety as experimental materials, high-yield cultivation method of mechanization planting of carpet seedlings was used in three different sites, i.e. Luoshan rice-growing district along the Huai River in,southern Henan Province, Xincai in central Henan Province and Yuanyang rice-growing district along the Yellow River in northern Henan Province. The effects of different seeding dates on yield, growth period and utilization of temperature and sunshine of mechanized planting rice were comparatively analyzed. Within the set range of seeding date in the experiment, except that the yields of conventional medium-maturing medium Japonica rice variety were highest for Luoshan and Xincai in the second sowing period (On May 16) and for Yuanyang in the first sowing period (On May 11), the yields of conventional and hybrid late-maturing medium Japonica rice varieties, conventional early-maturing late Japonica rice variety and hybrid late-maturing medium indica rice variety were all highest in the first seeding period (On May 11) for every site, and it showed a trend of gradual decline along with the seeding date delaying(P<0.01), but significance differences were all different among different variety types and sites. With the delaying of seeding date, yield differences among variety types gradually increased in the same site(P<0.01), of which grain yield of hybrid late-maturing medium Japonica rice variety was the highest in every site, and was significantly higher than other variety types in each period. With the delaying of seeding date, the periods of jointing, heading and maturity of all varieties were correspondingly delayed, and whole growth period, and its accumulated temperature, sunshine hours and utilization rate of TPS all showed a significant decreasing trend (P<0.01). And the reduction of growth period along with the delaying of seeding date, was mainly in vegetative growth phase, i.e. from seeding to jointing stages. Therefore, under the condition of rice-wheat cropping system with mechanical planting in Henan Province, the preferred variety that was firstly chosen should be hybird and conventional late-maturing medium Japonica rice varieties in southern Henan, and the variety that was secondly chosen should be conventional early-maturing late Japonica rice variety, and their suitable seeding dates were all from May 11 to May 25. In the northern Henan, the preferred varieties should be the conventional late-maturing medium Japonica rice variety and medium-maturing medium Japonica rice variety, followed by conventional late-maturing medium Japonica rice variety, and their suitable seeding dates were all from May 11 to May 21. The result will provide a reference for the scientific division and the distribution of different rice variety types under mechanical high-yield cultivation and the choosing of its possible seeding date in different ecological areas in Henan Province. [ABSTRACT FROM AUTHOR]

The technology of rice potted-seedlings, which adopts a new type of transplanter, is one of the feasible approaches to explore the new models of rice planting mechanization in China. Plastic pots in the rice potted-seedling tray, which are independent of each other, are used to cultivate strong seedlings with a complete nutrition clod wrapped around their root systems. And then the seedlings are transplanted without injury in the field with a certain line of planting distance. In recent years, the research and extension have fully proved the production demonstration effect around China. In order to promote the combination and application of agricultural machinery with its supporting agronomy technology, this paper attempted to ascertain the rulers of tillers and the appropriate seedlings per hole for high-yield cultivation of rice potted-seedlings in mechanical transplanting. Wuyunjing24 was selected as the experimental material to investigate tillers emerging, panicles formation, and yield characteristics under different seedlings per hole. The results indicated: the tillers from the 1st to 9th tilling positions of the main stem and the simultaneous secondary tillers, which were greatly influenced by the seedlings per hole, had emerged and formed panicles in certain proportion. It was beneficial for the emerging of the low tillers from 1st and 2nd tilling positions when there were 1 or 2 strains of plants per plastic hole during the seedling period. Accordingly, the high tillers from the 8th tilling position and secondary tillers got a higher level of tilling rate during the field period. The number of final panicles was mainly from tillers with wide source parts in the maturation stage. The middle tillers from the 3rd and 4th tilling positions were promoted under the condition of 3 or 4 seedlings per hole, with the final panicles mainly from the 5th to 7th tilling positions while also a little bit low and the secondary tillers. When the seedlings per hole increased to 5 or 6 seedlings, the tilling rate and productive tiller percentage of each leaf significantly declined, with the final panicles mainly counting on the main stem and the middle tillers. The tillers from the middle positions showed a higher productive tiller percentage, and the tillers were the main source of the final panicles and the tiller panicles. The harvest yield of 5 or 6 seedlings per hole was lower than that from 3 or 4 seedlings per hole, but was higher than that from 1 or 2 seedlings per hole. There was a positive correlation between the population base and the effective panicles, and a negative correlation between seedlings per hole and grain per panicle; panicles and grain per panicle were the fundamental factors in deciding the yield. The suitable population base of the normal japonica rice, Wuyunjing24, with a large fringe, was 3-4 strains of plants per plastic hole, 3-4 seedlings per hole, through analysis of the multiple regression function of seedlings per hole on yield and consistent with the harvest yield. The experiment indicated the rules of tillers emergence and panicles formation for rice potted-seedling in mechanical transplanting, which provided a theoretical basis for the density of sowing and planting of the farm equipment in field production. According to the tilling characteristics of rice potted-seedlings, management measures of manure and water should be studied, for giving full play to the middle tillers of main stem. Appropriate seedlings per hole is the premise of high-yield cultivation, which particularly increases the grain yield, not only the panicle numbers, the grain numbers, setting percentage, and the gain weights but also for more harmonious yield factors. [ABSTRACT FROM AUTHOR]

A mixture of controlled-release nitrogen (N) fertilizers (CRNFs) and conventional urea (CU) as a single application of basal fertilizer could simplify fertilization in rice cultivation from the traditional and more labor-intensive fertilization strategy of multiple applications of nitrogen. However, the reported benefits of this combined approach in increasing rice yield have varied substantially for various reasons, including that various types of rice are characterized by different N requirements to obtain high yield. In this study, two late japonica rice cultivars, Jia58 (J58) and Jia67(J67), were used to determine the best combination of one of two short-acting CRNFs (release periods were 40 and 60 days) and one of three long-acting CRNFs (release periods were 80, 100 and 120 days) to apply with the CU as a one-time application of basal fertilizer. Six combinations of CRNFs were established based on their release periods: A1, 40 + 80 days; A2, 40 + 100 days; A3, 40 + 120 days; B1, 60 + 80 days; B2, 60 + 100 days; and B3, 60 + 120 days. CU applied split at basal, tillering and panicle differentiation stages, respectively as control (CK). The effects of the different treatment combinations of CRNFs on late-rice grain yield, N accumulation and N-use efficiency in a two-year field experiment were determined. Results showed that, the A2 treatment achieved the same yield as that of CK, and yield of the B2 treatment exceeded the yield of CK. Yield of J58 applied with B2 was 7.35% higher in 2018 and 7.40% higher in 2019 than that of the corresponding yield of CK; yield of J67 applied with B2 was 6.05% higher in 2018 and 6.87% higher in 2019 than that of CK. Compared with other CRNF treatments, the release of N from A2 and B2 was most synchronized with nitrogen uptake by the two cultivars, which indicates that fertilizer combination completely met the nitrogen demands during each growth stage of rice. Rice of the A2 and B2 treatments had higher N accumulation, higher aboveground biomass accumulation and LAI (leaf area index) at the heading and maturity stages and higher photosynthetic activity than those of other CRNF treatments. In conclusion, for late japonica rice in China, the application of the A2 and B2 treatments as optimal type of CRNF can achieve labor saving and yield increasing simultaneously in rice production. [ABSTRACT FROM AUTHOR]

The main purpose of the present study was to explore the optimum timing for mid-stage nitrogen (N) application to improve fragrant rice performance. The field experiment was conducted in 2019 and 2020 with two fragrant rice cultivars, i.e., YNX28 and NG9108, and five timings of mid-stage nitrogen application: at the emergence of the top-fifth-leaf (TL5), the top-fourth-leaf (TL4), the top-third-leaf (TL3), the top-second-leaf (TL2), and the top-first-leaf (TL1) of the main stem. The control condition received no mid-stage nitrogen application (CK). The results revealed that the TL5, TL4, TL3 and TL2 treatments significantly increased grain yield of both varieties in 2019 and 2020, compared with CK. Grain yield reached a maximum value under the TL3 treatment of YNX28 and the TL4 treatment of NG9108. Moreover, the TL4, TL3 and TL2 treatments significantly increased the brown rice rate, milled rice rate, head rice rate and protein content of both varieties in 2019 and 2020, compared with CK, whereas the TL2 and TL1 treatments of YNX28 and the TL3, TL2 and TL1 treatments of NG9108 significantly increased the chalky rice rate and chalkiness. Further, appropriate mid-stage nitrogen application timing also improved the grain 2-AP content due to regulation of the contents of synthesis-related precursors (proline, GABA) and enzymatic activities (ProDH, OAT, P5CS, BADH2). Compared with CK, the TL4 and TL3 treatments of YNX28 significantly increased the 2-AP content in the rice grains by 21.8–27.4%, while the TL5 and TL4 treatments of NG9108 significantly increased the 2-AP content in the rice grains by 15.6–31.6%. These results suggest that the TL3 treatment of YNX28 and the TL4 treatment of NG9108 are the optimum timings of mid-stage nitrogen application for fragrant rice production. The optimal mid-stage nitrogen application timing of NG9108 is earlier than that of YNX28. • Delayed timing of mid-stage nitrogen application deteriorated the appearance quality of rice. • Appropriate mid-stage nitrogen application timing also improved the grain 2-AP content. • In terms of 2-AP and its synthesis-related parameters, TL4 of NG9108 and TL3 of YNX28 differed most from CK treatment. [ABSTRACT FROM AUTHOR]