水稻耕作栽培Rice Physiology · Biochemistry · Cultivation · Tillage
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.
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.
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.
Coupling of reduced inorganic fertilizer with plant-based organic fertilizer as a promising fertilizer management strategy for colored rice in tropical regions
Colored rice is a type of high-quality, high-added-value rice that has attracted increasing attention in recent years. The use of large amounts of inorganic nitrogen fertilizer in rice fields results in low fertilizer use efficiency and high environmental pollution. Organic fertilizer is a promising way to improve soil quality and sustain high yields. However, most studies focus on the effect of animal-based organic fertilizers. The effects of different ratios of plant-based organic fertilizer and inorganic fertilizer on the grain yield and quality of colored rice have rarely been reported. Therefore, a two-year field experiment was conducted in 2020 and 2021 to study the effects of replacing inorganic N fertilizers with plant-based organic fertilizers on the yield, nitrogen use efficiency (NUE), and anthocyanin content of two colored rice varieties in a tropical region in China. The experimental treatments included no nitrogen fertilization (T1), 100% inorganic nitrogen fertilizer (T2), 30% inorganic nitrogen fertilizer substitution with plant-based organic fertilizer (T3), 60% inorganic nitrogen fertilizer substitution with plant-based organic fertilizer (T4), and 100% plant-based organic fertilizer (T5). The total nitrogen provided to all the treatments except T1 was the same at 120 kg ha–1. Our results showed that the T3 treatment enhanced the grain yield and anthocyanin content of colored rice by increasing nitrogen use efficiency compared with T2. On average, grain yields were increased by 9 and 8%, while the anthocyanin content increased by 16 and 10% in the two colored rice varieties under T3 across the two years, respectively, as compared with T2. Further study of the residual effect of partial substitution of inorganic fertilizers showed that the substitution of inorganic fertilizer with plant-based organic fertilizer improved the soil physio-chemical properties, and thus increased the rice grain yield, in the subsequent seasons. The highest grain yield of the subsequent rice crop was observed under the T5 treatment. Our results suggested that the application of plant-based organic fertilizers can sustain the production of colored rice with high anthocyanin content in tropical regions, which is beneficial in reconciling the relationship between rice production and environmental protection.
Rice canopy temperature is affected by nitrogen fertilizer
Regulation of 2-acetyl-1-pyrroline and grain quality in early-season indica fragrant rice by nitrogen and silicon fertilization under different plantation methods
Irrigation regimes modulate non-structural carbohydrate remobilization and improve grain filling in rice (Oryza sativa L.) by regulating starch metabolism
Recently developed ‘super’ rice cultivars with greater yield potentials often suffer from the problem of poor grain filling, especially in inferior spikelets. Here, we studied the activities of enzymes related to starch metabolism in rice stems and grains, and the microstructures related to carbohydrate accumulation and transportation to investigate the effects of different water regimes on grain filling. Two ‘super’ rice cultivars were grown under two irrigation regimes of well-watered (WW) and alternate wetting and moderate soil drying (AWMD). Compared with the WW treatment, the activities of ADP glucose pyrophosphorylase (AGPase), starch synthase (StSase) and starch branching enzyme (SBE), and the accumulation of non-structural carbohydrates (NSCs) in the stems before heading were significantly improved, and more starch granules were stored in the stems in the AWMD treatment. After heading, the activities of α-amylase, β-amylase, sucrose phosphate synthase (SPS) and sucrose synthase in the synthetic direction (SSs) were increased in the stems to promote the remobilization of NSCs for grain filling under AWMD. During grain filling, the enzymatic activities of sucrose synthase in the cleavage direction (SSc), AGPase, StSase and SBE in the inferior spikelets were increased, which promoted grain filling, especially for the inferior spikelets under AWMD. However, there were no significant differences in vascular microstructures. The grain yield and grain weight could be improved by 13.1 and 7.5%, respectively, by optimizing of the irrigation regime. We concluded that the low activities of key enzymes in carbon metabolism is the key limitation for the poor grain filling, as opposed to the vascular microstructures, and AWMD can increase the amount of NSC accumulation in the stems before heading, improve the utilization rate of NSCs after heading, and increase the grain filling, especially in the inferior spikelets, by altering the activities of key enzymes in carbon metabolism.
Optimized tillage methods increase mechanically transplanted rice yield and reduce the greenhouse gas emissions
A phenology-based vegetation index for improving ratoon rice mapping using harmonized Landsat and Sentinel-2 data
Ratoon rice, which refers to a second harvest of rice obtained from the regenerated tillers originating from the stubble of the first harvested crop, plays an important role in both food security and agroecology while requiring minimal agricultural inputs. However, accurately identifying ratoon rice crops is challenging due to the similarity of its spectral features with other rice cropping systems (e.g., double rice). Moreover, images with a high spatiotemporal resolution are essential since ratoon rice is generally cultivated in fragmented croplands within regions that frequently exhibit cloudy and rainy weather. In this study, taking Qichun County in Hubei Province, China as an example, we developed a new phenology-based ratoon rice vegetation index (PRVI) for the purpose of ratoon rice mapping at a 30 m spatial resolution using a robust time series generated from Harmonized Landsat and Sentinel-2 (HLS) images. The PRVI that incorporated the red, near-infrared, and shortwave infrared 1 bands was developed based on the analysis of spectro-phenological separability and feature selection. Based on actual field samples, the performance of the PRVI for ratoon rice mapping was carefully evaluated by comparing it to several vegetation indices, including normalized difference vegetation index (NDVI), enhanced vegetation index (EVI) and land surface water index (LSWI). The results suggested that the PRVI could sufficiently capture the specific characteristics of ratoon rice, leading to a favorable separability between ratoon rice and other land cover types. Furthermore, the PRVI showed the best performance for identifying ratoon rice in the phenological phases characterized by grain filling and harvesting to tillering of the ratoon crop (GHS-TS2), indicating that only several images are required to obtain an accurate ratoon rice map. Finally, the PRVI performed better than NDVI, EVI, LSWI and their combination at the GHS-TS2 stages, with producer’s accuracy and user’s accuracy of 92.22 and 89.30%, respectively. These results demonstrate that the proposed PRVI based on HLS data can effectively identify ratoon rice in fragmented croplands at crucial phenological stages, which is promising for identifying the earliest timing of ratoon rice planting and can provide a fundamental dataset for crop management activities.
The underlying mechanism of variety–water–nitrogen–stubble damage interactions on yield formation in ratoon rice with low stubble height under mechanized harvesting
Agronomic measures are the key to promote the sustainable development of ratoon rice by reducing the damage from mechanical crushing to the residual stubble of the main crop, thereby mitigating the impact on axillary bud sprouting and yield formation in ratoon rice. This study used widely recommended conventional rice Jiafuzhan and hybrid rice Yongyou 2640 as the test materials to conduct a four-factor block design field experiment in a greenhouse of the experimental farm of Fujian Agricultural and Forestry University, China from 2018 to 2019. The treatments included fertilization and no fertilization, alternate wetting and drying irrigation and continuous water flooding irrigation, and plots with and without artificial crushing damage on the rice stubble. At the same time, a 13C stable isotope in-situ detection technology was used to fertilize the pot experiment. The results showed significant interactions among varieties, water management, nitrogen application and stubble status. Relative to the long-term water flooding treatment, the treatment with sequential application of nitrogen fertilizer coupled with moderate field drought for root-vigor and tiller promotion before and after harvesting of the main crop, significantly improved the effective tillers from low position nodes. This in turn increased the effective panicles per plant and grains per panicle by reducing the influence of artificial crushing damage on rice stubble and achieving a high yield of the regenerated rice. Furthermore, the partitioning of 13C assimilates to the residual stubble and its axillary buds were significantly improved at the mature stage of the main crop, while the translocation rate to roots and rhizosphere soil was reduced at the later growth stage of ratooning season rice. This was triggered by the metabolism of hormones and polyamines at the stem base regulated by the interaction of water and fertilizer at this time. We therefore suggest that to achieve a high yield of ratoon rice with low stubble height under mechanized harvesting, the timely application of nitrogen fertilizer is fundamental, coupled with moderate field drying for root-vigor preservation and tiller promotion before and after the mechanical harvesting of the main crop.
The response of roots and the rhizosphere environment to integrative cultivation practices in paddy rice
Integrative cultivation practices (ICPs) are essential for enhancing cereal yield and resource use efficiency. However, the effects of ICP on the rhizosphere environment and roots of paddy rice are still poorly understood. In this study, four rice varieties were produced in the field. Each variety was treated with six different cultivation techniques, including zero nitrogen application (0 N), local farmers’ practice (LFP), nitrogen reduction (NR), and three progressive ICP techniques comprised of enhanced fertilizer N practice and increased plant density (ICP1), a treatment similar to ICP1 but with alternate wetting and moderate drying instead of continuous flooding (ICP2), and the same practices as ICP2 with the application of organic fertilizer (ICP3). The ICPs had greater grain production and nitrogen use efficiency than the other three methods. Root length, dry weight, root diameter, activity of root oxidation, root bleeding rate, zeatin and zeatin riboside compositions, and total organic acids in root exudates were elevated with the introduction of the successive cultivation practices. ICPs enhanced nitrate nitrogen, the activities of urease and invertase, and the diversity of microbes (bacteria) in rhizosphere and non-rhizosphere soil, while reducing the ammonium nitrogen content. The nutrient contents (ammonium nitrogen, total nitrogen, total potassium, total phosphorus, nitrate, and available phosphorus) and urease activity in rhizosphere soil were reduced in all treatments in comparison with the non-rhizosphere soil, but the invertase activity and bacterial diversity were greater. The main root morphology and physiology, and the ammonium nitrogen contents in rhizosphere soil at the primary stages were closely correlated with grain yield and internal nitrogen use efficiency. These findings suggest that the coordinated enhancement of the root system and the environment of the rhizosphere under integrative cultivation approaches may lead to higher rice production.
Salinity is one of the most significant risks to crop production and food security as it harms plant physiology and biochemistry. The salt stress during the rice emergence stages severely hampers the seed germination and seedling growth of direct-seeded rice. Recently, nanoparticles (NPs) have been reported to be effectively involved in many plant physiological processes, particularly under abiotic stresses. To our knowledge, no comparative studies have been performed to study the efficiency of conventional, chemical, and seed nanopriming for better plant stress tolerance. Therefore, we conducted growth chamber and field experiments with different salinity levels (0, 1.5, and 3‰), two rice varieties (CY1000 and LLY506), and different priming techniques such as hydropriming, chemical priming (ascorbic acid, salicylic acid, and γ-aminobutyric acid), and nanopriming (zinc oxide nanoparticles). Salt stress inhibited rice seed germination, germination index, vigor index, and seedling growth. Also, salt stress increased the over accumulation of reactive oxygen species (H2O2 and O2-·) and malondialdehyde (MDA) contents. Furthermore, salt-stressed seedlings accumulated higher sodium (Na+) ions and significantly lower potassium (K+) ions. Moreover, the findings of our study demonstrated that, among the different priming techniques, seed nanopriming with zinc oxide nanoparticles (NanoZnO) significantly contributed to rice salt tolerance. ZnO nanopriming improved rice seed germination and seedling growth in the pot and field experiments under salt stress. The possible mechanism behind ZnO nanopriming improved rice salt tolerance included higher contents of α-amylase, soluble sugar, and soluble protein and higher activities of antioxidant enzymes to sustain better seed germination and seedling growth. Moreover, another mechanism of ZnO nanopriming induced rice salt tolerance was associated with better maintenance of K+ ions content. Our research concluded that NanoZnO could promote plant salt tolerance and be adopted as a practical nanopriming technique, promoting global crop production in salt-affected agricultural lands.