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Planting density is an important factor affecting plant growth and yield formation in rapeseed. However, the understanding of the mechanism underlying the impact of planting density on biomass, canopy, and ultimate seed yield remains limited. A field experiment was conducted to investigate the effect of planting density on seed yield, yield components, biomass accumulation and partitioning, and canopy structure. Five planting density levels were set as D1 (2.4 × 105 plants ha−1), D2 (3.6 × 105 plants ha−1), D3 (5.4 × 105 plants ha−1), D4 (6.0 × 105 plants ha−1), and D5 (7.2 × 105 plants ha−1). The results showed that with planting density increasing from D1 to D3, the seed yield, number of pods in population, and 1000-seed weight increased, while seedling survival rate, yield per plant, number of pods per plant, and number of seeds per plant decreased. When planting density increased to D4 and D5, seed yield dramatically decreased due to a decreased number of seeds per pod and 1000-seed weight. Increasing planting density from D1 to D3 increased biomass accumulation in all organs. D3 produced the highest biomass partitioning in seeds. In addition, D2 and D3 treatments had a high level of pod area index (5.3–5.8), which caused an approximately 93% of the light to be intercepted. The distribution of light in D2 and D3 was more evenly spread, with the upper and lower parts of the canopy displaying a distribution ratio of roughly 7:3. Therefore, D2 and D3 produced the highest seed yields. In conclusion, D2 and D3 are recommended in rapeseed production due to their role in improving biomass accumulation and partitioning and canopy structure. [ABSTRACT FROM AUTHOR]

Salt stress is one of the major adverse factors affecting plant growth and crop production. Rapeseed is an important oil crop, providing high-quality edible oil for human consumption. This experiment was conducted to investigate the effects of salt stress on the phenotypic traits and physiological processes of rapeseed. The soil salinity was manipulated by setting three different levels: 0 g NaCl kg−1 soil (referred to as S0), 1.5 g NaCl kg−1 soil (referred to as S1), and 3.0 g NaCl kg−1 soil (referred to as S2). In general, the results indicated that the plant height, leaf area, and root neck diameter decreased with an increase in soil salinity. In addition, the biomass of various organs at all growth stages decreased as soil salinity increased from S0 to S2. The increasing soil salinity improved the distribution of biomass in the root and leaf at the seedling and flowering stages, indicating that rapeseed plants subjected to salt stress during the vegetative stage are capable of adapting their growth pattern to sustain their capacity for nutrient and water uptake, as well as leaf photosynthesis. However, as the soil salinity increased, there was a decrease in the distribution of biomass in the pod and seed at the maturity stage, while an increase was observed in the root and stem, suggesting that salt stress inhibited carbohydrate transport into reproductive organs. Moreover, the C and N accumulation at the flowering and maturity stages exhibited a reduction in direct correlation with the increase in soil salinity. High soil salinity resulted in a reduction in the C/N, indicating that salt stress exerted a greater adverse effect on C assimilation compared to N assimilation, leading to an increase in seed protein content and a decrease in oil content. Furthermore, as soil salinity increased from S0 to S2, the activity of superoxide dismutase (SOD) and catalase (CAT) and the content of soluble protein and sugar increased by 58.39%, 33.38%, 15.57%, and 13.88% at the seedling stage, and 38.69%, 22.85%, 12.04%, and 8.26% at the flowering stage, respectively. In summary, this study revealed that salt stress inhibited C and N assimilation, leading to a suppressed phenotype and biomass accumulation. The imbalanced C and N assimilation under salt stress contributed to the alterations in the seed oil and protein content. Rapeseed had a certain degree of salt tolerance by improving antioxidants and osmolytes. [ABSTRACT FROM AUTHOR]

Having nursery rapeseed (Brassica napus L.) seedlings at a high density in a tray is an indispensable step to realizing mechanized transplanting for rapeseed. The reduction in seedling quality caused by high sowing density is one of the key factors affecting transplanting quality and yield. Uniconazole has been considered as a potential plant growth regulator to improve plant growth under diverse unfavorable circumstances. In two sowing densities (400 and 800 seeds per tray), an experiment was carried out between 2021 and 2022 to investigate the effects of uniconazole seed-coating treatments on pre-transplant and post-transplant seedling characteristics. The results demonstrate that uniconazole treatment can effectively reduce the high-density-induced reduction in seedling dry matter and leaf area, stem thinness, and stem and petiole overgrowth. Further evidence that uniconazole can improve seedling quality, enhance yield, and lessen yield loss due to high-density sowing was provided by yield at maturity. However, because of the uncontrolled growth during the late stage in the tray, the relative growth rate of seedlings after transplant in the transplant shock stage revealed that lower doses of uniconazole treatment have a negative effect on the seedling recovery. The results of principal coordinate analysis and partial correlation analysis proved that the yield and net assimilation rate were related to the improvement of seedling high-density tolerance by uniconazole treatment. Consequently, 500–750 mg L−1 uniconazole coating per 100 g of seeds in 5 mL is recommended by this study, considering the potential risk of seedling emergence and growth caused by an overdose of uniconazole treatment. [ABSTRACT FROM AUTHOR]

Cultivating a high quality rapeseed blanket seedling is crucial if the mechanized transplant of rapeseed is to become an effective part of oilseed production in China. Nitrogen (N) strongly affects the growth and quality of the rapeseed seedling. This study investigated the agronomic traits, physiological indexes, the surviving number of blanket seedlings, and the survival rate after transplanting two canola (Brassica napus L.) cultivars (Ningza 1838 and Yangyou 9) treated with five N rates (0, 0.5, 1.0, 1.5 and 2.0 g N per tray). Plant height, leaf age, leaf area, collar length, fresh and dry weights, moisture content, and N concentration in root and shoot all increased as the N rate increased. The survival number, collar diameter, root to shoot ratio at the 30th day after sowing and the survival rate at the 10th day after transplanting increased at first then decreased as N rate consecutively increased. The survival number and survival rate under the 1.0 and 1.5 g N per tray treatments were most improved amongst N treatments, although there was no significant difference between these two N treatments. This suggests that to achieve high-quality blanket seedling needed for mechanized transplanting, the application of N at rates of 1.0 to 1.5 g N per tray at the one-leaf and one-heart stages is recommended. [ABSTRACT FROM AUTHOR]

Mechanized transplanting of rapeseed (Brassica napus L.) blanket seedling is an effective strategy to cope with the seasonal conflict and large labor cost in rapeseed production. The sowing density is a key factor to cultivate high-quality seedlings suitable for mechanized transplanting. An experiment was conducted to investigate the effects of different sowing density levels of 638, 696, 754, 812, 870 and 928 seeds per tray (referred as D1, D2, D3, D4, D5 and D6, respectively) on agronomic traits and survival rate after mechanized transplanting of two rapeseed cultivars (Zheyouza108 and Heza17) in 2020 and 2021. The results showed that high sowing density increased plant height but decreased leaf area, collar diameter, biomass accumulation, the ratio of root to shoot and seedling fullness. These negative effects jointly decreased the seedling rate and survival rate after mechanized transplanting. However, the seedlings under D1 and D2 posed a great plant survival rate of more than 95% after mechanized transplanting, suggesting that the seedlings under the two densities were perfect for mechanized transplanting. In addition, hierarchical analysis grouped D1 and D2 into the same class, indicating that their seedling qualities were not significantly different, though the blanket seedlings under D1 outperformed those under D2 in some traits. A sowing density of 696 seeds per tray (D2) is then recommended in this study, altogether considering its high-quality seedlings suitable for mechanized transplanting, and economically, fewer seedling trays required. [ABSTRACT FROM AUTHOR]

Winter rapeseed is an important oilseed crop in the Yangtze River Basin. To optimize its cultivation in this area and improve its production efficiency, a split-plot experiment with various planting dates (25 September and 10 October), nitrogen applications (120, 240 and 360 kg ha −1 ) and planting densities (3.0 × 10 5 , 4.5 × 10 5 and 6.0 × 10 5 plants ha −1 ) was performed to investigate their effects and interactions on the seed yield of rapeseed, its lodging index and weed occurrence in farmland. Our results indicated that (1) Delay in planting led to the decrease in the net photosynthetic rate ( Pn ) of leaf, nitrogen seed production efficiency (NUE), pod number per plant and yield, but aggravated weed occurrence. The increase in nitrogen fertilization resulted in reduced NUE, elevated Pn of leaves, improved pod number per plant and yield, and facilitated weed growth. The increase of planting density elevated NUE, reduced Pn and yield per plant because of the lowered number of pods per plant, but enhanced the population yield and substantially inhibited weed growth. (2) Delayed planting inhibited rapeseed growth, showing significant reductions in plant height, rhizome diameter, root dry weight, aboveground dry weight and root/shoot ratio, and resulted in lower snapping resistance but a higher lodging index. Although higher nitrogen application improved root dry weight, rhizome diameter and snapping resistance, it resulted in the increase of plant height and aboveground dry weight, which led to a reduced root/shoot ratio and a greater lodging index. The increase in planting density lowered the rhizome diameter, root dry weight and snapping resistance, significantly reduced the plant height and aboveground dry weight, hence increasing the root/shoot ratio, which further decreased the lodging index. A linear relationship was observed between the seed oil content and lodging index (2013–2014, R 2  = 0.3783**; 2014–2015, R 2  = 0.5641**). Oil content was reduced while the lodging index increased, indicating that lodging index was a key factor determining oil content under various planting dates, nitrogen amounts, densities and their interactions. [ABSTRACT FROM AUTHOR]

The seed emergence and yield of rainfed rapeseed ( Brassica napus L.) are commonly limited by soil water availability during the growing season. The return of straw to the field helps maintain soil moisture status, but can cause long hypocotyls of seedlings and result in yield reduction. Using the swede rape hybrid Huayouza 62 as material, the effects of sowing depth and soil compaction on seedling growth and yield under conditions of straw return to the field were investigated. The bulk density and water content for the soil layers of 0–10 and 10–20 cm significantly increased and total porosity decreased under the compaction of shallow (2 cm) and deep sowing (3 cm), and the effect was greater for the 0–10 cm layer. Without soil compaction, the seedling emergence rate was substantially improved with increased sowing depth, but was dramatically decreased in the case of compacted soil. The soil compaction significantly elevated the seedling emergence rate with shallow sowing, and increases were 15.57 and 17.08% for 2013–2014 and 2014–2015, respectively; however, with deep sowing, compaction had no significant effect. The variation in seedling density was consistent with that of the seedling emergence rate. Compared to shallow sowing, deep sowing induced a thinner rapeseed stem, but soil compaction had an opposite effect. Increasing the sowing depth or soil compaction improved the overall yield by elevating the root/shoot ratio of seedlings and lodging resistance, effectively eliminating weed infestation. Significant interactions were found between sowing depth and soil compaction in yield and siliques. Shallow sowing with soil compaction had a positive effect on growth and development, and dramatically increased seedling density and siliques, leading to improved yield. [ABSTRACT FROM AUTHOR]

Salt stress is a major negative factor affecting the sustainable development of agriculture. Phosphorus (P) deficiency often occurs in saline soil, and their interaction inhibits plant growth and seed yield for canola (Brassica napus L.). P supply is considered an effective way to alleviate the damage of salt stress. However, the knowledge of how P supply can promote plant growth in saline environment was limited. A field experiment was conducted to explore the effects of P rate on accumulation, and partitioning, of biomass and P, leaf photosynthesis traits, and yield performance in saline soil in the coastal area of Yancheng City, Jiangsu Province, China, during the 2018–2019 and 2019–2020 growing seasons. P supply increased biomass and P accumulation in all organs, and root had the most increments among different organs. At flowering stage, P supply increased the biomass and P partitioning in root and leaf, but it decreased the partitioning in stem. At maturity stage, P supply facilitated the biomass and P partitioning in seed, but it decreased the partitioning in stem and shell, and it increased the reproductive-vegetative ratio, suggesting that P supply can improve the nutrients transporting from vegetative organs to reproductive organs. Besides, P supply improved the leaf area index and photosynthetic rate at the flowering stage. As a result, the seed yield and oil yield were increased. In conclusion, P supply can improve the canola plant growth and seed yield in a saline environment. P fertilizer at the rate of 120 kg P2O5 ha−1 was recommended in this saline soil. [ABSTRACT FROM AUTHOR]

Crop lodging detrimentally affects crop yield and mechanical harvest efficiency. Traditional remote sensing-based methods primarily focus on the identification and area extraction of lodging using image texture and spectrum. However, the response of image texture and spectrum to lodging is indirect and varies under diverse conditions. Moreover, other important finer details of lodging phenotyping, such as lodging angle and lodging type, have frequently been neglected. In this study, a robust and accurate method was developed for investigating lodging phenotypes in the field. The method was based on the three-dimensional morphological information of rapeseed (Brassica napus L.) canopy reconstructed from unmanned aerial vehicle (UAV) images. In contrast to traditional remote sensing methods that only identify lodging targets and their respective areas, the novel method in this study calculated the total lodging angle (TLA), root lodging angle (RLA), stem lodging angle (SLA = TLA - RLA), and lodging types according to a morphological method and a lodging classification model. Initially, the method employed a geometric model to characterize the stalk shape of lodged rapeseed. After assessing numerous lodging samples from individual rapeseed plants, the circle function was identified as the optimal geometric model. With this optimal function, the canopy height derived from the UAV images was found effective in calculating TLA, RLA, and SLA across 24 rapeseed cultivars in five climatic zones within the Yangtze River Basin (YRB) in China. Results showed that the average root mean square error (RMSE) was 8.3° for TLA and 7.4° for RLA. Subsequently, based on field measured data of SLA and RLA, a decision tree model was constructed to classify lodging types and an accuracy of 95.4% was achieved. Using the classification model and estimated values of RLA and SLA, the spatial distribution information and specific area estimates for different lodging types were obtained. Based on the analysis of these results, the rapeseed cultivars Zhongshuang 11 and Dadi 199 were determined to be the dominant cultivars with lodging resistance in the YRB, even though they did not achieve the mean high yields in multiple climatic zones. However, the lodging-prone cultivars such as Qinyou7 and Qinyou33 fell under the low-yield level in all climatic zones. The robust and cost-effective method proposed in this study for acquiring detailed crop lodging phenotyping data has the potential to enhance mechanized harvesting, accurately estimate the risk of low yield, and assess the lodging status of various crops. • Circle functions can simulate most stalk shapes of lodged rapeseed. • Two phases of UAV images are found effective to estimate total lodging angle. • Root and stem lodging angle can be estimated using circle functions and UAV images. • Lodging types can be distinguished by root lodging angle and stem lodging angle. [ABSTRACT FROM AUTHOR]

• The LUT optimization method effectively removed parameter combinations that were not relevant to biochemical and structural features of field rapeseed in raw LUT. • Optimized VI - LUT significantly improve the accuracy of rapeseed LAI inversion. • These findings provide a practical approach for LAI inversion in various spatial–temporal scenarios. For winter rapeseed, timely monitoring of the leaf area index (LAI) near the winter solstice is critical for estimating its overwintering survival rate and yield. While unmanned aerial vehicle (UAV) remote sensing techniques have emerged as a promising means for crop LAI monitoring, many existing crop LAI models have only been evaluated using a single sensor system, a single cultivar, a single development stage, and/or a single site. As a result, the generalization capability of these LAI models is limited. In this study, four empirical statistical models (ESMs) and a new PROSAIL-based lookup table (LUT) method were developed to estimate the LAI of 24 winter rapeseed cultivars mainly grown in the Yangtze River Basin. The raw LUT was optimized using a vegetation index (VI) strategy after screening out inefficient parameter combinations using in-situ UAV reflectance and measured LAIs. The model transferability was evaluated across three years, six regional sites around Yangtze River Basin, different development stages, and two data sources from different sensors. An artificial neural network model in the ESMs performed best for data acquired in 2019 and 2020, but could not be used to estimate the LAI in 2018 due to the use of different sensors for data acquisition. In contrast, the optimized VI-LUT method was robust and outperformed the raw LUT for LAI retrieval with a root mean squared error of <0.7 for all data sets. These findings suggest that the optimized VI-LUT method has potential for estimating LAI at different spatial and temporal scales, especially for the situation where sensor types are difficult to be unified in multiple locations. Moreover, the genotype in these cultivars did not appear to dominate LAI generation before overwintering, but the climatic zone did. These findings have implications for the study of genotype-environment interactions in rapeseed cultivation. [ABSTRACT FROM AUTHOR]

Using the rapeseed Huayouza 62 as experimental material, yield and lodging related traits were evaluated under various nitrogen applications [120,240 and 360 kg ha −1 (N1–N3, respectively)] and planting densities [15 × 10 4 , 30 × 10 4 and 45 × 10 4 plants ha −1 (D1–D3, respectively)]. Results showed: (1) the increase of nitrogen fertilizer elevated the leaf (and silique) area index (LAI) and light interception rate (LIR), significantly affecting the bud stage. In addition, the radiation use efficiency (RUE) for different growth stages and biomass accumulation were increased, which improved yield by facilitating formation of siliques in both single plants and populations. The increase of planting density significantly elevated the population LAI and LIR in seedlings, and the RUE in various growth stages, increased population biomass accumulation, which may have also improved yield by promoting the formation of siliques in the population. The correlation between LIR/LAI and yield was the highest at the bud stage, while the strongest correlation between RUE and yield was at silique development. (2) More nitrogen increased the lodging angle, base lodging index (LIL) and the upper lodging index (LIU), resulting in elevated whole plant lodging risk. With increases in nitrogen fertilizer, expression of phenylalanine ammonia-lyase ( PAL ) of lignin biosynthesis decreased in the upper stem, leading to lower lignin content and lodging resistance. However, higher plant density reduced the lodging angle and LIU, but increased LIL. The increase in planting density induced the expression of PAL , cinnamoyl-CoA reductase 1 ( CCR1 ), 4-coumarate: CoA ligase (4CL) in the stem, which showed their highest expression in the N2D3 treatment, leading to higher lignin content and lodging resistance. (3) In this study, N2D3 achieved relative high yield and the lowest lodging index, which will meet the requirements for mechanized harvest. [ABSTRACT FROM AUTHOR]

This 2-year field study investigated the effects of time and paclobutrazol concentration on the seed yield and the lodging and pod shatter resistance of oilseed rape ( Brassica napus L.). Paclobutrazol was sprayed on the foliar tissue of two rapeseed cultivars, Yangguang 2009 and Fengyou 520, at the closed canopy stage and the early bud stage at concentrations of 0, 150 and 300 mg L −1 . Our results demonstrated the following: (1) Paclobutrazol significantly increased lodging resistance, pod shatter resistance. Paclobutrazol reduced the number of seeds per pod but increased the number of pods per plant, the 1000-seed weight and the yield. With increasing paclobutrazol concentrations, the resistance to lodging and pod shattering increased, whereas the increment in yield decreased. Compared with treatment at the early bud stage, the application of 150 mg L −1 paclobutrazol at the closed canopy stage significantly enhanced the lodging and pod shatter resistance and increased the yield increment in both cultivars. (2) After treatment with paclobutrazol, the increment of lodging resistance and pod shatter resistance were higher for Fengyou 520 than for Yangguang 2009, and the yield increment was less. (3) The increased root-top ratio, increased snapping resistance and reduced plant height resulting from paclobutrazol treatment reduced the angle of plant lodging, which improved the ability of the culm to resist lodging. Pod shatter resistance increased as pod water content and pod dry weight increased. In summary, 150 mg L −1 of paclobutrazol sprayed on foliar tissue at the closed canopy stage significantly enhanced lodging resistance, pod shatter resistance and yield. These improvements could help augment the mechanical production of rapeseed in China. [ABSTRACT FROM AUTHOR]