Next Article in Journal
Nutritional, Phytochemical, and Rheological Profiles of Different Oat Varieties and Their Potential in the Flour Industry
Previous Article in Journal
Bioindicators for Assessing Soil Quality in Ecuador’s Jun Jun Micro-Watershed
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Agronomy
Volume 14
Issue 7
10.3390/agronomy14071437
agronomy-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Effects of Nitrogen Application and Planting Density Interaction on the Silique-Shattering Resistance and Yield of Direct-Seeding Rapeseed (Brassica napus L.) in Sichuan

by
Yuqin Luo
1,
Huayu Jiang
1,
Yue Hu
1,
Li Liu
1,
Kamran Ghaffor
1,
Hafiz Hassan Javed
1,
Xiao Peng
1,
Xiang Guo
2 and
Yongcheng Wu
1,3,4,*
1
College of Agronomy, Sichuan Agricultural University, Chengdu 611130, China
2
Sichuan Province Agro-Meteorological Center, Chengdu 610072, China
3
Key Laboratory of Crop Eco-Physiology and Farming System in Southwest, Chengdu 611130, China
4
Crop Eco Physiology and Cultivation Key Laboratory of Sichuan Province, Chengdu 611130, China
*
Author to whom correspondence should be addressed.
Agronomy 2024, 14(7), 1437; https://doi.org/10.3390/agronomy14071437
Submission received: 24 May 2024 / Revised: 28 June 2024 / Accepted: 28 June 2024 / Published: 1 July 2024
(This article belongs to the Section Innovative Cropping Systems)
Browse Figures
Versions Notes

Abstract

:
Rapeseed siliques easily shatter after ripening, resulting in a significant amount of grain loss, which delimits the development of rapeseed machine harvest. However, the effect of nitrogen (N) and density interaction on the characteristics of rape siliques and shattering resistance index is still vague. During the 2021–2022 and 2022–2023 growing seasons, we selected the Jiayou No. 5 rapeseed variety and set three N application levels (N1: 90 kg ha−1, N2: 180 kg ha−1, N3: 270 kg ha−1) and two density treatments (M1: 150,000 plants ha−1, M2: 300,000 plants ha−1) to research the effects of N and density interaction on morphological indexes, physiological indexes, shatter resistance index and yield of direct-seeding rapeseed siliques. The silique shatter resistance index, silique’s length, weight, moisture content, silique shell’s weight, thickness, lignin content, cellulose content and phenylalaninase (PAL) activity all increased first and then decreased with the increase in the N application rate; the N2 treatment increased by 18.38% and 26.92%, respectively, compared to the N1 and N3 treatments; 3.65%, 2.48%; 6.70%, 3.58%; 20.46%, 18.33%; 5.97%, 5.96%; 8.82%, 9.60%; 9.12%, 19.90%; 43.85%, 69%; 2.10%, 11.04%. Compared with the M1 treatment, the silique shatter resistance index, silique’s length, weight, moisture content, silique shell’s weight, thickness, lignin content, cellulose content and PAL activity were lower under M2 treatment. Correlation analysis demonstrated that the silique’s length, water content, silique shell’s weight, thickness, lignin content, cellulose content and PAL activity were significantly positively correlated with the silique shatter resistance index. Therefore, this study shows that N2M1 treatment can carry off synergy between silique shatter resistance and yield.

1. Introduction

Rapeseed is one of the most important oil crops in the world, accounting for about 13% of the global edible oil [1]. It has the characteristics of multiple branches and un-synchronous ripening of the silique. Presuming the green ripe silique is harvested in advance. Then, it must undergo a post-ripening procedure before being threshed, which specifically affects the quantity and caliber of rape seed [2]. Suppose the harvest is delayed during the harvesting process of the combine harvester; under these conditions, the rape siliques are prone to rupture due to mechanical collision, resulting in a rupture loss ratio of more than 12% [3,4]. Therefore, compared with wheat, soybean, rice, etc., rapeseed’s mechanized harvest is relatively not suitable, which restricts its sustainable development and yield [5]. At present, it is critical to ameliorate the shatter resistance of rape to better adapt to mechanized production [6,7].
There is a specific correlation between the morphology and physiological characteristics of rape siliques and shattering resistance, but the research conclusions are not consistent. Studies have shown that water content affects metabolism and delays aging [8]. Studies have shown that the water content of rapeseed siliques is closely related to the shatter resistance. The higher the water content of rapeseed siliques, the more convalescent their shatter resistance [9]. Qing et al. [5] showed that the silique shell weight, 1000-grain weight, silique thickness, and silique volume were significantly related to shattering resistance. The silique shell’s weight and pod water content are correlated with the content of carbohydrates, including soluble sugar, cellulose, lignin, and other substances conducive to the growth and development of the silique and structural stability [9]. At the same time, the shattering process of rape kernels is also regulated by a series of physiological and biochemical factors [10]. Few studies indicate that from the 40th day after flowering, the cellulose activity in the disassembly layer has been continuously increasing [11], and with the increase in cellulose activity, the two types of linear and crust-shaped silique petals of the rape curb will gradually shatter, resulting in the shattering of the curb, and the cellulose activity is closely related to the cellulose content [12]. Zhang [13] made a cytological comparison of varieties with more prominent differences in the shattering of siliques and found that the lignification status of the tissue at the junction of the pseudo-diaphragm and silique shell was very different, suggesting that the lignin content of the silique peel may also be a factor causing the shatter of siliques. At the same time [14], it is considered that there was a correlation between lignification at the junction of canola and shatter resistance, and the latter would increase with the improvement of the previous. Few studies have also shown that once the silique is mature and completely dehydrated, it will cause cell separation under the influence of two hydrolases, cellulose and polygalactoaltalase, thus causing the shatter of the pod [15].
Planting density and N fertilizer application are essential factors affecting rapeseed mechanical harvest yield loss [16]. Nitrogen is a vital nutrient element in rapeseed production, and the N fertilizer’s effect on increasing rapeseed yield is discernible. Insufficient N fertilizer inhibited the growth and development of siliques in the late growth stage of rape [17]. The increase in N application in a particular range can increase the N accumulation of siliques, which is conducive to improving silique morphogenesis and shatter resistance index. Excessive N fertilizer leads to the easy growth of plants and unfavorable development of siliques [18,19]. Previous studies have shown that the number of grains per silique, the weight of grains, and the importance of silique shells vary with different N application rates [20,21]. The rational application of N fertilizer is beneficial to the vegetative growth of rapeseed in the later stage. It makes the silique shell thicken to improve the shatter resistance to rape. At the same time, it is impossible to neglect the supply of N needed as one of the essential ingredients for plant function. Studies have shown that improving the N use efficiency of rapeseed is of great significance to the increase in rapeseed yield and the sustainable development of the rapeseed industry [22,23]. There are also research findings that the N yield of low N treatment was the highest, and the N use efficiency of legume residues was the highest [24].
Density is a yield component and a vital cultivation factor, coordinating population and individuals. The number of grains per silique was affected by planting density and decreased with the increased rate of planting density, but the surface area of the rape silique peel and the thickness of the silique layer also increased [25,26]. It has been pointed out [16] that the planting density suitable for improving the shatter resistance of rape varies with different varieties, indicating that planting density has a specific impact on the shattering resistance of rape and with the increase in planting density, the plant height, branch number, main sequence angle number and corner number per plant decreased significantly, which affected the ripeness and shatter resistance of the kernels.
It can be seen that the amount of planting density and N application have significant effects on the rape silique characteristics, and there is a certain correlation between the silique characteristics and the shatter resistance index, which then affects the rapeseed silique shatter resistance. At present, it is not clear how to influence the morphological index, physiological index and silique shatter resistance index of rape siliques under the interaction of N application and planting density. Therefore, the purpose of this study was to explore the effects of N and density interaction on the morphology index, water content, carbohydrate content, enzyme activity and shatter resistance index of siliques in direct seeding and the correlation between them, as well as to determine the appropriate amount of N fertilizer application and planting density to improve the shatter resistance and yield of rapeseed.

2. Materials and Methods

2.1. Experimental Site

The two-year experiment (2021–2023) was conducted at the rapeseed mechanized production Demonstration base in Liyan Village, Gaoping Town, Guanghan City (Longitude 104.25, latitude 30.99), China. The region belongs to the subtropical humid climate zone. The previous crop cultivated was rice, which belongs to alluvial paddy soil in the Chengdu plain. Earlier from sowing, the soil of the test plot was sampled and analyzed by the 5-point sampling method. That is, the midpoint of the diagonal line is first determined as the central sampling point, and then four points on the diagonal line with the same distance from the central sample point are selected as the sample point. The primary soil nutrients of the two years’ cultivation layer are shown in Table 1 (surface depth 0–20 cm). Figure 1 displays the primary weather information for the rape growing season during the previous two years. The meteorological data were provided by the Agricultural Meteorological Center of Sichuan Province, China.

2.2. Experimental Design and Field Management

The rape variety tested was Jiayou 5, which was provided by Sichuan Kele Rapeseed Research and Development Co., Ltd. (Deyang, China).
The experiment was designed in a randomized block with two factors: N rate and density. Two planting densities were set: 150,000 plants ha−1 (M1) and 300,000 plants ha−1 (M2). Three N applications were formed: 90 kg ha−1 (N1), 180 kg ha−1 (N2) and 270 kg ha−1 (N3). There was a total of 6 N and density interaction treatments, with each treatment repeated 3 times. There are 18 test areas, each 5 m long and 4 m wide, with an area of 20 m2. The sowing dates of this experiment were 14 October 2021 and 5 October 2022, respectively, and both were manual direct seeding. The row spacing was 33 cm, M1 density: 20 cm hole spacing, one plant per hole, M2 density: 10 cm hole spacing, one plant per hole, and the base fertilizer was 600 kg ha−1 compound fertilizer (NPK ratio was 15:15:15). When base fertilizer was applied, the amount of N applied in each plot was the same, 90 kg ha−1. Therefore, when top dressing, N fertilizer application amounts were N1: 0 kg ha−1, N2: 90 kg ha−1 and N3: 180 kg ha−1 respectively, and N fertilizer topdressing would take place between 28 November and 4 December. The two years of leaving seedlings evenly and filling the gaps with seedlings dates are 20 November and 10 November, respectively, to ensure the accuracy of density. High-yield cultivation requirements are compatible with other cultivation practices including pest control and field management.

2.3. Measurement Items and Methods

The yellow ripening stage of the rape silique was the sampling time for the morphological and physiological indices, and the sampling portion fell in the middle of the rape main sequence (the sampling date is the same for different treatments).

2.3.1. Determination of Morphological Indexes of Rapeseed Siliques

The length, width and shell thicknesses of 20 siliques were measured with digital vernier calipers, and then the average value was recorded (the width of the silique is the largest part in the middle of the silique. The thickness of the silique shell is the thickest part in the middle of the silique shell).
Single silique weight, silique shell weight: use a scale of 1/10,000 to weigh the 20 siliques and the weight of the siliques’ shells, and then find the average.
Silique surface area: After measuring the length and width of the silique, calculate the silique surface area with the formula: S = 2.4 × La × Bm − 0.60 (where Bm is the maximum width of the silique and La is the length of the silique) [27].

2.3.2. Moisture Content of the Siliques

Using the dry weighing method, the 10 siliques were wiped out and cleaned, and the fresh weight of the 10 siliques was weighed with an electronic balance. Then, the samples were put into the oven at 80 °C for drying and weighing, and the dry weight of the siliques was also measured. Calculation formula: silique water content = (total fresh weight − total dry weight)/total fresh weight × 100%.

2.3.3. Determination of Soluble Sugar Content in Silique Peel

The middle siliques of the main sequence of 3 representative plants were randomly selected in each plot and wrapped in a zip-lock bag. The zip-lock bag was immediately placed in an ice box and quickly brought back to the laboratory. Then, 0.2 g of fresh silique peel samples was weighed. The content of soluble sugar in silique peel was determined by anthrone colorimetry [28].

2.3.4. Determination of Lignin and Cellulose Content in Silique Peel

Each plot selected 60 rapeseed central sequence siliques. The silique shell was placed in the oven at 80 °C to dry to constant weight and then crushed with a powder machine and put into a mortar for grinding to ensure the uniformity of the grinding degree of each sample. The cellulose content and lignin content of the silique shell were determined with the cellulose content detection kit (BC4205, micromethod, 96 samples) produced by Beijing China Solaibao Technology Co., Ltd. (Beijing, China).

2.3.5. Enzyme Activity Determination

Thirty rapeseed central sequence siliques were selected from each plot, which were quickly frozen in liquid N and stored in the refrigerator at −80 °C for later use. The cellulase, phenylalaninase, and polygalacturonase activities were measured using a Fankew Elisa kit (Shanghai China Kexing Trading Co., Ltd., Shanghai, China).

2.3.6. Cross-Section Structure of Silique Shell

The silique was separated from the silique shell and grain; the middle of the silique shell was selected and quickly fixed in a tube containing FAA (formaldehyde acetate ethanol) curing agent. The method of staining was used for determination by Wuhan China Xavier Biotechnology Company (Wuhan, China).

2.3.7. Measurement of Yield and Its Component Factors

Six labeled plants were selected from each plot at the time of maturity stage, and the yield components were investigated: number of siliques per plant, number of seeds per pod, and thousand-grain weight. During the harvest period, the seeds in each plot were weighed, and then 800–900 g of seeds were taken out back to the laboratory, dried and cluttered, and weighed to calculate the grain yield. The oil content of the seeds was measured by the near-infrared quality analyzer (FuSi NIRS DS2500), from Fushua Technology & Trade Co., Ltd., (Beijing, China), and the oil content of the seeds was calculated (rapeseed oil yield = oil content of the seeds × actual production per plot).

2.3.8. Determination of Silique Shatter Resistance Index

In the yellow ripening stage of rapeseed, 100 middle siliques of the main sequence were selected in each plot. The silique shatter resistance index was measured after the samples were air-dried in a cool place. Specific methods: The random collision method improved by Morgan et al. [29] was applied. That is, 20 siliques were taken each time and placed into a circular plastic container with a lid with an inner diameter of 15.0 cm and a height of 14.0 cm, and 13 steel balls with a diameter of 14.0 mm were placed inside the container. The container was placed on the HY-5A rotary oscillator, the speed was set to 300 r/min, and the number of broken siliques was recorded once every 1 min of oscillation with 50% of the pod damaged or rape seeds visible as the standard of pod breakage. A total of 10 times were recorded, and each treatment was recorded 30 times (that is, each treatment was repeated three times, and 20 siliques were placed each time). The calculation formula is S R I = 1 − ∑ i = 1 i = 10 x i ( 11 − i ) number   of   pods   ∗   total   number (where SRI is the shatter resistance index; Xi is the number of siliques damaged for I time, 1 ≤ i ≤ 10).

2.4. Statistical Analysis

The experimental data were calculated using Excel 2021 software. The data for each trait were analyzed using IBM SPSS Statistics 22. An analysis of variance (ANOVA) test was used to determine the treatment effects on the measured variables. The least significance difference (LSD) test was performed to compare means at a 5% probability level.

3. Results

3.1. Effect of Nitrogen and Density Interaction on Silique Shatter Resistance Index

In 2021–2022, the N density interaction effect of the silique shatter resistance index is significant, and both the N dose and sowing density have a significant impact on the silique shatter resistance index (Table S1). The silique shatter resistance index reaches the maximum value under N2M1 treatment and the minimum value under N1M2 treatment. At both density levels, the silique shatter resistance index increased first and then decreased with the increase in N application rate, and there were significant differences among N1, N2 and N3 treatments. Under the N application levels of N1 and N2, the silique shatter resistance index of M1 treatment was significantly higher than that of M2 treatment. At the N3 level, the silique shatter resistance index of M1 treatment was higher than that of M2 treatment, but the difference was not significant (Figure 2).
In 2022–2023, the N density interaction effect of the shatter resistance index was not significant, and both N application amount and density had significant effects on the silique shatter resistance index (Table S1). With the increase in N application rate, the silique shatter resistance index showed a trend of first increasing and then decreasing, and N2 treatment increased by 15.62% and 33.41% compared with N1 and N3 treatment, respectively, with significant differences among different N application treatments (Figure 2). The silique shatter resistance index under M1 treatment was significantly higher than that under M2 treatment.

3.2. Effects of Nitrogen Density Interaction on Morphological and Physiological Indexes of Siliques

At two density levels, the silique’s length, weight, shell weight, and water content all increased first and then decreased with the increase in N application; at the M1 level, they increased by 3.29%, 5.22%, 5.58%, and 24.58%, and they decreased by 3.36%, 4.49%, 5.83% and 16.22%, respectively; at the M2 level, they increased by 4.09%, 8.88%, 6.71% and 19.47%, and they decreased by 1.46%, 2.41%, 5.96% and 12.35%, respectively, and all of them were at the highest significant level under N2 treatment. The width of siliques increased gradually with the increase in N application rate, which increased by 5.76% and 1.76% at the M1 level and by 6.60% and 0.85% at the M2 level; there was no significant difference among different nitrogen application treatments (Figure 3). The silique surface area increased with the N application rate, but there was no significant difference among N1, N2, and N3 treatments. At three N levels, the silique’s length, weight, shell weight, water content, and surface area density were higher under M1 treatment; the width of the silique was higher under M2 treatment.
Nitrogen application had a significant effect on the shell thickness at maturity, and planting density had no significant effect on the shell thickness of silique (Table S2). With the increase in N application rate, the shell thickness of silique increased at first and then decreased, the thickness of silique under N2 treatment increased by 8.82% and 9.60% compared with N1 and N3 treatment, and N2 treatment was significantly higher than N1 and N3 treatment. Compared with M1 treatment, the shell thickness of silique under M2 treatment was lower (Figure 4).
As can be seen from the structure diagram of the transverse section of the silique shell in Figure 5, the carapace is divided into three functional layers: namely, outer pericarp layer, middle pericarp layer and inner pericarp layer. The exocarp layer is the oblong cell in the outermost layer of the fruit flap, and there are pores scattered among the oblong cells. The mesocarp layer is composed of parenchyma cells containing chloroplasts, which can provide nutrients for the growth of silique during the development of silique. The endopericarp layer is composed of a lignified endopericarp layer and parenchyma endopericarp layer, and the endopericarp layer of parenchyma cell breaks down with the development and maturity of the silique. As can be seen from the figure, the shell thickness under N2M1 and N2M2 treatments is significantly higher than that under other treatments. This is consistent with the research results of higher shell thickness under N2 treatment as reflected in Figure 4. At the same time, it can be seen that the vascular bundle structure under N2M1 and N2M2 treatment is significantly more than that under other treatments. The vascular bundle is composed of xylem and phloem arranged in bundles, which can channel water and organic nutrients for plants, and it can also support plants. It can be seen that there are more vascular bundle structures under N2M1 and N2M2 treatment, which is more conducive to supporting and protecting the silique shell.

3.3. Effect of Nitrogen and Density Interaction on Carbohydrate in Silique Shell

The results of two years of experiments showed that N application amount and density had significant effects on carbohydrates, and the N density interaction of soluble sugar content in the silique shell was significant (Table S3). At two density levels, with the increase in N application rate, the soluble sugar content of the silique shell gradually decreased, which decreased by 14.78% and 11.06% at the M1 level; and 3.29% and 11.14% in the M2 level, and there was no significant difference among the treatments. The silique shell’s lignin and cellulose content increased first, then they decreased with the increase in N application rate, which increased by 8.91% and 42.12% before decreasing by 16.61% and 42.98% at the M1 level, respectively, while at the M2 level, the highest significant level under N2 treatment, they increased by 9.71% and 45.92% before decreasing by 15.74% and 37.46%, respectively. At three N application levels, the content of cellulose and lignin in the silique shell treated with M1 was significantly higher than that treated with M2, but the content of soluble sugar in the silique shell under M2 treatment was higher than that under M1 (Figure 6).

3.4. Effect of Nitrogen and Density Interaction on Parameter Characteristics of Lignin Accumulation Model in Silique Shell

With the increase in days after flowering, the lignin content of silique peel increased first and then decreased (Figure 7). At 20–40 d after flowering, the lignin content in the silique peel increased rapidly, reaching 214~279 mg·g−1. At 40–50 d after flowering, the lignin content increased slowly and reached a peak at 50 d after flowering, ranging from 230 to 297 mg·g−1. At 50–60 d after flowering, the lignin content in the silique peel began to decrease, reaching 187–263 mg·g−1.
Under different N density interaction treatments, the changing trend of lignin accumulation in the silique peel could be expressed by the logistic growth function. The maximum time of lignin accumulation rate (t0, days after flowering) was the earliest under N3M1 and N3M2 treatments, and the time of maximum lignin accumulation rate under other treatments was the same. The initial time (t1) of rapid lignin accumulation in silique peel appeared at the earliest under N3M1 treatment and at the latest under N1M2 and N2M2 treatment. The end time (t2) of rapid accumulation of lignin in silique peel appeared at the latest under N1M1 and N2M1 treatments, which was 1 day later than other treatments. Under the treatment of N3M1, the lignin rapid accumulation duration (Δt) was the longest 1–3 days longer than other treatments (Table 2).
The maximum rate time (t0), initial time (t1), end time (t2) and duration (Δt) of rapid accumulation of lignin in silique shell under N1 and N2 treatment were consistent, but they were all higher than those under N3 treatment. The start time (t1) of rapid lignin accumulation in M1-treated silique shell was earlier than M2 treatment, and the end time (t2) and duration (Δt) were later than M2 treatment. In conclusion, lower planting density is beneficial to advance the start time of rapid accumulation of silique peel lignin (t1) and prolong the end time of rapid accumulation of silique peel lignin (t2) and duration (∆t), which is conducive to the later silique peel morphogenesis (Table 2).

3.5. Effect of Nitrogen and Density Interaction on Enzyme Activity in Silique Shell

The sowing density and N application had significant effects on the enzyme activity in the silique shell, and the interaction effect of PAL activity in the silique shell was significant, with the maximum value under N2M1 treatment and the minimum value under N3M2 treatment (Table S4). At two planting density levels, the activity of Cx and PG in the silique shell increased with the increase in N application rate, and N3 treatment was significantly greater than N1 and N2 treatment; PAL activity increased first and then decreased with the increase in N application: it increased by 2.07% and then decreased by 12.44% at the M1 level; it increased by 0.95% and then decreased by 5.82% at the M2 level; and there was no significant difference among different N application treatments (Figure 8). At three N application levels, the activity of Cx and PG in a pod shell under M2 treatment was higher than that under M1 treatment, but the PAL activity under M1 treatment was significantly higher than that under M2 treatment.

3.6. Effects of Nitrogen Density Interaction on Yield and Yield Components

From the perspective of yield components, the number of siliques per plant, the number of seeds per silique, and the 1000-grain weight all increased first and then decreased with the increase in N application rate, at the M1 level, increasing by 33.82%, 6.60% and 3.76%, respectively, and decreasing by 13.83%, 2.52% and 0.87%; at the M2 level, increasing by 42.83%, 4.91% and 4.26%, and decreasing by 17.62%, 9.64% and 0.77%, respectively. The silique numbers per plant, seeds number per silique and 1000-grain weight under M2 treatment were significantly higher than those under M1 treatment. In terms of yield, grain yield and oil yield also increased first and then decreased with the increase in N application, at the M1 level, increasing by 84.44% and 70.04%, respectively, and decreasing by 10.65% and 6.00%. At the M2 level, they increased by 73.26% and 61.19% and then decreased by 12.93% and 8.32%, respectively. Compared with M1 treatment, the grain yield and oil yield under M2 treatment were higher. Under N -dense interaction treatment, the yield characteristics of the above two years showed a similar trend, and both of them reached the maximum value under the N2M2 treatment (Table 3).

3.7. Correlation Analysis between Silique Characteristics and Shatter Resistance Index

Correlation analysis showed that water content of the silique, silique length, silique shell’s weight, thickness, lignin content, cellulose content and PAL activity were significantly positively correlated with silique shatter resistance index at maturity, and the correlation coefficients were 0.93, 0.89, 0.94, 0.89, 0.95, 0.93 and 0.81, respectively (Figure 9). The weight and surface area of the silique were positively correlated with the silique shatter resistance index. The silique shatter resistance index was negatively correlated with silique width, silique shell’s soluble sugar content, PG activity and Cx activity, but not significantly.

4. Discussion

4.1. Effects of Nitrogen and Density Interaction on Silique Characteristics

Nitrogen fertilizer and density, as the main cultivation control measures, play a vital role in the growth and development of rape siliques. This study showed that the optimal N application rate (N2: 180 kg ha−1), the silique’s length, weight, shell weight, shell thickness and moisture content first increased and then decreased with the increase in N application rate. This may be because N is an important component of photosynthetic pigments, photosynthetic intermediates and related enzymes involved in photosynthesis, which has an impact on the photosynthetic characteristics of crops [30], thus enhancing the growth and development of the silique itself. At the same time, the increased application of N fertilizer can promote the accumulation of dry matter in the upper part of the rapeseed field, which is conducive to the nutrient accumulation and further development of rape silique in the later stage [31], thus increasing the weight of the silique, the thickness of the silique shell and the weight of the silique shell. A reasonable increase in density can improve the population structure, increase photosynthetic efficiency, promote dry matter accumulation and transport [16], and is also conducive to the development and formation of siliques. However, the results of this study showed that the lower planting density (M1 treatment: 150,000 plants ha−1) was more conducive to increasing the silique’s length, weight, shell weight and shell thickness. This may be due to the different growing environment, climatic conditions and varieties of crops, and the suitable planting density of rape silique traits is also different.
Carbohydrates do not provide plant energy but participate in forming a plant cell wall structure and play an essential role in physiological and biochemical metabolism in plants. The results of this study showed that the cellulose content and lignin content of the silique shell increased first and then decreased with the increase in N application rate, which was consistent with the results of Zhang et al. [32]. The reason for the increase in lignin and cellulose content in the silique shell may be that increasing N application can promote the increase in enzyme activity of Rubisco, improve photosynthetic performance [33], promote the accumulation of photosynthetic products, and thus increase the lignin and cellulose content in the silique shell. The results of this study showed that the content of cellulose and lignin in silique shells under lower planting density (M1: 150,000 plants ha−1) was higher than that under M2 treatment (300,000 plants ha−1). This may be due to the fact that at lower planting density (150,000 plants ha−1), the onset time of rapid accumulation of lignin in silique peel was advanced (t1), and the duration of rapid accumulation was prolonged (Δt) (Table 2).
As two hydrolases, Cx and PG are the main enzymes involved in the destruction of the cell wall structure. The results showed that the activity of Cx and PG increased with the increase in N application. This may be because N fertilizer is a component of chlorophyll and protein in plants, and increasing N fertilizer can increase the content of protein and chlorophyll in plants, thus increasing the PG and Cx activities of silique shells. The results of this study showed that the activities of PG and Cx under M2 density treatment (300,000 plants ha−1) were higher than those under M1 density treatment (150,000 plants ha−1). In conclusion, the high N application rate and high planting density can increase the PG and Cx activities of the silique shell, which can reduce the shatter resistance of rape by destroying the cell wall structure. PAL is the most important enzyme in the lignin synthesis pathway. The results of this study showed that with the increase in N application, PAL activity increased and lignin content also increased, which was consistent with the results of previous studies [34].

4.2. Influence of Nitrogen and Density Interaction on Silique Shatter Resistance Index and Yield

As an index to measure the shatter resistance of rapeseed, the shatter resistance is vital in improving the shatter resistance of rapeseed during mechanical harvesting, thereby increasing the yield of rapeseed. The results showed that the crush resistance index increased first and then decreased with the increase in N application. We speculate that the reason why the shatter resistance index increases first and then decreases with the increase in N application rate may be that the siliques, as primary photosynthetic organs, need to provide 2/3 of the raw materials for the kernels through photosynthesis of the silique shell [35]. Therefore, when the amount of N is increased too much, the photosynthetic products and carbohydrates will be further transported to the grain, resulting in a decrease in the lignin and cellulose content in the silique shell, thus affecting the shell weight of the silique, and reducing the silique shatter resistance index. As for the change in planting density, some studies have found [36] that with the increase in planting density, the number of siliques per plant gradually decreases, the silique can better use light energy, and the photosynthetic efficiency also increases, which strengthens the silique’s growth and development; thus, the thickness of the silique peel was increased, and the shatter resistance of rape was enhanced. However, the results of this study showed that a lower planting density (M1 treatment: 150,000 plants ha−1) was more beneficial to improve the shatter resistance index of rapeseed. It can be seen that the effect of planting density on the shatter resistance index of rapeseed is not consistent. This may be due to different researchers using different varieties of rapeseed in different climatic conditions, which affect rapeseed growth.
Density and N fertilizer are important factors affecting crop growth and yield. Reasonable N application and planting density are beneficial to coordinate the relationship between seed number and seed weight, establish a suitable population structure, and ensure the yield of rapeseed. Previous studies have shown [37] that the highest seed yield of rapeseed when treated with 180 kg ha−1 N and 300,000 plants ha−1. Due to the different cultivation conditions, ecological climate and other conditions, the yield results under the interaction between density and N application amount are very different. The results showed that the seed yield of rapeseed was 300,000 plants ha−1 of planting density and 180 kg ha−1 N dose, and the treatment of 150,000 plants ha−1 and 180 kg ha−1 can reach a higher level. This is consistent with the results of previous studies [37].

4.3. Correlation between Silique Characteristics and Silique Shatter Resistance Index

Previous research data have shown that the morphological and physiological characteristics of siliques are closely related to the shatter resistance of rapeseed. Kuai et al. and Zhang et al. [38,39] showed that there was a significant positive correlation between the shell weight and the water content of the silique and the shatter resistance index. Morgan et al. [29] showed that shattering resistance was positively correlated with the thickness of the silique shell but not with the density, length and width of the silique shell. Studies have also shown a positive correlation between silique length and shatter resistance [40]. The results of this experiment show that the silique’s length, water content, shell weight, and shell thickness had a significant positive correlation with the silique shatter resistance index; the weight and surface area of silique were positively correlated with the silique shatter resistance index but negatively correlated with the silique width. Although the results are not entirely consistent with the experimental results, they all indicate that the silique’s length, shell thickness, moisture content and shell weight are important factors affecting the shatter resistance index.
The degree of senescence of the silique and the content of cellulose and lignin in the silique are related to the shatter resistance to rape [41,42]. Cellulose and lignin, as essential components of the cell wall of the silique, directly affect the resistance of the silique to mechanical damage. Cellulose ensures the toughness of the cell wall. At the same time, lignin is a critical phenolic compound in plants with complex structures, which enhances the hydrophobicity, hardness, physical strength and water conductivity of the cell wall [43]. Therefore, the content of both has an impact on the shatter resistance of rape. The results of this study show that the cellulose and lignin content were significantly positively correlated with the silique shatter resistance index, which is consistent with the results of Wu et al. [44]. At the same time, the enzyme activity also affected the shatter of the siliques. Some studies show that polygalactoaltalase degrades the cells in the cracked zone [45] and separates them along the central septal line after the breakage [46]. The results of this study show that the PG activity and Cx activity of the silique shell were negatively correlated with the silique shatter resistance index, which was consistent with the results of previous studies [46,47]. PAL is the first and most important enzyme in the lignin synthesis pathway, and it has an important effect on the synthesis of lignin. According to the correlation analysis (Figure 9), there was a significant positive correlation between the lignin content. Therefore, the increase rate of PAL activity can promote the accumulation of lignin content in the silique shell, which is conducive to improving the shatter resistance index.

5. Conclusions

Under the optimal nitrogen application rate (180 kg ha−1) and low planting density (150,000 plants ha−1), the silique’s weight, shell weight and shell thickness of rapeseed could be increased, the silique shatter resistance index and moisture content of rape siliques were improved, and the lignin content, cellulose content and PAL activity of the rapeseed silique shell were also significantly increased. Therefore, under the conditions of this experiment, N2M1 (180 kg ha−1 nitrogen application, planting density of 150,000 plants ha−1) treatment is conducive to realizing the synergy between rape yield and silique shatter resistance. At the same time, in the future process of rapeseed breeding, it is helpful to select the materials with high dry weight of the silique, water content, dry weight of the silique shell, thickness, lignin content, cellulose content and PAL activity at maturity.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/agronomy14071437/s1, Table S1. Variance analysis table of pod shatter resistance index. Table S2. Variance analysis table of morphological and physiological indexes of pod. Table S3. Variance analysis table of carbohydrate in pod shell. Table S4. Variance analysis table of enzyme activity in pod shell.

Author Contributions

Conceptualization: Y.W. and Y.L.; methodology: Y.L. and H.J.; formal analysis and investigation: Y.L., H.J., Y.H., L.L., X.G. and X.P.; writing—original draft preparation: Y.L. and H.J.; writing—review and editing: Y.L., Y.H., K.G. and H.H.J.; supervision: Y.W. All authors have read and agreed to the published version of the manuscript.

Funding

Biological breeding major science and technology project of Sichuan Province (2022ZDZX0015), Sichuan Province Crop Breeding Research Project (2021YFYZ0005), National Modern Agricultural Industrial Technology System Sichuan Rape Innovation Team (sccxtd-2022-03).

Data Availability Statement

For additional information, contact the author by correspondence.

Acknowledgments

Thank Sichuan Kole Oil Co., Ltd. for providing Jia You No. 5 rape variety.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Cheng, H.; Hao, M.; Ding, B.; Mei, D.; Wang, W.; Wang, H.; Zhou, R.; Liu, J.; Li, C.; Hu, Q. Base editing with high efficiency in allotetraploid oilseed rape by A3A—PBE system. Plant Biotechnology J. 2021, 19, 87–97. [Google Scholar] [CrossRef] [PubMed]
  2. Vera, C.L.; Downey, R.K.; Woods, S.M.; Raney, J.P.; McGregor, D.I.; Elliott, R.H.; Johnson, E.N. Yield and quality of canola seed as affected by stage of maturity at swathing. Can. J. Plant Sci. 2007, 87, 13–26. [Google Scholar] [CrossRef]
  3. Pari, L.; Assirelli, A.; Suardi, A.; Civitarese, V.; Del Giudice, A.; Santangelo, E. Seed losses during the harvesting of oilseed rape (Brassica napus L.) at on-farm scale. J. Agric. Eng. 2013, 44, e136. [Google Scholar] [CrossRef]
  4. Gulden, R.H.; Andrea, C.; Syrovy, L.D.; Shirtliffe, S.J. Pod drop in Brassica napus is linked to weight-ad justed pod-retention resistance. Field Crop Res. 2017, 205, 34–44. [Google Scholar] [CrossRef]
  5. Qing, Y.; Li, Y.; Xu, L.; Ma, Z.; Tan, X.; Wang, Z. Oilseed rape (Brassica napus L.) pod shatter resistance and its relationship with whole plant and pod characteristics. Ind. Crop Prod. 2021, 166, 113459. [Google Scholar] [CrossRef]
  6. Hu, Q.; Hua, W.; Yin, Y.; Zhang, X.; Liu, L.; Shi, J.; Zhao, Y.; Qin, L.; Chen, C.; Wang, H. Rapeseed research and production in China. The Crop J. 2017, 5, 127–135. [Google Scholar] [CrossRef]
  7. Wang, Z.; Yang, C.; Chen, H.; Wang, P.; Wang, P.; Song, C.; Zhang, X.; Wang, D. Multi-gene co-expression can improve compre hensive resistance to multiple abiotic stresses in Brassica napus L. Plant Sci. 2018, 274, 410–419. [Google Scholar] [CrossRef] [PubMed]
  8. Liu, Y.H.; Cao, J.S.; Li, G.J.; Wu, X.H.; Wang, B.G.; Xu, P.; Hu, T.T.; Lu, Z.F.; Patrick, J.W.; Ruan, Y.L. Genotypic differences in pod wall and seed growth relate to invertase activities and assimilate transport pathways in asparagus bean. Ann. Bot. 2012, 109, 1277–1284. [Google Scholar] [CrossRef] [PubMed]
  9. Kuai, J.; Sun, Y.; Liu, T.; Zhang, P.; Zhou, M.; Wu, J.; Zhou, G. Physiological mechanisms behind differences in pod shattering resistance in rapeseed (Brassica napus L.) varieties. PLoS ONE 2016, 11, e0157341. [Google Scholar] [CrossRef] [PubMed]
  10. Li, Y.L.; Yu, Y.K.; Zhu, K.M.; Ding, L.N.; Wang, Z.; Yang, Y.H.; Cao, J.; Xu, L.Z.; Li, Y.M.; Tan, X.L. Down-regulation of MAN NANASE7 gene in Brassica napus L. enhances silique dehiscence-resistance. Plant Cell Rep. 2021, 40, 361–374. [Google Scholar] [CrossRef] [PubMed]
  11. Agrawal, A.P.; Basarkar, P.W.; Salimath, P.M.; Patil, S.A. Role of cell wall-degrading enzymes in pod-shattering process of soybean, Glycine max (L.). Merrill. Curr. Sci. 2002, 82, 58–61. [Google Scholar]
  12. Wen, Y.C.; Dong, T.; Zhi, C.; Shen, J.X.; Zhang, S.F. Advances in studies of pod shattering resistance in rapeseed. J. Plant Genet. Resour. 2009, 1, 140–145. [Google Scholar]
  13. Tao, Z.; Huang, Y.; Zhang, L.; Wang, X.; Liu, G.; Wang, H. BnLATE, a Cys2/His2-type zinc-finger protein, enhances silique shat tering resistance by negatively regulating lignin accumulation in the silique walls of Brassica napus. PLoS ONE 2017, 12, e0168046. [Google Scholar] [CrossRef] [PubMed]
  14. Chu, W.; Liu, J.; Cheng, H.; Li, C.; Fu, L.; Wang, W.; Wang, H.; Hao, M.; Mei, D.; Liu, K.; et al. A lignified-layer bridge controlled by a single recessive gene is associated with high pod-shatter resistance in Brassica napus L. Crop J. 2022, 10, 638–646. [Google Scholar] [CrossRef]
  15. Liu, X.; Tu, B.; Zhang, Q.; Herbert, S.J. Physiological and molecular aspects of pod shattering resistance in crops. Czech J. Genet. Plant Breed. 2019, 55, 87–92. [Google Scholar] [CrossRef]
  16. Li, Y.S.; Yu, C.B.; Zhu, S.; Hu, X.J.; Liao, X.; Liao, X.S.; Che, Z. High planting density benefits to mechanized harvest and nitrogen application rates of oilseed rape (Brassica napus L.). Soil Sci. Plant Nutr. 2014, 60, 384–392. [Google Scholar] [CrossRef]
  17. Li, Z.; Gao, G.; Xu, L.; Wang, Z.; Wang, C.; Yang, T.; Kuai, J.; Wang, B.; Xu, Z.; Zhao, J.; et al. Reducing nitrogen application at high planting density enhances secondary cell wall formation and decreases stem lodging in rapeseed. Eur. J. Agron. 2024, 156, 127162. [Google Scholar] [CrossRef]
  18. Xiong, X.; Chang, L.; Khalid, M.; Zhang, J.; Huang, D. Alleviation of drought stress by nitrogen application in Brassica campestris ssp. Chinensis L. Agron. J. 2018, 8, 66. [Google Scholar] [CrossRef]
  19. Wang, L.; Liu, Q.; Dong, X.; Liu, Y.; Lu, J. Herbicide and nitrogen rate effects on weed suppression, N uptake, use efficiency and yield in winter oilseed rape (Brassica napus L.). Glob. Ecol. Conserv. 2019, 17, e00529. [Google Scholar] [CrossRef]
  20. Zuo, Q.; Liu, J.; Wang, L.; Yang, G.; Leng, S. Yield, dry matter and N characteristics in canola as affected by fertilizer N rate and split-application ratio under high soil fertility condition. J. Plant Nutr. 2020, 43, 655–666. [Google Scholar] [CrossRef]
  21. Wen, G.; Ma, B.L.; Luce, M.S.; Liu, K.; Mooleki, P.S.; Crittenden, S.; Gulden, R.; Semach, G.; Tiege, P.; Lokuruge, P. Optimizing nitrogen fertilization for hybrid canola (Brassica napus L.) production across Canada. Field Crop Res. 2023, 302, 109048. [Google Scholar] [CrossRef]
  22. Zhan, N.; Xu, K.; Ji, G.; Yan, G.; Chen, B.; Wu, X.; Cai, G. Research progress in high-efficiency utilization of nitrogen in rape seed. Int. J. Mol. Sci. 2023, 24, 7752. [Google Scholar] [CrossRef] [PubMed]
  23. Laidig, F.; Feike, T.; Lichthardt, C.; Schierholt, A.; Piepho, H.P. Breeding progress of nitrogen use efficiency of cereal crops, winter oilseed rape and peas in long-term variety trials. Theor. Appl. Genet. 2024, 137, 45. [Google Scholar] [CrossRef] [PubMed]
  24. Ghorbani, M.; Konvalina, P.; Neugschwandtner, R.W.; Kopecký, M.; Amirahmadi, E.; Bucur, D.; Walkiewicz, A. Interaction of biochar with chemical, green and biological nitrogen fertilizers on nitrogen use efficiency indices. Agron. J. 2022, 12, 2106. [Google Scholar] [CrossRef]
  25. Gu, X.; Cheng, Z.; Du, Y.; Cai, H.; Li, Y.; Li, Y.; Fang, H.; Sun, S. Optimizing planting density to improve growth, yield and resources use efficiencies of winter oilseed rape under ridge-furrow film mulching. J. Integr. Agric. 2024. [Google Scholar] [CrossRef]
  26. Mongkolporn, O.; Kadkol, G.P.; Pang, E.C.K.; Taylor, P.W.J. Identification of RAPD markers linked to recessive genes confer ring siliqua shatter resistance in Brassica rapa. Plant Breed. 2003, 122, 479–484. [Google Scholar] [CrossRef]
  27. Hu, Y.; Javed, H.H.; Du, Y.L.; Liao, Q.W.; Ye, W.; Zhou, J.; Peng, X.; Arslan, M.; Raza, A.; Wu, Y.C. Improving lignin metabolism, lodging resistance, and yield of rapeseed (Brassica napus L.) by applying straw-fermented fertilizer. J. Soil Sci. Plant Nut. 2023, 23, 2832–2848. [Google Scholar] [CrossRef]
  28. Khan, A.A.; McNeilly, T.; Collins, J.C. Accumulation of amino acids, proline, and carbohydrates in response to aluminum and manganese stress in maize. J. Plant Nut. 2000, 23, 1303–1314. [Google Scholar] [CrossRef]
  29. Morgan, C.L.; Bruce, D.M.; Child, R.; Ladbrooke, Z.L.; Arthur, A.E. Genetic variation for pod shatter resistance among lines of oilseed rape developed from synthetic B. napus. Field Crop Res. 1998, 58, 153–165. [Google Scholar] [CrossRef]
  30. Noda, H.M.; Muraoka, H.; Nasahara, K.N.; Saigusa, N.; Murayama, S.; Koizumi, H. Phenology of leaf morphological, photo synthetic, and nitrogen use characteristics of canopy trees in a cool-temperate deciduous broadleaf forest at Takayama, central Japan. Ecol. Res. 2015, 30, 247–266. [Google Scholar] [CrossRef]
  31. Song, Z.; Xu, G.; Feng, Y.; Li, J.; Luo, J.; Wang, X.; Gao, Y.; You, X.; Ren, H. Effects of Annual Straw Incorporation Combined with Application of Nitrogen Fertilizer in Rice Season on Dry Matter and Nutrient Accumulation Characteristics of Subsequent Rapeseed. Agron. J. 2023, 13, 1514. [Google Scholar] [CrossRef]
  32. Zhang, W.; Wu, L.; Ding, Y.; Yao, X.; Wu, X.; Weng, F.; Li, G.; Liu, Z.; Tang, S.; Ding, C.; et al. Nitrogen fertilizer application affects lodging resistance by altering secondary cell wall synthesis in japonica rice (Oryza sativa). J. Plant Res. 2017, 130, 859–871. [Google Scholar] [CrossRef] [PubMed]
  33. Yu, W.; Yang, Y.; Liu, L.; Li, Z.; Zhu, C.; Hu, Q.; Liu, J. Decryption of superior allele and candidate genes for total lignin contents of rapeseed. Ind. Crop Prod. 2024, 214, 118483. [Google Scholar] [CrossRef]
  34. Kuai, J.; Sun, Y.; Zhou, M.; Zhang, P.; Zuo, Q.; Wu, J.; Zhou, G. The effect of nitrogen application and planting density on the radiation use efficiency and the stem lignin metabolism in rapeseed (Brassica napus L.). Field Crop Res. 2016, 199, 89–98. [Google Scholar] [CrossRef]
  35. Hua, S.; Chen, Z.H.; Zhang, Y.; Yu, H.; Lin, B.; Zhang, D. Chlorophyll and carbohydrate metabolism in developing silique and seed are prerequisite to seed oil content of Brassica napus L. Bot. Stud. 2014, 55, 1–19. [Google Scholar] [CrossRef] [PubMed]
  36. Wang, Z.; Wang, B.; Kuai, J.; Li, Z.; Bai, R.; Zhou, G. Planting density and variety intercropping improve organ biomass distribution of rapeseed to alleviate the trade--off between yield and lodging resistance. Crop Sci. 2021, 61, 2696–2712. [Google Scholar] [CrossRef]
  37. Khan, S.; Anwar, S.; Kuai, J.; Ullah, S.; Fahad, S.; Zhou, G. Optimization of nitrogen rate and planting density for improving yield, nitrogen use efficiency, and lodging resistance in oilseed rape. Front. Plant Sci. 2017, 8, 246598. [Google Scholar] [CrossRef] [PubMed]
  38. Kuai, J.; Yang, Y.; Sun, Y.; Zhou, G.; Zuo, Q.; Wu, J.; Ling, X. Paclobutrazol increases canola seed yield by enhancing lodging and pod shatter resistance in Brassica napus L. Field Crop Res. 2015, 180, 10–20. [Google Scholar] [CrossRef]
  39. Zhang, M.; Li, G.; Yang, Y.; Jin, M.; Wang, G. Test trials and analysis of pod-shattering characteristics of harvested rapeseed silique. Appl. Sci. 2023, 13, 9369. [Google Scholar] [CrossRef]
  40. Braatz, J.; Harloff, H.J.; Emrani, N.; Elisha, C.; Heepe, L.; Gorb, S.N.; Jung, C. The effect of INDEHISCENT point mutations on silique shatter resistance in oilseed rape (Brassica napus). Theor. Appl. Genet. 2018, 131, 959–971. [Google Scholar] [CrossRef] [PubMed]
  41. Gan, Y.; Malhi, S.S.; Brandt, S.A.; McDonald, C.L. Assessment of seed shattering resistance and yield loss in five oilseed crops. Can. J. Plant Sci. 2008, 88, 267–270. [Google Scholar] [CrossRef]
  42. Holzenkamp, K.; Link, W.; Möllers, C. Effect of a low seed lignin content on seed yield and quality in winter oilseed rape (Bras- sica napus). Plant Breed. 2022, 141, 801–806. [Google Scholar] [CrossRef]
  43. Liu, J.; Zhang, Y.; Jiang, Y.; Sun, H.; Duan, R.; Qu, J.; Yao, D.; Liu, S.; Guan, S. Formation mechanism and occurrence law of pod shattering in soybean: A Review. Phyton 2022, 91, 1327–1340. [Google Scholar] [CrossRef]
  44. Wu, B.; Cui, Z.; Ma, L.; Li, X.; Wang, H.; Wang, Y.; Yan, B.; Dong, H.; Gao, Y. Effects of planting density—Potassium interaction on the coordination among the lignin synthesis, stem lodging resistance, and grain yield in oil flax. Agron. J. 2023, 13, 2556. [Google Scholar] [CrossRef]
  45. Bennett, E.J.; Roberts, J.A.; Wagstaff, C. The role of the pod in seed development: Strategies for manipulating yield. New Phytol. 2011, 190, 838–853. [Google Scholar] [CrossRef] [PubMed]
  46. Dong, Y.; Wang, Y.Z. Seed shattering: From models to crops. Front. Plant Sci. 2015, 6, 146140. [Google Scholar] [CrossRef] [PubMed]
  47. Ridley, B.L.; O’Neill, M.A.; Mohnen, D. Pectins: Structure, biosynthesis, and oligogalacturonide-related signaling. Phytochemistry 2001, 57, 929–967. [Google Scholar] [CrossRef] [PubMed]
Agronomy 14 01437 g001
Figure 1. Meteorological conditions of rape growing season in experimental area.
Figure 1. Meteorological conditions of rape growing season in experimental area.
Agronomy 14 01437 g001
Agronomy 14 01437 g002
Figure 2. Effect of nitrogen and density interaction on silique shatter resistance index. Note: 3 N levels: N1 (90 kg ha−1), N2 (180 kg ha−1), N3 (270 kg ha−1); two densities: M1 (150,000 plants ha−1) and M2 (300,000 plants ha−1). Different letters in the figure indicate significant differences at 0.05 level (LSD test).
Figure 2. Effect of nitrogen and density interaction on silique shatter resistance index. Note: 3 N levels: N1 (90 kg ha−1), N2 (180 kg ha−1), N3 (270 kg ha−1); two densities: M1 (150,000 plants ha−1) and M2 (300,000 plants ha−1). Different letters in the figure indicate significant differences at 0.05 level (LSD test).
Agronomy 14 01437 g002
Agronomy 14 01437 g003
Figure 3. Effect of nitrogen and density interaction on morphological and physiological characteristics of siliques. Note: 3 N levels: N1 (90 kg ha−1), N2 (180 kg ha−1), N3 (270 kg ha−1); two densities: M1 (150,000 plants ha−1) and M2 (300,000 plants ha−1). Different letters in the figure indicate significant differences at 0.05 level. (A–F) represent the siliques width, length, surface area, weight, shell weight, and water content, respectively.
Figure 3. Effect of nitrogen and density interaction on morphological and physiological characteristics of siliques. Note: 3 N levels: N1 (90 kg ha−1), N2 (180 kg ha−1), N3 (270 kg ha−1); two densities: M1 (150,000 plants ha−1) and M2 (300,000 plants ha−1). Different letters in the figure indicate significant differences at 0.05 level. (A–F) represent the siliques width, length, surface area, weight, shell weight, and water content, respectively.
Agronomy 14 01437 g003
Agronomy 14 01437 g004
Figure 4. Effect of nitrogen and density interaction on shell thickness of silique. Different letters in the figure indicate significant differences at 0.05 level.
Figure 4. Effect of nitrogen and density interaction on shell thickness of silique. Different letters in the figure indicate significant differences at 0.05 level.
Agronomy 14 01437 g004
Agronomy 14 01437 g005
Figure 5. Structure diagram of cross-section of silique shell. Note: The cross-sectional structure of the silique shell in the yellow ripening stage of summer rape was measured. (A–F) stand for N1M1, N1M2, N2M1, N2M2, N3M1 and N3M2, respectively. EX: exocarp; M: mesocarp; EN: endocarp; V: vascular bundle. The length of the red arrow indicates the thickness of the silique shell. Scale = 100 μm.
Figure 5. Structure diagram of cross-section of silique shell. Note: The cross-sectional structure of the silique shell in the yellow ripening stage of summer rape was measured. (A–F) stand for N1M1, N1M2, N2M1, N2M2, N3M1 and N3M2, respectively. EX: exocarp; M: mesocarp; EN: endocarp; V: vascular bundle. The length of the red arrow indicates the thickness of the silique shell. Scale = 100 μm.
Agronomy 14 01437 g005
Agronomy 14 01437 g006
Figure 6. Effect of nitrogen and density interaction on carbohydrate in silique shell. Note: 3 N levels: N1 (90 kg ha−1), N2 (180 kg ha−1), N3 (270 kg ha−1); two densities: M1 (150,000 plants ha−1) and M2 (300,000 plants ha−1). Different letters in the figure indicate significant differences at 0.05 level. (A–C) represent the lignin, cellulose, and soluble sugar content, respectively.
Figure 6. Effect of nitrogen and density interaction on carbohydrate in silique shell. Note: 3 N levels: N1 (90 kg ha−1), N2 (180 kg ha−1), N3 (270 kg ha−1); two densities: M1 (150,000 plants ha−1) and M2 (300,000 plants ha−1). Different letters in the figure indicate significant differences at 0.05 level. (A–C) represent the lignin, cellulose, and soluble sugar content, respectively.
Agronomy 14 01437 g006
Agronomy 14 01437 g007
Figure 7. Dynamic changes of lignin content in silique peel under nitrogen and density interaction (2021–2022). Note: The sampling period of the measurement index is the development and maturity stage of siliques.
Figure 7. Dynamic changes of lignin content in silique peel under nitrogen and density interaction (2021–2022). Note: The sampling period of the measurement index is the development and maturity stage of siliques.
Agronomy 14 01437 g007
Agronomy 14 01437 g008
Figure 8. Effect of nitrogen and density interaction on enzyme activity of silique shell. Note: 3 N levels: N1 (90 kg ha−1), N2 (180 kg ha−1), N3 (270 kg ha−1); two densities: M1 (150,000 plants ha−1) and M2 (300,000 plants ha−1). Different letters in the figure indicate significant differences at 0.05 level. (A–C) represent polygalactoaldolase activity, cellulase activity, and phenylalaninase activity, respectively. PG, polygalactoaldolase; Cx, cellulase; PAL, phenylalaninase.
Figure 8. Effect of nitrogen and density interaction on enzyme activity of silique shell. Note: 3 N levels: N1 (90 kg ha−1), N2 (180 kg ha−1), N3 (270 kg ha−1); two densities: M1 (150,000 plants ha−1) and M2 (300,000 plants ha−1). Different letters in the figure indicate significant differences at 0.05 level. (A–C) represent polygalactoaldolase activity, cellulase activity, and phenylalaninase activity, respectively. PG, polygalactoaldolase; Cx, cellulase; PAL, phenylalaninase.
Agronomy 14 01437 g008
Agronomy 14 01437 g009
Figure 9. Correlation analysis between silique characteristics and silique shatter resistance index. Note: Red and blue colors represent the positive and negative correlation. The size and intensity of color exhibited the significance of the variables. SWE, silique weight; SMC, silique moisture content; SL, silique length; SW, silique width; SSA, silique superficial area; SSW, silique shell weight; SST, silique shell thickness; LC, lignin content; CC, cellulose content; SSC, soluble sugar content; Cx, cellulase; PG, polygalacturonase; PAL, phenylalanine enzyme; SRI, shatter resistance index. * p ≤ 0.05.
Figure 9. Correlation analysis between silique characteristics and silique shatter resistance index. Note: Red and blue colors represent the positive and negative correlation. The size and intensity of color exhibited the significance of the variables. SWE, silique weight; SMC, silique moisture content; SL, silique length; SW, silique width; SSA, silique superficial area; SSW, silique shell weight; SST, silique shell thickness; LC, lignin content; CC, cellulose content; SSC, soluble sugar content; Cx, cellulase; PG, polygalacturonase; PAL, phenylalanine enzyme; SRI, shatter resistance index. * p ≤ 0.05.
Agronomy 14 01437 g009
Table 1. Soil nutrient status of the cultivated layer in the experimental field for two years.
Table 1. Soil nutrient status of the cultivated layer in the experimental field for two years.
YearspHTotal N
(g·kg−1)		Available K
(mg·kg−1)		Available P
(mg·kg−1)		Organic C
(g·kg−1)
2021–20225.942.13131.979.7934.40
2022–20235.961.93128.659.6533.93
Table 2. Effects of nitrogen and density interaction on characteristics of lignin accumulation model (2021–2022).
Table 2. Effects of nitrogen and density interaction on characteristics of lignin accumulation model (2021–2022).
TreatmentLignin Accumulation Model EquationR2t0t1t2Δt
N1M1y = 259.52/(1 + 86.75e−0.1642t)0.97727193516
N1M2y = 224.19/(1 + 158.90e−0.1905t)0.95427203414
N2M1y = 288.69/(1 + 96.93e−0.1684t)0.97627193516
N2M2y = 258.15/(1 + 123.74e−0.1782t)0.96827203414
N3M1y = 225.61/(1 + 62.04e−0.1612t)0.95826173417
N3M2y = 215.10/(1 + 105.21e−0.1761t)0.96026193415
Note: The formula of logistic curve equation is y = K/1 + ae−bt. t1 = lna − 1.317/b, t2 = lna + 1.317/b. t0 = lna/b. t is the days after flowering of rape (d), y is the accumulation of lignin in rape silique peel (g/piece); t0 is the maximum time of lignin accumulation rate. t1 and t2 are the two inflection points of logistic growth function, respectively. Δt = t2 − t1, is the rapid accumulation period of lignin in rape silique peel.
Table 3. Effects of nitrogen and density interaction on yield and yield components of rapeseed.
Table 3. Effects of nitrogen and density interaction on yield and yield components of rapeseed.
YearsNitrogen Dose (N)Sowing Density (M)Effective Siliques Per PlantSeeds Per Pod1000-Seed Weight (g)Seed Yield (kg ha−1)Oil Yield
(kg ha−1)		Oil Content
(%)
2021–2022N1M1135.97 d18.27 ab4.15 b1974.33 d985.33 d49.91 a
M2108.94 e17.30 c4.06 c2124.67 c1043.45 c49.11 b
N2M1169.17 a18.57 a4.19 a3651.33 a1684.73 a46.14 d
M2144.03 c17.66 bc4.15 b3711.83 a1703.81 a45.90 d
N3M1161.20 b18.47 a4.18 a3141.67 b1519.92 b48.37 bc
M2131.06 d17.56 bc4.14 b3205.17 b1531.71 b47.79 c
Variance analysisN**ns********
M**********
N × MNsns**nsnsns
2022–2023N1M1122.86 d21.93 bc3.77 d1821.39 e901.25 d49.47 a
M2101.28 e21.19 c3.68 e2110.94 d1036.61 c49.10 ab
N2M1175.97 a24.47 a4.02 a3350.08 b1523.99 b45.44 d
M2155.42 b22.83 bc3.91 b3627.14 a1649.16 a45.50 d
N3M1143.14 c23.42 ab3.96 b3104.31 c1490.16 b47.99 bc
M2123.11 d21.42 c3.86 c3232.71 bc1541.42 b47.67 c
Variance analysisN***********
M**********ns
N × MNsnsnsnsnsns
Note: 3 N levels: N1 (90 kg ha−1), N2 (180 kg ha−1), N3 (270 kg ha−1); Two densities: M1 (150,000 plants ha−1) and M2 (300,000 plants ha−1). Different letters in the figure indicate significant differences at 0.05 level (LSD test). *, **, and ns denote the significant, highly significant, and non-significant at 0.05 probability level, respectively. * p < 0.05, ** p < 0.01.
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Luo, Y.; Jiang, H.; Hu, Y.; Liu, L.; Ghaffor, K.; Javed, H.H.; Peng, X.; Guo, X.; Wu, Y. Effects of Nitrogen Application and Planting Density Interaction on the Silique-Shattering Resistance and Yield of Direct-Seeding Rapeseed (Brassica napus L.) in Sichuan. Agronomy 2024, 14, 1437. https://doi.org/10.3390/agronomy14071437

AMA Style

Luo Y, Jiang H, Hu Y, Liu L, Ghaffor K, Javed HH, Peng X, Guo X, Wu Y. Effects of Nitrogen Application and Planting Density Interaction on the Silique-Shattering Resistance and Yield of Direct-Seeding Rapeseed (Brassica napus L.) in Sichuan. Agronomy. 2024; 14(7):1437. https://doi.org/10.3390/agronomy14071437

Chicago/Turabian Style

Luo, Yuqin, Huayu Jiang, Yue Hu, Li Liu, Kamran Ghaffor, Hafiz Hassan Javed, Xiao Peng, Xiang Guo, and Yongcheng Wu. 2024. "Effects of Nitrogen Application and Planting Density Interaction on the Silique-Shattering Resistance and Yield of Direct-Seeding Rapeseed (Brassica napus L.) in Sichuan" Agronomy 14, no. 7: 1437. https://doi.org/10.3390/agronomy14071437

APA Style

Luo, Y., Jiang, H., Hu, Y., Liu, L., Ghaffor, K., Javed, H. H., Peng, X., Guo, X., & Wu, Y. (2024). Effects of Nitrogen Application and Planting Density Interaction on the Silique-Shattering Resistance and Yield of Direct-Seeding Rapeseed (Brassica napus L.) in Sichuan. Agronomy, 14(7), 1437. https://doi.org/10.3390/agronomy14071437

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop