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Article

Influence of Mechanical Transplanting Methods and Planting Geometry on Grain Yield and Lodging Resistance of Indica Rice Taoyouxiangzhan under Rice–Crayfish Rotation System

by
Hui Gao
1,2,3,*,†,
Yangyang Li
3,4,†,
Yicheng Zhou
3,
Halun Guo
3,
Linrong Chen
3,
Qian Yang
3,
Yao Lu
3,
Zhi Dou
1,3 and
Qiang Xu
2,3
1
Jiangsu Co-Innovation Center for Modern Production Technology of Grain Crops, Yangzhou University, Yangzhou 225009, China
2
Jiangsu Key Laboratory of Crop Genetics and Physiology, Yangzhou University, Yangzhou 225009, China
3
Research Institute of Rice Industrial Engineering Technology, Yangzhou University, Yangzhou 225009, China
4
Jiangsu Xuhuai Regional Agricultural Academy of Sciences, Xuzhou 221131, China
*
Author to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Agronomy 2022, 12(5), 1029; https://doi.org/10.3390/agronomy12051029
Submission received: 18 March 2022 / Revised: 7 April 2022 / Accepted: 20 April 2022 / Published: 25 April 2022
Browse Figures
Review Reports Versions Notes

Abstract

:
Rice–crayfish rotation expanded rapidly in China, as it provides considerable profit and reduces pesticide application. This study investigated the impact of different mechanical transplanting methods and planting geometry on the yield and lodging resistance of an indica rice variety under a rice–crayfish rotation system in 2018 and 2019 in Hongze Lake district, using an excellent-quality variety Taoyouxiangzhan. Seedlings were mechanically transplanted using two mechanically transplanted carpet seedling (MTCS) with equal spacing (30 cm) at five spacings and mechanically transplanted pot seedling (MTPS) with wide and narrow rows (23 cm + 33 cm) at five spacings. The yield of MTPS was 8.3% higher across 2 years under the most optimum density than MTCS using the same density, mainly due to a significantly increased number of spikelets per panicle. Accompanied by the decrease in planting density, rice yield first increased and then decreased under each mechanically transplanting method, and reached the maximum in the A4 and B4 treatments (63.9 × 104 seedlings ha−1), respectively. Compared with MTCS, MTPS significantly increased the fresh weight of single stem, plant height, gravity center height, ear weight, length and area of the upper three leaves, so as to increase the bending moment at basal internodes by whole plant (WP), while it also increased the stem diameter, wall thickness and stem and leaf sheath dry weight per unit length of the second internode at the base, resulting in a significant increase in the force applied to break the base segment (F) and the bending moment of whole plant (M). The higher increase percentage in M than WP led to a decreased lodging index. The lodging index of both mechanically transplanting methods reduced with declined planting density in virtue of the improved breaking load of the basal internode, and it was primarily a result of increased stem diameter, wall thickness and plumpness of basal internode. The balance between the high yield and lodging resistance of Taoyouxiangzhan under a rice–crayfish rotation system can be realized at 63.9 × 104 seedlings ha−1, with MTCS at 15.7 cm plant spacing and MTPS at 16.8 cm. Generally, MTPS showed obvious advantages in yield and lodging resistance than MTCS.

1. Introduction

Rice (Oryza sativa L.) is a staple food crop in China. It is critical to increase rice grain yield to ensure food security and to promote the increase in rice farmer’s income. In recent years, although China’s grain harvest performed continuously well, rice price fluctuated across the different years, while planting costs including agricultural materials, land rent and labor generally rose in recent years, thus squeezing the profit space of traditional rice-producing modes, such as rice–wheat rotation and rice–oilseed rape rotation. In this context, rice–crayfish (Procambrus clarkii) rotation expanded rapidly in lots of areas in China because of the booming crayfish consumer market, and accounted for approximately 4% of the total rice planting area in China by 2020 [1].
There existed some problems in rice–crayfish rotation production according to our previous survey, such as low rates of mechanized planting and frequent lodging. Rice lodging would not only reduce yield and quality but also delayed maturity time, therefore restricting subsequent crayfish breeding, emergence and time to market in the following year and thus affecting the overall benefits of rice–crayfish rotation. Rice lodging could be classified into stem lodging and root lodging, the former being the predominant form in transplanted rice [2]. Stem lodging resistance has a close relationship with plant type, the stem’s internode configuration and the mechanical tissue development of basal internodes. Lower lodging indices and higher yield levels of rice could be synergistically achieved by appropriately shortening the length of the basal internode, increasing the thickness of the stem wall and the weight of the stem leaf sheath per unit length and the length of the internode under the panicle [3,4,5]. Morphological and anatomical research has indicated that increasing the thickness of mechanical tissue and enlarging the area and density of large and small vascular bundles are very important for enhancing the mechanical strength of rice stems’ basal internodes [6,7]. In addition, the lodging resistance of the crop stem was also integrally related to its biochemical contents, including lignin, cellulose, soluble sugar, silicon, nitrogen and potassium [6,8,9].
Since entering the 21st century, mechanical transplanting developed quickly during the urbanization process as it has less requirements for labor [10]. The mechanical transplanting method generally includes mechanically transplanted pot seedling (MTPS) and mechanically transplanted carpet seedling (MTCS). Some researchers compared the lodging resistance between the two machine-transplanting methods, and the study of Guo et al. 2016 [11] showed that rice stems under mechanically transplanted pot seedling were stronger than those of mechanically transplanted carpet seedlings and exhibited higher breaking loads of the basal internode, which induced a better lodging resistance. The planting density was also a key factor in determining mechanically transplanted rice lodging resistance. Hu et al. 2015 [12] found that compact planting was an effective measure to shorten the length of the basal internode and increase the wall thickness and fullness of basal internodes under pot seedling machine transplanting, so as to improve the breaking load and reduce the lodging index. Previous studies focused on the effects of planting geometry under rice–wheat rotation on the lodging resistance of machine-transplanted rice. The area of rice–crayfish rotation enlarged rapidly in China due to its higher profit and lower pesticide application compared with conventional rice–wheat rotation [13], but studies on rice cultivation under rice–crayfish rotation have been rarely reported by far. The paddy soil under rice–crayfish rotation system was more silted than that under rice–wheat rotation, and formed higher soil fertility due to the excreta and feed residues of crayfish and waterweed returning to the field [14]. Our survey illustrated that carpet-seedling transplanters exhibited slow operation speeds, and their tires were easily trapped in the soil when working in paddy fields after continuous rice–crayfish rotation. Meanwhile, pot-seedling transplanters showed better adaptability, and could thus run and transplant seedling more efficiently. Planting density directly or indirectly affects rice population quality, plant type characteristics and basal internode development of rice and exhibits an important influence on the lodging resistance of rice stems [15]. Up to now, few studies had concerned the response of rice lodging resistance performance to mechanical transplanting method and geometry under rice–crayfish rotation systems. This study investigated rice yield, plant type, the traits of stem mechanics and the morphology with the aim of clarifying the effects of mechanically transplanting methods and geometry on rice yield and lodging resistance under rice–crayfish rotation. The results can provide a theoretical basis for cultivation to achieve both optimal yield and lodging resistance under rice–crayfish rotation in the Hongze Lake district of Jiangsu Province, China.

2. Materials and Methods

2.1. Experiment Site

The field experiment was carried out in Xuyi County, Jiangsu Province, China, in 2018 and 2019, which was located on the south bank of Hongze Lake (Figure 1), and famous for its crayfish industry. The average daily temperature and sunshine hours of the rice growing seasons of 2018 and 2019 were presented in Figure 2. The soil type is clay loam, and its parameters at the 0~20 cm layer were as follows: pH 7.32, 20.6 g·kg−1 organic matter content, 2.5 g·kg−1 total nitrogen, 17.6 mg·kg−1 Olsen-P and 165.6 mg·kg−1 available K. Total nitrogen content was measured using semi-micro Kjeldahl method. Olsen-P and available K was determined according to NY-T 1849-2010. Crayfish were cultivated from mid-November to mid-June of the following year, then the field was drained with waterweed while drying up, then soil tillage was conducted mechanically to prepare for rice seedling transplanting, and rice was planted from mid-June to mid-November to form the rice–crayfish rotation.

2.2. Experiment Design

The rice variety selected for this experiment was Taoyouxiangzhan, an indica three-line hybrid rice with excellent appearance and eating quality, and it was suitable for cultivation under rice–crayfish rotation system with in Hongze Lake district, Jiangsu Province.
The experiment was arranged in a split plot design, with the mechanical transplanting method as the main plot and the planting density as the split plot, and it was undertaken with three replicates. The size of each subplot was 20 m2. The two mechanical transplanting methods were carpet-seedlings mechanically transplanted (with equal spacing: 30 cm, (A)) and pot-seedlings, mechanically transplanted (with unequal spacing: wide and narrow rows, 23 cm + 33 cm, (B)). Moreover, to ensure the consistency of seedlings at the same planting density under different mechanical transplanting methods, 5 plant distances of 11.5 cm, 12.8 cm, 14.4 cm, 15.7 cm and 16.7 cm were designed for the carpet-seedlings, which were recorded as A1, A2, A3, A4 and A5, respectively, while 5 plant distances of 12.4 cm, 13.8 cm, 15.5 cm, 16.8 cm and 17.9 cm were designed for the pot-seedlings, which were recorded as B1, B2, B3, B4 and B5, respectively. In theory, the plant spacing of carpet-seedlings can be infinitely graded by the mechanical transplanter, whereas the spacing of the pot-seedling mechanical transplanter was set according to the specific spacing that could be regulated by the pot-seedling transplanter. The plant spacing for the carpet-seedling transplanter in this experiment had a one-to-one correspondence to the planting density of the pot-seedling transplanter. The detailed two mechanical transplanting methods and their plant spacing combinations were displayed in Table 1.
For MTCS, 90 g of seeds was sown in each tray manually on 7 June in both years, simulating the seeding rate in production. For MTPS, seeds were raised in 448-hole plastic trays (dry seedling raising) on 28 May in both years using a 2BD-600 (LSPE-60AM) pot-seedling seeder, and we achieved 3–5 seeds landed per hole by regulating seeding density, thereby guaranteeing 2–3 seedlings per hole. Seedlings for both mechanical transplanting methods were transplanted on 28 June. The carpet-seedlings were cut off by seedling claws to simulate mechanical injury. Rice planted by MTCS and MTPS were harvested on 3 November and 29 October, respectively.
Nitrogen application rate set for rice was 180.0 kg·ha−1, which was 25% lower relative to local rice–wheat rotation due to the high soil fertility after two years of rice–crayfish rotation. It was applied at a ratio of 4:3:3 as base, tillering and panicle initiation, respectively. The application amounts of pure P and K were 39.3 kg·ha−1 and 119.5 kg·ha−1. Compound fertilizer (N:P2O5:K2O = 15%:15%:15%) and potassium chloride were used as the base fertilizers, while urea was applied as tillering and panicle initiation fertilizers. The prevention and control of diseases, insect pests and weeds were the same as the standard green prevention and control plan for local rice–crayfish cultivation. Biological pesticides were mainly used to prevent and control rice diseases and insect pests, chemical pesticides with high efficiency and low toxicity were applied, solar powered insect-killing lamps were installed at the edge of the field and sex attractants were arranged in the field. Vetiver grass was planted around the experimental field to control borers and other pests. Weeds were removed manually.

2.3. Sampling and Measures

2.3.1. Yield and Yield Components

At maturity stage, the number of panicles was determined from 60 panicles. The rice panicles of three whole plants were harvested and put into net bags to measure spikelets per panicle, filled grain rate and 1000-grain weight. During the maturity stage, 50 holes were harvested continuously in each plot, except for 3 border rows. An LDS-1G grain moisture meter was used to measure the grain moisture content, and actual yield was determined according to 13.5% moisture content.

2.3.2. Apparent Lodging Rate

The lodging area of each plot was investigated at maturity stage. If the angle between the plant and the ground was less than 45°, it was deemed as lodging, and the lodging area as a percentage of the total area of the plot was the apparent lodging rate (ALR, %).

2.3.3. Mechanical and Morphological Indices of Stem Lodging Resistance

At 30 days after heading, 10 tagged main stems were sampled from each plot to measure main stem height, panicle neck height and gravity center height. A 9 cm long stem was cut off at the base and a push–pull dynamometer (AIKON RZ-5, Japan) was used to break the midpoint of the second basal internode and measure the bending load at a distance of 8 cm between 2 fulcrum points. The second basal internode was then cut off from the midpoint, and a vernier caliper was used to measure the inner and outer diameters of the major and minor axes in the hollow oval stem after the removal of the leaf sheath. Physical parameters were calculated using the following formulas [16]:
(1)
Bending moment at basal internodes by whole plant (WP, g·cm−1) = SL × FW
where SL is the length from breaking basal internode to top (cm), and FW is the fresh weight from breaking basal internode to top (g);
(2)
Breaking strength (M, g·cm), M = F × L/4,
where F is the force applied to break the base segment (kg), and L is the distance between two fulcrum points (cm);
(3)
Cross-section modulus of the base oval hollow internode (Z, mm3), Z = π/32 × (a13b1−a23b2)/a1;
where a1 and a2 represent the outer and inner diameters of the minor axis, respectively, while b1 and b2 represent the outer and inner diameters along the major axis in an oval cross-section, respectively (mm);
(4)
Bending stress (BS, g·mm−2), BS = M/Z, representing the bending stress of the material strength of culm;
(5)
Lodging Index (LI, %), LI = WP/M.
The sampled plants were separated into culms and leaf sheaths, deactivated at 105 °C for 30 min and dried at 80 °C before measuring dry weight. The fullness of stem and sheath were calculated as the weight of stem and sheath per unit length.

2.3.4. Plant Type Parameters of Rice

At 30 days after heading, the length and width of top three leaves located at the main stem were determined, and the leaf area was calculated. The dry weight of a single panicle was measured.

2.4. Statistical Analysis

Data were processed using Microsoft Excel 2013. The data were analyzed with SPSS 23.0 (IBM, Armonk City, NY, USA). Differences among the treatments were examined by the least significant difference (LSD) test at the probability level of 0.05. Analysis of variance was performed by Duncan’s new multiple-range test.

3. Results

3.1. Yield and Its Components

The analysis of variance results showed that the year, mechanical transplanting method, and planting density all had significant effects on the theoretical and actual rice yield (Table 1). The year exhibited a significant effect on all yield components, except for the panicles. The mechanical transplanting method had a significant effect on panicles and spikelets per panicle. The 1000-grain weight was only significantly affected by the year. The interaction between the mechanical transplanting method and the planting density had a significant effect on the spikelets per panicle and actual yield. Spikelets per panicle was also significantly influenced by the interaction of two factors.
As shown in Table 2, there were significant differences in rice yield between the two mechanical transplanting methods. Under MTCS, the theoretical yield ranged from 9.2 to 10.4 t·ha−1, and the actual yield ranged from 8.1 to 10.1 t·ha−1. Under MTPS, the theoretical yield ranged from 9.6 to 11.3 t·ha−1, and the actual yield ranged from 8.9 to 10.6 t·ha−1. The rice yield of MTPS was generally higher than that under MTCS at the same planting density, especially at low planting densities. Under both mechanical transplanting methods, the rice yield first increased and then decreased later as the plant density increased. Rice yield reached the highest value under the A4 and B4 treatments, and the average yield of the A4 treatment between 2 years was 8.3% higher than that of the B4 treatment. In terms of yield components, the tiller number per unit area of MTPS increased more slowly than that of MTCS under the same planting density, but the significant difference was only observed between A2 and B2 in 2019. In the same year, the number of spikelets per panicle of MTPS was significantly higher than that of MTPS. Under the same planting density, the increase in average spikelets per panicle between 2 years ranged from 3.9% to 9.4%, especially at lower planting densities. Within the same year, there was no significant difference in 1000-grain weight between different mechanical transplanting methods and planting densities. Under the same mechanical transplanting method, spikelets per panicle and filled grain rate increased with decreasing planting density, while panicles showed decreasing trend when exposed to sparse planting, and a similar changing trend was found between two years.

3.2. Lodging Resistance Parameters

The mechanical morphological parameters of the main rice stem were significantly affected by year, while no significant year impact was detected on the lodging index (Table 3). The mechanical transplanting methods and planting densities had significant effects on the mechanical indices of the rice stems. No significant effects of the interaction between two or three factors were observed on the mechanical indices of the main rice stem.
As shown in Table 3, under the same planting density, WP and M under MTPS both had significant higher values than those under MTCS, but the rate of increase in WP was greater than that of M, leading to a lower lodging index of MTPS relative to MTCS. Under each mechanical transplanting method, WP and M showed increasing trends when exposed to decreasing planting densities, while the lodging index tended to decrease at lower planting densities. With the increase in plant spacing, SL increased in both machine transplanting methods, but significant differences were only detected in 2019 between the B1 and B5 treatments. Under the same mechanical transplanting method, FW showed an increasing trend with decreasing planting density, and the amplification after the mechanical transplanting of MTPS was greater than that under MTCS.

3.3. Morphological Parameters of Main Stem

Under the same planting density, the morphological parameters of the main stem of rice significantly generally differed markedly between the two mechanical transplanting methods (Table 4). Compared with MTCS, the main stem height of MTPS increased significantly, the panicle neck height and gravity center height also showed an increasing tendency, and there were no significant differences in the relative center of gravity height between the two mechanical transplanting methods. The leaf length and area of the top three leaves under MTPS were generally larger than those under MTCS, especially for the flag leaf. The fresh weight of single panicle under MTPS was a bit higher than that under MTCS at the same density, but the differences were not significant.
As shown in Figure 3, under the same planting density, three basal internode lengths of MTPS were lower relative to MTCS, whereas two internodes under the panicle had longer lengths. The results of each year were basically similar. Planting density exhibited significant influence on the morphology of the main stem, and the detailed effects were similar regardless of the mechanical transplanting method. With the decrease in planting density, the plant height, panicle neck height, gravity center height, single panicle weight, length and area of the top three leaves increased, and the relative center of gravity height did not change significantly. Planting density had no significant effect on the length of the basal internode, but the length of the internode under the panicle increased as the planting density declined.

3.4. Physicochemical Characterization of Basal Internodes

The F of the second basal internode and the dry weight of stem and sheath per unit length were significantly higher for MTPS than those of MTCS (Table 5). The culm diameter, wall thickness and leaf sheath dry weight per unit length were slightly higher for MTPS than those of MTCS. In addition, the BS and Z of MTCS were lower than those of MTPS. Under the same mechanical transplanting method, the F of the basal second internode increased as planting density decreased; the F value differed significantly between high-density and low-density treatments, but the differences between adjacent densities were not significant. The stem and sheath dry weights per unit length increased by decreased planting density, and the differences in 2019 were obviously larger, but there were no significant differences between adjacent density treatments. There were no significant differences for basal internode diameter, wall thickness and Z across different planting densities within the same mechanical transplanting method.

4. Discussion

4.1. Effects of Mechanical Transplanting Method and Planting Density on Grain Yield

The method of MTCS developed earlier than MTPS in China. It has the advantages of high seedling raising efficiency, convenient seedling transportation and low application cost. However, the seedling quality of MTCS is relatively weaker. In contrast, the method of MTPS developed later. Its advantages contain several aspects including no transplanting injury, high population starting point, sufficient accumulation of photosynthate during the middle and late growth stages and better stress resistance. However, MTPS required a comparatively higher primary input-cost of the whole equipment system than MTCS and usually puts forward higher technical requirements for raising seedlings; moreover, its whole seedling-raising process is more laborious than MTPS [17]. At present, MTCS accounts for a higher proportion of mechanical rice transplanting in China than MTPS, and it is also the current major method of mechanically transplanting rice under rice–crayfish rotation.
The recent research and practice of our team indicated that transplanters usually worked inefficiently and had high risk of becoming trapped in sticky rotten soil, which is caused by long-time deep irrigation for crayfish culture. The new wide and narrow row pot-seedling transplanter equips larger wheel diameters, including a 75 cm front wheel and a 95 cm rear wheel, has a stronger driving force compared to previous transplanting models and showed higher transplanting efficiency and better trafficability under rice–crayfish rotation. In addition to the advantages in seedling raising and transplanting, MTPS can also advance the rice maturity time, which is conducive to crayfish breeding and cultivation after rice harvest. In this study, we investigated the effects of the mechanical transplanting method on the yield of high-quality indica rice under the rice–crayfish rotation system. The results showed that MTPS increased grain yield when compared with MTCS and realized the largest yield increase rate under the basic seedling densities of 63.9 × 104 seedlings ha−1, a planting density achieving the peak yield level for both mechanical transplanting methods. At the highest yield level, the spikelets per panicle were approximately 3.3 million ha−1 for both mechanical transplanting methods; the spikelets per panicle of MTPS and MTCS were more than 130 and 120, respectively, close to the high-yielding structure of Taoyouxiangzhan according to the recommendation from its breeding company, suggesting that rice effective panicles and spikelets per panicle could achieve optimal balance at the basic seedling density of 63.9 × 104 seedlings ha−1.
Comparing with MTCS, panicles per unit area and spikelets per panicle showed a higher value and lower value under MTPS, respectively. Under the same planting density, the maximum yield increase reached 9.4% by MTPS. The mechanical transplanting method presented no significant effect on filled grain rate and 1000-grain weight. Thus, yield advantage in MTPS than MTCS was mainly due to more spikelets per panicle. Our results are consistent with previous reports of Xing et al. [18] and Dou et al. [19], which also observed that MTPS reduced the number of effective panicles and significantly increased spikelets per panicle, while the seed-setting rate and 1000-grain weight remained steady when between mechanical planting methods. The research of Hu et al. [12] observed that MTPS significantly improved the panicle length, panicle weight, grain density, number of primary branches and secondary branches of medium-panicle and large-panicle rice varieties relative to MTCS, while it presented little effect on panicle parameters of small-panicle varieties. In this study, panicle length and spikelets per panicle were markedly increased by MTCS when comparing with MTCS, with increased rate of the two parameters from 0.5% to 5.5% and 2.2% to 10.9%, respectively. We believed that the improvement in the spikelets per panicle under MTCS may be linked to more sufficient development of the basal internode according to our results. Most previous research certified that a strong and substantial stem is not only conducive to lodging resistance but also provides the basis for the formation of large panicles, since the number of primary branches in the panicles rose with the increase in the number of large vascular bundles of the stem [20,21,22].
Planting density is considered as a key factor in regulating rice growth. Reasonable planting density can optimize rice population structure and enhance the mechanical strength of the stems while ensuring biomass and economic yield, thus realizing a balance between high yield and favorable lodging resistance [23,24]. The most suitable planting density varied a lot among different rice varieties, especially related closely with the panicle size. It was generally believed that large-panicle varieties should be compactly planted to give full play to their individual advantage, while small-panicle varieties should strive for more panicles through dense planting and increasing amount of tillering fertilizer, so as to make up for the lack of spikelets per panicle [25]. Productive tiller percentage and panicle quality of rice differed across different planting methods, which will also affect the most suitable planting density of a specific rice variety [18,21]. The results of this study showed that the number of panicles per unit area increased significantly while the spikelets per panicle and filled grain rate decreased significantly as planting density increased. Rice yield was generally higher under the lower planting density, but a significant difference was not detected. In addition, the plant height, length of two nodes under the panicle increased, dry weight of the basal internode and length of panicle exhibited increasing tendency when exposed to decreasing planting densities, thereby building the morphology that is conducive to realizing a high yield level.

4.2. Effects of Mechanical Transplanting Method and Planting Density on Stem Lodging Resistance of Rice

Large population biomass is the basis for high rice yield, but excessive population biomass usually raises the risk of lodging. Therefore, the key to achieving high and stable yield production of rice depends on balancing the contradiction between rice biomass gain and lodging resistance. The lodging index evaluation method connects the physical parameters and morphological parameters of the rice stem with the physical principle of stem lodging and is widely used in the assessment of rice stem lodging resistance. The lodging index is the ratio of WP and M. WP is the product of the length and weight from the breaking basal internode to the top. M is basically determined by the measured force applied to break the base segment.
Hu et al. [12] reported that MTPS significantly improved plant height, gravity center height, leaf length, leaf width and specific leaf weight of top three leaves compared with MTCS. In this study, the panicle length, panicle weight and plant height under MTPS increased compared with MTCS, while leaf length and the area of the top three leaves were also raised by MTPS, which caused the increased FW and SL and finally led to a higher WP. Although the increase in WP is not conducive to lowering the lodging index, M showed a higher increasing rate under MTPS relative to MTCS, thus reducing the lodging index. M is mainly determined by mechanical strength. Some studies had indicated that the mechanical strength of the basal internode is closely related to stem diameter, wall thickness and fullness [4,26,27]. This study showed that MTPS induced thicker stems, larger wall thickness and higher stem sheath fullness of the basal internode, which significantly improved F and M compared to MTCS. In 2020, our studying team conducted a comparative study on light transmission in the lower part of the rice population between MTPS and MTCS in a rice–crayfish rotation system, and suggested that light transmission under the canopy under the wide and narrow row configuration (33 cm + 23 cm) of MTPS performed higher than that under the equal row spacing of MTCS, illustrating the internodes and leaves located at lower parts of rice plants could receive more sufficient light (data not shown). The study of Hu et al. [28] also certified that the combination of wide and narrow rows obtained higher rice yield than equidistant rows of pot-seedlings and carpet-seedlings owing to its larger sink size, which was attributed to the reasonable population quality and increased dry matter accumulation from heading to maturity stage. It had been broadly believed that more sufficient light could promote the accumulation of structural carbohydrates in the stem and the development of vascular bundles in parenchyma cells, such as cellulose and lignin, making the mechanical tissue of rice basal internodes stronger [7,29,30]. This may be the reason for the better development of rice basal internodes under MTPS relative to MTCS.
Planting density is an effective cultivation measure to regulate rice plant morphology and the basal internode fullness of rice [15]. The high-yield cultivation theory pointed out that “small population, strong individual and high accumulation” is a scientific approach to achieve high yield, and it emphasizes that high rice yields can be achieved by exploiting large panicles and striving for higher panicle quality under the basis of suitable populations, which could take count of lodging resistance synchronously [31]. In this research, we investigated the morphology of rice main stem and observed that compact planting could increase the fresh weight of a single stem, plant height, single panicle weight, leaf length and leaf area under each mechanical planting method, so as to improve aboveground biomass accumulation per unit area, and inducing a higher value of WP, which was unfavorable to rice lodging resistance. Meanwhile, our results indicated that reducing planting density increased the dry weight per unit length of the basal internode, wall thickness and stem diameter, thus facilitating the plumpness of basal internode, which tended to improve F and M. The amplification of M exceeded WP clearly under proper compact planting, contributing to the declined LI and improved the lodging resistance. Enrichment of the basal internodes of rice mainly depends on photosynthesis in the leaves located at the lower part of a plant. Reducing planting density appropriately could increase the quantity of illumination for internodes and leaves located at the lower part of rice population, which was conducive to the formation of vigorous stems.
Some recent rice varieties with super high yields were bred in China, such as the Yongyou series and the Jiayouzhongke series. These varieties usually have plant heights higher than 110 cm and large panicle sizes with more than 200 spikelets, and they generally possess favorable light-receiving posture and vigorous stem, also showing great lodging resistance [32,33]. Their yield could achieve 13,500 kg·ha−1 repeatedly under optimal cultivation measures. The success provided the direction in realizing reconciliation between high yield and favorable lodging resistance. In this study, compared with mechanically transplanted carpet seedling, mechanically transplanted pot seedling along with appropriate compact planting resulted in enough aboveground population biomass and proper leaf area index, which laid the foundation for high yield formation. This combination can also significantly enhance the mechanical strength and breaking moment of the basal internode and covered the negative impact on the lodging resistance caused by an increased bending moment.

5. Conclusions

Taoyouxiangzhan obtained a higher yield under mechanically transplanted pot seedlings than mechanically transplanted carpet seedlings, mainly due to more spikelets per panicle, whereas the maximum yield both appeared at 63.9 × 104 ha−1 seedlings for two mechanical transplanting methods. Mechanically transplanting pot seedlings shortened the length of the basal internode and improved the stem diameter, wall thickness and fullness of the basal internode, compared with mechanically transplanting carpet seedlings, so as to enhance the mechanical strength and breaking moment, resulting in the reduced lodging index. The mechanical strength of the rice basal internode and the lodging resistance declined by planting density, but there was no distinct space to improve lodging resistance below 63.9 × 104 ha−1 seedlings. In conclusion, under a rice–crayfish rotation, the rice variety Taoyouxiangzhan could achieve the optimal balance between yield and lodging resistance with a plant spacing of 15.7 cm and 16.8 cm (63.9 × 104 ha−1 seedlings) under mechanically transplanted carpet seedlings and mechanically transplanted pot seedlings, respectively. Finally, mechanically transplanted pot seedlings showed advantages over mechanically transplanted carpet seedlings in both yield and lodging resistance.

Author Contributions

H.G. (Hui Gao), Y.L. (Yangyang Li), Y.Z. and Z.D. involved in designing the manuscript; Y.L. (Yangyang Li), H.G. (Hui Gao), Y.Z., H.G. (Halun Guo), L.C., Q.Y., Y.L. (Yao Lu) and Z.D carried out this experiment; H.G. (Hui Gao), Y.L. (Yangyang Li), Z.D. and Q.X. analyzed the data and wrote the manuscript; H.G. (Hui Gao) and Z.D. acquired funding. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the National Key Research and Development Project (2018YFD300804), the Consulting Project Funds of Chinese Academy of Engineering (2021-XZ-30), the National Natural Science Foundation of China (31901446) and the Key Agricultural Technology Extension Project of Nanjing City and Huaian City (NH(19)0410).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

References

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Agronomy 12 01029 g001 550
Figure 1. Location of the experimental site.
Figure 1. Location of the experimental site.
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Agronomy 12 01029 g002 550
Figure 2. Average sunshine hours and temperature during rice growth season of 2018 and 2019 in the experimental site.
Figure 2. Average sunshine hours and temperature during rice growth season of 2018 and 2019 in the experimental site.
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Agronomy 12 01029 g003 550
Figure 3. Rice internode configuration as affected by mechanical transplanting method and planting density.
Figure 3. Rice internode configuration as affected by mechanical transplanting method and planting density.
Agronomy 12 01029 g003
Table
Table 1. Rice transplanting spacing allocation and basic seedling of different mechanical transplanting method.
Table 1. Rice transplanting spacing allocation and basic seedling of different mechanical transplanting method.
Mechanical Transplanting MethodTreatmentRow Spacing (cm)Density
(×104 ha−1)		Seedlings per HillBasic Seedlings
(×104 ha−1)
Carpet seedling mechanically transplanted
Equal spacing (30 cm)		A111.529257.9
A212.826.1252.2
A314.423.1246.2
A415.721.3242.6
A516.720239.9
Pot seedling mechanically transplanted
Wide narrow row (33 cm/23 cm)		B112.428.8257.6
B213.826251.9
B315.523.1246.2
B416.821.3242.6
B517.920239.9
Table
Table 2. Rice yield and its components as affected by mechanical transplanting method and planting density.
Table 2. Rice yield and its components as affected by mechanical transplanting method and planting density.
YearTreatmentPanicle (×104·ha−1)Spikelets per PanicleFilled Grain Rate (%)1000-Grain Weight (g)Theoretical Yield (t·ha−1)Harvest Yield (t·ha−1)Apparent Lodging Rate (%)
2018A1384.1 a103.6 g87.6 c26.5 a9.2 d8.7 e5.0
A2360.0abc108.7 f90.6 abc26.9 a9.5 bcd9.1 de0.0
A3345.5 bcd115.3 e91.2 ab26.7 a9.7 bcd9.2 de0.0
A4333.8 cd121.4 d92.6 a27.0 a10.1 bc9.5 cd0.0
A5303.1 e126.9 c93.1 a26.4 a9.5 cd9.0 e0.0
B1369.4 ab110.2 f88.7 bc26.6 a9.6 bcd8.9 e0.0
B2353.6 bcd114.6 e91.3 ab26.6 a9.8 bcd9.0 de0.0
B3337.0 cd119.6 d93.3 a26.5 a10.0 bc9.6 bc0.0
B4328.2 de131.2 b93.5 a27.0 a10.9 a10.4 a0.0
B5303.7 e137.3 a93.3 a26.2 a10.2 b10.0 ab0.0
2019A1373.6 a110.2 f85.1 g26.9 ab9.4 e8.9 e0.0
A2363.0 a116.6 e86.4 f26.7 b9.8 de9.1 cde0.0
A3344.7 b121.0 d89.7 cd27.1 ab10.1 cd9.5 c0.0
A4333.7 bc125.4 c90.1 bc27.5 a10.4 bc10.1 b0.0
A5308.4 d130.1 b90.8 a27.4 a10.0 d9.4 cd0.0
B1366.5 a112.6 f85.8 f27.5 a9.8 de9.0 de0.0
B2346.1 b119.4 de87.2 e27.4 a9.9 d9.4 cd0.0
B3336.2 bc130.4 b89.2 d27.0 ab10.6 b10.0 b0.0
B4331.2 c139.1 a90.3 ab27.2 ab11.3 a10.6 a0.0
B5306.0 d141.7 a90.4 ab27.0 ab10.5 b10.2 ab0.0
Year (Y)0.11 ns132.12 **111.81 **28.91 **20.80 **16.91 **
VariancePattern (P)6.94 *233.57 **4.30 ns0.01 ns46.18 **49.69 **
analysisDensities (D)69.97 **326.15 **45.00 **2.28 ns30.88 **40.08 **
Y × P0.01 ns0.34 ns2.13 ns1.60 ns0.01 ns0.19 ns
Y × D0.42 ns2.33 ns0.98 ns1.46 ns1.12 ns0.65 ns
P × D0.57 ns9.79 **0.42 ns1.60 ns2.56 ns5.02 **
Y × P × D0.31 ns3.40 *0.62 ns1.72 ns0.31 ns0.90 ns
Note: In a given column, different letters denote significant differences at 5% probability level. ns, not significant; *, significant at 0.05 level; **, significant at 0.01 level. The same as below.
Table
Table 3. Rice lodging index and its stem mechanics parameters as affected by mechanical transplanting method and planting density.
Table 3. Rice lodging index and its stem mechanics parameters as affected by mechanical transplanting method and planting density.
YearTreatmentLI (%)WP (g·cm)SL (cm)FW
(g)		M
(g·cm)
2018A1140.7 a1742.7 e107.2 d16.3 d1239.4 e
A2131.0 ab1817.9 de107.6 d16.9 cd1387.8 de
A3130.3 ab1835.8 de107.7 d17.0 cd1410.1 de
A4123.6 abc1867.7 de108.3 d17.2 cd1512.8 cde
A5118.1 bcd1944.2 d108.8 d17.9 bc1646.8 cd
B1113.6 bcd1917.9 d109.0 d17.6 c1695.6 c
B2107.0 cd2093.5 c111.1 c18.8 b1970.5 b
B3106.4 cd2248.3 b111.8 bc20.1 a2128.8 b
B4105.5 cd2303.4 ab113.1 ab20.4 a2192.2 ab
B5101.0 d2427.1 a114.7 a21.2 a2405.0 a
2019A1134.5 a2003.0 d108.9 e18.4 d1507.7 f
A2131.3 a2151.1 cd109.9 de19.6 cd1640.2 ef
A3125.3 abc2189.4 cd110.9 cde19.7 bcd1763.3 de
A4119.5 bcd2248.0 bc112.3 bcde20.0 bc1881.0 cd
A5116.6 cde2277.4 bc112.4 bcde20.3 bc1953.3 cd
B1128.2 ab2309.0 bc112.3 bcde20.6 bc1803.8 de
B2116.1 cde2402.0 b112.8 abcd21.3 b2070.8 c
B3114.1 de2628.4 a114.2 abc23.0 a2305.8 b
B4108.8 de2720.2 a115.5 ab23.5 a2501.2 ab
B5108.1 e2798.4 a116.2 a24.1 a2589.1 a
Year (Y)0.69 ns126.62 **40.45 **117.69 **37.84 **
VariancePattern (P)28.26 **144.63 **81.28 **119.26 **209.69 **
analysisDensities (D)4.21 *17.04 **10.28 **13.79 **26.54 **
Y × P3.67 ns0.44 ns0.65 ns0.50 ns2.86 ns
Y × D0.09 ns0.21 ns0.22 ns0.11 ns0.55 ns
P × D0.15 ns2.82 ns0.85 ns2.41 ns2.17 ns
Y × P × D0.16 ns0.16 ns0.59 ns0.13 ns0.07 ns
Note: LI, lodging index; WP, bending moment by whole plant, SL, culm length from breaking basal internodes to top; FW, fresh weight from breaking basal internodes to top; M, breaking strength. In a given column, different letters denote significant differences at 5% probability level. *, significant at p < 0.05; **, significant at p < 0.01; ns, no significant.
Table
Table 4. Rice plant type characteristics as affected by mechanical transplanting method and planting density.
Table 4. Rice plant type characteristics as affected by mechanical transplanting method and planting density.
YearTreatmentPlant Height (cm)Height of Panicle Neck (cm)Gravity Height (cm)Relative Height of Gravity Center (%)Individual Panicle Weight (g)Flag LeafSecond Leaf from TopThird Leaf from Top
Leaf Length (cm)Leaf Area (cm2)Leaf Length (cm)Leaf Area (cm2)Leaf Length (cm)Leaf Area (cm2)
2018A1112.8 f86.2 d48.3 c42.8 ab2.67 c26.8 cd31.9 d38.3 d39.8 cd43.3 d40.8 c
A2113.5 ef86.4 d49.1 bc43.3 ab2.77 c26.5 d31.6 d39.1 cd40.5 cd43.0 d41.8 bc
A3113.8 ef87.0 cd50.4 abc44.3 a2.92 bc28.9 bc35.0 bcd41.7 b40.7 bcd45.4 bcd43.0 bc
A4114.5 ef88.0 bcd50.6 abc44.2 ab3.03 abc29.2 abc35.0 bcd41.5 b43.4 bcd47.7 ab45.5 abc
A5115.1 cde88.3 bcd50.5 abc43.9 ab3.27 ab30.2 ab36.8 bc42.6 b46.2 ab47.0 abc48.8 abc
B1114.8 de88.4 bcd48.5 c42.3 b2.74 c28.1 bcd34.2 cd39.2 cd38.6 d44.6 cd42.0 bc
B2116.4 cd89.9 abc49.8 abc42.8 ab2.93 bc29.5 ab36.3 bc40.0 c43.7 bcd45.3 bcd47.4 abc
B3116.7 bc90.3 ab50.8 abc43.5 ab3.12 abc30.0 ab38.5 ab40.0 c40.7 bcd45.3 bcd49.7 ab
B4118.4 ab91.8 a51.1 ab43.2 ab3.30 ab31.4 a41.0 a42.4 b44.4 abc47.3 abc50.0 ab
B5119.8 a92.0 a51.7 a43.2 ab3.41 a31.4 a42.5 a44.3 a49.2 a48.9 a53.2 a
2019A1115.0 f91.6 c49.7 c43.2 a2.80 c27.0 b34.4 d41.6 d46.6 d49.5 d51.3 c
A2116.0 ef92.4 bc50.7 abc43.7 a2.89 bc27.5 b35.9 cd42.3 cd48.7 cd49.8 cd52.3c
A3116.5 de92.9 abc50.9 abc43.7 a3.11 abc26.9 b35.6 cd42.5 bcd48.7 cd49.9 cd53.5 c
A4118.8 bc94.4 ab51.0 abc43.0 a3.17 abc27.4 b37.1 cd43.0 abcd51.6 bc51.8 c57.2 bc
A5119.1 bc95.0 a51.3 ab43.1 a3.31 ab27.5 b38.0 bcd43.0 abcd52.8 b52.0 c58.1 bc
B1117.6 cd92.1 c50.3 bc42.8 a2.86 bc31.0 a39.8 abcd43.7 abcd48.3 d49.5 d51.5 c
B2118.7 bc92.4 bc50.8 abc42.8 a3.18 abc31.5 a41.1 abc44.3 abcd48.9 cd51.7 cd54.5 bc
B3119.2 b92.5 bc51.1 ab42.9 a3.22 abc32.3 a43.6 ab45.4 abc51.5 bc54.8 b58.1 bc
B4122.0 a92.9 abc51.5 ab42.2 a3.48 a32.8 a44.4 a45.5 ab54.2 ab56.6 ab61.5 ab
B5122.5 a93.6 abc51.7 a42.2 a3.53 a32.5 a45.0 a45.6 a55.9 a57.8 a65.8 a
Note: In a given column, different letters denote significant differences at 5% probability level.
Table
Table 5. Morphological characteristics of rice basal stem as affected by mechanical transplanting method and planting density.
Table 5. Morphological characteristics of rice basal stem as affected by mechanical transplanting method and planting density.
YearTreatmentF (kg)Stem Wall Thickness (mm)Stem Diameter (mm)Dry Weight of Stem (mg cm−1)Dry weight of sheath (mg cm−1)Total Dry Weight of Stem and Sheath (mg cm−1)b1 (mm)a1 (mm)b2 (mm)a2 (mm)Z (mm3)BS (g mm−2)
2018A10.620 e0.646 a5.79 c32.6 c25.8 c58.4 f6.34 a5.24 b5.08 b3.91 a11.4 a1098.1 d
A20.693 de0.654 a5.85 bc33.4 c26.3 bc59.8 f6.41 a5.28 b5.11 b3.97 a11.6 a1194.4 bcd
A30.705 de0.665 a5.88 bc33.7 c26.5 bc60.1 ef6.34 a5.30 b5.17 b3.92 a12.0 a1179.5 cd
A40.757 cde0.682 a6.12 abc35.6 bc26.9 bc62.5 def6.50 a5.42 ab5.28 ab4.24 a12.4 a1219.2 bcd
A50.823 cd0.697 a6.21 ab37.8 abc27.4 abc65.1 cde6.80 a5.55 ab5.39 ab4.24 a13.5 a1223.2 abcd
B10.848 c0.684 a6.06 abc40.5 abc26.9 abc67.5 cd6.56 a5.45 ab5.18 b4.21 a12.5 a1440.6 abc
B20.985 b0.697 a6.15 abc41.8 abc27.2 abc69.0 bc6.61 a5.58 ab5.24 ab4.28 a13.3 a1494.2 abc
B31.064 b0.699 a6.18 ab42.2 abc27.6 abc69.8 bc6.59 a5.64 ab5.32 ab4.24 a14.0 a1539.1 a
B41.096 ab0.709 a6.29 a44.9 ab28.2 ab73.1 ab6.61 a5.84 ab5.43 ab4.32 a15.2 a1442.5 abc
B51.202 a0.721 a6.41 a46.5 a29.1 a75.6 a6.61 a5.95 a5.57 a4.37 a16.2 a1500.6 ab
2019A10.754 e0.680 a6.36 c35.9 c26.1 d62.0 f7.17 a5.55 a5.41 a4.59 a12.4 b1224.4 c
A20.821 de0.697 a6.39 c36.0 c26.7 cd62.7 f7.24 a5.53 a5.48 a4.51 a12.8 ab1302.9 abc
A30.882 cde0.713 a6.42 bc38.1 c26.7 cd64.8 ef7.37 a5.57 a5.55 a4.43 a13.5 ab1275.0 abc
A40.941 cd0.717 a6.54 abc38.9 c26.8 cd65.7 ef7.33 a5.72 a5.71 a4.49 a14.7 ab1299.4 abc
A50.977 cd0.736 a6.66 abc39.6 c27.2 cd66.8 e7.51 a5.84 a5.79 a4.57 a15.7 ab1250.0 bc
B10.902 cde0.778 a6.69 abc49.8 b27.3 cd77.0 d7.59 a5.57 a5.76 a4.51 a14.5 ab1304.2 abc
B21.036 bc0.785 a6.82 abc51.4 ab28.4 bcd79.9 cd7.51 a5.76 a5.89 a4.61 a15.9 ab1306.9 abc
B31.153 ab0.792 a6.96 abc53.5 ab29.5 abc83.0 bc7.68 a5.98 a5.99 a4.76 a17.3 ab1338.7 abc
B41.250 a0.795 a7.01 ab54.5 a31.0 ab85.5 ab7.55 a6.06 a6.03 a4.82 a17.9 ab1420.1 a
B51.294 a0.813 a7.12 a55.0 a31.6 a86.6 a7.80 a6.12 a6.16 a4.82 a18.7 a1384.1 ab
Note: F, the force applied to break the base segment (kg); a1 and a2, the outer and inner diameters of the minor axis in an oval cross-section, respectively; b1 and b2, that of the major axis in an oval cross-section, respectively; Z, cross-section modulus; BS, bending stress. In a given column, different letters denote significant differences at 5% probability level.
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Gao, H.; Li, Y.; Zhou, Y.; Guo, H.; Chen, L.; Yang, Q.; Lu, Y.; Dou, Z.; Xu, Q. Influence of Mechanical Transplanting Methods and Planting Geometry on Grain Yield and Lodging Resistance of Indica Rice Taoyouxiangzhan under Rice–Crayfish Rotation System. Agronomy 2022, 12, 1029. https://doi.org/10.3390/agronomy12051029

AMA Style

Gao H, Li Y, Zhou Y, Guo H, Chen L, Yang Q, Lu Y, Dou Z, Xu Q. Influence of Mechanical Transplanting Methods and Planting Geometry on Grain Yield and Lodging Resistance of Indica Rice Taoyouxiangzhan under Rice–Crayfish Rotation System. Agronomy. 2022; 12(5):1029. https://doi.org/10.3390/agronomy12051029

Chicago/Turabian Style

Gao, Hui, Yangyang Li, Yicheng Zhou, Halun Guo, Linrong Chen, Qian Yang, Yao Lu, Zhi Dou, and Qiang Xu. 2022. "Influence of Mechanical Transplanting Methods and Planting Geometry on Grain Yield and Lodging Resistance of Indica Rice Taoyouxiangzhan under Rice–Crayfish Rotation System" Agronomy 12, no. 5: 1029. https://doi.org/10.3390/agronomy12051029

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