Effects of Plant Spacing, Row Spacing and Seedling Number Allocation on the Growth Dynamics of Different Populations of Two Types of Rice Varieties

Jingfang XUE Guangshan ZHAO Shuqiang CHEN Xiaodong DU Limin YANG Haixin ZHAO Yongsheng CAI Tong ZHOU Linan WANG Mingxu ZHOU

Abstract ［Objectives］ This study was conducted to construct high-yielding, high-quality, and high-light-efficiency population structures of different types of rice varieties.

［Methods］The effects of plant spacing, row spacing and seedling number allocation on stems and tillers, leaf area and dynamic traits of high-yielding rice populations (more than 9 750 kg/hm2) and low-yielding populations (less than 9 750 kg/hm2) were studied by two kinds of representative rice varieties with different tiller ability and panicle sizes in cold regions.

［Results］ Decreasing the plant and row spacing and increasing the number of planted seedlings per hole advanced the heading date and made the number of stems and tillers in the population increase. The impact on the super rice variety with fewer tillers and heavier panicles was greater than that of conventional variety with more tillers and lighter panicles. The stems and tillers of the high-yielding high-quality populations grew steadily in the early stage of development, until an appropriate number of panicles was reached at the critical leaf age for productive tillers (June 25), and the peak seedlings should appear in the jointing stage (July 9) with a small number (that value of Longjing 21, the super rice variety with fewer tillers and heavier panicles, was about 1.2 times the expected panicle number, and that of the conventional variety with more tillers and lighter panicles, Kongyu 131, was about 1.1 times the expected panicle number). The populations gradually declined since then, until reaching an appropriate number of panicles at the heading stage. The high-yielding high-quality populations had a higher leaf area index at the heading stage. The value of Longjing 21, the super rice variety with fewer tiller and heavier panicles, reached about 6.0, and that of Kongyu 131, the conventional variety with more tillers and lighter panicles, reached about 4.5. The values decreased thereafter. At the maturation stage, the leaf area index of Longjing 21 remained above 2.5, and that of Kongyu 131 remained above 2.0.

［Conclusions］This study has an important guiding role and significance for their high-yielding and high-quality supporting cultivation in cold regions.

Key words Cold region; Rice; High yield; Quality; Density; Seeding number

Received: November 23, 2020  Accepted: January 29, 2021

Supported by Natural Science Foundation of Heilongjiang Province (LH2019C063); "Agricultural Science and Technology Innovation Project" of Heilongjiang Academy of Agriculture Sciences (HNK2019CX12-08); Academy-level Project of Heilongjiang Academy of Agriculture Sciences (2020YYYF021); National Key R&D Project (2017YFD0300505-4).

Jingfang XUE (1978-), female, PhD, associate researcher, devoted to research about rice breeding and cultivation technology.

*Corresponding author. E-mail: chenshuqiang@163.com.

The rice planting area in Heilongjiang Province is about 4.33×106 hm2, and the yield of japonica rice ranks first in China. It is the most important food production base in China. However, Heilongjiang belongs to the cold rice cultivation area, and low temperature and cold damage often occur during the growth period, thereby affecting vegetative growth and reproductive growth［1-3］. In order to obtain high yield and high quality, strong seedlings must be cultivated to make them grow early and quickly after transplanting, and obtain sufficient effective panicles in a short time. To strive for high yield in the practice of rice cultivation in cold regions, we must obtain enough panicles per unit area among the four components of yield composition to obtain a larger storage capacity and a higher yield. The number of panicles per unit area is related to the tillering ability and planting densities of varieties. The tillering ability of different varieties is quite different, especially for super rice varieties with large panicles and few tillers, which have weak tillering ability, but strong stalks and good tolerance to fertilizer and lodging, and are suitable for cultivation under high nitrogen levels［4］. The main varieties currently planted in Heilongjiang Province are mainly divided into two types, one of which is the conventional small panicle type of varieties with strong tillering ability, such as Kongyu 131 and Longjing 25, and the other is the large panicle type of rice varieties with weaker tillering ability, such as Longjing 21 and Longjing 31. Different types of high-yielding and high-quality populations have different planting specifications and seedlings per hole. Reasonable planting density and number of seedlings per hole can not only help with reducing the occurrence of ineffective tillers, quickly reaching the appropriate number of effective tillers, but also with reducing diseases and obtaining high yield and high quality. In this study, we used a conventional variety and a super rice variety with different tillering ability and different panicle sizes to investigate the effects of plant spacing, row spacing and the number of transplanted seedlings per hole on the tillering, leaf area and dynamics of high- and low-yielding populations of different types of rice varieties, so as to construct high-yielding, high-quality, and high-light-efficiency population structures of different types of rice varieties. This study has an important guiding role and significance for their high-yielding and high-quality supporting cultivation in cold regions.

Materials and Methods

Experimental varieties

The experiment was carried out in the experimental area of the Rice Research Institute, Heilongjiang Academy of Agriculture Sciences in 2014 and 2015. Two rice varieties currently mainly grown in the second and third accumulative temperature zones of Heilongjiang were selected: Longjing 21 (a super rice variety with fewer tillers and heavier panicles) and Kongyu 131 (a conventional variety with more tillers and lighter panicles).

Experimental treatments

The experiment set up 2 row spacing treatments, namely, Rd1=24 cm, Rd2=30 cm, 3 plant hole spacing treatments, namely, Hd1=10 cm, Hd2=13.3 cm, Hd3=16.7 cm, and 3 hole basic seedling treatments, namely, Hn1=2 seedlings, Hn2=5 seedlings, Hn3=8 seedlings.

The experiment adopted a split block design, with variety as the main plot, and the planting density as the sub-plot, in 3 replicates, and there were a total of 108 plots, each with a plot area of 10 m2. The fertility was at the local level, that is the pure nitrogen rate of 138 kg/hm2 and N∶P2O5∶K2O=2∶1∶1. 100% of diammonium phosphate was applied as the base fertilizer at one time, and potassium sulfate was used as the base fertilizer and panicle fertilizer, each accounting for 50%. Nitrogen fertilizer (46% urea) was divided into the base fertilizer, tillering fertilizer (4-leaf age), panicle fertilizer (9.1-leaf age), and grain fertilizer (after heading), 40% as base fertilizer, 30% as tillering fertilizer, and 20% as panicle fertilizer, 10% as grain fertilizer, specifically.

Determination items and methods

(i) Tillering dynamics: From the beginning of transplanting, the basic seedling number should be observed first, and until 10 d after the full heading stage, the number of tillers was investigated once every 7 d. For the 3 replicates of each treatment, 1 point was investigated in each replicate, and 5 consecutive holes were positioned at each point.

(ii) Dry matter and leaf area: According to the field tillering investigation results at the heading stage, the average number of stems was calculated. In the two periods of full heading stage and maturation stage, for the 3 replicates of each treatment, 3 holes of representative plants were selected from each replicate according to the average number of stems. After the number of panicles was recorded in each hole, 1 medium single stem was selected from each hole, and the leaves were cut off from the selected 3 medium single stems in total, for the measurement of the length and width of the leaves in the order of flag leaf, the 1st and 2nd leaves from the top. The leaves of the 3 medium single stems were individually wrapped, dried and weighed. Remaining leaves, panicles (including the determined 3 panicles), the stems and sheaths (including the measured 3 panicles) were separated, and the 4 parts (leaves for weight measurement, remaining leaves weight, panicles weight, and weight of the stems and sheaths) were put together and deactivated in an oven at 105 ℃ for 30 min, dried at 80 ℃ to constant weight and weighed at the full heading stage. The leaf area was calculated using the length-width coefficient method.

Planting methods

The planting method of raising seedlings in upland fields in greenhouses and transplanting was adopted. The soil fertility of the experimental fields was medium. Other operations in rice sowing and transplanting periods and water management and pest control methods were the same as those in production fields.

Data processing

Microsoft Office Excel 2003, dps 7.05 and spss11.5 software were used for data reduction and difference analysis with the significance level of P<0.05. Because the experimental results in 2015 were basically the same as those in 2014, the data in the text adopted the test results in 2014.

Results and Analysis

Dynamic tillering characteristics in different populations of two types of varieties

Among the 18 different population structures set up in the experiment, the yield exceeding 975 0 kg/hm2 was regarded as a high-yielding population, and the yield below 975 0 kg/hm2 was regarded as a low-yielding population. The differences in the dynamic tillering characteristic between populations of different yield levels were analyzed. During the entire growth period, the number of tillers had always been higher in the high-yielding populations than in the low-yielding populations (Fig. 1). The high-yielding populations of Kongyu 131, the conventional variety with more tillers and lighter panicles, reached an appropriate number of panicles (550 panicles/m2) at the critical leaf age for productive tillers (June 25), which was about 7 d earlier than the low-yielding population. The high-yielding populations of the super rice variety Longjing 21 with fewer tillers and heavier panicles also reached an appropriate number of panicles (500 panicles/m2) around June 25, while the highest number of stems in its low-yielding populations only reached 500 panicles/m2.

The peak seedlings of high-yielding and high-quality populations should appear at the jointing stage (July 9), and the number was small. The number of panicles of the conventional variety Kongyu 131 with more tillers and lighter panicles was about 1.1 times the expected number of panicles (it was about 1.2 times for Longjing 21, the super rice variety with fewer tillers and heavier panicles). After that, the populations declined gently, reaching an appropriate number of panicles at the heading stage.

The relationship between the number of tillered seedlings and the yield of the population at the critical leaf age for productive tillers was analyzed. The number of tillered seedlings and yield showed a quadratic curve for the two types of varieties (Fig. 2), and the correlation coefficients reached a significant level. It showed that there was an optimal value for the number of stems and tillers in the seedling stage. If the number of stems and tillers in the population at the critical leaf age for productive effective tillers was too small, the population would be insufficient, while too large would lead to a too-large population. The suitable panicle number of Kongyu 131, the conventional variety with more tillers and lighter panicles, was about 550 panicles/m2, and the optimal panicle number of Longjing 21, the super rice variety with fewer tillers and heavier panicles, was about 500 panicles/m2. The final yields of suitable populations were the highest, which were significantly higher than those of insufficient and oversized populations.

Jingfang XUE et al. Effects of Plant Spacing, Row Spacing and Seedling Number Allocation on the Growth Dynamics of Different Populations of Two Types of Rice Varieties

Effects of plant spacing, row spacing, and number of planted seedlings on the dynamics of stems and tillers

From transplanting on May 25, the population stems and tillers increased steadily in different plant spacing treatments, until reaching a final number of panicles in the heading stage on July 20. The number of stems and tillers in the three treatments of the two types of varieties always showed as follows: 10.0 cm＞13.3 cm＞16.7 cm (Fig. 3). The difference between the different treatments was that Longjing 21, the super rice variety with fewer tillers and heavier panicles, was higher than that of the conventional variety, Kongyu 131, with more tillers and lighter panicles throughout the growth period. The peak seedlings of the three treatments of Kongyu 131 appeared around July 9, while the peak seedlings of the Longjing 21 treatment with a plant spacing of 10 cm appeared on June 29, which was 10 d earlier than that of Kongyu 131, but other 2 treatments showed their peaks on July 9.

The effect of the row spacing factor on populations tiller dynamics was roughly the same as that of plant spacing (Fig. 4). From transplanting on May 25, the stems and tillers of different treatments grew steadily, reaching the final panicle number at the heading stage. The numbers of tillers of the two types of varieties in 2 treatments showed that: 24 cm＞30 cm. The difference between the two treatments was that the super rice variety Longjing 21 with fewer tillers and heavier panicles was higher than the conventional variety Kongyu 131 with more tillers and lighter panicles throughout the growth period. The peak seedlings of the two treatments of Kongyu 131 appeared around July 6, while the peak seedlings of the Longjing 21 treatment with a row spacing of 24 cm appeared around June 29, and the 30 cm row spacing treatment appeared around July 9.

Treatments with different numbers of seedlings per hole had a certain impact on the population tillering dynamics (Fig. 5). From planting to July 13, the conventional variety Kongyu 131 with more tillers and lighter panicles had the highest number of stems and tillers in the population of 8 seedlings/hole, followed by the 5 seedlings/hole treatment, and the lowest value was observed in the 2 seedlings/hole treatment. The magnitude of difference was relatively uniform. At the heading stage, the numbers of stems and tillers reached in the populations of the 2 and 5 seedlings/hole treatments were almost the same. The peak seedlings of the three treatments appeared around July 6. From planting to the beginning of tillering (around June 10), the number of stems and tillers of the super rice variety Longjing 21 with fewer tillers and heavier panicles was 8 seedlings/hole>5 seedlings/hole>2 seedlings/hole; and from the beginning of full tillering stage to the heading stage, the numbers of stems and tillers of the 8 and 5 seedlings/hole treatments were much higher than that of the 2 seedlings/hole treatment, while the numbers of stems and tillers of the 8 and 5 seedlings/hole treatments were always the same, and the 5 seedlings/hole treatment was slightly higher than the 8 seedlings/hole when the final stem number was reached. The peak seedlings of the 8 and 5 seedlings/hole treatments appeared around June 29, and the peak of the 2 seedlings/holes treatment appeared around July 6.

From the perspective of different number of planted seedlings per hole, the change dynamics of population stems and tillers of different types of varieties under high density (plant spacing 10 cm, row spacing 24 cm, density 41.7 holes/m2) and low density (plant spacing 16.7 cm, row spacing 30 cm, density 20 holes/m2) were analyzed. The number of stems and tillers in the early growth stage of the conventional variety Kongyu 131 with more tillers and lighter panicles under the high-density treatment (plant spacing 10 cm, row spacing 24 cm, density 41.7 holes/m2) was always highest in the 8 seedlings/hole treatment, followed by the 5 seedlings/hole treatment, and least in the 2 seedlings/holes (Fig. 6). About 7 d before heading, the numbers of stems and tillers in the populations of the 2 seedlings/hole treatment and 5 seedlings/hole treatment were nearly the same, slightly lower than that of the 8 seedlings/hole treatment, and finally reached more than 580 panicles/m2. As to the super rice variety Longjing 21 with fewer tillers and heavier panicles, after planting until heading, the numbers of stems and tillers of the 5 seedlings/hole treatment and 8 seedlings/hole treatment were always much higher than that of the 2 seedlings/hole treatment, and the number of stems and tillers of the 8 seedlings/hole treatment was slightly higher than that of the 5 seedlings/hole treatment. At the heading stage, the numbers of stems and tillers of the 5 seedlings/hole treatment and the 8 seedlings/hole treatment were close to the same, and finally reached more than 700 panicles/m2, and the 2 seedlings/hole treatment only reached 370 panicles/m2, that is to say that the number of stems and tillers was seriously insufficient. Under the high density, the peak seedling period of the three treatments of Kongyu 131, the conventional variety with more tillers and lighter panicles, appeared around July 6, and that in the three treatments of Longjing 21, the super rice variety with few tillers and heavier panicles, appeared around June 29. With the increase of density, the increase in the number of basic seedlings led to the condition that the peak seedling date appeared about 6-10 d earlier than the treatment with low density and less number of planted seedlings.

The number of stems and tillers of the conventional variety Kongyu 131 with multiple tillers and light panicles under the low density (plant spacing 16.7 cm, row spacing 30 cm, and 20 holes/m2) in the early growth period (before July 6) was always the highest in the 8 seedlings/hole treatment, followed by the 5 seedlings/hole treatment, and the least in the 2 seedlings/hole treatment (Fig. 7). At the time of reaching the heading stage, the numbers of stems and tillers in the 2 seedlings/hole treatment and 8 seedlings/hole treatment were close to the same, both reached 490 panicles/m2 or more, which was slightly higher than the 5 seedlings/hole treatment. For the super rice variety Longjing 21 with fewer tiller and heavier panicles, the numbers of stems and tillers of the 5 seedlings/hole treatment and 8 seedlings/hole treatments were similar after planting until heading, and were always higher than that of the 2 seedlings/hole treatment. The 5 seedlings/hole treatment and the 8 seedlings/hole treatment finally reached about 400 panicles/m2, and the 2 seedlings/hole treatment only reached 320 panicles/m2. The number of stems and tillers was obviously insufficient in the 3 treatments. The peak seedling dates of the 5 seedlings/hole and 8 seedlings/hole treatments of Kongyu 131, the conventional variety with more tillers and lighter panicles under low density treatment, appeared around July 6, and that of the 2 seedlings/hole treatment appeared around July 12. The peak seedling dates of the three treatments of the super rice variety Longjing 21 with fewer tillers and heavier panicles appeared around July 6.

Under the high density, the number of seedlings of the conventional variety with more tillers and lighter panicles could be reduced (2-5 seedlings/hole), while at the low density, there should be slightly more seedlings (5 seedlings/hole), so as to reach sufficient tillers at the critical leaf age for productive tillers. Excessive number of planting seedlings will cause the early stage population to be too large and the photosynthetic products to be wasted, resulting in too many ineffective tillers, which will lead to a closed population and occurrences of diseases and lodging. Regardless of high or low density conditions, especially under the low density condition, more seedlings (5-8 seedlings/hole) should be planted for the super rice variety with fewer tillers and heavier panicles to increase the number of main stems, and to achieve a sufficient number of stem tillers in the population at the critical leaf age for productive tillers as soon as possible, so as to reduce the risk of insufficient stems and tillers in the population before June 25.

Dynamics of leaf area index in different populations of the two types of varieties

The leaf area index of the high-yielding populations of the two types of varieties was higher than that of the low-yielding populations in both the heading stage and the maturation stage, and the differences in the heading stage reached a significant level, while no significant differences were observed in the maturation stage (Fig. 8). The leaf area index of Longjing 21, the super rice variety with fewer tillers and heavier panicles, was greater than that of Kongyu 131, the conventional variety with more tillers and lighter panicles.

The high-yielding populations had a higher leaf area index at the heading stage. The value of Longjing 21, the super rice variety with fewer tiller and heavier panicles, reached about 6.0, and that of Kongyu 131, the conventional variety with more tillers and lighter panicles, reached about 4.5. The values decreased thereafter. At the maturation stage, the leaf area index of Longjing 21 remained above 2.5, and that of Kongyu 131 remained above 2.0.

Effects of plant spacing, row spacing and number of planted seedlings on leaf area index

Different plant spacing treatments had obvious effects on the leaf area indexes of the two varieties at the heading stage. The 10 cm plant spacing treatment had the highest LAI, followed by the 13.3 cm plant spacing, and the 16.7 cm plant spacing treatment showed the lowest value. Longjing 21, the super rice variety with fewer tillers and heavier panicles, had greater differences in magnitude between different treatments than Kongyu 131, the conventional variety with more tillers and lighter panicles. Different plant spacing treatments had no significant effects on the leaf area indexes of the two types of varieties at the maturation stage. The LAI of Kongyu 131 was similar among its three treatments. The 16.7 cm plant spacing treatment of Longjing 21 was higher than its 10 cm plant spacing and 13.3 cm plant spacing treatments (Fig. 9).

Different row spacing treatments had obvious effects on the leaf area index of the super rice variety Longjing 21 with fewer tillers and heavier panicles at the heading stage. Specifically, the 24 cm row spacing was higher than the 30 cm row spacing treatment. No obvious effects were found on the conventional variety Kongyu 131 with more tillers and lighter panicles (Fig. 10). Different row spacing treatments had little effects on the leaf area indexes of the two types of varieties at the maturation stage, and the two treatments showed almost the same LAI values.

The effects of different numbers of planted seedlings on the leaf area indexes of the two types of varieties at the heading stage were slightly different. The LAI values of the 2 seedlings/hole and 5 seedlings/hole treatments of the conventional variety with more tillers and lighter panicles, Kongyu131, were almost the same, significantly lower than that of the 8 seedlings/hole. However, for Longjing 21, the super rice variety with fewer tillers and heavier panicles, the LAI was the highest in the 5 seedlings/hole treatment, followed by the 8 seedlings/hole treatment, and the 2 seedlings/hole treatment was the lowest (Fig. 11). The effects on the leaf area indexes of the two types of varieties at the maturation stage were also different. The LAI values of the three treatments of Kongyu 131 were similar, and the 2 seedlings/hole treatment of Longjing 21 was significantly lower than the 5 seedlings/hole and 8 seedlings/hole treatments.

Discussion

In order to obtain high yield in the practice of Heilongjiang rice production, it is necessary to obtain enough panicles per unit area to obtain a larger storage capacity. Since the temperature is often low after transplanting, the cultivation and management of seedlings has been required to grow strong seedlings and apply the tillering fertilizer early to promote the early growth and rapid onset of tillering, so as to reach an appropriate number of panicles at the critical leaf age for productive tillers［5］. The number of tillers per unit area is closely related to the planting density and the number of seedlings per hole, and it is also related to the tillering ability of varieties, because the tillering ability of different varieties is still quite different［6］. In this study, Kongyu 131, the conventional variety with more tillers and lighter panicles, is a variety with strong tillering ability, of which the number of harvested panicles reached 557.8 panicles/m2 in the high-yielding populations (>975 0 kg/hm2), and only reached 508.8 panicles/m2 in the low-yielding populations (<975 0 kg/hm2), while the super rice variety Longjing 21 with fewer tillers and heavier panicles, is a variety with weak tillering ability, of which the harvested panicle number only reached 504.2 panicles/m2 in the high-yielding populations (>975 0 kg/hm2), and only reached 420.3 panicles/m2 in the low-yielding populations. It can be seen that the number of harvested panicles of the more-tiller variety contributed far more to high yield than other yield factors, while a high yield of the super rice variety with fewer tillers and heavier panicles required striving for large panicles and more grains in addition to ensuring enough panicles.

Yang et al.［7］ and Zhang et al.［8］ believed that the dynamic characteristic of the stems and tillers of super-high-yielding populations was steadily increasing in the early stage of growth, reaching the expected number of panicles at the critical leaf age for productive tillers, and the peak seedling date appeared at the jointing stage, with the number about 1.3 times the expected number of panicles. After that, the populations declined gently until an appropriate number of panicles was reached at the heading stage, and the percentage of panicle-bearing tillers was over 80%. This study showed that the super-high-yielding populations of the two types of varieties should grow steadily in the early stage of development, until an appropriate number of panicles was reached at the critical leaf age for productive tillers (June 25), and the peak seedlings should appear in the jointing stage (July 6) with a small number (that value of Longjing 21, the super rice variety with fewer tillers and heavier panicles, was about 1.2 times the expected panicle number, and that of the conventional variety with more tillers and lighter panicles, Kongyu 131, was about 1.1 times the expected panicle number). The populations gradually declined since then, until reaching an appropriate number of panicles at the heading stage, when the percentage of productive tillers was over 85% for Kongyu 131, over 80% for Longjing 21, and the percentage of panicle-bearing tillers was over 90% for Kongyu 131, over 85% for Longjing 21. Wang et al.［9］ believed that when the number of holes is the same and the number of seedlings per hole is too small, the number of panicles is insufficient, which restricts the increase in yield, and although the panicles are large, the increase in the number of grains per panicle cannot compensate for the loss of the reduction of the panicle number. On the contrary, if the number of seedlings per hole is too high, the number of panicles will not increase significantly, but the contradiction between panicles and grains will cause the number of grains per panicles to decrease and the 1 000-grain weight to decrease, which is not conducive to high yield. In this study, the treatments of different plant and row spacing and numbers of seedlings per holes had greater effects on the population stem and tiller dynamics of the super rice variety Longjing 21 with fewer tillers and heavier panicles, and reducing the plant and row spacing and increasing the number of planted seedlings per hole all made the heading date earlier and the number of stems and tillers increase significantly. Under the low density condition, more seedlings (5-8 seedlings/hole) should be planted for the super rice variety Longjing 21 with fewer tillers and heavier panicles to increase the number of main stems and reach sufficient stems and tillers as soon as possible at the critical leaf age for productive tillers, so as to reduce the risk of insufficient total stems and tillers in the population before June 25.

Conclusions

This study clarified the effects of the population composition factors on the growth dynamics of the two types of varieties, and proposed the dynamic tillering characteristics of the high-yielding and high-quality populations of the two types of varieties.

Decreasing the plant and row spacing and increasing the number of planted seedlings per hole advanced the heading date and made the number of stems and tillers in the population increase. The impact on the super rice variety with fewer tillers and heavier panicles was greater than that of conventional variety with more tillers and lighter panicles. The stems and tillers of the high-yielding high-quality populations grew steadily in the early stage of development, until an appropriate number of panicles was reached at the critical leaf age for productive tillers (June 25), and the peak seedlings should appear in the jointing stage (July 6) with a small number (that value of Longjing 21, the super rice variety with fewer tillers and heavier panicles, was about 1.2 times the expected panicle number, and that of the conventional variety with more tillers and lighter panicles, Kongyu 131, was about 1.1 times the expected panicle number). The populations gradually declined since then, until reaching an appropriate number of panicles at the heading stage.

Reducing plant and row spacing and increasing the number of planted seedlings per hole would increase the population leaf area index at the heading stage, but the differences were not obvious at the maturation stage. The high-yielding high-quality populations had a higher leaf area index at the heading stage. The value of Longjing 21, the super rice variety with fewer tiller and heavier panicles, reached about 6.0, and that of Kongyu 131, the conventional variety with more tillers and lighter panicles, reached about 4.5. The values decreased thereafter. At the maturation stage, the leaf area index of Longjing 21 remained above 2.5, and that of Kongyu 131 remained above 2.0.

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