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Abstract Ningqiao 1 was selected as the material to study the effects of planting density on physiological indices, agronomic traits and yield of buckwheat. The results showed that high density resulted in decreases of chlorophyll content, soluble protein content and activity of SOD, POD and CAT, and acceleration of MDA accumulation under drought conditions. Low density could effectively improve the grain number per plant, grain weight per plant, 1 000-grain weight and yield in drought conditions.
Key words Buckwheat (Fagopyrum esculentum Moench.); Planting density; Physiological index; Agronomic trait; Yield
Received: December 23, 2020 Accepted: February 27, 2021
Supported by Ningxia Natural Science Foundation (NZ15270); National Agriculture Research System of Oat and Buckwheat (CARS-08-E-5).
Yaojun CHANG (1965-), male, P. R. China, engineer, devoted to research about agricultural meteorology and ecology.
*Corresponding author. E-mail: muyangxiu@aliyun.com.
Buckwheat (Fagopyrum esculentum Moench.) belongs to Fagopyrum of Polygonaceae, and is one of the main food crops in the mountains of southern Ningxia. Planting density is an important factor affecting the yield of buckwheat. The impact of different planting densities on the yield of buckwheat is mainly reflected by the impact on agronomic traits and physiological indices related to yield formation. Luo et al.［1］ pointed out that the increase of maize planting density led to weakening of light transmittance in the population, thereby shortening the function period of leaves and accelerating the senescence process. The research of Hu［2］ showed that as the density of maize increased, the soluble protein content showed a downward trend, the MDA content increased, and the SOD and POD activity both increased first and then decreased. The research of Yu et al.［3］ showed that appropriately reducing the number of basic seedlings and establishing a reasonable population structure could effectively improve the physiological activity of wheat plants after flowering, prolong the slow-down period of leaf senescence, strengthen the synthesis of assimilation, and improve grain weight. The study of Wang et al.［4］ showed that low-density treatments effectively slowed down the senescence of wheat flag leaves, and increased the 1 000-grain weight and the number of grains per panicles, but the planting density should be set combining with yield. Zhang et al.［5］ studied the effects of some physiological characteristics of senescence of the flag leaves of rice after heading, and found that the chlorophyll content, soluble protein content and SOD activity all showed a downward trend, while the MDA content showed an upward trend. In summary, the effects of planting density on crop physiological characteristics and yield have been studied on maize［6-8］, millet［9］, wheat［10-11］, rice［12-13］ and other crops, but no studies have been reported on the relationship between planting density and buckwheat physiological indexes. In this study, planting density, physiological indices, agronomic characteristics and yield were combined to investigate the optimal planting density of buckwheat, hoping to provide a theoretical basis for high-yielding and high-efficiency cultivation of buckwheat. Materials and Methods
Experimental materials
The experimental buckwheat variety was Ningqiao 1, provided by Guyuan Branch of Ningxia Academy of Agricultural and Forestry Sciences.
Experimental methods
The experiment was conducted at the Oats and Buckwheat Experimental Base in Pengbao Village, Pengbao Town, Yuanzhou District, Guyuan City, Ningxia from June to September 2016. The field was located at 106°9′ east longitude, 36°5′ north latitude, and 1 660 m above sea level. The experiment adopted a randomized block experiment design and was set with 3 density gradients, i.e., 600 000/hm2 (40 plants per row, plant spacing 5 cm), 900 000/hm2 (60 plants per row, plant spacing 3.33 cm), and 1 200 000/hm2 (80 plants per row, plant spacing 2.5 cm), which were recorded in turn as T1, T2, and T3, each of which was repeated 3 times. The sowing method was ditching and sowing in drill, and artificial thinning and final singling were adopted. Each plot had an area of 10 m2 (2.5 m×4.0 m), and included 9 short rows with row spacing of about 33 cm. The management of fertilizer, water, diseases, pests and weeds was carried out according to the national buckwheat regional test requirements. After the plants had grown to the beginning of the flowering period, sampling was performed every 7 d. The chlorophyll content, soluble protein content, malondialdehyde (MDA) content, and activity of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) in buckwheat leaves were measured at 1, 8, 15, and 22 d after the initial flowering period, and the average value of 3 replicates was taken for each item.
After the plants matured, 10 plants were randomly sampled from each plot to investigate plant height, stem thickness, number of main stem nodes, number of effective branches, number of grains per plant, grain weight per plant, and 1 000-seed weight. Harvesting was performed by plot, followed by threshing, drying, and weighing.
Determination items and methods
The chlorophyll content was determined by 80% acetone extraction method［14］; the soluble protein content was determined by Coomassie Brilliant Blue G-250 method［15］; the SOD activity was measured by nitroblue tetrazolium (NBT) photoreduction method［16］; the POD activity was measured by guaiacol method［16］; the CAT activity was measured by ultraviolet absorption method［16］; and the MDA content was measured by thiobarbituric acid (TBA)colorimetric method［16］.
Data processing The test data were preliminarily processed using Excel 2007, and SPSS16.0 software was used to perform LSD multiple comparisons on different treatments.
Results and Analysis
Effects of planting density on the physiological indices of buckwheat
Effects of planting density on the leaf chlorophyll content of buckwheat
It can be seen from Table 1 that at different sampling time, the chlorophyll content varied significantly between different density treatments. At 1 d after flowering, the chlorophyll content of treatment T3 was significantly higher than those of treatments T1 and T2, by 33.1% and 5.3%, respectively. As the growth process progressed, 22 d after the beginning of flowering, the result was just the opposite. The chlorophyll content of treatment T3 was significantly lower than those of treatments T1 and T2, 10.7% and 5.6% lower, respectively. It showed that after the initial flowering period, with the extension of growth time, treatment T3 could significantly accelerate the decomposition of chlorophyll.
Effects of planting density on leaf soluble protein content of buckwheat
It can be seen from Table 1 that the leaf soluble protein content of treatment T3 was the lowest at the beginning of flowering, there were no significant differences in the soluble protein content between treatments T2 and T1 at 1, 8 and 15 d after flowering, but with the extension of growth time, the soluble protein content of treatment T3 was significantly lower than those of treatments T1 and T2 at 22 d after flowering. It showed that treatment T3 could reduce the protein content of buckwheat leaves and accelerate the senescence of buckwheat plants.
Effects of planting density on antioxidant enzyme activity of buckwheat
It can be seen from Table 1 that during the sampling period, under different planting density treatments, the SOD activity of buckwheat leaves increased first and then decreased, and the effects of different densities on the SOD activity of buckwheat leaves were significantly different. At 1 d after flowering, the SOD activity of treatment T2 was significantly lower than that of treatments T1 and T3, but as the growth process progressed, at 22 d after flowering, the SOD activity of treatment T2 was significantly higher than that of treatments T1 and T3, and the SOD activity of treatment T3 was the lowest, significantly lower than that of treatments T1 and T2. During the sampling period, there were significant differences in the POD activity of buckwheat leaves under different density treatment conditions. Then there were different manifestations. POD activity increased at 22 d after flowering, while CAT activity decreased at 22 d after flowering. At 22 d after flowering, the POD activity of treatment T3 was significantly lower than that of treatment T1, and the CAT activity of treatment T3 was significantly lower than that of treatments T1 and T2. It showed that the low-density treatment T1 could effectively increase POD activity and delay leaf senescence, and the high-density treatment T3 could accelerate the decline of SOD and CAT activity and promote plant senescence. Effects of planting density on MDA content
It can be seen from Table 1 that there were no significant differences in the MDA content of buckwheat leaves under different planting densities. It can be seen from Table 1 that the MDA content of treatment T3 was lower than those of treatments T1 and T2 1 d after the beginning of flowering, but at 22 d after the beginning of flowering, the MDA content of treatment T3 was higher than those of treatments T1 and T2. It showed that the accumulation rate of MDA content of treatment T3 was higher than those of treatments T1 and T2.
Effects of planting density on agronomic traits and yield of buckwheat
It can be seen from Table 2 that the plant height of buckwheat treated with T3 was significantly lower than those of treatments T1 and T2; the plant stem thickness of treatment T3 was lower than those of treatments T1 and T2, and had a significant difference from treatment T1; treatment T3 had no significant differences in the number of main stem nodes and number of effective branches per plant from treatments T1 and T2; the number of grains per plant and the grain weight per plant were significantly lower in treatment T3 than treatments T1 and T2; the 1 000-grain weight of treatment T3 was lower than those in treatments T1 and T2, and the difference from treatment T2 was significant; and the yield of treatment T3 was lower than those of treatments T1 and T2, and the yield difference between the three treatments were not significant, but the yield of treatment T2 was the highest. The number of grains per plant, grain weight per plant, 1 000-seed weight and yield were all highest in T2, which had no significant differences from treatment T1. It showed that the high-density treatment was not conducive to increasing the number of grains per plant, grain weight per plant, 1 000-grain weight and yield, and the low-density treatment was beneficial to increase the number of grains per plant, grain weight per plant, 1 000-grain weight and yield.
Conclusions and Discussion
Effects of planting density on the physiological indices of buckwheat
The research of Zhang et al.［11］ showed that with the increase of planting density, the chlorophyll content and soluble protein content of wheat flag leaves continued to decrease. Wang［9］ found that the SOD and POD activity of the two kinds of broom corn millet increased with the planting density, the content of MDA increased with the increase of planting density, and the increase of planting density intensified leaf senescence. The research of Hu et al.［13］ showed that the soluble protein content of rice cultivated at the low density increased, the leaf senescence was delayed, and the 1 000-grain weight increased. The study of Du et al.［17］ showed that as the planting density increased, the physiological indices and yield traits of soybean decreased. The results of this study showed that with the increase of planting density, the chlorophyll content and soluble protein content of buckwheat leaves decreased. Meanwhile, the high-density treatment reduced the protective enzyme activity of buckwheat leaves and accelerated the accumulation of MDA content, which is consistent with the results of previous studies. Effects of planting density on agronomic traits and yield of buckwheat
Planting density has a relatively great impact on the agronomic characteristics and yield of buckwheat［18］. The yield of buckwheat increases first and then decreases with the increase of planting density［19-20］. The research of Jiang et al.［21］ showed that the planting density had no significant effect on the plant height, the number of main stem branches and the number of main stem nodes of buckwheat, but it had a significant impact on the yield component factor, grain weight per plant. This study showed that planting density had significant effects on the number of grains per plant and the grain weight per plant of Ningqiao No.1, and the yield increased first and then decreased with the increase of density, which is consistent with the results of previous studies. However, the results of this study showed that density had no significant effect on the yield of buckwheat, which is inconsistent with the results of Wang et al.［19］, which might be caused by the climate of different regions. In this study, Ningqiao No. 1 had been in a drought state during its growth period. Under drought condition, the low-density treatment was beneficial to increasing the number of grains per plant, grain weight per plant, 1 000-grain weight and yield.
References
［1］ LUO YN, ZHANG JH. Effect of planting density on maize leaf senescence［J］. Journal of Maize Sciences, 1994(4): 23-25. (in Chinese)
［2］ HU M. Effect of Density on Photosynthetic and senescence physiology and yield of spring corn［D］. Harbin: Northeast Agricultural University, 2009. (in Chinese)
［3］ YU ZW, YUE SS, SHEN CG, et al. Effects of different densities on leaf senescence and grain weight of winter wheat after flowering［J］. Acta Agronomica Sinica, 1995, 21(4): 412-418. (in Chinese)
［4］ WANG ZH, JIANG LN, LI CX, et al. Effect of planting density and growth regulator on caducity and yield components in wheat ［J］. Crops, 2003(2): 15-17. (in Chinese)
［5］ ZHANG RP, DAI HY, MA J, et al. Effects of different density on some senescence physiology characteristics of flag leaf in colored rice after heading［J］. Journal of Xichang University: Natural Science Edition, 2009, 23(3): 13-16. (in Chinese)
［6］ MA RX, ZHANG AQ, LIU WC. The influence of different density on yield and main physiologcal index of different types of corn variety ［J］. Chinese Agricultural Science Bulletin, 2006(5): 171-173. (in Chinese) ［7］ CHEN SB. Study on Physiological characteristics and yield traits of high oil corn in different densities［D］. Beijing: China Agricultural University, 2005. (in Chinese)
［8］ MA C, HUANG XS, LI PK, et al. Effects of planting density on physiological decline on ear leaf of summer maize ［J］. Journal of Maize Sciences, 2010(2): 50-53. (in Chinese)
［9］ WANG DH. Effect of while film mulch on yield, quality and physiological basis in broomcorn millet under different planting densities［D］. Hohhot: Inner Mongolia Agricultural University, 2015. (in Chinese)
［10］ GUO TC, SHENG K, FENG W, et al. Effects of plant density on physiological characteristics of different stems during tillering stage in two spike-types winter wheat cultivars［J］. Acta Botanica Boreali-Occidentalia Sinica, 2009, 29(2): 350-355. (in Chinese)
［11］ ZHANG YL, XIAO K, LI YM. Effects and physiological mechanism of planting densities on photosynthesis characteristics of flag leaf and grain yield in wheat hybrid C6-38/Py85-1［J］. Acta Agronomica Sinica, 2005, 31(4): 498-505. (in Chinese)
［12］ ZHU CC. Effect of planting density on yield and ecophysiological characteristics in different types of rice with bowl mechanical-transplanting method［D］. Yangzhou: Yangzhou University, 2014. (in Chinese)
［13］ HU WH, WANG XL, LIU ZK. Study on rice physiological characters for different planting density after earing ［J］. Journal of Jilin Agricultural Universit, 2006, 28(6): 594-596,605. (in Chinese)
［14］ CHEN YQ. Biochemical experimental methods and techniques［M］. Beijing: Science Press, 2002. (in Chinese)
［15］ LI HS. Principles and techniques of plant physiological and biochemical experiments［M］. Beijing: Higher Education Press, 2000. (in Chinese)
［16］ GAO JF. Plant physiological experiment guidance［M］. Beijing: World Book Inc, 2001. (in Chinese)
［17］ DU CY, HU XG, HE ZR, et al. Effect of density on soja bean yield and its physiological index ［J］. Inner Mongolia Agricultural Science and Technology, 2006(2): 35-36. (in Chinese)
［18］ YI JL, LI LJ, HUANG YB, et al. Preliminary study on high-yield cultivation techniques of buckwheat［J］. Crop Research, 2007(2): 108-110. (in Chinese)
［19］ WANG C, LI M, WANG SX, et al. Effects of different sowing date,seeding rate and fertilization on yield and agronomic traits of Fagopyrum esculentum Xinnong 1 planted in spring ［J］. Guizhou Agricultural Sciences, 2014, 42(3): 52-55. (in Chinese)
［20］ ZHANG Q, WANG AH, YANG JY. Effect of different zinc concentration and density on biological characteristics and yield of tartary buckwheat［J］. Seed, 2010(11): 9-13. (in Chinese)
［21］ JIANG T, LI W. Effect of different sowing dates and planting densities on agronomic traits and yield of Fagopyrum esculentum Moench［J］. Chinese Agricultural Science Bulletin, 2015, 31(30): 169-172. (in Chinese)
Key words Buckwheat (Fagopyrum esculentum Moench.); Planting density; Physiological index; Agronomic trait; Yield
Received: December 23, 2020 Accepted: February 27, 2021
Supported by Ningxia Natural Science Foundation (NZ15270); National Agriculture Research System of Oat and Buckwheat (CARS-08-E-5).
Yaojun CHANG (1965-), male, P. R. China, engineer, devoted to research about agricultural meteorology and ecology.
*Corresponding author. E-mail: muyangxiu@aliyun.com.
Buckwheat (Fagopyrum esculentum Moench.) belongs to Fagopyrum of Polygonaceae, and is one of the main food crops in the mountains of southern Ningxia. Planting density is an important factor affecting the yield of buckwheat. The impact of different planting densities on the yield of buckwheat is mainly reflected by the impact on agronomic traits and physiological indices related to yield formation. Luo et al.［1］ pointed out that the increase of maize planting density led to weakening of light transmittance in the population, thereby shortening the function period of leaves and accelerating the senescence process. The research of Hu［2］ showed that as the density of maize increased, the soluble protein content showed a downward trend, the MDA content increased, and the SOD and POD activity both increased first and then decreased. The research of Yu et al.［3］ showed that appropriately reducing the number of basic seedlings and establishing a reasonable population structure could effectively improve the physiological activity of wheat plants after flowering, prolong the slow-down period of leaf senescence, strengthen the synthesis of assimilation, and improve grain weight. The study of Wang et al.［4］ showed that low-density treatments effectively slowed down the senescence of wheat flag leaves, and increased the 1 000-grain weight and the number of grains per panicles, but the planting density should be set combining with yield. Zhang et al.［5］ studied the effects of some physiological characteristics of senescence of the flag leaves of rice after heading, and found that the chlorophyll content, soluble protein content and SOD activity all showed a downward trend, while the MDA content showed an upward trend. In summary, the effects of planting density on crop physiological characteristics and yield have been studied on maize［6-8］, millet［9］, wheat［10-11］, rice［12-13］ and other crops, but no studies have been reported on the relationship between planting density and buckwheat physiological indexes. In this study, planting density, physiological indices, agronomic characteristics and yield were combined to investigate the optimal planting density of buckwheat, hoping to provide a theoretical basis for high-yielding and high-efficiency cultivation of buckwheat. Materials and Methods
Experimental materials
The experimental buckwheat variety was Ningqiao 1, provided by Guyuan Branch of Ningxia Academy of Agricultural and Forestry Sciences.
Experimental methods
The experiment was conducted at the Oats and Buckwheat Experimental Base in Pengbao Village, Pengbao Town, Yuanzhou District, Guyuan City, Ningxia from June to September 2016. The field was located at 106°9′ east longitude, 36°5′ north latitude, and 1 660 m above sea level. The experiment adopted a randomized block experiment design and was set with 3 density gradients, i.e., 600 000/hm2 (40 plants per row, plant spacing 5 cm), 900 000/hm2 (60 plants per row, plant spacing 3.33 cm), and 1 200 000/hm2 (80 plants per row, plant spacing 2.5 cm), which were recorded in turn as T1, T2, and T3, each of which was repeated 3 times. The sowing method was ditching and sowing in drill, and artificial thinning and final singling were adopted. Each plot had an area of 10 m2 (2.5 m×4.0 m), and included 9 short rows with row spacing of about 33 cm. The management of fertilizer, water, diseases, pests and weeds was carried out according to the national buckwheat regional test requirements. After the plants had grown to the beginning of the flowering period, sampling was performed every 7 d. The chlorophyll content, soluble protein content, malondialdehyde (MDA) content, and activity of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) in buckwheat leaves were measured at 1, 8, 15, and 22 d after the initial flowering period, and the average value of 3 replicates was taken for each item.
After the plants matured, 10 plants were randomly sampled from each plot to investigate plant height, stem thickness, number of main stem nodes, number of effective branches, number of grains per plant, grain weight per plant, and 1 000-seed weight. Harvesting was performed by plot, followed by threshing, drying, and weighing.
Determination items and methods
The chlorophyll content was determined by 80% acetone extraction method［14］; the soluble protein content was determined by Coomassie Brilliant Blue G-250 method［15］; the SOD activity was measured by nitroblue tetrazolium (NBT) photoreduction method［16］; the POD activity was measured by guaiacol method［16］; the CAT activity was measured by ultraviolet absorption method［16］; and the MDA content was measured by thiobarbituric acid (TBA)colorimetric method［16］.
Data processing The test data were preliminarily processed using Excel 2007, and SPSS16.0 software was used to perform LSD multiple comparisons on different treatments.
Results and Analysis
Effects of planting density on the physiological indices of buckwheat
Effects of planting density on the leaf chlorophyll content of buckwheat
It can be seen from Table 1 that at different sampling time, the chlorophyll content varied significantly between different density treatments. At 1 d after flowering, the chlorophyll content of treatment T3 was significantly higher than those of treatments T1 and T2, by 33.1% and 5.3%, respectively. As the growth process progressed, 22 d after the beginning of flowering, the result was just the opposite. The chlorophyll content of treatment T3 was significantly lower than those of treatments T1 and T2, 10.7% and 5.6% lower, respectively. It showed that after the initial flowering period, with the extension of growth time, treatment T3 could significantly accelerate the decomposition of chlorophyll.
Effects of planting density on leaf soluble protein content of buckwheat
It can be seen from Table 1 that the leaf soluble protein content of treatment T3 was the lowest at the beginning of flowering, there were no significant differences in the soluble protein content between treatments T2 and T1 at 1, 8 and 15 d after flowering, but with the extension of growth time, the soluble protein content of treatment T3 was significantly lower than those of treatments T1 and T2 at 22 d after flowering. It showed that treatment T3 could reduce the protein content of buckwheat leaves and accelerate the senescence of buckwheat plants.
Effects of planting density on antioxidant enzyme activity of buckwheat
It can be seen from Table 1 that during the sampling period, under different planting density treatments, the SOD activity of buckwheat leaves increased first and then decreased, and the effects of different densities on the SOD activity of buckwheat leaves were significantly different. At 1 d after flowering, the SOD activity of treatment T2 was significantly lower than that of treatments T1 and T3, but as the growth process progressed, at 22 d after flowering, the SOD activity of treatment T2 was significantly higher than that of treatments T1 and T3, and the SOD activity of treatment T3 was the lowest, significantly lower than that of treatments T1 and T2. During the sampling period, there were significant differences in the POD activity of buckwheat leaves under different density treatment conditions. Then there were different manifestations. POD activity increased at 22 d after flowering, while CAT activity decreased at 22 d after flowering. At 22 d after flowering, the POD activity of treatment T3 was significantly lower than that of treatment T1, and the CAT activity of treatment T3 was significantly lower than that of treatments T1 and T2. It showed that the low-density treatment T1 could effectively increase POD activity and delay leaf senescence, and the high-density treatment T3 could accelerate the decline of SOD and CAT activity and promote plant senescence. Effects of planting density on MDA content
It can be seen from Table 1 that there were no significant differences in the MDA content of buckwheat leaves under different planting densities. It can be seen from Table 1 that the MDA content of treatment T3 was lower than those of treatments T1 and T2 1 d after the beginning of flowering, but at 22 d after the beginning of flowering, the MDA content of treatment T3 was higher than those of treatments T1 and T2. It showed that the accumulation rate of MDA content of treatment T3 was higher than those of treatments T1 and T2.
Effects of planting density on agronomic traits and yield of buckwheat
It can be seen from Table 2 that the plant height of buckwheat treated with T3 was significantly lower than those of treatments T1 and T2; the plant stem thickness of treatment T3 was lower than those of treatments T1 and T2, and had a significant difference from treatment T1; treatment T3 had no significant differences in the number of main stem nodes and number of effective branches per plant from treatments T1 and T2; the number of grains per plant and the grain weight per plant were significantly lower in treatment T3 than treatments T1 and T2; the 1 000-grain weight of treatment T3 was lower than those in treatments T1 and T2, and the difference from treatment T2 was significant; and the yield of treatment T3 was lower than those of treatments T1 and T2, and the yield difference between the three treatments were not significant, but the yield of treatment T2 was the highest. The number of grains per plant, grain weight per plant, 1 000-seed weight and yield were all highest in T2, which had no significant differences from treatment T1. It showed that the high-density treatment was not conducive to increasing the number of grains per plant, grain weight per plant, 1 000-grain weight and yield, and the low-density treatment was beneficial to increase the number of grains per plant, grain weight per plant, 1 000-grain weight and yield.
Conclusions and Discussion
Effects of planting density on the physiological indices of buckwheat
The research of Zhang et al.［11］ showed that with the increase of planting density, the chlorophyll content and soluble protein content of wheat flag leaves continued to decrease. Wang［9］ found that the SOD and POD activity of the two kinds of broom corn millet increased with the planting density, the content of MDA increased with the increase of planting density, and the increase of planting density intensified leaf senescence. The research of Hu et al.［13］ showed that the soluble protein content of rice cultivated at the low density increased, the leaf senescence was delayed, and the 1 000-grain weight increased. The study of Du et al.［17］ showed that as the planting density increased, the physiological indices and yield traits of soybean decreased. The results of this study showed that with the increase of planting density, the chlorophyll content and soluble protein content of buckwheat leaves decreased. Meanwhile, the high-density treatment reduced the protective enzyme activity of buckwheat leaves and accelerated the accumulation of MDA content, which is consistent with the results of previous studies. Effects of planting density on agronomic traits and yield of buckwheat
Planting density has a relatively great impact on the agronomic characteristics and yield of buckwheat［18］. The yield of buckwheat increases first and then decreases with the increase of planting density［19-20］. The research of Jiang et al.［21］ showed that the planting density had no significant effect on the plant height, the number of main stem branches and the number of main stem nodes of buckwheat, but it had a significant impact on the yield component factor, grain weight per plant. This study showed that planting density had significant effects on the number of grains per plant and the grain weight per plant of Ningqiao No.1, and the yield increased first and then decreased with the increase of density, which is consistent with the results of previous studies. However, the results of this study showed that density had no significant effect on the yield of buckwheat, which is inconsistent with the results of Wang et al.［19］, which might be caused by the climate of different regions. In this study, Ningqiao No. 1 had been in a drought state during its growth period. Under drought condition, the low-density treatment was beneficial to increasing the number of grains per plant, grain weight per plant, 1 000-grain weight and yield.
References
［1］ LUO YN, ZHANG JH. Effect of planting density on maize leaf senescence［J］. Journal of Maize Sciences, 1994(4): 23-25. (in Chinese)
［2］ HU M. Effect of Density on Photosynthetic and senescence physiology and yield of spring corn［D］. Harbin: Northeast Agricultural University, 2009. (in Chinese)
［3］ YU ZW, YUE SS, SHEN CG, et al. Effects of different densities on leaf senescence and grain weight of winter wheat after flowering［J］. Acta Agronomica Sinica, 1995, 21(4): 412-418. (in Chinese)
［4］ WANG ZH, JIANG LN, LI CX, et al. Effect of planting density and growth regulator on caducity and yield components in wheat ［J］. Crops, 2003(2): 15-17. (in Chinese)
［5］ ZHANG RP, DAI HY, MA J, et al. Effects of different density on some senescence physiology characteristics of flag leaf in colored rice after heading［J］. Journal of Xichang University: Natural Science Edition, 2009, 23(3): 13-16. (in Chinese)
［6］ MA RX, ZHANG AQ, LIU WC. The influence of different density on yield and main physiologcal index of different types of corn variety ［J］. Chinese Agricultural Science Bulletin, 2006(5): 171-173. (in Chinese) ［7］ CHEN SB. Study on Physiological characteristics and yield traits of high oil corn in different densities［D］. Beijing: China Agricultural University, 2005. (in Chinese)
［8］ MA C, HUANG XS, LI PK, et al. Effects of planting density on physiological decline on ear leaf of summer maize ［J］. Journal of Maize Sciences, 2010(2): 50-53. (in Chinese)
［9］ WANG DH. Effect of while film mulch on yield, quality and physiological basis in broomcorn millet under different planting densities［D］. Hohhot: Inner Mongolia Agricultural University, 2015. (in Chinese)
［10］ GUO TC, SHENG K, FENG W, et al. Effects of plant density on physiological characteristics of different stems during tillering stage in two spike-types winter wheat cultivars［J］. Acta Botanica Boreali-Occidentalia Sinica, 2009, 29(2): 350-355. (in Chinese)
［11］ ZHANG YL, XIAO K, LI YM. Effects and physiological mechanism of planting densities on photosynthesis characteristics of flag leaf and grain yield in wheat hybrid C6-38/Py85-1［J］. Acta Agronomica Sinica, 2005, 31(4): 498-505. (in Chinese)
［12］ ZHU CC. Effect of planting density on yield and ecophysiological characteristics in different types of rice with bowl mechanical-transplanting method［D］. Yangzhou: Yangzhou University, 2014. (in Chinese)
［13］ HU WH, WANG XL, LIU ZK. Study on rice physiological characters for different planting density after earing ［J］. Journal of Jilin Agricultural Universit, 2006, 28(6): 594-596,605. (in Chinese)
［14］ CHEN YQ. Biochemical experimental methods and techniques［M］. Beijing: Science Press, 2002. (in Chinese)
［15］ LI HS. Principles and techniques of plant physiological and biochemical experiments［M］. Beijing: Higher Education Press, 2000. (in Chinese)
［16］ GAO JF. Plant physiological experiment guidance［M］. Beijing: World Book Inc, 2001. (in Chinese)
［17］ DU CY, HU XG, HE ZR, et al. Effect of density on soja bean yield and its physiological index ［J］. Inner Mongolia Agricultural Science and Technology, 2006(2): 35-36. (in Chinese)
［18］ YI JL, LI LJ, HUANG YB, et al. Preliminary study on high-yield cultivation techniques of buckwheat［J］. Crop Research, 2007(2): 108-110. (in Chinese)
［19］ WANG C, LI M, WANG SX, et al. Effects of different sowing date,seeding rate and fertilization on yield and agronomic traits of Fagopyrum esculentum Xinnong 1 planted in spring ［J］. Guizhou Agricultural Sciences, 2014, 42(3): 52-55. (in Chinese)
［20］ ZHANG Q, WANG AH, YANG JY. Effect of different zinc concentration and density on biological characteristics and yield of tartary buckwheat［J］. Seed, 2010(11): 9-13. (in Chinese)
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