论文部分内容阅读
Abstract [Objectives]This study was conducted to screen small watermelon varieties suitable for spring greenhouses. [Methods]The field traits， yield traits， quality traits and commodity of 6 new red-flesh watermelon varieties were compared. [Results]"Jingmei 3K" and "Sumeng No.5" had obvious advantages in quality traits， yield traits， and commodity traits. The yield reached 62 163.3 and 63 733.5 kg/hm2， respectively; the single melon weights reached 2.16 and 2.21 kg， respectively; and the central sugar content reached 13.2% and 13.1%， respectively. Meanwhile， the juice contents were high， and the taste was sweet and refreshing. They are suitable for planting under the condition of substrate cultivation technology. [Conclusions]This study provides a theoretical basis for large-area substrate cultivation and production.
Key words Substrate cultivation; Small watermelon; Variety; Screening
As a traditional advantage crop in Beijing， watermelon has obvious industrial advantages. In recent years， with the adjustment and upgrading of Beijing's agricultural structure， higher requirements have been put forward for the standardization and balanced production of watermelon industry， branded and differentiated operation， and ecological and high-efficiency requirements， and the direction for industrial upgrading and development has also been pointed out.
Conventional watermelon cultivation in Beijing area is mainly based on soil cultivation. There are problems such as low utilization of land resources， low utilization of water and fertilizer， high labor intensity， serious soil-borne diseases such as fusarium wilt and nematodes. In addition， planting is based on experience， and the degree of standardization and modernization is not high.
With the gradual development of substrate cultivation in vegetable protected field cultivation in China[1]， the use of substrate cultivation can effectively overcome soil-borne diseases and continuous cropping obstacles， reduce the amount of pesticides， save water and labor， increase the yield per unit area， increase the yield per unit area， and even realize annual planting in facilities that are not suitable for farming or rotation of crops， thereby having obvious comparative advantages with soil cultivation[2]. Therefore， this technology is an effective way to solve the problem of continuous watermelon in facilities. Due to fixed nutrient solution formulas and automatic water and fertilizer irrigation， large-scale and standardized production can be realized， and the product quality is stable， which is conducive to the development of green， safe and efficient watermelon industry[3-7]. Therefore， in the substrate cultivation mode， how to choose suitable planting varieties to achieve the purpose of not only enabling plants to make full use of external conditions such as light， temperature， water， air， and fertilizer， but also increasing their yield and improving quality， is of great significance. However， how to choose suitable varieties will be affected by many factors， such as fertilizer and water management， cultivation techniques， environmental conditions， etc.[8-10].
At present， research at home on the selection of watermelon varieties in facility is mainly carried out under soil cultivation conditions， while there are few researches on substrate cultivation of small watermelons in greenhouses.
In this study， the field traits， yield traits， quality traits， and commercial traits of 6 new red-flesh types of small watermelon varieties were compared， in order to screen out small watermelon varieties suitable for substrate cultivation and provide a theoretical basis for large-scale substrate cultivation.
Materials and Methods
Experimental materials and Experimental location
The main watermelon varieties tested were "Jingmei 1K"， "Jingmei 2K"， "Jingmei 3K"， "Sumeng No.5"， "Sumeng No.6" and "Chaoyuemengxiang"， among which " Chaoyuemengxiang " was the control variety （Table 1）.
Experimental design
The planting method was one ridge with two rows， hanging vine cultivation， and the pruning method is "one main and one side， remaining melons on the main vine". The plant spacing was 35 cm， and the density was 30 000 plants/hm2. The experiment was done in three repetitions， and there were 18 plots in total， each of which covered an area of 37 m2， and planted with 110 plants. In addition to the varieties， the field management measures were the same for all treatments， and micro-spray watering was adopted.
Experimental methods
Greenhouse specifications
The greenhouses were 10 m wide from east to west and 58 m long from north to south. The shed film was made of non-dripping PO film produced by a regular manufacturer， and both sides of the shed film can be ventilated. The experiment used nutrient bowls， nutrient plates， and substrate nutrient soil to grow seedlings， and adopted the technique of contact grafting. The rootstock used was Jingxinzhen No.4.
Cultivation mode
Black cultivation tanks were adopted， and the size of the cultivation tanks was set to 25-30-25 cm. During cultivation， a thickened insect-proof net was laid in each tank， and the substrate was placed on the insect-proof net. Substrate selection
The cultivation substrate formula was peat∶perlite∶vermiculite=7∶3∶4 （w/w）. When mixing the substrate， 33 kg of chicken manure was added per square meter [organic matter content≥20%; PH 5.5-6.5; total nitrogen （calculated in N）≥0.8%; total phosphorus （calculated in P2O5）≥0.3%; total potassium （calculated in K2O）≥0.4%]. The prepared cultivation substrate was disinfected with 800 times dilution of 50% carbendazim wettable powder， and then filled in the cultivation tanks after mixing.
Water and fertilizer system
Two drip irrigation belts were laid in parallel in each cultivation tank. The diameter of the drip irrigation belts was 15 mm， and the water outlets were separated by 30 cm. A precision fertilization system was used to make the water outlet of each drip irrigation belt uniform， and a filter device was installed to prevent the water outlets from clogging.
pH and EC control
EC value： The EC value during the entire growth period was controlled in the range of 1.5-2.5 ms/cm. The EC value in the seedling stage was controlled in the range of 1.5-1.8 ms/cm; the EC value in the vine-stretching stage was controlled in the range of 1.8-2.0 ms/cm; and the EC value in the fruit setting stage was controlled in the range of 2.0-2.5 ms/cm.
pH value： The pH value of the whole growth period was controlled in the range of 5.5-6.0. The pH value at the seedling stage was controlled in the range of 5.5-5.8; the pH value at the vine-stretching stage was controlled in the range of 5.8-6.0; and the pH at the fruit setting stage was controlled in the range of 5.8-6.0.
Disease and pest control
During the vine-stretching and fruit-bearing stages， agents such as score， chlorothalonil and triadimefon were applied to control powdery mildew and spider mites; imidacloprid was used to control aphids; and Gongfu water aqua was used to control cotton bollworms and tobacco budworms. The plants was planted in the field on March 15， pollinated on April 16， and harvested on May 25.
Investigation indicators and determination methods
Investigation time
The growth period investigation time was from January to May; the field trait investigation time was from March to May; the yield and quality trait investigation time was May; and the disease resistance investigation time was from January to May. The disease resistance of each variety （divided into 5 grades： strong， moderately strong， moderate， moderately weak and weak） was visually inspected three times， i.e.， at the seedling stage， fruit setting stage and fruit ripening stage， mainly for such four kinds as anthracnose， fusarium wilt， gummy stem blight and virus diseases. Calculation formula
Survival rate （%） = Number of surviving plants/Total number of plants investigated×100
Fruit setting rate （%） = Number of fruits set/Total number of plants investigated×100
Rate of deformed fruits （%） = Number of deformed fruits/Total number of plants investigated×100
Determination methods
During the maturity period， 5 mature fruits were randomly selected from each plot to calculate the average fruit weight; 10 representative fruits were selected from each plot during the fruit maturity period to measure the flesh thickness， fruit shape index， and soluble solid content， and the averages were taken; and the taste was recorded. Various plots were harvested， separately. The actual yield was recorded.
Data processing
The test data was analyzed by SAS software for variance analysis， and Duncan's new multiple range method （P<0.05） was used for significance test.
Results and Analysis
Comparison of main traits in the field
It can be seen from Table 2 that under the condition of consistent field management measures， the fruit development period of each variety ranged from 35 to 37 d. Among them， the fruit development period of Jingmei 1K and Sumeng No.6 was the shortest， being 35 d; the next was Chaoyuemengxiang and Jingmei 2K， the fruit development period of which was 36 d; and the third was Jingmei 3K and Sumeng No.5， the fruit development period of which was 37 d. The whole growth period of each variety had the same trend as the fruit development period. The fruit-setting nodes of various varieties ranged from 13.2-14.2： Sumeng No.6 had the best fruit-setting properties， and the fruit-setting node was 13.2. Jingmei 2K had the highest fruit setting node at 14.2. The interval between female flowers of each variety ranged from 6.3 to 6.9： the interval between female flowers of Sumeng No.6 was the smallest， at 6.3， and the interval between female flowers of Sumeng No.5 was the largest， at 6.9; and the values of other 4 varieties were between 6.5 and 6.8. The differences between varieties were not significant. The growth of the plants of various varieties was inconsistent. Among the difference varieties， Chaoyuemengxiang and Sumeng No.6 grew weakly， Jingmei 2K grew more prosperously， and other three varieties grew moderately.
Comparison of yield traits
Yield
It can be seen from Table 3 that the plot of Sumeng No.5 had the highest yield， which was 236.05 kg， which was significantly higher than other varieties; and the plot of Jingmei 1K had the lowest yield of 168.38 kg. The plot yields of other varieties were in the range of 175.53-230.23 kg. The change trend of yield per unit area was consistent with the plot yield. The yield of Sumeng No.5 was highest， at 63 733.5 kg/hm2， followed by Jingmei 3K which was 62 163.3 kg/hm2， and the yields of the remaining 4 varieties were between 45 463.35 and 55 772.10 kg/hm2. Sumeng No.6 and Jingmei 1K showed lower yields， only 47 394.42 and 45 463.35 kg/hm2， respectively， which were significantly lower than other varieties. Single fruit weight
It can be seen from Table 2 that the average single fruit weights of different watermelon varieties ranked from high to low： Sumeng No.5 （2.21 kg）>Jingmei 3K （2.16 kg）>Jingmei 2K（1.95 kg）>Chaoyuemengxiang （1.73 kg）>Sumeng No.6 （1.63 kg）>Jingmei 1K （1.57 kg）. Among them， Sumeng No.5 had the highest single fruit weight of 2.21 kg， while Jingmei 1K and Sumeng No.6 showed lower single fruit weights and poor yielding ability. The fruit setting rates of various varieties ranged from 96.3% to 97.9%. The fruit setting rate of Sumeng No.6 was the highest， at 97.9%， while Jingmei 2K had the lowest fruit setting rate of 96.3%. The differences in fruit setting rate between the various varieties were not significant.
Comparison of fruit commodity traits
It can be seen from Table 4 that among the 6 tested varieties， Zhongjingmei 1K and Sumeng No.6 were round in appearance， and the remaining 4 varieties were oval; and the background color of Sumeng No.5 was light green covered with green fine-toothed stripes， and the rest were green background with dark green fine-toothed stripes or dark green in peel color. The fruit shape indexes were in the range of 1.04-1.50. The fruit shape indexes of Jingmei 3K and Sumeng No.5 were higher， 1.50 and 1.42， respectively; and the fruit shape index of Jingmei 1K was the lowest， at 1.04. Through comprehensive comparison of fruit characteristics， it could be seen that Jingmei 3K's peel was bright green， with clear and neat stripes， hot pink flesh， exhibiting good commodity， and the peel hardness also reached 1.41 kg/cm2.
Fruit quality comparison
It can be seen from Table 5 that the contents of soluble solids in the center of Jingmei 3K reached 13.20%， which was higher than other varieties; and Sumeng No.5 took the second place， with a central soluble solid content of 13.10%. The central soluble solid contents of Jingmei 1K and Sumeng No.6 also reached 13%， and they belong to the small watermelon varieties with high sugar contents. Jingmei 2K had the lowest central soluble solid content of 12.80%. Jingmei 3K showed the smallest difference in soluble solid content between the middle and border areas， at 2.4%; and the largest value was in Jingmei 2K， which was 2.7%. Jingmei 3K and Chaoyuemengxiang had better flesh quality and taste. The peel thicknesses of the 6 varieties were between 0.45 and 0.58 cm， and Sumeng No.6 had the thinnest peel of 0.45 cm.
Discussion and Conclusions Conventional watermelon cultivation in Beijing area is mainly based on soil cultivation， and there are problems such as low land resource utilization， low water and fertilizer utilization， high labor intensity， and serious soil-borne diseases such as fusarium wilt and nematodes. Substrate cultivation is an effective way to solve the problem of continuous watermelon setting in facilities. Through the comparison test of small watermelon under the condition of substrate cultivation technology， the results showed that "Jingmei 3K" and "Sumeng No.5" belong to crack-tolerant and crispy-flesh varieties， which are obviously advantageous in quality traits， yield traits， and commodity. Their yields per unit area reached 62 163.3 and 63 733.5 kg/hm2， respectively; the single melon weights reached 2.16 and 2.21 kg， respectively; and the central sugar contents reached 13.2% and 13.1%， respectively. Meanwhile， they had high juice contents and tasted sweet and refreshing. Therefore， "Jingmei 3K" and "Sumeng No.5" are suitable for planting under the condition of substrate cultivation technology.
References
[1]LIU W， YU HJ， JIANG WJ， et al. Review on research progress and application of growing media for vegetable production in China[J]. Chinese Journal of Eco-Agriculture， 2006， 14（3）： 4-7. （in Chinese）
[2]LI SJ， GAO LH， ZHUANG ZL. Achtievement new technology of the recent past in soilless culture in china and its trend[J]. Journal of Changjiang Vegetables， 1997（5）： 1-5. （in Chinese）
[3]MA C， ZENG JB， ZENG X， et al. Early hanging-vine and dense-planting cultivation techniques of small watermelon in spring greenhouse in Beijing area[J]. China Vegetables， 2014（1）： 83-85. （in Chinese）
[4]TIAN JL， WANG YH. Current situations and prospects of researches on soilless-culture substrates[J]. Acta Agriculturae Shanghai， 2000， 16（4）： 87-92. （in Chinese）
[5]ZUO SP. Organic ecological soilless cultivation techniques of small watermelon[J]. Zhongguo Gua-cai， 2006（5）： 36-37. （in Chinese）
[6]ZHANG BD， CUI GL， JIA WH， et al. Soilless hanging-vine cultivation techniques of small fruit watermelon in multi-span greenhouse[J]. China Cucurbits and Vegetables， 2017（5）： 42-44 （in Chinese）
[7]GONG HG. Study on organic soilless hanging vines cultivation techniques of watermelon[J]. Horticulture & Seed， 2014（12）： 41-43. （in Chinese）
[8]MA C， ZHU L， SENG JB， et al. Mixed substrate soilless cultivation techniques for mini water-melon in spring greenhouse of Beijing area[J]. Journal of Agricultural Science and Technology， 2017（12）： 2282-2285. （in Chinese）
[8]MA C， ZHU L， ZENG JB， et al. Control methods and data analysis of environmental factors of facilities watermelon in Beijing area[J]. Northern Horticulture， 2017（18）： 85-89. （in Chinese）
[9]JIANG WJ， DENG J， YU HJ. Development situation， problems and suggestions on industrial development of protected horticulture[J]. Scientia Agricultura Sinica， 2015， 48（17）： 3515-3523. （in Chinese）
[10]MA C， ZHU L， ZENG JB， et al. Study on the comparative experiment of different kinds of basal fertilizer applied to watermelon[J]. Chinese Horticulture Abstracts， 2015（10）： 17-19， 62. （in Chinese）
Key words Substrate cultivation; Small watermelon; Variety; Screening
As a traditional advantage crop in Beijing， watermelon has obvious industrial advantages. In recent years， with the adjustment and upgrading of Beijing's agricultural structure， higher requirements have been put forward for the standardization and balanced production of watermelon industry， branded and differentiated operation， and ecological and high-efficiency requirements， and the direction for industrial upgrading and development has also been pointed out.
Conventional watermelon cultivation in Beijing area is mainly based on soil cultivation. There are problems such as low utilization of land resources， low utilization of water and fertilizer， high labor intensity， serious soil-borne diseases such as fusarium wilt and nematodes. In addition， planting is based on experience， and the degree of standardization and modernization is not high.
With the gradual development of substrate cultivation in vegetable protected field cultivation in China[1]， the use of substrate cultivation can effectively overcome soil-borne diseases and continuous cropping obstacles， reduce the amount of pesticides， save water and labor， increase the yield per unit area， increase the yield per unit area， and even realize annual planting in facilities that are not suitable for farming or rotation of crops， thereby having obvious comparative advantages with soil cultivation[2]. Therefore， this technology is an effective way to solve the problem of continuous watermelon in facilities. Due to fixed nutrient solution formulas and automatic water and fertilizer irrigation， large-scale and standardized production can be realized， and the product quality is stable， which is conducive to the development of green， safe and efficient watermelon industry[3-7]. Therefore， in the substrate cultivation mode， how to choose suitable planting varieties to achieve the purpose of not only enabling plants to make full use of external conditions such as light， temperature， water， air， and fertilizer， but also increasing their yield and improving quality， is of great significance. However， how to choose suitable varieties will be affected by many factors， such as fertilizer and water management， cultivation techniques， environmental conditions， etc.[8-10].
At present， research at home on the selection of watermelon varieties in facility is mainly carried out under soil cultivation conditions， while there are few researches on substrate cultivation of small watermelons in greenhouses.
In this study， the field traits， yield traits， quality traits， and commercial traits of 6 new red-flesh types of small watermelon varieties were compared， in order to screen out small watermelon varieties suitable for substrate cultivation and provide a theoretical basis for large-scale substrate cultivation.
Materials and Methods
Experimental materials and Experimental location
The main watermelon varieties tested were "Jingmei 1K"， "Jingmei 2K"， "Jingmei 3K"， "Sumeng No.5"， "Sumeng No.6" and "Chaoyuemengxiang"， among which " Chaoyuemengxiang " was the control variety （Table 1）.
Experimental design
The planting method was one ridge with two rows， hanging vine cultivation， and the pruning method is "one main and one side， remaining melons on the main vine". The plant spacing was 35 cm， and the density was 30 000 plants/hm2. The experiment was done in three repetitions， and there were 18 plots in total， each of which covered an area of 37 m2， and planted with 110 plants. In addition to the varieties， the field management measures were the same for all treatments， and micro-spray watering was adopted.
Experimental methods
Greenhouse specifications
The greenhouses were 10 m wide from east to west and 58 m long from north to south. The shed film was made of non-dripping PO film produced by a regular manufacturer， and both sides of the shed film can be ventilated. The experiment used nutrient bowls， nutrient plates， and substrate nutrient soil to grow seedlings， and adopted the technique of contact grafting. The rootstock used was Jingxinzhen No.4.
Cultivation mode
Black cultivation tanks were adopted， and the size of the cultivation tanks was set to 25-30-25 cm. During cultivation， a thickened insect-proof net was laid in each tank， and the substrate was placed on the insect-proof net. Substrate selection
The cultivation substrate formula was peat∶perlite∶vermiculite=7∶3∶4 （w/w）. When mixing the substrate， 33 kg of chicken manure was added per square meter [organic matter content≥20%; PH 5.5-6.5; total nitrogen （calculated in N）≥0.8%; total phosphorus （calculated in P2O5）≥0.3%; total potassium （calculated in K2O）≥0.4%]. The prepared cultivation substrate was disinfected with 800 times dilution of 50% carbendazim wettable powder， and then filled in the cultivation tanks after mixing.
Water and fertilizer system
Two drip irrigation belts were laid in parallel in each cultivation tank. The diameter of the drip irrigation belts was 15 mm， and the water outlets were separated by 30 cm. A precision fertilization system was used to make the water outlet of each drip irrigation belt uniform， and a filter device was installed to prevent the water outlets from clogging.
pH and EC control
EC value： The EC value during the entire growth period was controlled in the range of 1.5-2.5 ms/cm. The EC value in the seedling stage was controlled in the range of 1.5-1.8 ms/cm; the EC value in the vine-stretching stage was controlled in the range of 1.8-2.0 ms/cm; and the EC value in the fruit setting stage was controlled in the range of 2.0-2.5 ms/cm.
pH value： The pH value of the whole growth period was controlled in the range of 5.5-6.0. The pH value at the seedling stage was controlled in the range of 5.5-5.8; the pH value at the vine-stretching stage was controlled in the range of 5.8-6.0; and the pH at the fruit setting stage was controlled in the range of 5.8-6.0.
Disease and pest control
During the vine-stretching and fruit-bearing stages， agents such as score， chlorothalonil and triadimefon were applied to control powdery mildew and spider mites; imidacloprid was used to control aphids; and Gongfu water aqua was used to control cotton bollworms and tobacco budworms. The plants was planted in the field on March 15， pollinated on April 16， and harvested on May 25.
Investigation indicators and determination methods
Investigation time
The growth period investigation time was from January to May; the field trait investigation time was from March to May; the yield and quality trait investigation time was May; and the disease resistance investigation time was from January to May. The disease resistance of each variety （divided into 5 grades： strong， moderately strong， moderate， moderately weak and weak） was visually inspected three times， i.e.， at the seedling stage， fruit setting stage and fruit ripening stage， mainly for such four kinds as anthracnose， fusarium wilt， gummy stem blight and virus diseases. Calculation formula
Survival rate （%） = Number of surviving plants/Total number of plants investigated×100
Fruit setting rate （%） = Number of fruits set/Total number of plants investigated×100
Rate of deformed fruits （%） = Number of deformed fruits/Total number of plants investigated×100
Determination methods
During the maturity period， 5 mature fruits were randomly selected from each plot to calculate the average fruit weight; 10 representative fruits were selected from each plot during the fruit maturity period to measure the flesh thickness， fruit shape index， and soluble solid content， and the averages were taken; and the taste was recorded. Various plots were harvested， separately. The actual yield was recorded.
Data processing
The test data was analyzed by SAS software for variance analysis， and Duncan's new multiple range method （P<0.05） was used for significance test.
Results and Analysis
Comparison of main traits in the field
It can be seen from Table 2 that under the condition of consistent field management measures， the fruit development period of each variety ranged from 35 to 37 d. Among them， the fruit development period of Jingmei 1K and Sumeng No.6 was the shortest， being 35 d; the next was Chaoyuemengxiang and Jingmei 2K， the fruit development period of which was 36 d; and the third was Jingmei 3K and Sumeng No.5， the fruit development period of which was 37 d. The whole growth period of each variety had the same trend as the fruit development period. The fruit-setting nodes of various varieties ranged from 13.2-14.2： Sumeng No.6 had the best fruit-setting properties， and the fruit-setting node was 13.2. Jingmei 2K had the highest fruit setting node at 14.2. The interval between female flowers of each variety ranged from 6.3 to 6.9： the interval between female flowers of Sumeng No.6 was the smallest， at 6.3， and the interval between female flowers of Sumeng No.5 was the largest， at 6.9; and the values of other 4 varieties were between 6.5 and 6.8. The differences between varieties were not significant. The growth of the plants of various varieties was inconsistent. Among the difference varieties， Chaoyuemengxiang and Sumeng No.6 grew weakly， Jingmei 2K grew more prosperously， and other three varieties grew moderately.
Comparison of yield traits
Yield
It can be seen from Table 3 that the plot of Sumeng No.5 had the highest yield， which was 236.05 kg， which was significantly higher than other varieties; and the plot of Jingmei 1K had the lowest yield of 168.38 kg. The plot yields of other varieties were in the range of 175.53-230.23 kg. The change trend of yield per unit area was consistent with the plot yield. The yield of Sumeng No.5 was highest， at 63 733.5 kg/hm2， followed by Jingmei 3K which was 62 163.3 kg/hm2， and the yields of the remaining 4 varieties were between 45 463.35 and 55 772.10 kg/hm2. Sumeng No.6 and Jingmei 1K showed lower yields， only 47 394.42 and 45 463.35 kg/hm2， respectively， which were significantly lower than other varieties. Single fruit weight
It can be seen from Table 2 that the average single fruit weights of different watermelon varieties ranked from high to low： Sumeng No.5 （2.21 kg）>Jingmei 3K （2.16 kg）>Jingmei 2K（1.95 kg）>Chaoyuemengxiang （1.73 kg）>Sumeng No.6 （1.63 kg）>Jingmei 1K （1.57 kg）. Among them， Sumeng No.5 had the highest single fruit weight of 2.21 kg， while Jingmei 1K and Sumeng No.6 showed lower single fruit weights and poor yielding ability. The fruit setting rates of various varieties ranged from 96.3% to 97.9%. The fruit setting rate of Sumeng No.6 was the highest， at 97.9%， while Jingmei 2K had the lowest fruit setting rate of 96.3%. The differences in fruit setting rate between the various varieties were not significant.
Comparison of fruit commodity traits
It can be seen from Table 4 that among the 6 tested varieties， Zhongjingmei 1K and Sumeng No.6 were round in appearance， and the remaining 4 varieties were oval; and the background color of Sumeng No.5 was light green covered with green fine-toothed stripes， and the rest were green background with dark green fine-toothed stripes or dark green in peel color. The fruit shape indexes were in the range of 1.04-1.50. The fruit shape indexes of Jingmei 3K and Sumeng No.5 were higher， 1.50 and 1.42， respectively; and the fruit shape index of Jingmei 1K was the lowest， at 1.04. Through comprehensive comparison of fruit characteristics， it could be seen that Jingmei 3K's peel was bright green， with clear and neat stripes， hot pink flesh， exhibiting good commodity， and the peel hardness also reached 1.41 kg/cm2.
Fruit quality comparison
It can be seen from Table 5 that the contents of soluble solids in the center of Jingmei 3K reached 13.20%， which was higher than other varieties; and Sumeng No.5 took the second place， with a central soluble solid content of 13.10%. The central soluble solid contents of Jingmei 1K and Sumeng No.6 also reached 13%， and they belong to the small watermelon varieties with high sugar contents. Jingmei 2K had the lowest central soluble solid content of 12.80%. Jingmei 3K showed the smallest difference in soluble solid content between the middle and border areas， at 2.4%; and the largest value was in Jingmei 2K， which was 2.7%. Jingmei 3K and Chaoyuemengxiang had better flesh quality and taste. The peel thicknesses of the 6 varieties were between 0.45 and 0.58 cm， and Sumeng No.6 had the thinnest peel of 0.45 cm.
Discussion and Conclusions Conventional watermelon cultivation in Beijing area is mainly based on soil cultivation， and there are problems such as low land resource utilization， low water and fertilizer utilization， high labor intensity， and serious soil-borne diseases such as fusarium wilt and nematodes. Substrate cultivation is an effective way to solve the problem of continuous watermelon setting in facilities. Through the comparison test of small watermelon under the condition of substrate cultivation technology， the results showed that "Jingmei 3K" and "Sumeng No.5" belong to crack-tolerant and crispy-flesh varieties， which are obviously advantageous in quality traits， yield traits， and commodity. Their yields per unit area reached 62 163.3 and 63 733.5 kg/hm2， respectively; the single melon weights reached 2.16 and 2.21 kg， respectively; and the central sugar contents reached 13.2% and 13.1%， respectively. Meanwhile， they had high juice contents and tasted sweet and refreshing. Therefore， "Jingmei 3K" and "Sumeng No.5" are suitable for planting under the condition of substrate cultivation technology.
References
[1]LIU W， YU HJ， JIANG WJ， et al. Review on research progress and application of growing media for vegetable production in China[J]. Chinese Journal of Eco-Agriculture， 2006， 14（3）： 4-7. （in Chinese）
[2]LI SJ， GAO LH， ZHUANG ZL. Achtievement new technology of the recent past in soilless culture in china and its trend[J]. Journal of Changjiang Vegetables， 1997（5）： 1-5. （in Chinese）
[3]MA C， ZENG JB， ZENG X， et al. Early hanging-vine and dense-planting cultivation techniques of small watermelon in spring greenhouse in Beijing area[J]. China Vegetables， 2014（1）： 83-85. （in Chinese）
[4]TIAN JL， WANG YH. Current situations and prospects of researches on soilless-culture substrates[J]. Acta Agriculturae Shanghai， 2000， 16（4）： 87-92. （in Chinese）
[5]ZUO SP. Organic ecological soilless cultivation techniques of small watermelon[J]. Zhongguo Gua-cai， 2006（5）： 36-37. （in Chinese）
[6]ZHANG BD， CUI GL， JIA WH， et al. Soilless hanging-vine cultivation techniques of small fruit watermelon in multi-span greenhouse[J]. China Cucurbits and Vegetables， 2017（5）： 42-44 （in Chinese）
[7]GONG HG. Study on organic soilless hanging vines cultivation techniques of watermelon[J]. Horticulture & Seed， 2014（12）： 41-43. （in Chinese）
[8]MA C， ZHU L， SENG JB， et al. Mixed substrate soilless cultivation techniques for mini water-melon in spring greenhouse of Beijing area[J]. Journal of Agricultural Science and Technology， 2017（12）： 2282-2285. （in Chinese）
[8]MA C， ZHU L， ZENG JB， et al. Control methods and data analysis of environmental factors of facilities watermelon in Beijing area[J]. Northern Horticulture， 2017（18）： 85-89. （in Chinese）
[9]JIANG WJ， DENG J， YU HJ. Development situation， problems and suggestions on industrial development of protected horticulture[J]. Scientia Agricultura Sinica， 2015， 48（17）： 3515-3523. （in Chinese）
[10]MA C， ZHU L， ZENG JB， et al. Study on the comparative experiment of different kinds of basal fertilizer applied to watermelon[J]. Chinese Horticulture Abstracts， 2015（10）： 17-19， 62. （in Chinese）