Effects of Different Water-saving Irrigation Methods on Fruit Quality and Yield of Snow Melon

Xiudong SUN Yafei SUN Zhongmou CHENG Weiqin XU Lili ZHOU Meixian GU Anna Guo Tingting JIANG Dongju ZHANG

Abstract ［Objectives］ This study was conducted to explore the most suitable irrigation integration mode for "Tinglin snow melon" in Jinshan District, Shanghai City.

［Methods］With the field water holding capacity as the standard, different upper limits of irrigation were set in the four growth stage of snow melon to investigate the effects of such three water-saving irrigation modes as single-row drip irrigation pipes, double-row drip irrigation pipes and drip arrows on the traits and yield of melon plants under the same growth conditions.

［Results］ The results showed that different irrigation modes had certain effects on the growth, comprehensive quality and yield of snow melon, and the drop arrow mode was better than other two modes. Under the drop arrow mode, the number of snow melons was the highest, 7.34 per plant, and the yield was the highest, reaching 15 463.35 kg/hm2, showing the best yield increasing effect. In addition, the contents of soluble solids and vitamin C in the drop arrow mode were higher than those in the drip irrigation pipe mode.

［Conclusions］Compared with other irrigation methods, the drop arrow mode was more suitable for the production of snow melon.

Key words Snow melon; Drop irrigation; Irrigation method; Waster use efficiency; Quality

Received: February 12, 2021  Accepted: April 13, 2021

Supported by Shanghai Agriculture Applied Technology Development Program, China(Grant No.T20180304); Jinshan District Science and Technology Innovation Fund Project(Grant No.T20200115).

Xiudong SUN (1963-), male, P. R. China, associate professor, facilities agriculture and equipment application.

*Corresponding author. E-mail: jiangting71@163.com; zhangdongju521@163.com.

"Tinglin snow melon" is a precious farm melon variety in Shanghai, as well as one of the four famous melons in Shanghai. It is famous for its tenderness, crispness, sweetness and refreshing taste. It has been registered as a geographical indication of agricultural products by the Ministry of Agriculture and is an ideal variety for "famous, special and excellent" agriculture. In recent years, with the gradual expansion of the planting scale of "Tinglin snow melon", it has gradually moved towards the direction of industrialization. However, under the traditional cultivation and management mode, the yield and quality characteristics of the melon are extremely unstable. It is difficult for extensive irrigation methods such as traditional channel irrigation and sprinkler irrigation to achieve better water-saving and production-increasing benefits, because these methods have low effective water control capability, and face many problems such as labor consuming, snow melon cracking, and frequent pests and diseases. Therefore, carrying out experiments on the suitable irrigation methods of snow melon in the greenhouse and studying the effects of several different water-saving irrigation methods on the growth of snow melon can provide a theoretical basis for exploring the irrigation methods of snow melon in the greenhouse in Tinglin Town, Jinshan District.

Materials and Methods

General situation of the experimental area

The experimental area was located in Hougang Village, Tinglin Town, Shanghai, in the southern part of the butterfly-shaped depression in the Taihu Lake Basin. The cultivated soil was paddy soil, which was highly matured, with high soil organic matter content and slightly high groundwater level［2］. The region has a subtropical monsoon climate, with warm temperature and more rain, four distinct seasons, abundant rain, and sufficient sunlight. The soil had medium fertility, which was conducive to the ripeness, high quality and high yield of snow melons. The annual average rainfall is 1 127.3 mm, and the evaporation is 896.41 mm; the frost-free period is longer; the annual average temperature is 15.7 ℃; the annual sunshine is 1 572.83 h; and the soil bulk density is 1.3 g/cm3, and the field maximum water holding rate is 45%.

Experimental design

The experiment was carried out at Tingzhong Xuegua Base in Jinshan District, Shanghai from March to June 2019. The tested variety was "Tinglin snow melon". The experimental field was divided into three plots, each of which was 30 m long and 2.5 m wide. 75 plants of snow melon were planted in each plot. The experimental treatments were as follows:

T0: Huawei 1 600 drip irrigation pipes laid under the film in a single row with a distance between water drippers of 40 cm, used with a dripper flow rate at 2 L/h.

T1: Huawei 1 600 drip irrigation pipes laid under the film in double rows with a distance between water drippers of 40 cm, used with a dripper flow rate at 2 L/h.

T2: Huawei 1 828 pressure-compensated drippers equipped with four-out-of-one drop arrows laid on the ground in a single row according to one set per plant with a distance between water drippers of 40 cm, used with a dripper flow rate at 4 L/h.

The water and fertilizer integrated system was installed in the greenhouse, and solenoid valves were used for automatic control. A valve and a water meter were installed at the foot of the big greenhouse to control irrigation and fertilization and record the flow rate. The solenoid valves were opened, and the water flowed into each plot through the field pipe network and the irrigation device.

"Tinglin snow melon" seedlings were raised in the greenhouse in January 2019, and transplanted on March 22, with a row spacing of 40 cm×300 cm. Each plot (double-layer shed 40 m×8 m) was planted with 75 melon seedlings. Before transplanting, deep plowing and soil preparation were performed, followed by fertilization with finished organic fertilizer based on cow dung at 2-3 t/shed+compound fertilizer (15-15-15) 15 kg/shed+sheep dung 200-250 kg/shed+soybean meal powder 40-50 kg/shed. The drip pipes and black plastic films were laid according to the experimental treatments. The drip pipes of treatments T0 and T1 were laid under the film. For treatment T2, PE pipes were laid on the film and installed with 1828 pressure-compensated drippers and four-out-of-one drop arrows. After transplanting the melon seedlings, small arch sheds were built and covered with films to increase the ground temperature and growth environment temperature, which was conducive to the growth of melons. In order to ensure the survival rate of melon seedlings, unified irrigation was performed during this period. After 10 d, irrigation was carried out according to different treatments during the seedling stage, flowering and fruit-setting stage, expansion stage (young fruit grew up to the size of an egg), and maturity stage. The harvest began in early June.

The fertilization was carried out using a Xigengtian Yunzhihui Fertilizer Applicator by plot. Snow melon was cultivated by the double-vine pruning method, planted in three rows, and a full-film mulching cultivation mode was adopted. All other field management (weeding, fertilization, spraying, pruning, vine pressing, etc.) measures were the same.

The experimental design divided the growth period of snow melon into four stages: the seedling stage, the flowering and fruit-setting stage, the expansion stage and the maturity stage.  The upper limit of irrigation control was set according to four stages. Before and after each implementation, the soil water contents at the depth of 0-10 cm and 10-20 cm soil layer were measured. Treatment dates: from March 22 to June 10, 2019, April 25, irrigation treatment during the flowering and fruit-bearing period, May 8 and May 18, irrigation treatment during the fruit expansion period, and May 31 during the maturity period.

Item determination

Soil moisture content determination

A soil moisture content meter was used to determine the moisture content. Two points are selected for the observation of each treatment. The observation depths were set as shown in Table 2. Observation was performed every 10 d, and additional measurements were made before and after irrigation and at the beginning and end of each stage.

Irrigation amount measurement

The irrigation volume was determined according to the field water holding capacity and soil moisture content. The irrigation volume of each treatment was calculated by a water meter, and the values before and after each irrigation, the irrigation time and the irrigation dates were recorded. Irrigation should be carried out separately, and the amount of irrigation should be consistent.

Plant growth traits

In each plot, 10 fixed plants of snow melon were selected as the test samples, and physiological indexes such as the diameter of snow melons, leaf thickness, number of melons set and number of cracked melons were measured, and the average values were taken. The measurement was performed once every 10 d. The stem thickness and leaf thickness were measured with vernier calipers, and the stem thickness between the fifth and sixth nodes of the melon plant level and the leaf thickness at the fifth node were measured. The same part was selected for corresponding measurement each time.

Yield

After the fruit expansion stage began, the longitudinal and transverse diameters of melons were measured with vernier calipers (accuracy 0.01 mm), and the fruit shape index (fruit longitudinal diameter/transverse diameter) was calculated. The measurement was performed once every 7-10 d, a total of 4 times, so as to record the dynamic growth and changes of snow melon fruit. After the melons were mature, 10 melon plants were randomly selected from each plot for yield measurement. The single melon mass was measured, and the number of melons set, the number of cracked melons and the number of shrunken melons in each plot were counted. The yield per plot was calculated, and converted to yield per unit area.

Fruit quality

Five plants were randomly selected from the mature area of each plot, and the melon fruit at the same location with the same color and size were selected, and homogenized for the determination of fruit quality. The determined indexes included soluble sugar content, titratable acid content, soluble solids, fruit firmness, and vitamin C content. The soluble sugar content was determined by the anthrone colorimetry method; the titratable acid content was determined by the standard sodium hydroxide solution titration method; the vitamin C content was determined by the spectrophotometer method; and the soluble solid content was determined by a handheld sugar content detector. Each treatment was determined for 3 times.

Water use efficiency

It was calculated with the ratio of yield to irrigation volume.

Data processing

Excel and SPSS software were employed to perform statistical analysis on the test data (P<0.05), and graphing was performed with graphPad Prism software.

Results and Analysis

Effects of different water-saving irrigation methods on the growth dynamics of snow melon

The stem thicknesses of snow melon under different treatments are shown in Fig. 1. During the whole growth period of the melon, the stem thickness of the melon plants showed a change process from rapidly growth to slow growth, reached its peak in the fruit expansion period (about 60 d after planting), and increased slightly in the maturity stage (Fig. 1). Throughout the growth process, the stem thickness of the plants in treatment T1 always remained higher than T0 and T2, and the differences were significant at 50 d after planting, while the difference between treatments T0 and T2 was not significant. It showed that different irrigation treatments could affect the thickening of the main stems of the melon plants.

During the whole growth period, the leaf thickness of the melon plants treated by various irrigation methods had the same changing trend of continuing to thicken, reaching the maximum during the fruit expansion stage (60 d after planting) and then gradually decreasing (Fig. 2). The differences between various treatments were not significant, indicating that in the later stage of the growth of snow melon, reproductive growth was dominant, and vegetative growth was gradually weakened.

Effects of different water-saving irrigation methods on the growth of snow melon fruit

Fig. 3 and Fig. 4 showed the dynamic changes of the longitudinal and transverse diameters of the melon fruit in each treatment. The growth trends of the melon fruit in various treatments were the same, and they all first experienced a period of rapid expansion, and then entered a period of slow expansion. The differences in the transverse and longitudinal diameters between various treatments were not significant, indicating that the three different water-saving irrigation methods had no obvious effects on the growth of the transverse and longitudinal diameters of the melon fruit. Fruit shape is an important index of the appearance and quality of melons［3］, and it is usually represented by shape index (longitudinal diameter/transverse diameter). The fruit shape indexes of the three treatments were close to 1, indicating that the shape of the melon fruit was approximately round, and the irrigation methods had little effects on the shape of the melon fruit. Fruit firmness is related to the storage tolerance of fruit. The flesh of treatment T2 was relatively firm and the storage tolerance was slightly better. From the point of view of fruit thickness, there were significant differences between treatments. Specifically, treatment T1 is the largest, and T0 was the smallest. There were also significant differences in fruit thickness ratio (fruit thickness/transverse diameter). The period from the flowering stage to the expansion stage of the melon is the period of rapid growth of the melon fruit. During this period, the water treatment of the melon has an important effect on the development of the fruit, and the robustness of the melon plants is the basis for ensuring the rapid expansion of the fruit, so treatment T2 was the most obvious in terms of fruit firmness.

Xiudong SUN et al. Effects of Different Water-saving Irrigation Methods on Fruit Quality and Yield of Snow Melon

Effects of different water-saving irrigation methods on the quality of snow melon fruit

The growth and development stages of snow melon are mainly the accumulation of dry matter, the formation and transformation of sugar and the synthesis of nutritional substances［4］; and under certain conditions, moisture has a greater impact on the formation of melon fruit quality［5］.

Table 4 shows the effects of different water-saving irrigation methods on the quality of melons during the maturity stage. From Table 4, it can be seen that the soluble solid contents of T0 and T2 were higher than that of T1, with significant differences, and the center and the edge data were similar, showing a small difference between the middle and the edge, that is to say, the taste was uniform among various parts. Treatment T1 had the highest titratable acid content, which was significantly different from other treatments, and the vitamin C content of treatment T2 was the highest and had significant differences from other treatments, indicating that the organic acid content and vitamin C content were affected by irrigation methods and had significant differences.

Effects of different water-saving irrigation methods on the yield and water use efficiency of snow melon

From the perspective of different water-saving irrigation methods, under the same irrigation amount, different irrigation methods caused significant differences in the fruit number per plant and single melon mass. Among them, treatment T2 showed a higher single melon mass, most melons per plant, while treatment T1 exhibited fewest melons per plant, as well as the most cracked melons and the lowest yield. The final theoretical yield of T2 was the highest, reaching 15 463.35 kg/hm2. It showed that different irrigation methods had a certain impact on the yield of snow melon.

Water consumption per unit yield refers to the actual irrigation volume per fruit yield, which is obtained from the ratio of actual irrigation volume to yield and can be used to characterize water use efficiency. From the results, it can be seen that the unit yield and water use efficiency were the highest under the condition of the same irrigation amount of T2.

Conclusions and Discussion

Yield, quality and water use efficiency are the main indexes for evaluating the economic benefits of snow melon. Reasonable water management is a necessary condition for plant yield formation and efficient water use［6］. The various growth stages of crops are inseparable from water supply, and different crops have different requirements for water at different growth stages.     Different irrigation modes affect the distribution of water in the soil, and the distribution of water directly affects the distribution of crop roots, which in turn affects the growth and development of crops. The morphology of snow melon mainly includes plant height, stem thickness, leaf thickness, leaf area, fruit number per plant and other agronomics traits. The scientific irrigation mode is conducive to promoting the growth of snow melon plants. The value of crop stem thickness affects the transportation of water and nutrients of the plant. Under the same irrigation conditions, the three water-saving irrigation methods had certain promotion effects on the growth and development of the melon. The results of this study showed that although the laying of drip irrigation pipes in double rows was beneficial to the increase of stem thickness and leaf thickness, which was beneficial to the vegetative growth of the plants, but was not conducive to the improvement of yield and quality in the later stage of growth in view of few melons set and more cracked melons. When choosing double-row drip irrigation pipes for drip irrigation under the mulch, attention should be paid to the mid-term water management of snow melon, and the soil moisture should be controlled during the vegetative growth period, so that the vegetative growth will not be too fast to affect the accumulation of photosynthetic products in the later period.

Dry matter is the basis for the formation of crop yield, and the growth conditions and growth stages of crops will affect the accumulation and distribution of dry matter. Water is the main factor affecting the accumulation and distribution of dry matter in plants. Some studies have shown that under soil drought conditions, crops can redistribute their own assimilate by adjusting their physiological and biochemical reactions, and when the growth environment conditions are appropriate, they will have a certain compensation effect［7-8］. Different irrigation modes cause different soil moisture distribution, and have different effects on the growth and development of snow melon. The dry matter mass of a single plant of "Tinglin snow melon" increases slowly during the vine-stretching period, and rapidly increases after entering the fruit-bearing period. The yield of crops depends on the supply of water, and the volume and uniformity of irrigation water are important factors that affect crop yields. How to use less water to ensure a certain yield of melons and improve water use efficiency is of key significance. The drop arrow mode achieved higher water use efficiency and the highest yield, as well as the fewest cracked melons, so this treatment performed excellent in melon yield and quality. It is speculated that this treatment can bring high economic value to production and help farmers increase income.

Water not only affects the physiological growth of crops, but also regulates the process of biochemical reactions in crop cells, which in turn affects the quality of fruits. Proper irrigation can improve the fruit quality of snow melon. The results of this study indicated that the three modes affected the fruit quality of snow melon, and the yields of snow melon showed similar laws. The drop arrow mode had high contents of soluble solids and vitamin C and could increase the firmness of melon flesh, while the double-row drip irrigation pipes had the highest soluble sugar and titratable acid contents. Therefore, choosing a suitable irrigation mode can not only increase the yield of the melon fruit, but also facilitate the formation of high quality.

Appropriate irrigation can promote the growth, quality and yield of snow melon. Choosing a suitable irrigation method can adjust the process of water use and the distribution of water in the soil, and improve water use efficiency. How to combine water-saving irrigation methods with irrigation systems and cultivation management requires further research on related work.

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