Changes of Soil Water and Heat Transport and Yield of Tomato ( Solanum lycopersicum ) in Greenhouses with Micro-Sprinkler Irrigation under Plastic Film

: This study aimed to expound the changes in soil water ﬂow, heat transport, and tomato production under micro-sprinkler irrigation and plastic ﬁlm (MSPF) conditions. The effects of different irrigation amounts (I1:0.7 Epan; I2:1.0 Epan; and I3:1.2 Epan (Epan is the cumulative evaporation from a 20 cm diameter standard pan, mm)) on soil water, soil temperature, and tomato yield were studied. A completely randomized trial design was used; meanwhile, the drip irrigation under plastic ﬁlm (CK1) and micro-sprinkler irrigation without mulch ﬁlm (CK2) were used as controls. The results showed that the shape of soil moisture was banded under MSPF; the soil wetting range was larger than that of CK1 and CK2 in the proﬁle of MSPF. The change range of 5 cm soil temperature of MSPF 1–5 days after irrigation was 4.05 ◦ C. The change range of 5 cm soil temperature of MSPF was lower than that of CK1 from 1 to 5 days after irrigation. During the growth period of spring and autumn tomato, the average soil moisture content of 0–40 cm with CK1 was 1.97% and 3.83% (spring and autumn, respectively) higher than that of MSPF, and the average soil temperature of 5–25 cm was 2.36% and 1.66% (spring and autumn, respectively) lower than that of MSPF. Compared with CK2, the average soil moisture content of 0–40 cm under MSPF increased by 8.30% and 3.83% (spring and autumn, respectively), and the average soil temperature of 5–25 cm under MSPF increased by 5.85% and 1.68% (spring and autumn, respectively). The spring and autumn tomato yield of MSPF was signiﬁcantly higher than that of CK1 by 19.39% and 4.54%, respectively. The spring and autumn tomato yield of MSPF were higher than that of CK2 by about 20.46% and 49.22%, respectively. With an increase in the irrigation amount of MSPF, the soil moisture and yield of spring and autumn tomato increase; the soil temperature and water use efﬁciency of spring and autumn tomato decrease. Considered comprehensively, the MSPF can be used as one of the methods of greenhouse tomato micro-irrigation, and 1.0 Epan is recommended for irrigation parameters in northwest China facility agriculture.


Introduction
Facility agriculture is the main vegetable production facility in the world, and it also brings huge economic benefits to local farmers [1]. As one of the vegetables often grown in facility agriculture, the demand of tomato is increasing year by year due to its high economic and nutritional value [2]. Water resource management is an important Agronomy 2022, 12, 664 2 of 17 factor to increase tomato yield, especially in northwest China, where there is a serious shortage of water resources [3,4]. Irrigation is the main source of physiological water demand in greenhouse tomatoes with high water demand. Excessive irrigation will reduce water productivity, and too little irrigation will make it difficult to ensure stable tomato production [5]. Therefore, it is necessary to realize precise irrigation of tomato is scarce in the northwest region of China.
Irrigation methods are the way to achieve precise irrigation of greenhouse tomatoes, involving the external form of irrigation water entering the soil in the root zone of the crop [6,7]. Irrigation methods can adjust the soil moisture and heat [8]. In production practice, farmers use different irrigation methods for different crops according to years of planting experience. At present, drip irrigation under plastic film is the most widely used in facility agriculture [9][10][11]. Previous studies have shown that drip irrigation under plastic film can change soil microenvironment, increase soil volume moisture content and soil temperature, and help to increase crop yield compared with conventional drip irrigation [12][13][14].
The irrigation amount is the size of precision irrigation of greenhouse tomato, which directly affects the amount of soil water content and the duration of dry and wet zones after irrigation water enters the soil [15]. Soil temperature is greatly affected by soil water content, and the same temperature difference drives the redistribution of soil moisture [16,17]. Previous studies have found that the soil temperature decreases with the increase in irrigation amount of drip irrigation under plastic film [14]. Drip irrigation under plastic film achieves around 35% of wetted soil which can provide suitable soil moisture and heat conditions [18]. Too high or too low soil moisture in the process of crop planting and irrigation will affect the yield of vegetables [19,20]. For example, the Sensoy [21] experiment showed that the yield of 0.9 Epan with muskmelon was higher than that of 0.6 Epan under drip irrigation; the Luo [22] experiment showed that, with increase in irrigation amount, the yield of tomato will increase, but the water use efficiency of tomato will decrease.
As a new water-saving technology, the micro-sprinkler hose is widely used in the field of food crops due to its simple structure and low investment cost [23,24]. Plastic film technology not only has the effect of heat preservation and moisturization, but also has the effect of increasing yield and improving fruit quality [25,26]. The micro-sprinkler hose and plastic film technology (micro-sprinkler irrigation under plastic film, MSPF) are combined to form porous outflow irrigation under a film pipeline. The MSPF can effectively restrain the problem of high humidity caused by traditional micro-sprinkler hose spray atomization [27]. At present, the application of MSPF has achieved good results in greenhouses growing crops such as cucumber, celery, and watermelon [28][29][30].
At present, the mechanism of greenhouse application of MSPF is not clear. For example, compared with traditional irrigation, what are the similarities and differences of soil water and soil heat dynamic transport of MSPF? How does MSPF affect tomato yield in greenhouse? Additionally, there is a lack of quantitative description of the relationship between soil volume moisture content, soil temperature, and yield under MSPF in greenhouse. Therefore, firstly, the dynamic law of soil water and soil heat transfer under different irrigation amounts under MSPF, drip irrigation with plastic film, and micro-sprinkler irrigation was clarified; secondly, the greenhouse tomato was taken as the research object to explore the characteristics of soil water and soil heat transfer and yield changes in the root zone of tomato under MSPF; Finally, regression analysis was used to quantitatively describe the relationship between soil volume moisture content, soil temperature, and yield of tomato under MSPF. This study provides data support for the sustainable development of the greenhouse tomato industry in this area.

Experimental Site and Management
The experimental greenhouse is located in the Modern Agricultural Science and Technology Exhibition Center of Xi'an City, Shaanxi Province (108 • 52 • E, 34 • 03 • N). The test center has a warm temperate, semi-humid continental monsoon climate, located in the arid and semi-arid regions of northwest China with an altitude of 43,500 cm. The soil volume field capacity is 39.58%, soil volume saturated moisture content is 54.34%, soil wilting volume moisture content is 8.13%, and the greenhouse soil type is sandy loam.
In this experiment, tomato varieties were selected from "Jingfan 401" produced by Jingyan Yinong seed Technology Co., Ltd. (Beijing,·China). Tomatoes were planted in one pipe and two rows on ridges. The plant spacing was 40 cm and the row spacing was 50 cm. A 1 m block copolymer waterproof membrane was embedded in each treatment of the experimental plot to prevent the interaction of horizontal water transport among the plots.
Spring tomatoes were planted on 27 March 2019 and irrigation treatment was initiated on 4 April 2019. The irrigation treatment was continued until 15 July 2019 and tomatoes were completely harvested on 25 July 2019. Autumn tomatoes were planted on 23 August 2019, irrigation treatment was continued between 30 August 2019 and 17 January 2020, and tomatoes were completely harvested on 30 January 2020. The division of growth period of spring and autumn tomato is shown in Table 1. The soil water and heat transfer experiment with different irrigation methods and irrigation amounts lasted 5 days. In order to maintain the soil moisture and consistency of each plot in this experiment, the spring tomatoes were harvested and irrigated 40 mm uniformly in each area on 26 July 2019, and 15 days later irrigation treatment was carried out in each plot. The soil moisture distribution of the soil profile under the emitter (single micropore group) was measured after irrigation with different treatments, and the time was 1, 3, and 5 days, respectively.
The micro-sprinkler hose selected for MSPF is Hebei Plentirain Irrigation Equipment Technology Co., Ltd. (Hebei, China) with thin-walled oblique holes with 3 micropore with a diameter of 32 mm and a micropore diameter of 0.08 cm; the working pressure is 0.60 bar. The drip irrigation used Hebei Plentirain Irrigation Equipment Technology Co., Ltd. (Hebei, China) with a thin-walled labyrinth tooth channel as control. The geometric parameters of the channel were 5.43 × 0.11 × 0.083 cm 3 , the distance between emitters was 30 cm, and the emitter flow rate was 2 L/h. The white agricultural insulation film is produced by Hedong pastoral plastic products factory (Hebei, China).

Experimental Design
Factors including the irrigation amounts of MSPF were set up in this study. The irrigation amount was controlled on the basis of the cumulative evaporation from a 20 cm diameter standard pan (Epan) [31], which was realized by a control coefficient (kcp). The kcp (the crop-pan coefficient) was set to 3 levels: 0.7, 1.0, and 1.2 Epan. Drip irrigation under plastic film (CK1, kcp = 1.0) and micro-sprinkler irrigation (no plastic film, CK2, kcp = 1.0) were used as control treatments. A total of 5 treatments were employed ( Table 2) and each of them was conducted three times, thus making a total of 15 plot. The distance between each plot was 400 cm. Pan evaporation amount was monitored at 8.00 am every fifth day. Equation (1) is used to calculate irrigation amount [19,32,33]. The records of temperature in greenhouses tomato growth period and the irrigation amount in each plot are shown in Figure 1 where W represents the irrigation amount and A represents the area of the plot; the A is 40,800 cm 2 . kcp = 1.0) were used as control treatments. A total of 5 treatments were employed ( Table  2) and each of them was conducted three times, thus making a total of 15 plot. The distance between each plot was 400 cm. Pan evaporation amount was monitored at 8.00 am every fifth day. Equation (1) is used to calculate irrigation amount [19,32,33]. The records of temperature in greenhouses tomato growth period and the irrigation amount in each plot are shown in Figure 1 = × × where W represents the irrigation amount and A represents the area of the plot; the A is 40,800 cm 2 .

Measurements and Computational Methods
(1) Soil moisture (a) Determination of soil moisture during the growth period of tomato in greenhouse Soil moisture sensor (TRIME-PICO-IPH, IMKO, Inc., Ettlingen, Germany) was used to measure soil moisture content. The location of the moisture sensor is shown in Figure  2

Measurements and Computational Methods
Determination of soil moisture during the growth period of tomato in greenhouse Soil moisture sensor (TRIME-PICO-IPH, IMKO, Inc., Ettlingen, Germany) was used to measure soil moisture content. The location of the moisture sensor is shown in Figure 2  soil sampling in the horizontal direction is to start sampling the soil just below the two groups of emitter (single micropore group), and 6 consecutive samples are taken at 5 cm intervals. A total of 48 soil samples were collected from each plot, which was sampled 1, 3, and 5 days after irrigation, and finally converted into volumetric soil water content.
(2) Soil temperature (a) Determination of soil temperature during the growth period of tomato in greenhouse After irrigation, the temperature of soil depth of 5, 15, and 25 cm was measured via geothermometer (Beijing Weixin Yiao Technology Development Co. LTD, Beijing, China). The geothermometer was buried at Position 4 in Figure 2.
Measurement of soil temperature under emitter (single micropore group) After 1, 3, and 5 days of irrigation, the temperatures of 5, 15, and 25 cm soil layers were measured via geothermometer. The ground thermometer was buried in the under emitter (single micropore group).
(3) Yield and water use efficiency (a) Yield When the fruits were ripe, 4 tomato plants were randomly selected in each plot, and the ripe fruits were collected every three days and weighed. The weights were recorded separately and converted into hectare yield (Y, kg/ha).
Water use efficiency Automatic detection of soil moisture was achieved with a soil moisture sensor (TRIME-PICO-IPH, IMKO, Inc., Ettlingen, Germany). The crop water consumption (ET a ) and crop water use efficiency (WUE) were calculated using Equations (2) and (3) [33,35]: In the formula, ET a is crop water consumption during growth period (mm); I is the irrigation quota of spring and autumn tomatoes growth period (mm); H is the depth (H = 80 cm); θ t1 and θ t2 is 0-80 cm average soil volumetric water contents at times t1 and t2 (cm 3 /cm 3 ), respectively.
In the formula, WUE is crop water use efficiency (kg/m 3 ); Y is yield (kg/ha).
(4) Constructional model Firstly, Pearson correlation analysis was carried out between soil volume moisture content/soil temperature and tomato yield in different periods of spring tomato and autumn tomato. Secondly, the data sets with the highest correlation coefficient between soil volume moisture content/soil temperature and tomato yield were selected. Finally, univariate quadratic polynomial regression analysis was carried out between soil volume moisture content and tomato yield of spring tomato and autumn tomato according to Equation (4). Univariate quadratic polynomial regression analysis was carried out between soil temperature and tomato yield of spring tomato and autumn tomato according to Equation (5). y = av 2 + bv + c (4) where y is the yield (kg/ha); v is the soil volume moisture content (%); t is the soil temperature ( • C); and a, b, c, d, e, and f are the parameters.  Figure 2. Schematic diagram of capillary and TRIME tube arrangement (unit: cm). Note: 1-tomat 2-monitoring point, it was arranged at the single micropore group; 3-monitoring point, it w arranged at distance of micro-sprinkler hose 25 cm between the two single micropore groups; 4 geothermometer; 5-single micropore group; and 6-micro-sprinkler hose.
(b) Measurement of soil moisture in the profile under emitter (single micropo group) The soil water distribution of different irrigation methods (MSPF, CK1, and CK2) an the irrigation amount (5, 17, and 29 mm, in which the 17 mm was obtained according the average irrigation amount of 1.0 Epan during 5 days of spring tomato) was main monitored.
This was determined by the drying method. The depth of soil sampling is 80 cm the longitudinal direction, and each 10 cm soil layer is a sample; the soil sampling in th horizontal direction is to start sampling the soil just below the two groups of emitter (si gle micropore group), and 6 consecutive samples are taken at 5 cm intervals. A total of 4 soil samples were collected from each plot, which was sampled 1, 3, and 5 days after irr gation, and finally converted into volumetric soil water content.
(2) Soil temperature (a) Determination of soil temperature during the growth period of tomato in gree house After irrigation, the temperature of soil depth of 5, 15, and 25 cm was measured v geothermometer (Beijing Weixin Yiao Technology Development Co. LTD, Beijing, China The geothermometer was buried at Position 4 in Figure 2. (b) Measurement of soil temperature under emitter (single micropore group) After 1, 3, and 5 days of irrigation, the temperatures of 5, 15, and 25 cm soil laye were measured via geothermometer. The ground thermometer was buried in the und emitter (single micropore group).
(3) Yield and water use efficiency (a) Yield When the fruits were ripe, 4 tomato plants were randomly selected in each plot, an the ripe fruits were collected every three days and weighed. The weights were recorde separately and converted into hectare yield (Y, kg/ha).
(b) Water use efficiency Automatic detection of soil moisture was achieved with a soil moisture sens (TRIME-PICO-IPH, IMKO, Inc., Ettlingen, Germany). The crop water consumption (ET and crop water use efficiency (WUE) were calculated using Equations (2) and (3) [33,35 Schematic diagram of capillary and TRIME tube arrangement (unit: cm). Note: 1-tomato; 2-monitoring point, it was arranged at the single micropore group; 3-monitoring point, it was arranged at distance of micro-sprinkler hose 25 cm between the two single micropore groups; 4-geothermometer; 5-single micropore group; and 6-micro-sprinkler hose.

The Dynamic Distribution of Soil Moisture under Different Treatments
(1) The dynamic movement of soil water under different irrigation methods and irrigation amount The MSPF has greater soil wetness in the tillage layer, and the soil profile of MSPF has a banded shape ( Figure 3). The soil profile water distribution of MSPF is relatively dispersed and there is no area where the water content is too high or too low. The soil profile moisture under CK1 shows an oval distribution. There is an obvious drying zone in drip irrigation under plastic film, in which the soil below the emitter is basically in a state of supersaturation, and the farther away from the emitter, the lower the soil water content. The CK2 increased air humidity, and the distribution of soil profile moisture was similar to that of MSPF, but the soil profile water content in the shallow layer was higher, and lower in the deep layer.
When the irrigation amount is 5 mm, the maximum soil moisture content of the 10 cm soil layer of MSPF, CK1, and CK2 is 32.37, 32.80, and 32.49 mm, respectively, and the minimum soil moisture content of the 10 cm soil layer of MSPF, CK1, and CK2 is 24.73, 22.89, and 23.60 mm, respectively. The range soil moisture content of the 10 cm soil layer of MSPF, CK1, and CK2 are 7.64, 9.91, and 8.89 mm, respectively. When the irrigation amount is 17 mm, the maximum soil moisture content of the 10 cm soil layer of MSPF, CK1, and CK2 is 33.75, 34.74, and 32.49 mm, respectively, and the minimum soil moisture content of the 10 cm soil layer of MSPF, CK1, and CK2 is 26.57, 22.16, and 23.61 mm, respectively. The range soil moisture content of the 10 cm soil layer of MSPF, CK1, and CK2 are 7.18, 12.58, and 8.88 mm, respectively. When the irrigation amount is 29 mm, the maximum soil moisture content of the 10 cm soil layer of MSPF, CK1, and CK2 is 34.88 35.58, and 32.95 mm, respectively, and the minimum soil moisture content of the 10 cm soil layer of MSPF, CK1, and CK2 is 27.88, 24.29, and 26.10 mm, respectively. The range soil moisture content of the 10 cm soil layer of MSPF, CK1, and CK2 are 7.00, 11.29, and 6.85 mm, respectively. This shows that the soil water dispersion uniformity of the tillage layer under MSPF was better than that of drip irrigation under plastic film and micro-sprinkler irrigation.  When the irrigation amount increased from 5 to 29 mm, the soil profile wetting area of MSPF, CK1, and CK2 increased by 47.37%, 70.00%, and 41.67% (p ≤ 0.05), respectively. This shows that MSPF can ensure larger soil wetting volume when the irrigation amount is small. When the irrigation amount is the same, the soil wetting volume decreases with the increase in irrigation duration.
(2) The dynamic change of volumetric soil water content during tomato growth period It can be seen from Figure 4 that closer to the soil surface there is a greater range of volumetric soil water content change during the growth period, which was greatly affected by irrigation, evaporation, and plant transpiration. The changing trend of the volumetric soil water content of the five treatments was basically the same. The change range of volumetric soil water content of spring tomato is higher than that of autumn tomato. In terms of irrigation methods, the average volumetric soil water content of spring and autumn tomato under MSPF was lower than that of CK1 about 1.97% and 3.83%, respectively, but significantly higher than that of micro-sprinkler irrigation by 8.30% and 3.83% (p < 0.05, the average value of 0-40 cm soil layer). During the growth period of tomato, the order of soil range of 0-10 cm was as follows: CK1 > MSPF > CK2 (spring tomato and autumn tomato), and the order of soil range of 10-40 cm was CK2 > MSPF > CK1 (spring tomato) and MSPF > CK1 > CK2 (autumn tomato).  The closer the soil volume water content is to the surface, the greater the variation range is, and the change range does not change with the change of irrigation amount, among which the range of spring and autumn tomatoes at 0-10 cm is 0.117 and 0.075, respectively. With the increase in irrigation amount, the soil volumetric water content showed an increasing trend. Among them, the soil volume water content range of 0-40 cm of I2 spring and autumn tomatoes were higher than that of I1 by about 7.44% and 4.18% (p ≤ 0.05), respectively; the soil volume water content range of 0-40 cm of I2 spring and autumn tomatoes were less than that of I3 by about 6.15% and 3.79% (p ≤ 0.05), respectively. The closer the soil volume water content is to the surface, the greater the variation range is, and the change range does not change with the change of irrigation amount, among which the range of spring and autumn tomatoes at 0-10 cm is 0.117 and 0.075, respectively. With the increase in irrigation amount, the soil volumetric water content showed an increasing trend. Among them, the soil volume water content range of 0-40 cm of I2 spring and autumn tomatoes were higher than that of I1 by about 7.44% and 4.18% Agronomy 2022, 12, 664 9 of 17 (p ≤ 0.05), respectively; the soil volume water content range of 0-40 cm of I2 spring and autumn tomatoes were less than that of I3 by about 6.15% and 3.79% (p ≤ 0.05), respectively.

The Dynamic Distribution Characteristics of Soil Temperature under Different Treatments
(1) The dynamic change of soil temperature under different irrigation methods and irrigation amount It can be seen from Table 3 that the daily change trends of the soil temperature at different depths of the three irrigation methods are basically the same. Taking 17 mm of irrigation amount as an example, the daily fluctuation of soil temperature decreased with the increase in soil depth, and the soil temperature ranges of 5, 15, and 25 cm soil layers were 2.00-4.12 • C, 0.66-1.24 • C, and 0.51-1.10 • C, respectively. The change range of 5 cm soil temperature of MSPF, CK1, and CK2 with 5 days after irrigation was 4.05, 4.12, and 2.02 • C, respectively. This shows that the effect of MSPF on soil temperature was less than that of drip irrigation under plastic film.
When the irrigation amount increased from 5 to 29 mm, the soil temperature of 5 cm decreased by 3.4, 2.33, and 2.93 • C, respectively. With the increase in irrigation amount, the soil temperature of 15 cm decreased by 1.37, 1.72, and 2.94 • C, respectively. When the irrigation amount increased from 15 mm to 29 mm, the soil temperature of 25 cm decreased by 0.47, 1.24, and 1.47 • C, respectively. This shows that the change of irrigation amount of MSPF has a great influence on the temperature of shallow soil.
(2) The dynamic change of soil temperature during tomato growth period It can be seen from Table 4 that solar radiation is the main factor affecting the soil temperature of the greenhouse, and the soil temperature changes synchronously with the change of the greenhouse temperature. Under the same irrigation amount, compared with CK1, the MSPF increases the soil temperature of 5, 15, 25, and 5-25 cm (the 5-25 represents the average of 5 to 25 cm layers, the same as blow) soil layers during the tomato growth period in spring and autumn by 2.32% and 1.36%, 3.21% and 2.93%, 1.63% and 0.68%, and 2.36% and 1.66%, respectively. Compared with CK2, MSPF increases the soil temperature of 5, 15, 25, and 5-25 cm soil layer in spring and autumn tomato growth period increased by 6.17% and −0.30%, 5.45% and 4.32%, 5.93% and 1.02%, and 5.85% and 1.68%, respectively. This shows that under the same irrigation amount, the effect of MSPF on soil temperature was lower than that of drip irrigation under plastic film and micro-sprinkler irrigation. The changing trend of soil temperature in each treatment with the growth period of tomato under different irrigation amount was basically the same. With the increase in irrigation amount, the soil temperature of MSPF decreased. The fluctuation range of soil temperature during the growth period of spring and autumn tomato treated with 5, 15, and 25 cm soil depth of I3 was lower than that of I1 by about 7.53% and 21.88%, 2.36% and 18.57%, and 4.95% and 6.65%, respectively. The fluctuation of soil temperature in different soil depths is consistent with that of external temperature in the soil layer. The fluctuation of soil temperature decreased with the increase in depth, and the fluctuation of 5 cm soil temperature with spring and autumn tomatoes were 1.16 and 0.94 times those of 15 cm and 1.67 and 1.03 times those of 25 cm.   Table 5 shows that irrigation methods had significant effects on yield, ET a , and WUE of spring and autumn tomato (p ≤ 0.05). The irrigation amount also had significant effects on yield, water consumption, and WUE of spring and autumn tomato (p ≤ 0.05). Compared with CK1, the yield and WUE of spring and autumn tomato under MSPF increased by 19.39% and 4.54%, and 10.30% and 2.32%, respectively. Compared with CK2, the yield and WUE of spring and autumn tomato under MSPF increased by 20.46% and 49.22%, and 31.02% and 58.04%, respectively. When the irrigation amount increased from 5 mm to 29 mm, the yield of spring and autumn tomato increased at first and then decreased, and the WUE of spring and autumn tomato decreased. Among them, the WUE of spring and autumn tomato of I2 was not significantly different from that of I1, but the yield of spring and autumn tomato of I2 was significantly higher than that of I1 by 31.88% and 28.03%, respectively; the yield of spring and autumn tomato of I2 was not significantly different from that of I3, but the WUE of spring and autumn tomato of I2 was significantly higher than that of I3 by 23.36% and 12.26%, respectively.

Correlation Analysis of Soil Water, Heat, and Yield of Greenhouse Tomato under MSPF
Through the T-test of the correlation between volumetric soil water content, soil temperature, and yield of tomato in different planting times and different soil layers, it was found that the correlation between volumetric soil water content, soil temperature, and yield of tomato gradually weakened with the increase in soil depth. Among them, the volumetric soil moisture content and soil temperature of 10-20 cm soil layer are most closely related to the yield.
When spring tomato was planted for 46-96 days and autumn tomato was planted for 65-130 days, there was a good correlation between volumetric soil water content and tomato yield. When spring tomato was planted for 41-101 days and autumn tomato was planted for 15-75 days, there was a good correlation between soil temperature and tomato yield. Considering the difference between soil volumetric moisture content and soil temperature of tomato in spring and autumn, therefore, the 10-20 cm soil layer with high correlation was selected for 71 days of spring tomato and 60 days of autumn tomato soil volumetric moisture content (0.709 and 0.865, spring and autumn tomato, respectively), soil temperature (−0.726 and−0.861, spring and autumn tomato, respectively), and tomato yield by multiple regression analysis ( Figure 5), in order to obtain the relationship between them quantitatively. perature of tomato in spring and autumn, therefore, the 10-20 cm soil layer with high correlation was selected for 71 days of spring tomato and 60 days of autumn tomato soil volumetric moisture content (0.709 and 0.865, spring and autumn tomato, respectively), soil temperature (−0.726 and−0.861, spring and autumn tomato, respectively), and tomato yield by multiple regression analysis ( Figure 5), in order to obtain the relationship between them quantitatively. It can be seen from Figure 5 that the relationship between volume soil moisture content (v) and yield (y) is the second parabolic curve; among them, the determination coefficient R 2 > 0.69. It shows that the v can explain y to 69% in the model, and v can be used to estimate y. In this model, when the v is 32.77% and 35.98%, the y of spring and autumn tomato can reach the peak value of 121,901.48 and 101,930.72 kg/hm 2 , respectively. The relationship between temperature (t) and yield (y) is the second parabolic curve, among them, the determination coefficient R 2 ≥ 0.63. It shows that this model can explain y to 63%, and t can be used to estimate y. In this model, when the t is 28.21 and 14.12 °C, the y of spring and autumn tomato can reach the peak value of 122,389.88 and 98,789.38 kg/ha, respectively. It can be seen from Figure 5 that the relationship between volume soil moisture content (v) and yield (y) is the second parabolic curve; among them, the determination coefficient R 2 > 0.69. It shows that the v can explain y to 69% in the model, and v can be used to estimate y. In this model, when the v is 32.77% and 35.98%, the y of spring and autumn tomato can reach the peak value of 121,901.48 and 101,930.72 kg/hm 2 , respectively. The relationship between temperature (t) and yield (y) is the second parabolic curve, among them, the determination coefficient R 2 ≥ 0.63. It shows that this model can explain y to 63%, and t can be used to estimate y. In this model, when the t is 28.21 and 14.12 • C, the y of spring and autumn tomato can reach the peak value of 122,389.88 and 98,789.38 kg/ha, respectively.

Effects of Different Irrigation Methods on Soil Water, Heat, and Yield of Tomato in Greenhouses
This paper found that MSPF is similar to drip irrigation under plastic film (CK1), both of which belong to localized irrigation model. The MSPF is different from CK1; under the same working pressure and irrigation amount, the flow of a single group of MSPF is about 45 times that of CK1, and the irrigation duration is shorter, so that the ratio of horizontal and vertical migration distance of soil water increases, and the wetting shape of soil with profile is a band, the wetting body per unit area of the tillage layer is larger, and the water distribution is more uniform. This study also found that, under the same irrigation amount, the average soil volume water content of 0-40 cm during the growth period of spring and autumn tomato with drip irrigation under plastic film was higher than that of MSPF by about 1.97% and 3.83%, respectively, indicating that MSPF could reduce the risk of hypoxia stress on tomato roots in the soil near the emitter. Previous studies have found that when other conditions are constant, the higher the soil volume moisture content, the higher the time required to increase the unit temperature, and the larger irrigation quota can effectively reduce the temperature under high-temperature irrigation [26,36]. This may also be one of the reasons why the average soil temperature of 5-25 cm of MSPF was 2.36% and 1.66% higher than that of drip irrigation under plastic film for spring and autumn tomato, respectively.
Previous studies have found that tomato is suitable for growing in a relatively stable environment with a soil hydrothermal microenvironment system, which can reduce the negative impact of local high-dry and high-humidity environment on greenhouse tomatoes and improve tomato dry matter accumulation [37,38]. In this study, the spring and autumn of tomato yield of MSPF was 19.39% and 18.21% higher than that of CK1, respectively. This is mainly due to the fact that the MSPF provides a suitable hydrothermal environment for the growth of greenhouse tomato, and there is no area with too high or too low soil moisture, which is conducive to the morphological development of tomato roots and photosynthesis, and provides a strong guarantee for the stable yield of greenhouse tomatoes [39,40].
Previous studies have found that plastic film treatment can not only effectively reduce ineffective water evapotranspiration, but also have the function of increasing temperature [23,41,42]. This study found that, compared with micro-sprinkler irrigation, the average soil volume moisture content of 0-40 cm under MSPF increased by 8.30% and 3.83%, respectively, and the average soil temperature of 5-25 cm under MSPF increased by 5.85% and 1.68%, respectively. It may be that plastic film absorbs more solar radiation and reduces soil heat loss to increase soil temperature [43]. The effect of heat preservation and moisture preservation of plastic film treatment was further verified. The decrease in soil water and heat may be one of the reasons why the yield of micro-sprinkler irrigation is lower than that of MSPF.

Effect of Different Irrigation Amount on Soil Water, Heat, and Yield of Tomato in Greenhouses
The movement of water and heat in the soil interact with each other. Soil moisture affects soil heat capacity and thermal conductivity, and then soil temperature. At the same time, the change of soil temperature will also affect the movement of soil water [44]. When the irrigation amount increased from 0.7 Epan to 1.2 Epan, the soil volume moisture content of MSPF increased and the soil temperature of MSPF decreased. This is because the soil water content and water distribution were changed by increasing the irrigation amount. The higher the volume of soil moisture under higher irrigation, the higher the energy required to increase the same temperature, resulting in a decrease in soil temperature with an increase in high irrigation. The higher soil volume moisture content could reduce soil drought stress, improve tomato vegetative growth, increase leaf area index and shading rate under high irrigation treatment, and reduce effective solar radiation per unit area of soil, resulting in a lower temperature [44]. Yang [26] found that different irrigation amounts had no significant effect on soil temperature under regulated deficit irrigation, which was inconsistent with the conclusion of this study. This may be due to the different kinds of crops planted; the apple trees planted by Yang were larger than the tomato canopy in this study, which reduced the amount of solar radiation reaching the ground and reduced the difference of surface temperature accumulation [45]. This study also found that the soil temperature decreased with the increase in soil depth, which may be due to the fact that the shallow soil fluctuated greatly, and the influence of temperature and irrigation outside the soil layer gradually weakened with the increase in soil depth [14,26].
In this paper, it was found that there was a quadratic polynomial relationship between soil moisture and yield of tomato, which was consistent with the conclusion of the relationship between soil moisture and yield under regulated deficit irrigation of apple trees in Yang [26], which further indicated that the relationship between soil moisture and yield did not change with the change of crop species. In this paper, the tomato yield increased at first and then decreased with the increase in irrigation amount, which may be due to the fact that the 0-40 cm soil moisture of spring tomato and autumn tomato in I1 irrigation treatment is about 7.44% and 4.18% lower than that in I2 treatment under MSPF, respectively, as well as the fact that insufficient irrigation water increases crop root water stress, crop root chemical environment will change, crop root absorption and utilization capacity of soil nutrients will be reduced, and the formation of aboveground fruit yield will be limited [46]. The 0-40 cm soil moisture of I3 irrigation treatment of spring tomato and autumn tomato was about 6.14% and 3.79% higher than that of I2 treatment under MSPF, respectively; the soil water-filled porosity increased, weakening the active oxygen metabolism of crops, limiting the activity of soil microorganisms and enzymes, and having a negative effect on tomato yield [40]. This is not consistent with the conclusions of Bush [47], Li [48], and Karaer [49], namely that tomato yield increases with the increase in irrigation amount in drip irrigation. This may be due to the difference of irrigation amount control. The maximum amount of irrigation in Adam, Li, and Karaer was 1.00 times of local standard pan evapotranspiration, and that of this study is 1.20 times of local standard pan evapotranspiration. With an increase in irrigation amount, Liu [4] found that tomato yield increased at first and then decreased, and Quezada [50] found that carrot yield increased at first and then decreased, which was consistent with the conclusion of this study, indicating that the effect of MSPF on crop yield was the same as drip irrigation, and higher irrigation amount was not conducive to the formation of crop yield.

Conclusions
In this experiment, the law of soil water and heat transfer under MSPF and the formation mechanism of tomato yield in greenhouses were studied. The results showed that the soil wetting range of MSPF was large, the shape of soil profile was banded, and the change of soil moisture was small within 5 days of irrigation. Compared with drip irrigation under plastic film and micro-sprinkler irrigation, the area where the distribution of soil water in the profile of MSPF is more uniform. Meanwhile, the change range of 5 cm soil temperature of MSPF was lower than that of CK1 from 1 to 5 days after irrigation. In greenhouse tomato planting, the soil heat preservation effect of spring and autumn tomato under MSPF is better than that of drip irrigation under plastic film by 2.36% and 1.66% (spring and autumn tomato, respectively), and is better than that of microsprinkler irrigation by 5.85% and 1.68% (spring and autumn tomato, respectively). The yield-increasing effect of MSPF is better than that of drip irrigation under plastic film (19.39% and 10.30% of spring and autumn tomato, respectively), and the effect of watersaving (49.22% and 58.40% of spring and autumn tomato, respectively) is better than that of micro-sprinkler irrigation. With an increase in irrigation amount of MSPF, the soil moisture and yield of spring tomato and autumn tomato increased; the soil temperature and WUE decreased. Through the correlation analysis between soil water, heat, and yield of MSPF, it was found that there was a quadratic relationship between soil volume moisture content, temperature, and yield in 10-20 cm soil layer 60 days after planting, and the fitting coefficient R 2 > 0.63. This model can explain at least 63% of the yield variation, indicating that this model can be used to predict tomato yield. Considered comprehensively, based on 1.0 times the evaporation of the ϕ20 standard, an evaporating pan with MSPF can provide a suitable soil water and heat environment for the growth of tomato in the greenhouse, and realize the effect of water-saving and yield-increasing with tomato.