Effects of Irrigation Approaches and Mulching on Greenhouse Melon Production and Water Use in Northern China

Abstract

To explore the effects of different irrigation approaches, mulching, and their interaction on greenhouse melon (Cucumis melo L.) production and water use, a field experiment was conducted in Northern China using four treatments: mulching drip irrigation (MDI), mulching furrow irrigation (MFI), drip irrigation (DI), and furrow irrigation (FI; CK). The plant biomass, yield, water consumption, and water use efficiency (WUE) of melons were measured at different growth stages. The results showed that mulching has significant positive impacts on the growth as well as the fruit yield of melons. However, the water use characteristics of the plant were more greatly determined by the various irrigation approaches, and there was a significant interaction between the irrigation approach and mulching for both the total water consumption and WUE of the greenhouse melon. Of these treatments, MDI resulted in the highest yield of 38.49 t/hm², which was significantly higher than the yields obtained with DI (32.36 t·hm⁻²) and FI (CK, 30.34 t·hm⁻²). In addition, the water consumption under MDI was 45.80% lower than FI (CK), which resulted in the promotion of WUE under MDI. The WUE range of the greenhouse melon is as follows: MDI (334.77 kg·mm⁻¹·hm⁻²) > DI (244.84 kg·mm⁻¹·hm⁻²) > MFI (189.78 kg·mm⁻¹·hm⁻²) > FI (CK; 142.94 kg·mm⁻¹·hm⁻²). The findings of this study indicate that mulching can boost melon yield, and drip irrigation can limit water consumption. This study provides a reference point for policymakers, indicating that drip irrigation with plastic mulching could be a feasible adaptation strategy for increasing greenhouse melon production in Northern China, as well as other agriculture regions that suffer from water shortages.

1. Introduction

Water scarcity is a major global problem, and the current effects of climate change are exacerbating the strain on freshwater resources [1,2]. In the 21st century, with the development of urbanization, economy, and population, the world’s demand for water resources is increasing at a rate of 1% per year [3]. According to the 2030 Agenda for Sustainable Development, water resources are the most important element of the global sustainable development goals. It is well known that irrigation is the primary input in agricultural activities to increase yield production, which requires a large amount of water resources each year [4]. For example, in China, agricultural water use has accounted for 64% of the total water consumption of the nation (600 billion cubic meters), which is far higher than the proportion of irrigated water consumption (34.85%) in America [5,6]. The continued depletion of water resources in agriculture poses the potential risk of unsustainable water resources. Moreover, the destruction of agricultural irrigation facilities and the confusion over the management of facilities has led to a serious wastage of water resources [7]. Thus, it is urgently necessary to improve the water-saving irrigation technology in water-limited regions, which is of great significance for the sustainable development of agriculture production.

Drip irrigation is considered one of the most effective water-saving technologies, which delivers low-pressure water via specialized piping systems and equipment that slowly and regularly drips into targeted soil using small emitters. It has been reported that this method can effectively maintain soil aggregate, prevent deep water leakage and loss, and reduce the risk of soil degradation and salinization [8,9,10]. Small amounts of water being delivered regularly according to a plant’s requirements can help in enhancing crop productivity and water use efficiency [11,12]. Drip-irrigated eggplant decreased water consumption by 28.4% and increased crop yield by 12.3% and water use efficiency by 100% [13]. Compared to traditional irrigation, drip fertilization produced water savings of 40% and increased the yield of chilis by 52% [14]. Mulching is an agricultural measure that is widely used in field crop production, such as maize, wheat, cotton, and potato cultivation, in areas with low temperatures and limited rainfall [15,16]. In contrast to traditional cultivation techniques, mulch cultivation reduces undesired soil water losses caused by evaporation. The mulching-induced growth improvement can be attributed to the enhancement in photosynthesis and other metabolic activities [17]. It was shown that mulching film increased corn yield in Ethiopia by 39% and net income by 93% compared to no mulching [18]. In China, film mulching increased corn and wheat yields by 69.4–76.2% and WUE by 64.5–73.1% compared to no mulching [19].

Mulching drip irrigation (MDI) is the combined technology of drip irrigation and mulching, which applies plastic mulching on the drip tape. It simultaneously has the advantages of drip irrigation and film mulching, which provide important guarantees in the improvement in water use efficiency and in ensuring food security and realizing agricultural modernization in arid regions [20,21]. It can not only increase soil temperature, preserve soil moisture, and reduce surface evaporation but can also regularly and quantitatively infiltrate the growth area of the crop root system and improve yield and water use efficiency [22,23,24]. A meta-analysis study reported that mulching drip irrigation (MDI) increased crop yield and WUE by about 20% and 30%, respectively, compared with non-mulching drip irrigation [25]. Although MDI is used widely in vegetable production [26,27,28,29], previous research has focused mainly on crops that physiologically consume high levels of water, such as cucumbers and tomatoes [30,31,32]. There is still a knowledge gap regarding systematic quantitative research on the water use characteristics of crops that require low levels of water physiologically, specifically the effects of irrigation methods on melon in facility cultivation. In addition, the interaction of the irrigation approach and mulching on yield production also needs to be explored under greenhouse conditions.

Melon is a common type of vegetable, mainly planted in facility cultivation conditions, and with the continuous increase in fruit consumption, the land area dedicated to its growth has been increasing year by year. In 2021, the land areas of melon cultivation in China consisted of more than 3.7 million hectares, with a yield of 13.2 million tons each year, ranking first in the world in terms of both cultivation area and yield [33]. Melon cultivation has become one of the preferred crops for farmers to cultivate in order to become prosperous, resulting in rural revitalization. However, many farmers are still using the traditional furrow irrigation method in melon cultivation, which leads to serious levels of water and fertilizer waste and groundwater pollution and also has negative impacts on melon production, such as increases in diseases and reductions in yield and fruit quality [34]. Thus, it is an urgent necessity to understand the water consumption characteristics of melons and to explore effective and water-saving irrigation management, as this is of great significance for the sustainable development of melon production in China. Our greenhouse experiment was conducted using different treatments, namely, mulching drip irrigation (MDI), mulching furrow irrigation (MFI), drip irrigation (DI), and furrow irrigation (FI; CK). DI and FI were the single irrigation approach without mulching, while MDI and MFI were the plastic mulching application with different irrigation approaches. The plant biomass, yield production, water consumption, and water use efficiency of melon were measured at different stages. This study contributes to promoting the sustainability of melon production, optimizing agricultural water use, and providing guidelines for managing melon production in arid and semi-arid regions.

2. Materials and Methods

2.1. Experimental Site

The experiment was conducted at the Dahe Comprehensive Agricultural Experimental Station of the Hebei Academy of Agriculture and Forestry, Shijiazhuang City, Hebei Province, North China (38°07′ N, 114°22′ W), from March to June 2021, in a plastic greenhouse (Figure 1). This region has a warm and temperate semi-humid continental monsoon climate, with an average annual temperature of 13.3 °C, a frost-free period of 205 days, 1776.9 h of sunshine, annual precipitation of 536 mm, and an altitude of 92 m.

The plastic greenhouse was 100 m in length and 20 m in width and covered with a drip-free polyethylene film. The tested soil was a clayey alluvial calcareous brown soil. More topsoil physical and chemical properties in study site are listed in

Table 1. Soil physical and chemical properties in study site.

Soil Texture	Bulk Density (g·cm−3)	Field Moisture Capacity (%)	pHe	Organic Matter (g·kg−1)	Alkaline N (mg·kg−1)	Available P (mg·kg−1)	Available K (mg·kg−1)
clay loam	1.63	21.2	7.74	19.6	86.1	32.7	185.4

.

2.2. Experimental Design

The experiment utilized four treatments: mulching drip irrigation (MDI), mulching furrow irrigation (FDI), drip irrigation (DI), and furrow irrigation (FI; CK). Each treatment was repeated three times. Each experimental area was 6 m × 5 m = 30 m², with a random block design. Plastic sheeting was buried at a depth of 100 cm between communities to isolate the plants and prevent water and fertilizer seepage on both sides of the planting row. Single rows were planted next to each other in each community, with a row spacing of 80 cm and a ridge width of 30 cm. The planting density of the sweet melons was 24,000 plants.hm⁻². The spacing between drip irrigation heads was 33 cm, the inner diameter of the drip irrigation pipe was 8 mm, the drip tap diameter was 0.5 mm, the drip flow rate was 1.6 L/h, the working pressure of the drip irrigation was 0.1 MPa, and the other management measures during the growth period were the same as in conventional planting.

The plastic film was a white and transparent high-pressure, low-density polyethylene plastic film with a thickness of 0.014. The tested melon variety was Xizhoumi 25, which was grown on a hole tray substrate. Seed germination was carried out on 8 February 2021 and was sown on a 50-hole tray on 10 February. On 16 March, seedlings that had grown three leaves and one heart were planted in the greenhouse test ridges. The individual vines were pruned up to the 10th node, leaving one melon per plant. On 7 June, the plants were topped at the 20th node, and the fruits were harvested.

Irrigation management was carried out according to the local standards for maintaining the rootzone soil moisture at 75 to 85% field capacity. The irrigation time and amounts during the growth period of melons are listed in

Table 2. Irrigation date and amounts of different treatments.

Treatments	Irrigation Amount (mm)						Thetotal Irrigation Amount (mm)
	16 March	27 March	22 April	5 May	17 May	26 May
FI (CK)	20.7	39.06	3.51	43.51	50.64	22.50	179.92
MFI	20.7	39.06	3.51	43.51	50.64	22.50	179.92
DI	20.7	16.5	3.51	18.00	24.00	7.35	90.06
MDI	20.7	16.5	3.51	18.00	24.00	7.35	90.06

Note: During the slow-growth period (16 March), drip irrigation was used for all treatments, with the same amount of water applied at 20.7 mm to facilitate the slow growth of the plant. On 22 April, a small level of irrigation was carried out in conjunction with top dressing and integrated water and fertilizer. This period lasted from 16 March to 18 April, the flowering and fruiting period lasted from 19 April to 28 April, the spreading period lasted from 29 April to 23 May, and the maturing period lasted from 24 May to 7 June.

. Fertilizer of urea, P₂O₅, and K₂O was performed with the dosage of 19.5 kg/ha, 13.5 kg/ha, and 24.0 kg/ha, respectively, for all the treatments.

2.3. Sample Measurement

Plant height was measured using a ruler, with 5 duplicates for each treatment. Using the crossing method, the stem diameter at the third internode of the plant base was measured using a vernier caliper with an accuracy of 0.01 mm. The length and width of the leaves of 5 uniformly growing melon plants were measured, and the leaf area was calculated using the following formula [35]:

leaf area = leaf length × maximum leaf width × 0.677

(1)

The fresh weight of a single fruit was measured using an electronic scale with an accuracy of 0.01 kg, and the yield per unit area was converted from the fresh weight of a single fruit and the area of the community. The leaf area index (LAI) was calculated by the ratio of the total plant leaf area to the land area [36]. After harvesting, samples were taken from different organs and dried to determine the dry weight of leaves, petioles, stems, and fruits. The values of the above items were taken as the averages of 5 melon plants with uniform growth in each community.

Before planting, after harvesting, during the main growth period, and before and after each irrigation period, soil samples were taken from three points in each plot in order to measure the soil moisture content at depths of 0 to 100 cm, with one layer per 10 cm, by weighing the soil sample after oven- drying at 105 °C.

The water consumption of crops in the field was calculated using the water balance method with the following formula [37]:

$$E{T}_{1-2}=10{\displaystyle \sum _{i=1}^n{\gamma }_i}{H}_i\left({\theta }_{i1}-{\theta }_{i2}\right)+M+P_0+K-C$$

(2)

where ET_1–2 is the water consumption (mm); I is the soil layer number; N is the total number of soil layers; γ_i is the volumetric mass of the i layer of soil (g·cm⁻³); H_i is the thickness of the i layer of soil (cm); θ_i1 and θ_i1 are the moisture contents of the i layer soil at the beginning and end of the time period, calculated as a percentage of dry soil mass; M is the irrigation amount during the time period (mm); P₀ is the effective rainfall (mm), and its value is 0 in greenhouse cultivation; K is the level of groundwater recharge during the time period (mm) (when the groundwater depth is greater than 2.5 m, the value of K can be ignored, and subsequently, this term is 0); and C is the surface runoff and leakage amount (mm).

The water consumption intensity (mm·d⁻¹) was calculated using the formula of the ratio of water consumption (mm) with time (days).

Water use efficiency (WUE) for each treatment was calculated using the following formula [38]:

$$WUE=Y/ET$$

(3)

where Y is the yield of melon fruit (kg·hm⁻²), and ET is the crop water consumption (m³·hm⁻²).

Following the method of Sun et al. [39], a micro-lysimeter was used to the measure soil evaporation between plants. The micro-evaporator was made of steel pipes with diameters of 5 cm and heights of 10 cm. During each sample preparation, the soil-filled bottoms of the samples were flattened, sealed with plastic film, and the micro-evapotranspiration meter was placed in a pre-embedded outer tube in the field, with its top level with the ground. The outer sleeve was made of a steel pipe with an inner diameter of 6 cm and a height of 10 cm. The micro-evaporator was weighed every 2 days at 9:00 am using an electronic balance with an accuracy of 0.01 g. By measuring the difference in quality between the two measurements before and after, combined with the upper mouth area of the micro-evapotranspiration meter, the soil stage and daily evaporation between trees was calculated. The undisturbed soil of the lysimeter was replaced every 4 days.

2.4. Data Analysis and Statistical Methods

SPSS 16.0 software (SPSS Inc., Chicago, IL, USA) was used for analysis of variance (ANOVA). The multiple comparisons of mean values and significant differences between treatments were determined using a least significant differences (LSD) test at p ≤ 0.05.

3. Results

3.1. Effects of Irrigation Approach and Mulching on the Growth of Melon

As shown in

Table 3. Plant height, stem diameter, and LAI for greenhouse melons at different stages.

Treatments	Seedling Stage			Spreading Stage			Fruiting Stage
	Plant Height (cm)	Stem Diameter (cm)	LAI	Plant Height (cm)	Stem Diameter (cm)	LAI	Plant Height (cm)	Stem Diameter (cm)	LAI
MDI	26.00 ± 1.00 a	8.44 ± 0.30 a	0.30 ± 0.0062 a	74.00 ± 5.29 a	10.65 ± 0.51 ab	0.45 ± 0.010 a	202.67 ± 15.37 a	11.55 ± 0.47 a	0.80 ± 0.050 a
MFI	28.67 ± 1.53 a	8.34 ± 0.10 a	0.29 ± 0.0029 a	75.00 ± 5.00 a	11.37 ± 1.39 a	0.44 ± 0.0100 a	192.67 ± 2.52 ab	11.21 ± 0.73 ab	0.71 ± 0.020 ab
DI	22.67 ± 0.58 b	7.16 ± 0.16 b	0.25 ± 0.033 b	61.33 ± 1.15 b	8.40 ± 0.68 b	0.39 ± 0.012 b	194.75 ± 11.20 ab	11.11 ± 0.22 ab	0.63 ± 0.010 b
FI (CK)	23.00 ± 1.73 b	7.46 ± 0.28 b	0.23 ± 0.036 b	58.33 ± 2.89 b	7.91 ± 0.86 b	0.37 ± 0.030 b	171.30 ± 3.21 b	10.38 ± 0.85 b	0.60 ± 0.076 b
F values
M	**	**	**	**	**	**	*	*	**
I	ns	ns	ns	ns	ns	ns	ns	ns	ns
M × I	ns	ns	ns	ns	ns	ns	ns	ns	ns

Note: M: mulching; I: irrigation approach; different letters and ** both indicate significance differences among treatments at p ≤ 0.05; * indicates significance differences among treatments at p ≤ 0.01; ns indicates no significant differences.

, mulching had a significant impact on the plant height, stem diameter, and leaf area index (LAI) in the seedling, spreading, and fruiting stages, while the irrigation approach had no significant impact on these various indicators. The interaction between the two has no significant impact on plant height, stem diameter, and LAI in each growth stage, indicating that the only factor with an impact on plant height, stem diameter, and LAI is mulching.

Mulching treatment was significantly higher than non-mulching treatments at both the seedling and vine stages. Mulching in the early stages of growth can significantly promote the growth of melon and significantly increase the plant height, stem diameter, and LAI in the early stages. Compared with DI, MDI significantly increased the plant height, stem diameter, and LAI at each growth stage, with increases of 4.06% to 20.65%, 3.96% to 26.78%, and 15.38% to 26.98%, respectively. For furrow irrigation conditions, compared with FI, MFI significantly promoted the plant height, stem diameter, and LAI growth during the seedling and vine stages, with increases of 12.47% to 25.57%, 7.96% to 43.74%, and 18.33% to 26.8%, respectively. As the growth process progresses, the mulching effect gradually decreases. The mulching effect is lowest during the fruit-bearing stage, which is related to the fact that as the soil temperature increases, the warming effect of mulching decreases.

Different treatments had a significant impact on the aboveground biomass of melons during the harvest period. According to the analysis of variance (

Table 4. Aboveground biomass of greenhouse melons under different irrigation modes.

Treatments	Fruit Weight (g/plant)	Plant Weight (g/plant)	The Total Aboveground Biomass (g/plant)	Harvest Index
MDI	5042.84 ± 23.46 a	2866.33 ± 11.09 a	7978.85 ± 14.31 a	0.63 ± 0.0019 a
MFI	4887.61 ± 80.84 a	3039.60 ± 50.37 a	7927.21 ± 131.12 a	0.62 ± 0.00029 b
DI	4173.66 ± 16.50 b	2775.47 ± 50.57 ab	6949.13 ± 65.20 b	0.60 ± 0.0036 c
FI (CK)	3974.54 ± 92.22 b	2453.20 ± 40.90 c	6427.74 ± 125.86 c	0.62 ± 0.0036 b
F values
M	**	**	**	ns
I	ns	**	**	ns
M × I	ns	**	**	ns

Note: M, mulching; I, irrigation approach; different letters and ** both indicate significant differences among treatments at p ≤ 0.05; ns indicates no significant differences.

), mulching had a significant impact on indicators such as fruit weight, plant weight, and total aboveground biomass. The irrigation approach had a significant impact on indicators such as plant weight and the total aboveground biomass, and there were significant interactions between the mulching and irrigation approaches on the plant weight and the total aboveground biomass.

Under mulching conditions, the increase in dry matter through MDI was less than that achieved via MFI, while the impacts of various indicators did not result in significant differences; without mulching, DI significantly increased the plant weight and the total aboveground biomass by 13.13% and 8.11%, respectively, compared to CK.

Under drip-irrigation conditions, compared with DI, MDI significantly increased the fruit weight and the total aboveground biomass of the plants, increasing by 20.82% and 14.81%, respectively. There was no significant impact on the harvest coefficient and plant weight; under furrow-irrigation conditions, compared with FI, MFI significantly increased the plant weight, the fruit weight, and the total aboveground biomass by 31.41%, 22.97%, and 23.32%, respectively.

3.2. Effects of Irrigation Approach and Mulching on the Water Consumption of Melon

The water consumption intensity of greenhouse melon fields under different water-management methods shows a trend of first increasing and then decreasing as the growth process advanced. According to the analysis of variance, different water-management methods have significant impacts on water consumption intensity at each growth stage (

Table 5. Water consumption intensity at different growth periods of melon.

Stage	Last Days	Index	Treatments				F values
			MDI	MFI	DI	FI (CK)	M	I	M × I
Spreading stage	37	Irrigation (mm)	40.71	63.27	40.71	63.27	-	-	-
		Water consumption (mm)	42.08 ± 0.53 d	61.69 ± 0.11 b	51.48 ± 0.36 c	66.85 ± 0.64 a	**	**	**
		Water consumption intensity (mm·d−1)	1.14 ± 0.014 d	1.67 ± 0.0029 b	1.39 ± 0.0098 c	1.81 ± 0.017 a	**	**	**
Fruit seedling stage	12	Irrigation (mm)	0.00	0.00	0.00	0.00	-	-	-
		Water consumption (mm)	13.61 ± 1.45 b	14.97 ± 2.19 b	28.70 ± 2.69 a	31.57 ± 1.08 a	**	**	ns
		Water consumption intensity (mm·d−1)	1.13 ± 0.12 b	1.25 ± 0.18 b	2.39 ± 0.22 a	2.63 ± 0.090 a	**	**	ns
Fruit development stage	21	Irrigation (mm)	42	94.15	42	94.15	-	-	-
		Water consumption (mm)	43.43 ± 0.26 c	93.74 ± 0.16 a	26.07 ± 1.60 d	76.62 ± 1.34 b	**	**	ns
		Water consumption intensity (mm·d−1)	2.07 ± 0.013 c	4.46 ± 0.0077 a	1.24 ± 0.076 d	3.65 ± 0.063 b	**	**	ns
Fruit maturing stage	13	Irrigation (mm)	7.35	22.5	7.35	22.5	-	-	-
		Water consumption (mm)	15.95 ± 0.57 c	26.25 ± 1.50 b	25.96 ± 0.92 b	37.25 ± 2.14 a	**	**	ns
		Water consumption intensity (mm·d−1)	1.22 ± 0.044 c	2.02 ± 0.12 b	2.00 ± 0.070 b	2.87 ± 0.16 a	**	**	ns
Whole growth stage	83	Irrigation (mm)	90.06	179.92	90.06	179.92	-	-	-
		Water consumption (mm)	115.07 ± 1.87 d	196.65 ± 2.56 b	132.21 ± 1.80 c	212.29 ± 1.62 a	**	**	ns
		Water consumption intensity (mm·d−1)	1.39 ± 0.023 d	2.37 ± 0.030 b	1.59 ± 0.021 c	2.56 ± 0.019 a	**	**	ns

Note: M, mulching; I, irrigation approach; different letters and ** both indicate significant differences among treatments at p ≤ 0.05; ns indicates no significant differences.

). Mulching and irrigation methods significantly (p ≤ 0.05) reduced the water consumption intensity and water consumption level at each growth stage. The interaction between the two significantly reduces the water consumption intensity and water consumption level at the seedling stage.

Under mulching conditions, compared with MFI, MDI significantly reduced water consumption in all growth stages except for the flowering and fruiting period, with reductions of 31.74%, 9.60%, 53.58%, 39.60%, and 41.35% throughout the entire growth period; under bare ground conditions, except for the insignificant difference (p ≤ 0.05) in flowering and fruiting stages, the other growth stages of DI and FI (CK) were significantly (p ≤ 0.05) reduced, with decreases of 23.20%, 9.12%, 66.02%, and 30.31% in each individual growth stage, and a decrease of 37.89% throughout the entire growth stage.

Under drip-irrigation conditions, compared with DI, MDI reduces water consumption in all growth stages, with decreases of 17.98%, 52.71%, −66.93%, and 39.00% and a decrease of 12.57% throughout the entire growth stage; under furrow-irrigation conditions, compared with FI, MFI reduces water consumption in all growth stages, with decreases of 7.73%, 52.47%, 22.19%, and 29.61% and a decrease of 7.42% throughout the entire growth period. Research has found that, except for the insignificant difference in field water consumption intensity between the film mulching irrigation treatments during the fruit enlargement period, the field water consumption intensity of the MDI during other growth stages of melons is significantly lower than that of other treatments. This is related to the increased accumulation of dry matter in the melon treated with MDI, which in turn increases transpiration water consumption.

As shown in

Table 6. Interplant evaporation during different growth periods.

Spreading Stage	Index	Treatments				F values
		MDI	MFI	DI	FI (CK)	M	I	M × IB
Fruit setting	Daily evaporation (mm/d)	0.16 ± 0.015 b	0.15 ± 0.010 b	0.69 ± 0.091 a	0.59 ± 0.040 a	**	ns	ns
	E/ET/%	14.36 ± 1.26 c	9.00 ± 0.60 c	49.57 ± 6.36 a	32.84 ± 2.30 b	**	**	*
Fruit development	Daily evaporation (mm/d)	0.14 ± 0.011 b	0.18 ± 0.011 b	0.54 ± 0.015 a	0.57 ± 0.025 a	**	ns	ns
	E/ET/%	12.39 ± 0.85 b	14.67 ± 2.53 b	35.29 ± 4.43 a	31.55 ± 1.33 a	**	ns	ns
Fruit maturing	Daily evaporation (mm/d)	0.14 ± 0.012 c	0.14 ± 0.020 c	0.65 ± 0.055 b	0.82 ± 0.066 a	**	*	*
	E/ET/%	6.77 ± 0.49 c	3.14 ± 0.44 c	38.17 ± 4.85 a	19.98 ± 1.88 b	**	**	*
Whole growth	Daily evaporation (mm/d)	0.11 ± 0.014 c	0.15 ± 0.009 c	0.91 ± 0.045 b	1.05 ± 0.043 a	**	**	*
	E/ET/%	8.97 ± 0.79 c	7.44 ± 0.48 c	45.47 ± 3.37 a	36.68 ± 1.38 b	**	**	*
Spreading	Daily evaporation (mm/d)	0.15 ± 0.011 b	0.15 ± 0.003 b	0.69 ± 0.023 a	0.72 ± 0.0094 a	**	ns	ns
	E/ET/%	10.50 ± 0.61 c	6.41 ± 0.060 d	43.55 ± 1.82 a	28.12 ± 0.24 b	**	**	**

Note: M, mulching; I, irrigation approach; different letters and ** both indicate significant differences among treatments at p ≤ 0.05; * indicates significance differences among treatments at p ≤ 0.01; ns indicates no significant differences.

, the evaporation between greenhouse melon plants varies with the growth process under different treatments. The evaporation between the two plastic film treatments was relatively small and did not change much with the growth process, while the bare land treatment first decreased and then increased with the growth process. The analysis of variance shows that different water-management methods had a significant impact on the interplant evaporation intensity at different growth stages. The mulching method significantly reduces the interplant evaporation intensity and proportion at each growth stage, while the irrigation method factor has a lower impact than the mulching method. The interplant evaporation intensity only reaches a very significant level in the spreading and maturing stages and does not reach a significant level in other stages.

The treatment factors of the irrigation method have a relatively small impact. Under mulching conditions, there was no significant difference in evaporation between MDI and MFI throughout the entire growth stage of sweet melons; without mulching, DI in bare land reduces interplant evaporation by 20.73% and 13.33% during the spreading and maturing stages, respectively, compared to FI (CK).

The treatment factors of mulching methods have a significant impact on each growth stage. Under drip-irrigation conditions, the interplant evaporation under MDI decreased by 45.49 mm (a decrease of 79.43%) compared to DI. Under MFI, the interplant evaporation decreased by 47.31 mm (a decrease of 79.16%) compared to FI (CK).

For the growing of greenhouse melons, the evaporation intensity between treatments with bare land irrigation increased. This may be because the evaporation intensity between melons treated with bare land irrigation increases throughout the growth process, mainly due to the gradual warming in spring. However, mulching significantly reduced the interplant evaporation intensity of greenhouse melons. The interplant evaporation intensity of sweet melons irrigated under mulching remained at low levels of 0.11 to 0.16 mm·d⁻¹, far lower than the high interplant evaporation intensity levels of 0.54 to 1.05 mm·d⁻¹, seen in irrigated in bare land.

The proportion of interplant evaporation throughout the entire growth period in plants under the film covering treatment was only 6.41% to10.51%, while the interplant evaporation in plants grown in bare land reached 28.2% to 43.55%, which means that the bare land method consumes more than 30% of water, which is ineffective water consumption. As the growth process advances, the interplant evaporation intensity of the subsurface irrigation treatment shows a stable and decreasing trend, and the later decrease in evaporation intensity may be related to the improvement in the leaf area index by mulching. It can be seen that subsurface irrigation significantly reduces interplant evaporation intensity and interplant evaporation throughout the entire growth period.

3.3. Effects of the Irrigation Approach and Mulching on the Yield, Water Use Efficiency, and Net Revenues of Melons

As shown in Figure 2, different treatments have significant impacts on melon yield, total water consumption throughout the entire growth period, and water use efficiency. An analysis of variance shows that mulching significantly increases yield, reduces water consumption, and improves water use efficiency; drip irrigation significantly reduces water consumption and improves water use efficiency, and the interactions between the two significantly reduce water consumption and improve water use efficiency.

Under mulching conditions, there was no significant difference in yield between MDI and MFI for greenhouse melons. However, drip irrigation significantly reduced the total water consumption throughout the entire growth period and significantly improved the water use efficiency: mulching drip irrigation reduced water consumption by 40.48% and improved water use efficiency by 76.39%. Without mulching, there were no significant differences in melon yield between DI and FI. However, the total water consumption throughout the entire growth period was significantly reduced, and the water use efficiency was significantly improved. DI reduced water consumption by 37.72% and improved water use efficiency by 71.28%.

Under drip-irrigation conditions, compared with DI, MDI significantly increased melon yield by 18.94%, reduced the total water consumption throughout the growth period by 12.96%, and improved the water use efficiency by 36.73%. Under furrow-irrigation conditions, compared with FI, MFI significantly increased melon yield by 22.97%, reduced the total water consumption throughout the growth period by 7.37%, and improved the water use efficiency by 32.76%. Even though the input of MDI treatment was greater than MFI, DI, and FI (CK), the highest yield and output of MDI resulted in the highest net revenues (12,970.5 CNY/ha), which was 26.1% and 32.4% higher than that of DI (10,287.0 CNY/ha) and FI (CK, 9798.0 CNY/ha) (

Table 7. Output, input, and net revenues for different treatments in greenhouse melon cultivation.

Treatments	Output (CNY/ha)	Input Values (CNY/ha)					Net Revenues (CNY/ha)
		Seedling	Fertilizer	Material	Irrigation	Total
MDI	17,320.5	2250.0	1500.0	525.0	75.0	43,500.0	12,970.5
MFI	16,789.5	2250.0	1500.0	75.0	105.0	3930.0	12,859.5
DI	14,562.0	2250.0	1500.0	450.0	75.0	4275.0	10,287.0
FI (CK)	13,653.0	2250.0	1500.0	0.0	105.0	3855.0	9798.0

Note: Material input includes the cost of the plastic mulch and drip tape; the irrigation input indicates the electric cost for irrigation.

).

4. Discussion

Many studies have reported higher yields and water use efficiency (WUE) of drip irrigation over the conventional irrigation methods throughout the world in different vegetable crops, such as potato [40], cucumber [41], capsicum [42], onion [43], eggplant, and pepper [44]. In agreement with the previous research [45,46], this study indicated that the MDI had greater impacts on water-saving production compared with the single drip-irrigation and mulching practice. In addition, we clarified the interaction relationship between irrigation and mulching on melon production and water consumption. In this study, the water consumption of greenhouse melons during the entire growth period was 115.07 mm, 196.65 mm, 132.21 mm, and 212.29 mm, respectively, when using MDI, MFI, DI, and FI (CK). During the entire growth period, MDI reduced water consumption by 17.14 mm compared to DI, and MFI reduced water consumption by 15.06 mm compared to FI. Therefore, whether it is drip irrigation or furrow irrigation, mulching has a significant water-saving effect, which is consistent with the research results of previous researchers [47,48,49]. At the same time, the water consumption of MDI was significantly reduced by 81.58 mm compared to MFI, and the water consumption of DI was significantly reduced by 80.08 mm compared to FI (CK). The water consumption of DI was also reduced by 64.44 mm compared to MFI. The above data show that drip irrigation has excellent water-saving effects, while furrow irrigation significantly increases the water consumption during the growth period of greenhouse melons, which is related to excessive single irrigation during furrow irrigation, causing root layer leakage. In addition, it was reported the materials and colors of plastic mulching had a remarkable impact on maize yield and WUE [50]; a similar study should further be conducted on greenhouse melon production.

According to a meta-analysis carried out on melons in China, mulching drip irrigation (MDI) could greatly improve yield and water use efficiency [51]. In this study, MDI and MFI were able to significantly reduce soil interplant evaporation loss through plastic film mulching. MDI and MFI systems are almost entirely covered, and thus, their interplant evaporation is extremely small. Only the section where the film gap connects and the film hole used for planting experience interplant evaporation, achieving the desired effect of reducing interplant evaporation. Due to the lack of plastic film mulching, the evaporation rates of DI and FI are significantly higher than the rate of mulching treatment, which is more than 4.7 times that of mulching treatment. Under the conditions of this experiment, MDI and DI did not significantly reduce interplant evaporation during the entire growth period compared to ditch irrigation under both conditions. This is related to the strong drought resistance of sweet melons and fewer irrigation cycles, as well as the prolonged drought state of the soil surface.

Due to the higher yield of greenhouse melons under MDI compared to bare land drip irrigation and the significantly higher yield under plastic film furrow irrigation compared to DI, this indicates that plastic film mulching has a significant yield-increasing effect on greenhouse melons. Consistent with the study by Meng et al. [52], no significant differences between DI and FI, with or without mulching, were found. This indicates that the irrigation method has a relatively limited impact on yield, mainly due to the strong drought resistance of melon. In the study by Hou et al. [53], a lower N loss and higher N use efficiency (NUE) of maize were observed under MDI, which indicates the importance of the irrigation approach for crop production, a result that is different from the results of our study, and the effect of fertilizer utilization in greenhouse conditions needs further research. In addition, it was found that the effectiveness of mulching in increasing crop yield and water productivity was better in combination with limited drip irrigation than with conventional furrow irrigation [54], which agrees with the results of our study.

5. Conclusions

Mulching and irrigation approaches both showed positive effects on water-saving in melon production under greenhouse conditions. Mulching had greater significant impacts on plant growth traits than irrigation. Compared With DI, MDI significantly improved the plant height, stem diameter, and LAI at various growth stages, with increases of 4.06% to 20.65%, 3.96% to 26.78%, and 15.38% to 26.98%, respectively; additionally, the yield was increased by 18.94%, the water use efficiency was reduced by 36.73%, and the total water consumption throughout the growth period was reduced by 12.96%. The impacts of irrigation approaches on the water consumption and water use efficiency of greenhouse melons were greater than those of mulching. There was no significant difference in plant growth traits, dry biomass, and soil evaporation between plants grown using MDI (DI) and MFI (FI), and compared with MFI and FI, MDI and DI reduced the total water consumption by 41.35% and 37.89%, respectively, with the water use efficiency improved by 76.39% and 71.28%, respectively. For water-saving production, MDI (mulching with drip irrigation) is the most effective approach for a higher yield and less water input, which is recommended for greenhouse melon production in a water resource-limited environment.