Potential Use of Subsurface Drip Irrigation Systems in Landscape Irrigation under Full and Limited Irrigation Conditions

Abstract

Water is an essential component of life in the world. In addition to being crucial to keeping plants alive, water is also used in various areas, such as landscape irrigation, decorative pools, and ponds. The use of water more efficiently is getting more and more important day by day because of the increasing demands of different sectors. In cities with limited water resources, such as Konya, water should be used even more efficiently to reduce irrigation water quantities and prevent water losses. The potential use of the sub-surface drip irrigation method in the irrigation of green areas in Selçuklu district of Konya province was investigated, and the sub-surface drip irrigation method was compared with the fixed sprinkler irrigation method (pop-up) in terms of irrigation parameters (amount of irrigation water applied, plant water consumption) and plant characteristics (germination, plant height, number of mows, mowing weight, root depth). In the present experiments, 18 different sub-surface drip irrigation treatments (100, 80, and 60% irrigations + 40, 60, and 80 cm lateral spacings + 10 and 15 cm lateral depths) and three different sprinkler irrigation treatments (100, 80, and 60% irrigations) were used. Present findings revealed that sub-surface drip irrigation systems were suitable for irrigation of green areas, and this system was more advantageous for municipalities in terms of water savings, irrigation labor, and maintenance. For sub-surface drip irrigation systems, S1 (supply 100% of evaporation from Class-A pan + 40 cm lateral spacing + 10 cm lateral depth) treatments were found to be the best system arrangement for landscape irrigations in Selçuklu district in Konya province.

1. Introduction

Green areas are important living spaces in cities. The importance of green areas increases even more for people who want to get away from busy business and city life in these areas, to stay away from stress, to take healthy, fresh air, and to have a pleasant time alone or with their families [1,2,3]. Green areas make great contributions to cities in terms of aesthetics, spaciousness, reducing the effects of some gases that cause air pollution, and creating an environment that people can enjoy. The need for green space in cities is directly proportional to population growth. The quality of urban life and the level of development of cities are closely related to the amount of green space the city has, as well as the amount of green space per capita. Since Konya province is growing rapidly, the amount of green space is increasing with the increasing population and settlements. Therefore, it is estimated that the amount of water to be used for irrigation of green areas will be higher than that used today [4].

Perennial grass species are widely used in the creation of green areas and parks. There are over 1200 grass species and varieties. Characteristics such as degree of coverage, length of growing season, tolerance to drought, type, and color are taken into consideration while selecting grass species [5]. In addition to all these features, varieties that are resistant to trampling are preferred, especially for grass species to be used in sports and recreation fields and parks. Turfgrass can be divided into two groups: cool-season and warm-season grasses. Cool-season grasses (Kentucky bluegrass, perennial ryegrass, tall fescue, Poa pratensis, Festuca rubra, Lolium perenne, Festuca arundinacea, etc.) are more cold-tolerant and exhibit a longer growing season than warm-season grasses (Bermudagrass, blue grama, buffalograss, zoysiagrass, etc.). Cold tolerance is usually the first desirable characteristic when selecting perennial plants, whether it is turfgrass or bushes and trees [6]. The water required for irrigation of landscape areas is generally supplied from the city’s drinking and utility water networks. Konya Province has quite limited water resources and low precipitation levels. Therefore, efficient use of irrigation water is essential, especially in green areas of the province [7].

Plant water consumption should be well understood for efficient use of irrigation water. Plant water consumption is also closely related to the development of irrigation projects [8,9,10]. Irrigation, briefly, is the balanced and controlled supply of water required for the development of plants but not met by natural precipitations in plant root zones. Irrigation plays a great role in the design and maintenance of landscape areas. For plants to survive, the required amount of water must be delivered through a system. The location of the area to be irrigated, current water resources, and plant characteristics should be taken into consideration while selecting an irrigation system. Improper system selection or inappropriate system design can lead to significant waste and loss of water [11].

In the irrigation of landscape areas, water is delivered to the plants at regular intervals, not all at once. Therefore, considering both labor cost and practicality, the most suitable irrigation systems should be preferred for irrigation of these areas [12]. In the planning of irrigation systems, a technical irrigation program and project should be prepared by taking cropping patterns, plant water consumption, the amount of irrigation water needed, water quality, and soil properties into consideration. After determining the actual water consumption, irrigation water needs, irrigation time, and irrigation intervals, monthly and seasonal irrigation water needs should be calculated. The most suitable irrigation system will then be designed and implemented accordingly [13].

The pop-up (fixed sprinkler) irrigation method is generally used for the irrigation of green areas. With this system, green areas are irrigated from above, which is affected by climate factors and causes water loss. In addition, system equipment is destroyed by people. In recent years, sub-surface drip irrigation systems, which have eliminated these problems, have started to be used for irrigation of lawns and landscape areas (Figure 1).

A sub-surface drip irrigation system was first introduced in 1959. In the 1980s, scientific research increased rapidly and was put into practice [14,15,16,17,18,19]. With a sub-surface drip irrigation system, the above-mentioned costs will be avoided, water losses will be reduced, and optimum development will be achieved with timely and adequate irrigation. The use of subsurface drip irrigation systems has been increasing and yields various benefits, including the ability to apply water close to the plant root system without wetting the soil surface, which results in small losses by evaporation and thus high application efficiency [20,21]. Because the drip lines are not exposed to the surface, mechanical damage and solar radiation are minimized, facilitating crop management practices and increasing the longevity of the system [22]. Sub-surface irrigation systems apply water directly to the root zone, thereby avoiding problems such as overspray, runoff, wind drift, and human exposure [23].

Deficit irrigation practices are becoming more and more important in regions with deficits or limited water resources [24,25]. Since there is no yield reduction problem in the irrigation of green areas, deficit irrigations are becoming more popular. Deficit irrigations are also popular since drinking and utility water are used for the irrigation of green areas in several cities. Therefore, deficits in irrigation water in a way that does not impair the quality and performance standards of the plants are highly significant for good water management [8].

Crop evapotranspiration is mostly estimated from the correlations between evaporations measured from class-A pans and reference crop evapotranspiration [26]. Since climate factors effective on pan evaporation are also effective on crop water consumption in the same fashion, quite accurate results can be achieved with this method. This method of estimation is commonly used worldwide [27,28].

The irreversibility of global climate change brings about serious reductions in freshwater resources. At the same time, the increasing world population and corresponding increase in water demand limit the use of water in crop production. The water and drought cause serious stress for both cool and warm-season grass species. While grass fields are an important source of recreation in many world capitals, increasing drought may cause these fields to become increasingly idle and perhaps decrease the national happiness index. These stress conditions can occur alone, or it is possible for many factors to come together. This situation can cause irreversible damage [29].

Nowadays, the importance of water and irrigation is increasing with decreasing water availability. In this sense, irrigation systems and irrigation durations also play a great role in the irrigation of central refuges and parks. In this study, the potential use of sub-surface drip irrigation methods in the irrigation of green areas was investigated, and the sub-surface drip irrigation method was compared with the fixed sprinkler irrigation method (pop-up). The effects of different system designs and irrigation programs on irrigation parameters and plant characteristics were also determined.

2. Materials and Methods

This study was conducted in parks and green areas within the borders of the Selçuklu district of Konya province (Figure 2).

Selçuklu district is located between 36°52′ North latitudes and 32°29′ East longitudes. Selçuklu is the largest district of Konya province in terms of population and development [30]. The area of the district is 2.056 km², and the altitude is 1020 m. The total area of green areas in Selçuklu District is 13,276.242m², and the active green area is 6928.130 m². The population is 648.850 people. Considering the district’s total active green area availability and population, there is 10.68 m² of active green area per person. This value is greater than the amount of green space per capita in many provinces and districts in Turkey.

Konya province has a semi-arid climate and is among the provinces with the least precipitation. The average annual rainfall is 322.4 mm, and it is one of the regions with the least rainfall in Turkey.

2.1. Experimental Design and Treatments

For the present experiments, a 1300 m² area was surrounded by wires, and a total of 570 m² of grass cover was generated (Figure 3). In the research, the grass seed mixture used by Selçuklu Municipality to create grass areas in parks and green areas was used. The grass seed mixture was sown so as to have 55–60 g of seeds per m². The seed mixture is composed of 40% Loliumperenne (British grass), 20% Festucarubracommutata (Common red festuca), 30% Festucarubrarubra (red festuca), and 10% Poapratensis (blue grass). Ammonium sulfate (21% nitrogen, 30 g/m²) was applied as a fertilizer.

Sub-surface drip irrigation and sprinkler irrigation (pop-up) methods were used in the present experiments. The sub-surface drip irrigation method was established with two different lateral depths (0.10 and 0.15 m) and three different lateral spacings (0.40, 0.60, and 0.80 m). Water deficits were also applied in both methods (100, 80, and 60% of cumulative evaporation from Class-A pan). Sub-surface drip irrigation treatments were applied on 54 plots (3 lateral spacings × 2 lateral depths × 3 water deficits × 3 replicates), and sprinkler irrigation treatments were applied on 9 plots (3 water deficits × 3 replicates). The total number of plots was 63 (Figure 4,

Table 1. Experimental treatments.

Treatments	Description
S1	100% Sub-surface drip irrigation with 0.40 m lateral spacing and 0.10 m lateral depth
S2	100% Sub-surface drip irrigation with 0.40 m lateral spacing and 0.15 m lateral depth
S3	100% Sub-surface drip irrigation with 0.60 m lateral spacing and 0.10 m lateral depth
S4	100% Sub-surface drip irrigation with 0.60 m lateral spacing and 0.15 m lateral depth
S5	100% Sub-surface drip irrigation with 0.80 m lateral spacing and 0.10 m lateral depth
S6	100% Sub-surface drip irrigation with 0.80 m lateral spacing and 0.15 m lateral depth
S7	80% Sub-surface drip irrigation with 0.40 m lateral spacing and 0.10 m lateral depth
S8	80% Sub-surface drip irrigation with 0.40 m lateral spacing and 0.15 m lateral depth
S9	80% Sub-surface drip irrigation with 0.60 m lateral spacing and 0.10 m lateral depth
S10	80% Sub-surface drip irrigation with 0.60 m lateral spacing and 0.15 m lateral depth
S11	80% Sub-surface drip irrigation with 0.80 m lateral spacing and 0.10 m lateral depth
S12	80% Sub-surface drip irrigation with 0.80 m lateral spacing and 0.15 m lateral depth
S13	60% Sub-surface drip irrigation with 0.40 m lateral spacing and 0.10 m lateral depth
S14	60% Sub-surface drip irrigation with 0.40 m lateral spacing and 0.15 m lateral depth
S15	60% Sub-surface drip irrigation with 0.60 m lateral spacing and 0.10 m lateral depth
S16	60% Sub-surface drip irrigation with 0.60 m lateral spacing and 0.15 m lateral depth
S17	60% Sub-surface drip irrigation with 0.80 m lateral spacing and 0.10 m lateral depth
S18	60% Sub-surface drip irrigation with 0.80 m lateral spacing and 0.15 m lateral depth
YS1	100% Sprinkler Irrigation
YS2	80% Sprinkler Irrigation
YS3	60% Sprinkler Irrigation

). Each plot had a size of 9 m² (3 × 3 m). Experiments were conducted in a randomized block design with three replications; 2 m spacing was provided between the blocks and 1 m between the plots.

Fixed sprinkler (pop-up) and sub-surface drip irrigation systems were established for irrigation. Spray pop-up heads, which have a 0.11 m³ h⁻¹ flow rate and 3 m irrigation radius with a 210 kPa operating pressure, were used in each plot. In the sub-surface drip irrigation system, 15.5 mm PE laterals with 1.0 L h^–1 in-line drippers spaced 40 cm apart and operating at 100 kPa pressure were installed.

Soil samples were taken from the 0–30 cm soil profile of experimental fields, and soil physico-chemical characteristics are provided in

Table 2. Soil physico-chemical properties.

Depth	Bulk Density (g cm−3)	Field Capacity (%)	Wilting Point (%)	Sand (%)	Silt (%)	Clay (%)	Texture	EC (mmhos cm−1)	pH	CaCO3 (%)	Organic Matter (%)
0–30	1.29	27.13	17.82	36.4	41.1	22.5	SCL	0.520	7.8	18.4	1.10

. As can be seen from Table 2, the soil texture was sandy clay-loam (SCL). Soil salinity was measured at 0.52 dS m⁻¹. Soil salinity measurements were made in saturation extract with a conductivity meter. A double-ring infiltrometer was used to measure the soil infiltration rate. The infiltration rate value for the experimental site was measured at 7.8 mm ha⁻¹.

Irrigation water was supplied from a groundwater well in experimental fields, and irrigation water quality parameters are provided in

Table 3. Irrigation water quality parameters.

Chemical Parameters	Analysis Results
pH	7.35
EC × 106 (µS cm−1)	481
Dissolved Sodium Percentage	8.92
Sodium Absorption Ratio	0.33
Hardness (FSD)	26.8
Sulphur (S) (mg L−1)	13.5
Boron (B) (mg L−1)	0.03
Calcium (Ca) (mg L−1)	62.3
Magnesium (Mg) (mg L−1)	26.9
Sodium (Na) (mg L−1)	12.3
Potassium (K) (mg L−1)	4.07

. As can be seen from Table 3, irrigation water can be classified as class C₂ S₁ [31].

2.2. Plant Water Consumptions

Soil moisture was measured with the TDR 300 device. The gravitational method was used for calibration of the TDR device. Plant water consumption was calculated using the following water-budget equation [32].

$$ET=I+R-Dp+Cp-Rf\pm ∆S$$

(1)

where ET indicates plant water consumption (mm); I indicates the amount of irrigation water to be applied (mm); R indicates effective precipitation (mm); Dp indicates deep percolation (mm); Cp indicates capillary rise; Rf indicates surface runoff; ΔS indicates change in soil moisture (mm); Dp values were checked with the use of TDR 300 and calculated gravimetrically from the soil samples taken from 30 and 45 cm soil depths before and after the irrigations. Since experiments were conducted under controlled conditions, Cp and Rf values were neglected.

2.3. Amount of Irrigation Water to Be Applied

The amount of irrigation water to be applied to each plot was calculated using the following equation [33].

$$I=A\times Epan\times Kpc\times P$$

(2)

where I indicates the amount of irrigation water to be applied (L); Epan indicates total evaporation from Class-A pan between successive irrigations (mm); Kpc indicates plant-pan coefficient; and P indicates wetting ratio (100%).

Irrigations were initiated when 30% of the available moisture at field capacity was depleted. In the other irrigations, a certain percentage of 2-day evaporation from the Class-A pan was applied. Irrigation water was passed through water meters installed at the entrance of each plot.

2.4. Plant Observations

Germination and emergence were checked 8 days after seeding. For homogenous emergence and initial set-up, sprinkler irrigation was applied to all plots. Plant heights were measured just before mowing from 10 different locations on each plot with a ruler. To prevent the negative effects of surface roughness, measurements were taken from the same locations on each plot with a piece of wood put on the soil surface. Mowing is usually performed when the grass height reaches about 10–12 cm, and mowing is practiced 4–5 cm above ground. Mowed grass was weighed in each time. At the end of the irrigation season, a profile pit was opened in each plot to measure root lengths with a ruler. The quality of the grass is determined visually. Therefore, periodic photographs were taken.

3. Results and Discussion

3.1. Irrigation Water Quantities

Irrigations were initiated in mid-April and terminated in mid-October. A total of 87 irrigations were practiced in 2017 and 83 irrigations in 2018. The amount of irrigation water applied in each treatment is provided in

Table 4. Irrigation water was applied to the experimental treatments (mm).

2017
	April	May	June	July	August	September	October	Total
S1–S6	35.60	115.20	150.40	255.80	216.20	159.80	33.60	966.60
S7–S12	28.48	92.16	120.32	204.64	172.96	127.84	26.88	773.28
S13–S18	21.36	69.12	90.24	153.48	129.72	95.88	20.16	579.96
YS1	40.92	132.41	172.87	294.02	248.51	183.68	38.62	1111.03
YS2	32.74	105.93	138.30	235.22	230.62	146.94	30.90	888.83
YS3	24.55	79.45	103.72	176.41	172.97	110.21	23.17	666.62
2018
S1–S6	46.40	126.20	178.60	250.80	224.60	150.40	30.80	1007.80
S7–S12	37.12	104.16	142.88	200.64	179.68	120.32	24.64	806.24
S13–S18	27.84	78.12	107.16	150.48	134.76	90.24	18.48	604.68
YS1	53.33	145.06	205.29	288.28	258.16	172.87	35.40	1158.39
YS2	42.67	116.05	164.23	230.62	206.53	138.30	28.32	926.71
YS3	32.00	87.03	123.17	172.97	154.90	103.72	21.24	695.03

.

In both years, the greatest amount of irrigation water was applied in YS1 treatments (100% sprinkler irrigation) (1111.03 and 1158.39 mm) and the lowest in S13–S18 treatments (60% sub-surface drip irrigation) (579.96 and 604.68 mm). Under full irrigation conditions, approximately 15% more irrigation water was applied in YS1 treatments than in S1–S6 treatments in both years. This ratio is very important for the sustainability of urban water resources, especially in arid and semi-arid regions such as the research area. In all treatments, the greatest amount of irrigation water was applied in July and the least in October. Changes in monthly irrigation water quantities are presented in Figure 5.

Ref. [8] conducted a study for the landscapes of Konya central town and reported the average amount of irrigation water applied through the sprinkler irrigation system as 803.33 mm. In a similar study, Ref. [34] reported the average amount of water applied through a sub-surface drip irrigation system as 712.15 mm. Ref. [35] conducted a study under Tekirdağ provincial conditions and reported the amount of irrigation water applied as between 238.5 and 501.6 mm for cool-season grass species and as between 140.7 and 416.7 mm for warm-season grass species. In a similar study conducted in the same region, Ref. [36] reported the amount of irrigation water applied as between 275.3 and 523.5 mm for cool-season grass species and as between 186.2 and 423.8 mm for warm-season grass species. Ref. [37] conducted a study to determine the effects of different irrigation levels on ET and the quality characteristics of turfgrass. In this study, four different irrigation treatments were examined: 100% (S1), 75% (S3), and 50% (S4) of the evaporation measured in Class-A Pan; the S2 irrigation treatment represented the irrigation level practiced by the golf course management. According to the trial subjects (S1, S2, S3, and S4), respectively, they applied 780.3, 690.0, 587.5, and 391.8 mm of irrigation water.

3.2. Plant Water Consumptions

While desired plant development was achieved in full irrigation treatments (100%) since plants were not exposed to water stress, some developmental problems were encountered in deficit irrigation treatments (80 and 60%). Since there is always available moisture at around field capacity levels in full irrigations, a healthy development was seen. Then, healthy plants had better leaf development and greater plant water consumption. However, there was not sufficient moisture within the root zone in deficit irrigations. Such a deficit in water recessed plant growth and development and reduced plant water consumption [7]. Monthly plant water consumptions are provided in

Table 5. Plant water consumptions (mm).

2017
	April	May	June	July	August	September	October	Total
S1–S6	37.1	141.4	175.7	257.1	226.5	160.8	36.3	1034.6
S7–S12	31.7	117.2	145.8	206.1	182.9	129.2	32.5	845.3
S13–S18	25.4	94.0	116.1	154.0	140.4	97.8	29.9	657.6
YS1	39.0	149.4	185.7	271.8	239.2	170.8	38.4	1094.3
YS2	32.8	123.5	153.2	216.4	192.3	135.7	33.9	887.8
YS3	26.3	98.5	121.6	161.4	147.4	102.1	31.16	688.5
2018
S1–S6	47.8	146.3	189.9	251.80	234.8	151.4	33.5	1055.4
S7–S12	40.3	119.9	154.4	202.0	189.6	121.6	29.7	857.8
S13–S18	31.9	94.3	119.0	151.1	145.5	92.1	28.1	662.1
YS1	49.5	152.6	197.8	261.9	244.9	157.2	34.8	1098.7
YS2	41.4	125.3	159.9	210.0	197.5	126.3	30.9	891.4
YS3	33.0	97.8	123.1	156.6	151.6	103.72	29.3	686.9

.

In both years, the greatest water consumption was seen in July and the least in April and October (Figure 6). In terms of experimental treatments, the greatest water consumption was seen in full irrigations (S1–S6 treatments, 1034.6 and 1055.4 mm; YS1 treatments, 1094.3 and 1098.7 mm) and the least in 60% deficit irrigations (S13–S18 treatments, 657.6 and 662.1 mm; YS3 treatments, 688.5 and 686.9 mm). Lateral spacing and depths did not have significant effects on plant water consumption in sub-surface drip irrigation treatments.

Ref. [8] reported the water consumption of grass species as 771 mm for full irrigations, 657 mm for 20% deficits, 563 mm for 40% deficits, and 459 mm for 60% deficits. Ref. [34] used sub-surface drip irrigations for landscape irrigations under Konya provincial conditions and reported the average water consumption of grass species as 766.56 mm. Ref. [35] used sprinkler irrigation in Tekirdag province and reported average water consumptions of grass species as between 317.8 and 610.5 mm for cool-season species and as between 211.0 and 488.8 mm for warm-season species. Ref. [38] conducted a similar study with the sub-surface drip irrigation method in the same region and reported average water consumptions as between 260.2 and 382.7 mm for cool-season species and as between 180.4 and 357.9 mm for warm-season species. Ref. [36] used sprinkler irrigation in the same region and reported water consumptions as between 521.9 and 754.8 mm for cool-season species and as between 521.5 and 590.1 mm for warm-season species. Ref. [37] conducted a study to determine the effects of different irrigation levels (100% (S1), 75% (S3), and 50% (S4) of the evaporation measured in Class-A Pan on ET and quality characteristics of turfgrass, which reported plant water consumptions of 895.7, 809.0, 710.7, and 524.7, respectively. In the research conducted by [39] using a lysimeter to determine the actual and reference plant water consumption and related plant coefficients of cold-climate grasses between April and October in the north of Colorado, water consumption of grass plants during vegetation was measured at 736 mm.

3.3. Effects of Different Irrigation Programs on Plant Characteristics

As a measure of healthy development, germination, and coverage, plant height, weight, appearance, and root lengths were measured. As it was indicated before, sowing was performed in 2016, and completion of root and vegetative development was awaited. Thus, measurements were taken in 2017 and 2018. Measurements were initiated in mid-April and terminated in mid-October.

3.4. Germination

The grass mixture was sown on 20 May 2016. Germination and emergence started 8 days after sowing (28 May 2016). About 50% emergence was seen on 4 June 2016 and 100% on 14 June 2016 (Figure 7). Emergence and coverage were realized almost at the same time in all plots. For homogeneous germination, emergence, and coverage, all plots were initially irrigated with a sprinkler (pop-up) irrigation system.

3.5. Plant Height

Since the plant is expected to reach a certain height for mowing, the time taken to reach a certain height is taken as a basis instead of the plant height. Plant height-related data are given in

Table 6. Grass mowing height (cm) and weight (g) values for 2017.

		1	2	3	4	5	6	7	8	9	10	Total
S1	Mowing date	17.04.	02.05.	16.05.	06.06.	07.07.	10.08.	20.09.	13.10.	16.11.	-	9
	Grass height	13–15	12–14	12–14	12–14	11–13	11–13	11–13	10–12	10–12
	Mowing weight	388	301	280	298	279	286	298	278	269		2674
S2	Mowing date	17.04.	02.05.	16.05.	06.06.	07.07.	10.08.	20.09.	13.10.	16.11.	-	9
	Grass height	13–15	12–14	12–14	12–14	11–13	11–13	11–13	10–12	10–12
	Mowing weight	387	296	269	280	260	264	277	261	265		2559
S3	Mowing date	17.04.	02.05.	16.05.	06.06.	07.07.	10.08.	20.09.	13.10.	16.11.	-	9
	Grass height	13–15	11–13	12–14	12–14	11–13	11–13	11–13	10–12	10–12
	Mowing weight	385	280	250	258	240	243	252	240	258		2407
S4	Mowing date	17.04.	02.05.	16.05.	06.06.	07.07.	10.08.	20.09.	13.10.	16.11.	-	9
	Grass height	13–15	11–13	12–14	12–14	11–13	11–13	11–13	10–12	10–12
	Mowing weight	384	272	241	255	224	225	236	230	252		2309
S5	Mowing date	17.04.	02.05.	16.05.	06.06.	07.07.	10.08.	20.09.	13.10.	16.11.	-	9
	Grass height	13–15	11–13	12–14	11–13	10–12	10–12	11–13	11–13	10–12
	Mowing weight	383	258	236	240	221	217	232	222	245		2254
S6	Mowing date	17.04.	02.05.	16.05.	06.06.	07.07.	10.08.	20.09.	13.10.	16.11.	-	9
	Grass height	13–15	11–13	12–14	11–13	10–12	10–12	11–13	11–13	10–12
	Mowing weight	381	246	225	229	206	200	216	204	235		2142
S7	Mowing date	17.04.	10.05.	06.06.	12.07.	21.08.	09.10.	16.11.	-	-	-	7
	Grass height	13–15	11–13	12–14	10–12	10–12	11–13	9–11
	Mowing weight	370	250	232	235	221	232	240				1780
S8	Mowing date	17.04.	10.05.	06.06.	12.07.	21.08.	09.10.	16.11.	-	-	-	7
	Grass height	13–15	11–13	12–14	10–12	10–12	11–13	9–11
	Mowing weight	372	242	221	221	206	221	234				1717
S9	Mowing date	17.04.	15.05.	16.06.	02.08.	09.10.	16.11.	-	-	-	-	6
	Grass height	13–15	11–13	12–14	10–12	11–13	9–11
	Mowing weight	372	236	221	219	225	227					1500
S10	Mowing date	17.04.	15.05.	16.06.	02.08.	09.10.	16.11.	-	-	-	-	6
	Grass height	13–15	11–13	12–14	10–12	11–13	9–11
	Mowing weight	366	227	210	210	215	220					1448
S11	Mowing date	17.04.	17.05.	21.06.	11.08.	11.10.	16.11.	-	-	-	-	6
	Grass height	13–15	10–12	12–14	10–12	11–13	9–11
	Mowing weight	359	205	201	200	203	214					1382
S12	Mowing date	17.04.	17.05.	21.06.	11.08.	11.10.	16.11.	-	-	-	-	6
	Grass height	13–15	10–12	12–14	10–12	10–12	9–11
	Mowing weight	355	198	194	191	192	209					1339
S13	Mowing date	17.04.	18.05.	27.06.	03.10.	16.11.	-	-	-	-	-	5
	Grass height	13–15	10–12	12–14	11–13	9–11
	Mowing weight	357	195	192	207	215						1166
S14	Mowing date	17.04.	18.05.	27.06.	03.10.	16.11.	-	-	-	-	-	5
	Grass height	13–15	10–12	12–14	11–13	9–11
	Mowing weight	359	185	181	197	208						1130
S15	Mowing date	17.04.	18.05.	03.07.	06.10.	16.11.	-	-	-	-	-	5
	Grass height	13–15	10–12	12–14	10–12	9–11
	Mowing weight	352	174	175	183	202						1086
S16	Mowing date	17.04.	18.05.	03.07.	06.10.	16.11.	-	-	-	-	-	5
	Grass height	13–15	10–12	12–14	10–12	9–11
	Mowing weight	351	170	170	176	197						1064
S17	Mowing date	17.04.	26.05.	24.07.	10.10.	16.11.	-	-	-	-	-	5
	Grass height	13–15	10–12	12–14	10–12	9–11
	Mowing weight	355	160	173	175	190						1033
S18	Mowing date	17.04.	26.05.	24.07.	10.10.	16.11.	-	-	-	-		5
	Grass height	13–15	10–12	12–14	10–12	9–11
	Mowing weight	327	150	162	165	180						984
YS1	Mowing date	17.04.	02.05.	16.05.	02.06.	05.07.	09.08.	06.09.	27.09.	13.10.	16.11.	10
	Grass height	13–15	12–14	12–14	12–14	11–13	11–13	11–13	11–13	10–12	10–12
	Mowing weight	394	312	296	306	292	293	292	282	285	279	3031
YS2	Mowing date	17.04.	05.05.	23.05.	19.06.	25.07.	31.08.	09.10.	16.11.	-	-	8
	Grass height	13–15	11–13	12–14	10–12	10–12	10–12	11–13	9–11
	Mowing weight	378	265	261	260	259	240	245	252			2160
YS3	Mowing date	17.04.	18.05.	27.06.	11.08.	03.10.	16.11.	-	-	-	-	6
	Grass height	13–15	10–12	12–14	10–12	10–12	9–11
	Mowing weight	362	202	195	190	198	211					1358

and

Table 7. Grass mowing height (cm) and weight (g) values for 2018.

		1	2	3	4	5	6	7	8	9	10	11	Total
S1	Mowing date	16.04.	30.04.	18.05.	04.06.	02.07.	03.08.	03.09.	27.09.	15.10.	19.11.		10
	Grass height	13–15	11–13	11–13	11–13	11–13	11–13	11–13	10–12	10–12	9–11
	Mowing weight	380	294	296	302	294	278	291	265	259	258		2917
S2	Mowing date	16.04.	30.04.	18.05.	04.06.	02.07.	03.08.	03.09.	27.09.	15.10.	19.11.		10
	Grass height	13–15	11–13	11–13	11–13	11–13	11–13	11–13	10–12	10–12	9–11
	Mowing weight	377	286	292	290	272	259	265	246	245	252		2784
S3	Mowing date	16.04.	30.04.	18.05.	04.06.	02.07.	03.08.	03.09.	27.09.	15.10.	19.11.		10
	Grass height	13–15	11–13	11–13	11–13	11–13	11–13	11–13	10–12	10–12	9–11
	Mowing weight	373	266	280	272	249	241	246	220	223	245		2615
S4	Mowing date	16.04.	30.04.	18.05.	04.06.	02.07.	03.08.	03.09.	27.09.	15.10.	19.11.		10
	Grass height	13–15	11–13	11–13	11–13	11–13	11–13	11–13	10–12	10–12	9–11
	Mowing weight	371	257	274	262	231	224	232	211	212	242		2516
S5	Mowing date	16.04.	30.04.	18.05.	04.06.	02.07.	03.08.	03.09.	27.09.	15.10.	19.11.		10
	Grass height	13–15	11–13	11–13	10–12	10–12	10–12	11–13	10–12	10–12	9–11
	Mowing weight	369	249	257	258	230	218	2222	225	221	237		2486
S6	Mowing date	1.04.	30.04.	18.05.	04.06.	02.07.	03.08.	03.09.	27.09.	15.10.	19.11.		10
	Grass height	13–15	11–13	11–13	10–12	10–12	10–12	11–13	10–12	10–12	9–11
	Mowing weight	365	242	248	249	212	203	209	210	209	229		2376
S7	Mowing date	16.04.	04.05.	21.05.	06.06.	11.07.	22.08.	24.09.	19.10.	19.11.	-		9
	Grass height	13–15	10–12	11–13	10–12	10–12	10–12	10–12	9–11	9–11
	Mowing weight	360	239	240	236	207	205	206	198	223			2114
S8	Mowing date	16.04.	04.05.	21.05.	06.06.	11.07.	22.08.	24.09.	19.10.	19.11.	-		9
	Grass height	13–15	10–12	11–13	10–12	10–12	10–12	10–12	9–11	9–11
	Mowing weight	359	232	229	225	200	197	195	185	216			2038
S9	Mowing date	16.04.	04.05.	25.05.	18.06.	27.07.	06.09.	15.10.	19.11.	-	-		8
	Grass height	13–15	10–12	11–13	10–12	10–12	9–11	10–12	9–11
	Mowing weight	355	226	232	230	222	211	209	212				1897
S10	Mowing date	16.04.	04.05.	25.05.	18.06.	27.07.	06.09.	15.10.	19.11.	-	-		8
	Grass height	13–15	10–12	11–13	10–12	10–12	9–11	10–12	9–11
	Mowing weight	352	217	225	222	214	202	201	207				1840
S11	Mowing date	16.04.	04.05.	25.05.	18.06.	27.07.	06.09.	15.10.	19.11.	-	-		8
	Grass height	13–15	10–12	11–13	10–12	10–12	9–11	10–12	9–11
	Mowing weight	347	197	218	212	195	194	199	200				1762
S12	Mowing date	16.04.	04.05.	25.05.	18.06.	27.07.	06.09.	15.10.	19.11.	-	-		8
	Grass height	13–15	10–12	11–13	10–12	10–12	9–11	10–12	9–11
	Mowing weight	342	190	211	205	19	188	190	194				1710
S13	Mowing date	16.04.	18.05.	15.06.	23.07.	04.09.	12.10.	19.11.	-	-	-		7
	Grass height	13–15	10–12	10–12	10–11	10–12	9–11	9–11
	Mowing weight	340	187	202	198	201	203	200					1531
S14	Mowing date	16.04.	18.05.	15.06.	23.07.	04.09.	12.10.	19.11.	-	-	-		7
	Grass height	13–15	10–12	10–12	10–11	10–12	9–11	9–11
	Mowing weight	338	178	197	186	192	191	193					1475
S15	Mowing date	16.04.	18.05.	15.06.	23.07.	04.09.	12.10.	19.11.	-	-	-		7
	Grass height	13–15	10–12	10–12	10–11	10–12	9–12	9–11
	Mowing weight	330	167	198	178	185	180	186					1424
S16	Mowing date	16.04.	18.05.	15.06.	23.07.	04.09.	12.10.	19.11.	-	-	-		7
	Grass height	13–15	10–12	10–12	10–11	10–12	9–11	9–11
	Mowing weight	328	162	188	170	180	174	178					1380
S17	Mowing date	16.04.	31.05.	29.06.	20.08.	08.10.	19.11.	-	-	-	-		6
	Grass height	13–15	10–12	10–11	9–11	9–11	8–10
	Mowing weight	320	164	181	168	170	172						1175
S18	Mowing date	16.04.	31.05.	29.06.	20.08.	08.10.	19.11.	-	-	-			6
	Grass height	13–15	10–12	10–11	9–11	9–11	8–10
	Mowing weight	314	155	172	155	158	160						1114
YS1	Mowing date	16.04.	30.04.	16.05.	31.05.	18.06.	02.07.	01.08.	31.08.	27.09.	15.10.	19.11.	11
	Grass height	13–15	11–13	11–13	11–13	11–13	11–13	11–13	11–13	10–12	10–12	9–11
	Mowing weight	390	316	312	318	300	296	293	295	290	281	276	3367
YS2	Mowing date	16.04.	30.04.	18.05.	06.06.	04.07.	07.08.	06.09.	28.09.	15.10.	19.11.		10
	Grass height	13–15	11–13	11–13	10–12	10–12	10–12	10–12	9–11	9–11	9–11
	Mowing weight	366	256	268	275	253	243	245	234	221	240		2601
YS3	Mowing date	16.04.	18.05.	15.06.	23.07.	04.09.	12.10.	19.11.	-	-	-		7
	Grass height	13–15	10–12	10–12	10–12	10–12	9–11	9–11
	Mowing weight	345	194	204	211	210	191	208					1563

. Plant height development was found to be close to each other with the effect of spring precipitations in all plots in the first days of measurements. Grass height showed a regular improvement during the experiment in S1, S2, S3, S4, S5, S6, and YS1 treatments with full irrigation. Among these treatments, grass heights increased more homogeneously in YS1, S1, and S2 treatments as compared to others (S3, S4, S5, and S6), mostly because of different lateral spacings.

Although plant heights were homogeneous in S1 and S2 treatments without water deficits and irrigated with the sub-surface drip irrigation method, there was a slight difference in mowing weights. Such a difference was due to plant height. S1 treatments had greater mowing weights than S2 treatments in both 2017 and 2018. In YS1 treatments irrigated with the sprinkler irrigation method, plant height increased more than in S1 treatments irrigated with the sub-surface drip irrigation method, so both the number of mows and mowing weights were higher than in S1 treatments.

In water deficit treatments, the development of plant height has slowed down over time due to water deficits, and the number of mows has also decreased. It took more time for the plant height to reach mowing height in the S17 and S18 treatments irrigated with the sub-surface drip irrigation method, and mowing weights were much less as compared to the S1 and S2 treatments. The same situation was encountered in YS3 treatments, which were given the same amount of water and irrigated with the sprinkler irrigation method. It was reported in previous studies that plant water consumption increased with increasing plant heights [6,40,41,42,43]. Similar findings were seen in the present study, and water deficits delayed plant height developments.

3.6. Number of Mows and Mowing Weights

The first mows at the beginning of the irrigation season could be made when the grass height was 13–15 cm, with the effect of spring rains. Since the growth rate of the grass plant was different based on experimental treatments, mowing dates also varied. The number of mows, mowing dates, mowing heights, and weights are given in Table 6 and Table 7. In 2017, the highest number of mows was 10 with a mowing weight of 3.031 g m⁻² (YS1 treatment), the least number of mows was 5, and the least mowing weight was 984 g m⁻² (S18 treatments). The number of mows was 9 in S1, S2, S3, S4, S5, and S6 treatments, which were irrigated with the sub-surface drip irrigation method without water deficits. In 80% deficit irrigation treatments, the number of mows was 7 in S7 and S8 treatments and 6 in S9, S10, S11, and S12 treatments. In 60% deficit irrigation treatments, the number of mows was 6 in S13, S14, S15, S16, S17, and S18 treatments. In 2018, the highest number of mows (11) and mowing weight (3.367 g m⁻²) were obtained from YS1 treatments (100% sprinkler irrigation). The least number of mows (6) and the least mowing weight (1.114 g m⁻²) were obtained from S18 (60% sub-surface drip irrigation) treatments. In sub-surface irrigation treatments, the number of mows was 10 in S1, S2, S3, S4, S5, and S6 treatments, 9 in S7 and S8 treatments, 8 in S9, S10, S11, and S12 treatments, 7 in S13, S14, S15, and S16 treatments, and 6 in S17 and S18 treatments.

In general, the number of mows and mowing weights was greater in 2018 than in 2017 because of the precipitation in 2018. In both years, the first mowing weights were close to each other in all treatments. Then, mowing weights decreased with decreasing irrigation water quantities. In sub-surface drip irrigation treatments with the same irrigation water quantity, the number of mows and mowing weights decreased with increasing lateral spacing and lateral depths (Figure 8).

Turfgrass irrigated with larger irrigation amounts showed higher dry matter production. It is important to highlight the positive correlation between turfgrass quality and daily dry matter production in irrigated turfgrass [44]. Ref. [8] conducted a landscape irrigation study with sprinkler (pop-up) irrigation methods (100, 60, 50, and 40% of total evaporation from Class-A pan) and reported the total number of mows as 11 for full irrigation, 7 for 60% irrigation, 5 for 50% irrigation, and 4 for 40% irrigation treatments. Total mowing weight was reported as 2.931 g m⁻² for full irrigation, 1.648, 1.059, and 857 g m⁻² for 60, 50, and 40% irrigations, respectively. [34] conducted a study with the sub-surface irrigation method and reported the total number of mows as 11 and the total mowing weight as 2.84 g m⁻².

3.7. Root Lengths

Since sufficient moisture was maintained within the root zone in subsurface drip irrigations, roots did not go much below the drip lines (Figure 7). In 100% sub-surface drip irrigations, root lengths were predominantly around 10–11 cm in S1, S3, and S5 treatments with a lateral depth of 10 cm and around 15–16 cm in S2, S4, and S6 treatments with a lateral depth of 15 cm. In 80% sub-surface irrigations, roots were mainly located around the lateral lines and went 3–5 cm below the lines in S7, S9, and S11 treatments with a lateral depth of 10 cm; went down till 20 cm and slightly till 22–25 cm in S8, S10, and S12 treatments with a lateral depth of 15 cm. In 60% sub-surface drip irrigations, roots were again dominantly located around the drip lines, and some went 5–7 cm below the lines and reached about 17 cm in S13, S15, and S17 treatments with a lateral depth of 10 cm; they went down to 25 cm in S14, S16, and S18 treatments with a lateral depth of 15 cm (Figure 7).

In sprinkler (pop-up) irrigations, grass roots were dominantly around 10 cm in YS1 treatments (100% sprinkler irrigation); around 12 cm and some 15 cm in YS2 treatments (80% sprinkle irrigations); and dominantly around 15–16 cm and some around 20 cm in YS3 treatments (60% sprinkler irrigations) (Figure 9).

Ref. [34] conducted a landscape irrigation study with the subsurface drip irrigation method and indicated that roots did not go much below the drip lines and reached up to 10–12 cm underground. Ref. [45] reported that roots were shallow in areas where water was not limited, whereas under drought conditions, roots developed downward in order to take up water. Ref. [37] conducted a study to determine the effects of different irrigation levels applied to golf courses on some quality characteristics of turf grass. As a result of the research, they reported that in conditions where water is not limited, the roots are shallow, and therefore their weight is low. According to some researchers, there was a relationship between irrigation amount and root development, depending on the species and varieties [46,47]. In general, no significant change in rooting was observed at different irrigation amounts between 60% and 100% ETa [48,49]. However, under a more severe deficit irrigation regime (20% ETa), Ref. [48] observed a greater number and length of roots, but this was accompanied by a reduction in turfgrass quality.

3.8. Visual Appearance of Experimental Plots

In terms of color and quality, 100% sub-surface drip irrigations (S1 with 40 cm lateral spacing and 10 cm lateral depth and S2 with 40 cm lateral spacing and 15 cm lateral depth) maintained appealing color and homogeneous coverage throughout the irrigation season. S1 treatments were found to be better than S2 treatments. Again, 100% sprinkler irrigation (YS1) has well-maintained color and coverage. When these two different methods were compared, S1 was found to be more advantageous in terms of the number of mows and the amount of irrigation water applied (Figure 10).

Deficit irrigations (S7–S18, YS2, and YS3) yielded poorer color and coverage than the full irrigations. Both grass quality and coverage rates decreased with increasing water deficits. Dry-outs were encountered at the highest water deficits (60% irrigations). Such dry-outs were even more remarkable in 2018 because water deficits have been applied since the beginning of experiments. Grass quality and coverage also decreased with increasing lateral spacing and depth of sub-surface drip irrigations (Figure 10).

Differences in turfgrass quality among species and varieties became more noticeable as the irrigation amount was reduced. In contrast to most agricultural systems, for turfgrass, any reductions in shoot growth are perceived to be beneficial, as long as visual and functional quality are not significantly sacrificed [50]. In general, during the growing season, average visual turf quality can be maintained at an acceptable level through deficit irrigation (up to 40% ETa), while turfgrass quality can be achieved with irrigation above 60–80% ETa [44].

Refs. [8,51] indicated that irrigation water was the primary criterion to meet quality and performance standards for green areas; thus, sufficient water should be supplied for the maintenance of color and coverage in dry regions. Refs. [35,36,38] irrigated cool and warm-season grass species with sub-surface drip and sprinkler irrigation methods and indicated that plant growth and quality parameters were significantly influenced by irrigation methods and applied irrigation water quantities. Similar findings were also reported by [52].

4. Conclusions

The potential use of the sub-surface drip irrigation method in irrigation of green areas was investigated, and the sub-surface drip irrigation method was compared with the fixed sprinkler irrigation method (pop-up) in terms of irrigation parameters (amount of irrigation water applied, plant water consumption) and plant characteristics (germination, plant height, number of mows, mowing weight, root depth). The greatest water consumption and irrigation water quantities were seen in July, with almost equal amounts of water applied in 100% sub-surface and sprinkler irrigations. Although deficit irrigations reduced the amount of irrigation water applied, they resulted in changes in grass quality, color, appearance, and homogeneous coverage. In terms of color and coverage, 100% sub-surface drip irrigations (S1 with 40 cm lateral spacing and 10 cm lateral depth and S2 with 40 cm lateral spacing and 15 cm lateral depth) maintained appealing color and homogeneous coverage throughout the irrigation season. S1 treatments were found to be better than S2 treatments. Again, 100% sprinkler irrigation (YS1) has well-maintained color and coverage. When these two different methods were compared, S1 was found to be more advantageous in terms of the number of mows and the amount of irrigation water applied. Since appealing color and homogenous coverage are the principal concerns and yield (mowing weight) is not the primary criteria in landscape irrigations, sub-surface drip irrigations with 40 cm lateral spacing and 10 cm lateral depth could be used in landscape irrigations in Konya province and similar ecologies.