Evaluation of Hydraulic and Irrigation Performances of Drip Systems in Nectarine Orchards (Prunus persica var. nucipersica) in The Mediterranean Region

Abstract

This study focused on evaluating the performance of the drip irrigation systems installed in 18 different nectarines (Prunus persica var. nucipersica) orchards in the Tarsus Plain in the Mediterranean region from 2017 through 2018. The performance of the drip systems was evaluated based on parameters like average emitter discharge (Qavg), Christiansen uniformity coefficient (CU), distribution uniformity (DU), emission uniformity (EU), and system application efficiency (Ea). The results indicated that the CU varied between 81 and 98%; DU changed from 82 to 97%; EU 61–92%; absolute emission uniformity (EUa) ranged between 93 and 98%; statistical uniformity (Us) changed from 85 to 97%; application efficiency of low-quarter (AELQ) varied between 45 and 97%; potential application efficiency of low-quarter (PELQ) ranged between 55 and 83%; system application efficiency (Ea) changed from 56 to 96%; storage efficiency (Es) fluctuated between 45 and 97%; and pressure variation (Pv) 17–81% and emitter flow variations (qv) of 2–36% were determined. Although the CU, DU, and EU values were acceptable, the variations in emitter flow rates and pressures were not acceptable. The results revealed that the lower performances might be attributed to physical clogging and/or lack of system design and application practices by the farmers. It is recommended that the farmers receive appropriate training on the operation and management of drip irrigation systems.

1. Introduction

As one of the most important precision irrigation technologies, microirrigation is used worldwide because it can supply water and fertilizer to the crop root zone in a highly controlled way and greatly improves irrigation water productivity [1]. Drip irrigation has the greatest potential for efficient water and fertilizer usage. To minimize irrigation and fertilization costs, drip irrigation is important to maximize nutrient intake while using a minimum amount of water and fertilizer. The drip irrigation system comprises a pressurized pipeline with an inline or an online emitter. The proper hydraulic design of lateral drip systems usually requires precise assessment of the total head loss represented by friction loss along the pipe and the emitter and the local loss due to the emitter’s connection [2]. Irrigation modernization plans are mainly focused on improving infrastructure, providing adequate irrigation system designs but paying no attention to farmer management skills [3]. Users are prone to operating systems at a lower pressure than designed, which significantly reduces the irrigation system’s uniformity. Obviously, these drip irrigation systems have difficulty meeting the requirements of precision irrigation [1]. However, to be efficiently applied, irrigation water must be uniformly applied. That is, with each irrigation, approximately the same amount of water must be applied to all of the irrigated plants. If irrigation is not uniformly applied, some areas will receive too much water, and others will receive too little. As a result, plant growth will also be non-uniform, and water will be wasted where too much is applied. Uniformity is especially important when the irrigation system is used to apply chemicals along with the irrigation water because the chemicals will only be applied as uniformly as the irrigation water. The successful performance of a drip irrigation system depends on the physical and hydraulic characteristics of the drip tubing. The best and most desirable feature of drip irrigation is that it makes the uniform distribution of water possible, which is one of the most important parameters in the design, management, and adoption of this system [4]. Ideally, a well-designed system applies nearly equal amounts of water to each plant, maintaining uniformity while meeting its water requirements and being economically feasible.

The uniformity of water distribution is one of the important parameters in determining the efficiency of the design of drip irrigation systems. Clogging for a long period of time has been a major obstacle in the development of drip irrigation. Emitter clogging can reduce the uniformity of the irrigation system, especially when fertilizer (fertigation) is applied. Therefore, proper assessment to select an appropriate emitter is necessary to prevent clogging [5]. The emitter’s hydraulic properties include the effects of emitter design, water quality, water temperature, and other factors on emitter flow rate. Factors such as emitter plugging and wear of emitter components will affect water distribution as emitters age.

Proper design ensures high potential efficiency that is achieved through adequate management [6]. The uniformity parameters are the main criteria for designing an efficient drip irrigation system [7]. The variation in water distribution by emitters may occur due to pressure changes, manufacturing variations, emitter sensitivity to clogging, temperature effects, and other factors [8].

Drip irrigation has made tremendous strides in the past four decades, and it has become the modern standard for efficient irrigation practices for water conservation and optimal plant responses. Microirrigation is an extremely flexible set of technologies that can be economically used on almost every crop, soil type, and climatic zone, but it requires a high level of management [9]. Obtaining the expected benefit from drip irrigation depends on projects designed and managed carefully by trained specialists as well as careful running of the drip irrigation. The system should be carried out and processed as suggested in the project. The initial investment costs of drip irrigation are high, and carrying out drip irrigation requires significant amounts of data and skill. Therefore, farmers should be informed about the management of drip irrigation systems, and they should be made conscious of these system. Thus, the systems should be used more effectively and efficiently.

It is stated that system evaluation techniques can be used to determine the system’s potential for more economical and efficient operation by revealing irrigation performance under current operating conditions [10]. Such studies are important in deciding whether to continue with current implementations or whether business adjustments can be made. Parameters that affect the system, such as system water application efficiency (Ea), lower quarter potential, and actual application efficiencies (PELQ and AELQ) to evaluate the irrigation performance of systems have been developed by researchers [11]. PELQ and AELQ indicate whether the system is properly operated and display operating errors.

The hydraulic performance of a drip irrigation system is indicated by water distribution uniformity, which is measured by the uniformity coefficient, emission uniformity, coefficient of variation, and coefficient of manufacturing variation [12]. The efficiency of a drip irrigation system depends on the uniformity of the water distribution, which can be evaluated by measuring the flow rate in each emitter [13]. The different measurements for the hydraulic performance of drip irrigation systems are very useful for the effective design and operation of the system [14]. The determination of the total head loss in a drip irrigation system is very important to ensure the system operates with sufficient pressure. The average operating pressure head for the emitter, distribution of uniformity, and head loss between lateral and manifold will arise as a result of the optimal economic impact [15]. Bralts et al. [16] stated that theoretically, the compensating drip emitter discharge should not show any variation under different pressure heads. Even if pressure head should be only observed in non-pressure-compensating emitters, a properly designed pressure-compensating drip emitter will behave like a non-pressure-compensating emitter if the pressure variation limits exceed certain predefined limits provided by the manufacturers [17].

The use of microirrigation is rapidly increasing around the world, and it is expected to continue to be a viable irrigation method for agricultural production in the foreseeable future. With increasing demand on limited water resources and the need to minimize the environmental consequences of irrigation, microirrigation technology will undoubtedly play an even more important role in the future [9]. The use of drip systems has increased since the early 2000s, converting surface irrigation systems to drip through a national subsidy system by the Turkish Government. Therefore, through this subsidy program, many farmers in Tarsus Plain located in the eastern Mediterranean region of Turkey have also converted their system to a drip system. Tarsus Plain has an important place in our country’s agricultural activities. In 2017, 106,674 tons of products were obtained from 7252 ha of nectarine orchards. In particular, nectarine plants have started to be preferred extensively by the producers in the region [18].

The objectives of this study are to evaluate the performance of drip irrigation systems in the young nectarine orchards in the Tarsus Plain located in the Eastern Mediterranean region of Türkiye. The performance evaluation of the drip systems was based on both the hydraulic performance criteria such as distribution uniformity, emission uniformity, Christiansen uniformity coefficient, pressure variation, flow rate variation, statistical uniformity coefficient, and irrigation management performance criteria such as application efficiency, potential application efficiency of the low quarter, actual application efficiency of the low quarter, and storage efficiency under the grower’s operation conditions. The performance parameters of the drip systems tested are compared with the standards set by the American Society of Agricultural and Biological Engineers (ASABE) [19].

2. Materials and Methods

2.1. Experimental Site and Soil

This research was carried out between 2017 and 2018 in eighteen nectarine orchards in Tarsus, located in the Eastern Mediterranean region of Türkiye. The elevation of Tarsus is 12 m above sea level, and a typical Mediterranean climate prevails in the region. The average annual temperature in the region is 18.2 °C. According to long-term historical measurements (1965–2018), the average relative humidity is 70.2% and the annual evaporation is 1478 mm. The average annual rainfall is 630 mm, mostly distributed from September to May, with a high inter-annual variability. The long-term historical average climate characteristics of this study are given in

Table 1. Long-term monthly mean climatic data for the nectarine orchards in Tarsus Plain (Turkish State Meteorological Service, 2019).

Months	February	March	April	May	June	July
Tmin °C	6.9	9.2	12.9	16.8	20.9	24.0
Tmax °C	15.5	18.1	21.6	24.9	28.1	30.7
Tmean °C	11.1	13.8	17.5	21.3	25.0	27.8
Sunshine time (h)	5.6	6.8	7.6	8.5	9.8	10.0
Number of rainy days	9.2	7.6	6.6	5.1	2.2	0.9
Monthly precipitation (mm)	85.1	55.2	34.7	23.4	9.0	6.8

Note: Tmax: maximum air temperature; Tmin: minimum air temperature; Tmean: mean air temperature.

[20].

This study was carried out on 18 selected nectarine orchards irrigated with a drip system in the Tarsus Plain. The nectarine orchard size ranged from 1.1 ha to 9.0 ha, and the age of the orchards varied from 1 to 9 years. In the orchards, trees were planted with 3 m row spacing and 5 m in the rows.

The soils in the selected orchards were examined by taking gravimetric soil samples at four locations in each orchard, and the following analyses were carried out to determine water holding capacity, texture class, soil salinity, bulk density, organic matter content, lime amounts, and pH. In addition, double-ring infiltrometer tests were carried out to determine the infiltration rate of the soils. The soil analysis in the laboratory revealed that soil water content at field capacity varied between 7.50 and 35.43%, wilting point values ranged from 5.35 to 27.12%, and bulk density values changed between 1.27 and 1.60 g cm⁻³. Soil infiltration rates (I) varied from 6.1 to 21.4 mm h⁻¹, and soil salinity values (EC) fluctuated between 0.398 and 6.10 dS m⁻¹. Organic matter contents ranged from 0.46 to 1.50%, lime amounts ranged between 7.37 and 34.32%, and pH values varied between 7.64 and 8.26. The soil textures were clay-loam in orchards P1 and P2, sandy-loam in orchards P7, P10, and P11, and clay in the other orchards. The physical and chemical properties of the soils of the selected orchards are given in

Table 2. Physical and chemical properties of the soils in the selected nectarine orchards.

Orchard No.	Soil Depth cm	BD g cm−3	FC % Pw	WP % Pw	Particle Size Distribution (%)			Texture Class	I mm h−1	pH	EC dS m−1
					Sand	Clay	Silt
1	0–30	1.38	26.86	17.57	33.9	29.5	36.7	CL	8.2	7.92	0.598
	30–60	1.27	27.53	18.18	31.7	31.6	36.8	CL		8.05	0.755
	60–90	1.33	32.17	22.07	29.1	38.1	32.8	CL		7.84	1.098
P2	0–30	1.40	27.13	17.88	27.2	31.7	41.1	CL	8.6	7.93	0.480
	30–60	1.43	25.93	17.60	31.5	29.6	38.9	CL		8	0.398
	60–90	1.44	27.25	18.43	29.4	31.6	38.9	CL		7.73	1.010
P3	0–30	1.33	32.43	26.57	6.3	70.1	23.6	C	6.5	7.84	4.240
	30–60	1.39	32.88	27.12	6.0	70.3	23.7	C		7.8	7.550
	60–90	1.35	33.53	24.16	13.5	54.6	31.9	C		7.82	4.240
P4	0–30	1.30	32.15	25.54	9.8	69.4	20.8	C	6.3	7.74	3.660
	30–60	1.32	32.12	26.44	7.6	67.3	25.1	C		7.85	4.680
	60–90	1.34	32.23	26.90	5.8	67.0	27.2	C		7.88	6.190
P5	0–30	1.36	30.81	20.17	22.4	40.1	37.5	C	7.9	7.72	0.795
	30–60	1.47	29.85	18.27	24.8	35.8	39.4	CL		7.74	0.792
	60–90	1.41	31.17	19.32	18.4	37.9	43.7	SiCL		7.71	0.977
P6	0–30	1.38	29.63	19.90	20.2	44.3	35.5	C	8.2	7.91	0.552
	30–60	1.37	30.62	20.68	22.1	40.2	37.6	C		7.88	0.626
	60–90	1.44	29.79	19.60	24.5	35.9	39.6	CL		7.9	0.634
P7	0–30	1.52	8.98	6.95	79.6	10.2	10.2	SL	18.4	7.48	0.629
	30–60	1.55	7.73	5.55	83.7	8.1	8.1	LS		7.38	0.603
	60–90	1.60	8.23	5.82	83.7	8.2	8.2	LS		7.47	0.589
P8	0–30	1.33	32.87	23.63	3.2	60.3	36.5	C	6.5	8.00	0.878
	30–60	1.39	32.91	25.04	11.4	54.1	34.5	C		7.98	1.311
	60–90	1.35	33.19	24.42	9.9	51.6	38.5	C		7.91	0.831
P9	0–30	1.33	32.04	24.14	13.2	53.1	33.7	C	6.4	7.64	0.678
	30–60	1.39	31.40	25.37	23.8	55.2	21.0	C		8.1	0.656
	60–90	1.35	32.47	25.38	15.4	57.3	27.3	C		8.26	0.945
P10	0–30	1.52	8.92	6.89	79.0	10.5	10.5	SL	19.6	7.45	0.633
	30–60	1.55	7.65	5.70	83.4	8.2	8.4	LS		7.33	0.608
	60–90	1.60	8.29	6.00	83.1	8.3	8.6	LS		7.44	0.594
P11	0–30	1.51	9.01	7.04	79.2	10.5	10.3	SL	21.4	7.40	0.638
	30–60	1.57	7.50	6.50	83.4	8.5	8.1	LS		7.39	0.615
	60–90	1.60	8.40	5.35	83.2	8.4	8.4	LS		7.46	0.590
P12	0–30	1.36	29.56	21.04	16.7	48.6	34.7	C	6.7	8.06	0.607
	30–60	1.43	32.52	23.79	11.4	57.7	30.8	SiC		8.02	0.756
	60–90	1.40	30.07	21.59	1.6	57.2	41.2	C		8.07	0.554
P13	0–30	1.32	33.05	23.90	11.6	56.1	32.3	C	6.4	7.98	0.666
	30–60	1.40	34.09	23.56	15.7	56.2	28	C		8.12	0.602
	60–90	1.42	35.27	23.70	13.6	56.2	30.2	C		8.14	0.674
P14	0–30	1.34	33.56	24.97	11.9	72.7	15.4	C	6.8	8.32	0.894
	30–60	1.44	33.82	25.35	9.8	74.9	15.4	C		8.46	1.295
	60–90	1.41	34.43	25.15	5.5	74.7	19.7	C		8.50	1.980
P15	0–30	1.35	33.00	23.70	11.6	56.1	32.3	C	7.1	7.96	0.680
	30–60	1.41	35.45	23.78	15.7	56.2	28	C		8.10	0.615
	60–90	1.40	33.56	23.60	13.6	56.2	30.2	C		8.12	0.680
P16	0–30	1.32	32.56	24.97	11.9	72.7	15.4	C	7	8.30	0.900
	30–60	1.41	32.82	24.35	9.8	74.9	15.4	C		8.40	1.300
	60–90	1.42	35.43	25.15	5.5	74.7	19.7	C		8.46	1.983
P17	0–30	1.34	27.61	19.37	19.4	19.4	44.0	C	6.4	8.01	0.504
	30–60	1.44	28.12	19.82	14.6	14.6	44.3	SiC		7.96	0.466
	60–90	1.41	29.35	21.48	12.2	12.2	44.5	SiC		7.91	0.684
P18	0–30	1.40	32.11	22.99	19.8	44.5	35.7	C	6.1	7.68	0.574
	30–60	1.40	32.11	21.69	19.7	44.6	35.7	C		7.83	0.502
	60–90	1.42	31.61	21.01	21.7	44.7	33.6	C		7.87	0.598

Note: FC, field capacity; WP, permanent wilting point; BD, bulk density; I, infiltration rate; EC, soil electrical conductivity; C, clay; CL, clay loam; SiCL, silty clay loam; SL, sandy loam; LS, loamy sand; SiC, silty clay.

.

2.2. General Properties of Drip Irrigation in Nectarine Orchards

The drip systems installed in the 18 nectarine orchards were inspected visually from the control unit to the laterals. On the control unit, the filter types, pressure gauges, and fertilizer tanks were inspected. Then, the mainline pipe material, length, and diameter; the manifold material, length, and diameter; and the lateral line length and emitter spacing were also examined. In the tarsus area where the nectarine orchards are located, the land slopes are below 1%. In the nectarine orchard with the longest lateral line (P9, 191 m), the differences in elevation between the beginning and end of the line is 1 m.

The general characteristics of the drip irrigation systems in the nectarine orchards are given in

Table A1. Drip irrigation system characteristics in the selected nectarine orchards and irrigation water supply and quality.

Orchard No/Properties	P1	P2	P3	P4	P5	P6	P7	P8	P9	P10
Area (ha)	1.5	3.5	2.5	2.5	5.0	5.0	2.0	9.0	9.0	1.8
Tree age (years)	8	3	6	6	7	2	4	2	2	4
Plant Row Spacing (m)	5	5	5	5	5	5	5	5	5	5
Plant Row (m)	3	3	3	3	3	3	3	3	3	3
Age of the System	7	2	5	5	6	1	3	1	1	3
Filter type	H + DF	H + MF + DF	H + MF + DF	H + MF + DF	H + MF + DF	H + MF + DF	H + DF	MF + DF	H + MF + DF	H + DF
Main Pipe Material	PVC-PE	PVC-PE	PVC-PE	PVC-PE	PVC-PE	PVC-PE	PVC-PE	PVC-PE	PVC-PE	PVC-PE
Main Pipe Diameter (mm)	75	140	110	110	110	110	90	140	140	110
Main Pipe Length (m)	226	223	172	487	168	465	135	450	400	100
Manifold Pipe Material	PE	PVC	PVC	PVC	PE	PE	PE	PE	PE	PE
Manifold Diameter (mm)	63	90–75–63	90–75–63	63	90–75–63	90–75–63	63	90–75–63	90–75–63	50
Manifold length (m)	207	385	131	120	70	103	200	140–160	150	185
Lateral Pipe Diameter (mm)	16	20	20	20	16	20	20	20	20	16
Lateral Pipe Length (m)	50	137	180	180	84	165	120	167	191	87
Lateral Spacing (m)	0.80	0.80	0.80	0.80	0.80	0.30	0.80	0.30	0.30	0.80
Emitter Flow (L h−1)	2	2	2	2	2	2	2	2	2	2
Measured Avg. Emitter Flow Rate (L h−1)	2.24	2.20	2.15	2.25	2.45	2.78	2.43	1.75	2.10	2.32
Measured Avg. Emitter Pressure (kPa)	85	125	166	118	103	173	117	87	113	75
Emitter spacing (cm)	50	50	50	50	50	50	50	40	50	50
Emitter type	PC	PC	PC	PC	PC	PC	PC	NPC	PC	PC
Operating Pressure (kPa)	110	280	350	350	150	150	300	150	180	200
System Age (years)	7	2	5	5	6	1	3	1	1	3
Water Supply	Deep well	Deep well	Canal	Canal	Canal	Canal	Deep well	Canal	Canal	Deep well
Irrigation Water (EC, dS m−1)	0.714	0.512	1.286	1.286	0.455	0.455	0.843	0.500	0.650	0.923
Irrigation Water (pH)	7.22	8.25	7.70	7.70	7.92	7.92	6.87	7.98	8.03	6.91
Orchard No/Properties	P11	P12	P13	P14		P15	P16		P17	P18
Area (ha)	1.3	6.3	1.2	1.8		1.1	1.3		2.0	1.7
Tree age (years)	4	6	4	4		4	4		10	5
Plant Row Spacing (m)	5	5	5	5		5	5		5	5
Plant Row (m)	3	3	3	3		3	3		3	3
Age of the System	3	8	3	3		3	3		9	4
Filter type	H + DF	H + MF + DF	H + MF + DF	H + MF + DF		H + MF + DF	H + MF + DF		MF + DF	H + MF + DF
Main Pipe Material	PVC-PE	PVC-PE	PVC-PE	PVC-PE		PVC-PE	PVC-PE		PVC-PE	PVC-PE
Main Pipe Diameter (mm)	110	110	110	90		110	90		110	125
Main Pipe Length (m)	100	210	170	147		170	147		220	200
Manifold Pipe Material	PE	PE	PE	PE		PE	PE		PE	PE
Manifold Diameter (mm)	50	75–63	75–63	90–75–63		75–63	90–75–63		75–63	90–75–63
Manifold length (m)	105	60	70	125		70	110		50	90
Lateral Pipe Diameter (mm)	16	20	20	20		20	20		20	20
Lateral Pipe Length (m)	100	140	171	110		159	120		114	75
Lateral Spacing (m)	0.80	0.80	0.80	0.80		0.80	0.80		0.80	0.80
Emitter type	PC	NPC	PC	PC		PC	PC		PC	PC
Emitter Flow (L h−1)	2	2	2	2		2	2		2	2
Measured Avg. Emitter Flow Rate (L h−1)	2.34	1.53	2.50	2.11		2.45	2.16		2.25	2.91
Measured Avg. Emitter Pressure (kPa)	163	78	91	148		125	165		207	146
Emitter spacing (cm)	50	40	33	50		33	50		50	60
Operating Pressure (kPa)	200	180	200	300		250	280		270	250
System Age (years)	3	5	3	3		3	3		9	4
Water Supply	Deep well	Canal	Canal	Canal		Canal	Canal		Deep well	Deep well
Irrigation Water (EC, dS m−1)	0.905	0.370	0.486	0.456		0.486	0.456		0.343	0.650
Irrigation Water (pH)	6.87	8.37	8.09	8.10		8.09	8.10		7.84	8.03

Note: H, Hydrocyclone; MF, Media filter; DF, Disk filter; PC, Pressure Compensating; NPC, Non-pressure compensating.

. The sizes of these orchards vary between 1.1 and 9.0 ha, the planting spacing of fruit trees (tree row spacing × tree spacing in rows) is 5 × 3 m and the tree ages are between 1 and 9 years. The system filters consist of hydrocyclone, media filters, disk filters, and their combinations. The farmers supply water from the deep wells using hydrocyclone and disk filters, while they obtain water from open channel systems utilizing media filters as primary filters along with disk filters. PE and PVC pipes are used in the main pipe and manifold pipelines. The manifold pipe diameters vary between 50 and 90 mm, the main pipe diameters are 75–140 mm, the manifold line lengths vary between 50 and 385 m, and the main pipe lengths change from 100 to 487 m. Lateral pipe diameters of 16 and 20 mm were used on the systems, and the lateral lengths varied between 50 and 191 m. Fertilizer tanks existed on the drip systems tested. However, only a few growers used them for fertigation, while the others used conventional fertilizer applications.

Inline emitters with 2 L h⁻¹ discharge rates are commonly used for irrigation of orchards in the project area. Some of them were pressure-compensating, and some of them were non-pressure-compensating emitters on their systems. About 10% of the orchards tested and measurements taken used non-compensating emitters, while 90% used pressure-compensating emitters.

2.3. Measurements and Analysis in the Field

Measurements and observations in the selected orchards were carried out in the irrigation system sub-units to represent the production area. The evaluation tests were carried out in one sub-unit to obtain the performance criteria. Some performance criteria, such as uniformity (application uniformity, distribution uniformity, statistical uniformity, emission uniformity, emitter discharge coefficient of variation due to hydraulics, change in hydraulics on manifold and laterals, etc.), irrigation efficiencies (maximum application depth, application efficiency, potential and actual application efficiencies in the low quarter, etc.), wetting patterns of the system, etc., were measured or estimated, analyzed, and evaluated using the mentioned measurement values. Emitter flow and pressure variation along the lateral line in selected irrigation subunits in each orchard were measured. How these measurements were made is explained in the following paragraphs.

2.4. Hydraulic Performance Parameters

2.4.1. Emitter Flow and Pressure Measurements

The emitter flow rate and pressure measurements in the trial orchards were carried out using the method given by Merriam and Keller [10]. By measuring the emitter flow rates and emitter pressures, the average, minimum, and maximum emitter flow rates and average emitter pressures were determined. Evaluations were made by comparing the values specified by ASABE [19]. Four different lateral pipelines were selected: the first one was at the beginning of the manifold, the second one was at 1/3 distance from the beginning of the manifold, the third one was at 2/3 distance, and the fourth one was at the end of the manifold. On each lateral pipeline, 4 drippers were selected. The first one was at the beginning of the lateral, the second one was at 1/3 the distance from the lateral entrance, the third one was at 2/3 distance, and the fourth one was at the end of the lateral.

Emitter pressure measurements were measured using a glycerin pressure gauge with a scale of 0–600 kPa at the point where the water flows from the dripper to the atmosphere.

Emitter flow rates were determined volumetrically using shallow plastic containers under the emitters in the tested laterals for 5 min durations. Thus, flow measurements were made on at least 16 drippers in each lateral and at least 64 drippers in each drip system. Mean emitter flow rates were determined using Equation (1), and average emitter pressures were determined using Equation (2).

$$qavg={\displaystyle \frac{1}{\mathrm{n}}}{\sum }_{\mathrm{i}=1}^{\mathrm{n}}\times {\mathrm{q}}_{\mathrm{i}}$$

(1)

In this equation, qavg is the average emitter flow rate, L h⁻¹; qi is the emitter flow rate of the i-th emitter, L h⁻¹; and n is the number of emitters.

$$Pavg={\displaystyle \frac{1}{\mathrm{n}}}{\sum }_{\mathrm{i}=1}^{\mathrm{n}}{\times \mathrm{P}}_{\mathrm{i}}$$

(2)

where Pavg is the average emitter pressure, kPa; Pi is the pressure at the i-th emitter, kPa; and n is the number of emitters.

Pressure Variations in Laterals (Pv)

Pressure measurements were made at the inlets and outlets of the selected subdomains, as well as 4 laterals on each subdomain (at the inlet of the manifold and lateral, 1/3, 2/3, and the end) using pressure gauges. Emitter flow rates and pressure measurements were made at the selected laterals. Pressure measurements were made at the inlet, 1/3 and 2/3 away from the inlet, and at the end of the lateral. The pressure variations were estimated using Equation (3).

$$P_v={(P}_{inlet}-P_{outlet})÷P_{inlet}$$

(3)

where Pv is the manifold or lateral pressure variation, %; P_inlet is the sub main or lateral inlet pressure (kPa); and P_outlet is the sub main or lateral outlet pressure (kPa). In drip irrigation system design, the maximum pressure variation allowed is 20% [10].

Emitter Flow Variation (qv)

Emitter flow variations in the laterals were calculated using Equation (4) [6].

$$q_v=\left[\left(q_{max}-q_{min}\right)/q_{max}\right]\times 100$$

(4)

where qv is the emitter flow variation, %; q_max is the maximum emitter flow rate, L h⁻¹; and q_min is the minimum emitter flow rate, L h⁻¹. The general standards for qv values are as follows: 10% or less is desired; 10% to 20% is acceptable; and above 25% is not acceptable based on the ASABE guidelines [19].

Coefficient of Variation (Cv) of the Emitter Flow

The manufacturing variation coefficient is a measure of the flow variation of a randomly selected emitter that has been manufactured by a producer in a certain model and size, has never been used, or has not been worn. The estimated producer modification coefficient must belong to a new emitter operating at a constant temperature and operating pressure. The manufacturing variation coefficient was determined using Equation (5), and it was evaluated according to the ASABE guidelines [19].

$$Cv={\displaystyle \frac{S_d}{qavg}}$$

(5)

Here, Cv is the manufacturing coefficient of variation; Sd is the standard deviation of emitter flow rates, L h⁻¹; and qavg is the average emitter flow rate, L h⁻¹. The guidelines for classifying the manufacturing coefficient of variation are specified by ASABE [19].

Christiansen Uniformity Coefficient (CU)

The Christiansen uniformity coefficient (CU) gives information regarding how efficiently water is distributed in the field. CU is calculated using Equation (6) [21]:

$$CU=100.0-80.0{\displaystyle \frac{s_d}{q_{avg}}}$$

(6)

where Sd is the standard deviation of the emitter flow rates, L h⁻¹; and qavg is the average emitter flow rate, L h⁻¹. The guidelines for classifying the Christiansen uniformity coefficient (CU) are shown in

Table 3. Classification of the performance criteria for different uniformity expressions [19].

Classification	Cv (%)	CU (%)	DU (%)	EU (%)	Us (%)
Excellent	<5	>90	>85	≥94	>90
Good	5–7	80–90	70–85	81–87	80–90
Fair	7–11	70–80	60–70	68–75	70–80
Low	11–15	60–70	50–60	56–62	60–70
Unacceptable	>15	<60	<50	≤50	<60

[19].

Distribution Uniformity (DU)

Distribution uniformity (DU) is another index of application uniformity. Distribution homogeneity (DU) is the ratio of the average amount of water in the 1/4 of the land receiving the least water to the average amount of water retained in the entire area. The dripper uniformity values are a strong indicator that all the drippers in the area provide nearly identical flow rates, ensuring an even distribution of water across the whole area. The distribution homogeneity (DU) was calculated using Equation (7), and it was evaluated according to Merriam and Keller [10].

$$DU=100\times {\displaystyle \frac{q_{lq}}{q_{avg}}}$$

(7)

In this equation, DU is the distribution homogeneity, %; qlq is the lower quarter average emitter flow rate, L h⁻¹; and qavg is the average emitter flow rate, L h⁻¹.

Emitter Flow Uniformity (EU)

For the emitter flow uniformity, ref. [21] presented a design method to determine irrigation depth and interval, system capacity, emitter flow characteristics and uniformity, and hydraulic design considerations. Furthermore, they developed two formulas to estimate the design emission uniformity for drip irrigation systems; these formulas are expressed as follows in Equation (8), and it was evaluated according to Table 3 [19].

$$EU=\left[1-1.27{\displaystyle \frac{Cv}{N^{0.5}}}\right]\times \hspace{0.33em}{\displaystyle \frac{q_{min}}{q_{avg}}}$$

(8)

Here, EU represents the dripper flow emission (output) uniformity, %; N is the evaluated number of emitters for each plant; Cv is the coefficient of variation; qmin is the minimum emitter flow rate, L h⁻¹; and qavg average emitter flow rate, L h⁻¹.

Statistical Uniformity (Us)

Statistical uniformity (Us) was calculated using the equation given below according to the principles given by Bralts and Kesner [16].

$$Us=100\times \left(1-C_v\right)=100\hspace{0.33em}\left(1-{\displaystyle \frac{S_d}{q_{avg}}}\right)$$

(9)

In the equation, Cv is the coefficient of variation; Sd is the standard deviation of emitter flow rates, L h⁻¹; and qavg is the average emitter flow rate, L h⁻¹. Statistical uniformity was evaluated according to ASABE [19] based on the classification criterion presented in Table 3.

2.4.2. Irrigation Management Performance Parameters

Irrigation performance was evaluated for the farmers’ operation conditions in the selected nectarine orchards in one irrigation application for each orchard, since the farmers apply fixed irrigation scheduling (weekly water application and durations set by growers). The following criteria were evaluated for irrigation management.

Wetting Percentage (P)

The wetting percentage (P) was determined using Equation (10) by measuring the wetted area in the field, taking into account the tree row spacing and tree spacing. The wetted area was estimated about 15 cm below the soil surface under an emitter following irrigation in the selected nectarine orchards.

$$\mathrm{P}=100\times \left({\displaystyle \frac{{\mathrm{A}}_{\mathrm{w}}}{{\mathrm{S}}_{\mathrm{s}}{\mathrm{S}}_{\mathrm{a}}}}\right)$$

(10)

Here, P is the wetting percentage, %; Aw is the wetted area, m²; Ss is the tree row spacing, m; and Sa: is the tree spacing, m.

Storage Efficiency (Es)

Storage efficiency is a criterion for irrigation efficiency determined by sufficient water application until the moisture deficit in the plant root zone reaches the field capacity. In the calculations, the equation given by James [22] was used.

$$E_s=100\times {\displaystyle \frac{S_{rz}}{SMD}}$$

(11)

In this equation, Es is the storage efficiency, %; Srz is the amount of water stored in the root zone (or depth of soil to be wetted) during irrigation, mm; and SMD is the amount of water deficit in the root zone before irrigation (the amount of water required to bring the available moisture to the field capacity), mm. SWD was determined via gravimetric soil sampling at three depths (0–30; 30–60; and 60–90 cm) one day before the date of scheduled irrigation.

Water Application Efficiency (Ea)

The application efficiency (Ea) of an irrigation system is defined as the percentage of total water applied accumulated in the plant root zone. When the plant root zone is fully irrigated according to the required water volume, the water application efficiency (Ea) ASAE [23] is calculated using Equation (12).

$$E_a=100\times {\displaystyle \frac{Vs}{V_a}}$$

(12)

In this equation, Ea is the water application efficiency, %; V_s is the required (water stored in the root zone) irrigation water, m³; and V_a is the total amount of water applied in the wetted area, m³.

Potential Application Efficiency of the Low Quarter (PELQ)

The potential application efficiency in the low quarter (PELQ) was calculated using the approach given by Meriam and Keller [10].

$$PELQ=0.9\times EU$$

(13)

In this equation, PELQ is the potential application in the low quarter and EU is emitter flow uniformity, %.

Actual Application Efficiency of the Low Quarter (AELQ)

AELQ is used as an indicator of the efficiency of drip irrigation systems and how much of the applied water is stored in the root zone and is available for plants. The actual application efficiency of the low quarter (AELQ) is calculated using the approach given by Meriam and Keller [10]:

$$AELQ=100\times {\displaystyle \frac{SMD}{d}}$$

(14)

where AELQ is the actual application efficiency of the low quarter, %; SMD is the soil moisture deficit in the rootzone, mm; and d is the average water depth applied through the emitters, mm.

2.5. Water Sources

Water was supplied from deep wells in seven of the orchards and from open-channel irrigation networks in 10 orchards for the performance evaluation study. Water samples were taken for each orchard, and water quality was analyzed in the laboratory. Information regarding the water quality of the canal water and well waters (EC and pH values) is presented in Table A1. In general, both water resources had good quality for irrigation, but they were rich in CO₃ and HCO₃, which causes emitter clogging in the drip systems.

3. Results

3.1. Evaluation of Hydraulic Performance Criteria

Lateral pressure variations (Pv) fluctuated between 17 and 81% and emitter flow variations ranged from 2 to 36%, as shown in

Table 4. Obtained drip system performance parameter values and yield for the selected nectarine orchards.

Orchard No.	qavg	Pavg	qv	Pv	Cv	CU	DU	EU	Us	Es	Ea	PELQ	AELQ	Wetting Percentage
	L h−1	kPa	%	%	%	%	%	%	%	%	%	%	%	%
P1	2.2	80	5	35	8	83	80	76	92	67	52	68	67	35
P2	2.2	130	2	36	3	82	80	75	97	45	74	67	45	33
P3	2.2	170	6	38	7	85	75	81	93	65	56	73	65	37
P4	2.3	120	5	30	8	88	79	78	92	55	66	70	55	37
P5	2.5	100	2	18	8	93	88	76	92	63	56	68	63	35
P6	2.8	170	6	19	9	86	82	81	91	52	71	73	52	37
P7	2.4	120	3	24	11	89	86	74	89	69	62	67	69	22
P8	1.8	90	19	39	15	81	80	61	85	50	74	55	50	37
P9	2.1	110	6	35	4	85	80	85	96	60	61	77	60	37
P10	2.3	80	19	27	10	80	76	78	90	85	71	70	85	20
P11	2.3	160	5.0	24	8	88	84	80	92	87	79	72	87	18
P12	1.5	80	36	26	15	78	76	63	85	49	76	57	49	37
P13	2.5	90	30	74	9	72	66	75	91	55	67	68	55	37
P14	2.1	150	2	31	4	95	90	89	96	86	71	80	86	30
P15	2.5	130	25	81	12	70	67	63	88	58	60	57	58	35
P16	2.2	170	8	17	5	86	80	87	95	79	40	78	79	32
P17	2.3	210	5	22	11	91	87	70	89	56	57	63	56	32
P18	2.9	150	3	23	4	94	90	88	96	76	68	79	76	37

. In drip irrigation design, the maximum pressure variation allowed, as stated by Evans et al. [9], is 20%. The lateral pressure variations in the tested plots remained above 20% in most of the 18 orchards except in P5, P6, and P16. The lateral lengths varied between 50 and 191 m in all the orchards. Orchard P9 had the longest lateral length of 191 m, while orchard P1 had the shortest lateral length of 50 m.

The emitter flow variations observed in the tested drip systems were usually at acceptable levels. The general standards for emitter flow variation (qv) values are as follows: 10% or less, desired; 10% to 20%, acceptable; and above 25%, not acceptable [4,23]. The emitter flow variation remained between 10 and 20%, within acceptable limits, in orchards P8 and P10. However, flow variations above 25% were observed in orchards P12, P13, and P15 which were unacceptable. The average emitter flow rates (q_avg) measured in the drip systems varied between 1.5 and 2.9 L h⁻¹, and the mean operating pressures (P_avg) changed between 110 and 350 kPa, as shown in Table A1.

The coefficient of variation of the emitter flows (Cv) for the tested drip systems varied between 3 and 15%, and their classifications were made according to ASABE guidelines [19], as shown in Table A1. The calculated performance values and the classification evaluation of select performance criteria for the selected nectarine orchards are given in Table 3 and

Table 5. Classification of performance criteria for the drip systems in selected nectarine orchards.

Orchard No	Classification Parameters
	CV	CU	DU	EU	Us	Yield (t ha−1)
P1	Fair	Good	Good	Fair	Excellent	45.02
P2	Excellent	Good	Good	Good	Excellent	46.49
P3	Fair	Good	Good	Fair	Excellent	44.71
P4	Fair	Good	Good	Fair	Excellent	43.55
P5	Fair	Excellent	Excellent	Fair	Excellent	45.11
P6	Fair	Excellent	Excellent	Fair	Excellent	46.44
P7	Fair	Excellent	Excellent	Low	Excellent	46.20
P8	Unacceptable	Fair	Fair	Low	Good	31.17
P9	Excellent	Good	Fair	Good	Good	42.69
P10	Fair	Fair	Fair	Fair	Excellent	38.55
P11	Fair	Excellent	Excellent	Fair	Good	49.33
P12	Unacceptable	Fair	Good	Low	Excellent	33.66
P13	Fair	Fair	Good	Fair	Good	36.49
P14	Excellent	Excellent	Excellent	Good	Excellent	51.02
P15	Low	Fair	Good	Low	Good	33.70
P16	Excellent	Excellent	Excellent	Good	Excellent	52.13
P17	Fair	Excellent	Excellent	Low	Good	37.82
P18	Excellent	Excellent	Excellent	Good	Excellent	49.94

, respectively. In the classification of the emitter flow rate change coefficient (Cv), point source emitters with Cv < 5% are classified as excellent; Cv = 5–7% are good; Cv = 7–11% are medium; Cv = 11–15% are low; and CV > 15% are unacceptable according to ASABE guidelines [20]. It is understood that emitter flow rate variation coefficients are excellent in five orchards (P2, P9, P14, P16, P18), good in P3, medium in nine orchards, and low in three orchards (P8, P12, P15). The research results revealed that the Cv values were classified as excellent and medium in general, thus considering the magnitude of Cv values as acceptable for the drip systems tested.

To evaluate the distribution of irrigation water in the tested drip irrigation systems, the Christiansen uniformity coefficient (CU) was determined for the tested irrigations. The Christiansen uniformity coefficient (CU) values of the test plots varied between 70 and 97% and are given in Table 4.

For the evaluation of CU, CU > 90% was considered excellent, CU = 80–90% was good, CU = 70–80% was medium, CU = 60–70% was low, and CU < 60% was unacceptable (Table 3). The classifications for the evaluation of select performance criteria applied to the nectarine orchards are given in Table 4. As shown in Table 4, the CU in four orchards was classified as excellent, it was good in ten orchards, and it was fair in four orchards. Therefore, the CU values observed in the tested drip systems were all at acceptable levels.

The distribution uniformity (DU) values of the test plots varied between 71 and 95% and are given in Table 4. The classification evaluation of select performance criteria for the nectarine orchards is given in Table 5. As shown in Table 5, the DU in five orchards was classified as excellent, it was good in twelve orchards, and it was fair in one orchard. Accordingly, it was observed that an acceptable level of uniform irrigation was applied. It was observed that the DU values for irrigation were always lower than the CU values, as expected.

The emission uniformity (EU) of the test orchards varied between 61.0 and 89.0%, as shown in Table 4. The classification evaluation of the performance criteria for the selected nectarine orchards is given in Table 5. As shown in Table 5, the EU values in six orchards were classified as good, in nine orchards as fair, and in three orchards as low. Considering the obtained values for EU, the low water emission uniformity values in orchards P7, P8, P12, P15, and P17 were not acceptable and were outside the recommended limit values. This non-uniformity of emitter discharge is the result of several factors. The hydraulic variation along the lateral line, submain, or manifold is a function of slope, pipe length and diameter, and emitter–discharge relations.

The statistical uniformity (Us) values for the tested drip systems varied between 85 and 97% and are given in Table 4. The classification evaluation of select performance criteria for the nectarine orchards is given in Table 5. When the Us values given in Table 4 are examined, drip systems in 13 orchards are in the excellent class and 5 orchards are in the good class.

In order to compare the hydraulic performance of the drip irrigation systems in the selected nectarine orchards, yield values were obtained, as given in Table 5. The lowest yield values were obtained from orchards P8 and P12 as 31.17 and 33.66 kg ha⁻¹, respectively. The Cv values of these orchards were classified as unacceptable, while their CU values were classified as fair. In the orchards with low CU values, it was observed that irrigation water was not efficiently distributed in the field. This situation prohibited the plant root zone from receiving water and decreased the yield. Also, the emitter types used in the nectarine orchards where the lowest yield values were obtained were non-pressure-regulated (P8–P12). The lowest emission uniformity (EU) values were obtained as 61 and 63% for orchards P8 and P12, respectively.

3.2. Evaluation of Irrigation Management

In this study, the drip systems in the selected nectarine orchards were operated by the farmers, and irrigation was scheduled based on their experience without using any sensors for soil water content or other factors. In general, the growers irrigated their orchards at 5- to 7-day intervals, adjusting irrigation duration by experience, using a short duration during the early season and longer durations during the flowering and fruit set and maturation stage. It was observed that none of the growers utilized scientific irrigation scheduling techniques.

The measured wetting percentages (P) of the parcels tested within the scope of the project varied between 18.3 and 37.3% and are given in Table 4. The lowest wetting area ratios were measured as 21.7%, 20%, and 18.3% in orchards P7, P10, and P11, respectively, where deficit irrigations were applied. This ratio generally varies between 30 and 37% of the total area, especially in orchards.

The storage efficiencies of the tested parcels varied between 45 and 87% (Es) depending on full irrigation, incomplete irrigation, and excessive irrigation conditions and are given in Table 4. Es values greater than 80% were found in three orchards (P10, P11, and P14); Es values between 70 and 80% were observed in two orchards (P16, and P18); Es values between 60 and 70% were found in five orchards (P1, P3, P5, P7, and P9); and Es values less than 60% were recorded in eight orchards.

The application efficiency (Ea) of an irrigation system is defined as the percentage of total applied water accumulated in the plant root zone. The application efficiency (Ea) values for the tested drip systems varied between 40% and 79% and are given in Table 4. In general, the Ea values were found to be low for the systems; in seven orchards, the Ea values were between 70 and 79%; in six orchards, the Ea values ranged from 60 to70%; and in five orchards, the Ea values were lower than 60%. These results revealed that there were serious irrigation management problems in the systems tested. When the Es and Ea values are considered together, the growers applied less irrigation than soil water deficit in the 90 cm root zone depth, which means that insufficient water was applied to the trees in the selected orchards. The duration of the irrigation should be increased in most of the systems tested to satisfy the soil water deficit in the root zone depth. The potential application efficiency of the low quarter (PELQ) values varied between 55 and 80%. When Table 4 is examined, the PELQ value was highest at 80% in the P14 orchard; in eight orchards, the PELQ values ranged between 70 and 80%; in six orchards, the PELQ values changed between 60 and 70%, and in three orchards, the PELQ values were lower than 60%.

The low-quarter application efficiency (AELQ) varied between 45 and 87%. Table 4 shows that the AELQ values were higher than 80% in orchards P10, P11, and P14, and the rest of the orchards remained below this value. The AELQ is the ratio of the water infiltrated and stored in the root zone in the least-watered quarter of the land to the average depth of irrigation water applied, expressed as a percentage. Although most of the systems’ performance was lower than the expected norms, they were within the range of what is normally found for in-field evaluations.

4. Discussion

According to the results of this research, lateral pressure variations were found to be above the allowable value of 20% [9]. The reason for greater pressure variations is due to using longer lateral lengths (>150 m) and partial clogging of emitters. Also, possible clogging in filtration may have reduced the optimum operating pressure of the systems, which can cause variations in pressure. The farmers did not use any chemicals (acid treatment) to prevent emitter clogging in their systems. Although the farmers used hydrocyclone and disk filters, the use of automatic filters and mesh numbers, selected according to the sediment sizes in the water source, will prevent possible clogging.

Only five orchards had excellent Cv values and, three of them were low. Farmers of orchards with low Cv values should consider design changes in their system to reduce the Cv values to acceptable levels. Emitter variation at a given operating pressure is caused by manufacturing variability, emitter plugging (complete or partial), water temperature changes, and emitter wear [24]. Therefore, the orchards with flow variations greater than 20% (P12, P13, and P15) should undergo modification of their system design in order to reduce flow variations.

Özer et al. [25] reported CU values between 80 and 96% and DU values ranging between 68 and 94% for 11 drip systems in corn fields and walnut orchards in the Thrace region of Türkiye. A similar result was also found in our research. The reason for this is that while the mean of deviations from the means is used in the calculation of the CU value, the lower quarter average is used in the calculation of the DU value.

The reason why the rate of wetting area varies across such a wide range is due to differences in lateral intervals and the amount of irrigation water applied. In drip irrigation system planning, it is extremely important to determine the wetting area percentage (P) correctly. For this reason, the wetting area percentage should be at least 30% in project designs. However, this value can be taken as the lower limit of 25% in humid regions and 35% in very arid regions [1].

Ashiri et al. [26] evaluated a drip system in Pakistan, and they found that the water application uniformity was above 80%, which indicates that the drip irrigation was designed with proper scale and dimensions. None of the orchards tested in this study were classified as having excellent EU values. Also, five orchards were not acceptable and were outside the recommended limit of EU values. System uniformity is important in terms of system performance and even distribution of water over a field. Additionally, in drip irrigation systems, EU directly affects the yield of the crops [27]. In some instances, the drip irrigation systems were installed with little concern for basic engineering hydraulic principles, resulting in nonuniform emitter discharges throughout the irrigated field. To overcome this lack of uniformity, researchers found it was necessary to over-irrigate [5]. Abdulhadi et al. [28] evaluated the existing drip irrigation network of Fadak Farm in Iraq, and they reported an EU value of 96.5%, a statistical uniformity coefficient of 97%, emitter flow variation of 6.85%, a coefficient of variation of 0.026, application efficiency of 96.5%, and pressure variation of 17%. They concluded that the drip irrigation system worked well and efficiently over the entire study region. Additionally Alaç et al. [29] stated that the water emission uniformity (EU) of the drip irrigation system of a ridge-planted citrus garden changed between 92 and 95%.

In general, Us values are at acceptable levels in tested drip systems. Soccol et al. [30] determined the performance of a drip system in an apple orchard, and they found an EU value of 74% and a Us value of 77.7%.

Although the uniformity parameters showed that the system performance was acceptable, the efficiency parameters (Es and Ea) indicated that irrigation management requires alterations to increase these values to acceptable levels. The most important factors affecting field water application efficiency are the irrigation method, soil type, and the amount of irrigation water applied. Soccol et al. [30] found an Ea value of 100% and an Es value of 47.8%. They concluded that increasing irrigation duration resulted in increased storage and application efficiency.

PELQ is an indication of how well a system can deliver water under optimum operating conditions. The PELQ values are generally good, but only three orchards were determined to be lower than 60%. A low PELQ is a sign of planning problems [10]. Alaç et al. [29] evaluated the drip performance in a citrus orchard and reported that the lower quarter potential application efficiency (PELQ) was 85%, the lower quarter actual application efficiency (AELQ) was 94%, and the wetted area percentage was 20%. Three orchards had an AELQ value higher than 80% in this research. A significant difference between AELQ and PELQ values has been identified as an indicator of poor operation of irrigation systems. Özer et al. [25] reported Ea values between 45 and 94%, AELQ values ranging between 54 and 86%, and PELQ values between 52 and 84% for 11 drip systems in corn fields and walnut orchards.

5. Conclusions

The performance of drip systems in young nectarine orchards in a Mediterranean environment was evaluated based on hydraulic performance parameters like average emitter discharge (Qavg), Christiansen uniformity coefficient (CU), and distribution uniformity (DU), emission uniformity (EU), as well as irrigation management performance parameters such as system application efficiency (Ea), storage efficiency, AELQ, and PELQ. Although the CU, DU, and EU values were at acceptable levels, the variations in emitter flow rates and pressure were not at acceptable levels. The results revealed that although hydraulic performance parameters were found to be at acceptable levels in general, in the tested drip systems, the irrigation efficiency parameters were lower than expected norms, indicating that the main problem with these systems was not the design but the management and operation of these systems. Thus, the lower performances might be attributed to clogging and/or lack of system design and application practices by the farmers. Regarding the pressure variations in the laterals that were generally greater than 20%, the farmers should alter their system design and use acid injection for the prevention of clogging to reduce pressure variations in their systems. A major problem encountered in drip irrigation is the plugging or clogging of emitters. In particular, physical clogging in drippers can be obvious depending on the type of water source. We recommend farmers use hydrocyclone and disk filters in their filtration systems. Also, a disk filter placed before the fertigation equipment will be a useful tool. In this study, the farmers generally cleaned their filters at the beginning and in the middle of the growing season.

While the drip method has great potential for high irrigation efficiencies, poor system design, management, or maintenance can lead to low efficiencies. In addition, the farmers have insufficient knowledge of drip irrigation systems and their operation, especially on irrigation scheduling. It is strongly recommended that the farmers obtain appropriate training on the operation and management of drip irrigation systems.

The success of any irrigation method, particularly drip irrigation, depends to a large degree on the management of the irrigation system. With drip irrigation, precise information on the amount of water that the crop is using is required to adequately determine the irrigation amount. Control strategies using feedback information on soil water or plant water status can be used to determine if the irrigation applications are either too large or too small.

Drip irrigation is an irrigation method that has a complex structure that can serve farmers for many years with proper design, maintenance, and repair operations performed at appropriate times. These are based on engineering calculations at every stage, from when the water is taken from the source to its delivery to the plant root zone. The selection of proper emitters depending on field and lateral length, filtration systems for the type of water sources, maintenance of fitting parts, and cleaning of the filters before and after irrigation applications are the most important applications of effective drip irrigation systems.

It is recommended that newly established drip irrigation systems be tested at various intervals throughout their operation to ensure long-lasting function and reduce maintenance costs. Performance measurements should be acquired before and during the production season and should be linked to the developing technology. Thus, possible problems in the system can be detected early, and drippers can be used for a longer period. Farmers should be trained to use the system and should maintain it at certain intervals. It is important to follow irrigation schedules, record the chemicals applied and maintenance procedures, and carry out economic analyses to improve these systems.