Population growth and rapid urbanization have led to increasing demand for fresh water resources over the past few decades [
1]. Agriculture, which is considered as the major consumer of water supplies, accounts for over 70% of freshwater use globally [
2]. In this context, finding a balance between the available water resources and the rising water demands for agricultural production is critical, especially in arid and semi-arid regions. Exploring alternative water resources for irrigation has already become one of the important ways to address water shortage and achieve sustainable agricultural development. Saline water has been widely used for irrigation in many countries [
3,
4]. Drip irrigation is the most efficient irrigation application for saline water [
5]. When compared to flood and furrow irrigations, drip irrigation is advantageous, as it increase the water use efficiency (WUE). Moreover, in sprinkler irrigation, the phenomenon of excessive leaf burn due to salt water is observed, which is completely avoided in drip irrigation. Owing to the patterns of soil water movement that was observed under drip irrigation, the accumulated salt contents move toward the regions of moist peaks, which is beneficial for plant growth. Long-term practices indicated that using drip irrigation with saline water could maintain high matric potential and low salt accumulation in the wetting zone, thus maintaining a low salinity level in the root zone [
6,
7]. In South Africa, low-cost drip irrigation was successfully used in combination with saline water for garden crop irrigation, and a higher yield than the average marketable yield was achieved [
8]. In India, higher cotton yields and water productivity were obtained when drip irrigation with saline water was used when compared with furrow irrigation. In Israel, reasonable potato yield could be obtained by drip irrigation with saline water (salinity < 7 dS/m) on deep sandy soils without extreme weather conditions [
9]. In China, the WUE and quality of watermelons improved when drip irrigation with saline water was used in Hetao District [
10]. The soil matric potential at 0.2 m depth was recommended to be kept above −20 kPa when drip irrigation with saline water was used in Northwest China to help alleviate the dangerous increase in the water table, while increasing the cotton seed yield [
11]. Irrigation emitters should be placed on the northern side of the plants when constructing shelterbelts for water conservation and soil salt reduction under saline drip irrigation in the Taklimakan Desert [
12]. In Caofeidian District, the drip irrigation with saline water was beneficial for salt leaching, and the highly saline soil became mildly saline after reclamation by leaching salts from the root zone of soil profiles irrigated with water of salinity level up to 7.8 dS/m [
13]. It is a common observation that using saline water for drip irrigation is a feasible solution in areas that lack freshwater resources. However, emitter clogging was indicated as a critical issue that was affecting the performance of drip irrigation with saline water in long-term practices, which need to be further evaluated for the sustainability of such a system [
14]. Highly saline water can easily form precipitates, resulting in chemical clogging. This enhances the potential for clogging, and the clogging mechanism becomes more complex [
15]. The emitter is the key part of a drip irrigation system, which irrigates the root zone of plants with small water droplets by dissipating the water energy through the internal flow path. The flow path of emitters is complex and narrow (with a size of 0.5 to 1.5 mm), which can easily be clogged. For the saline water drip irrigation system, the emitter clogging degrades irrigation uniformity obviously. The poor irrigation uniformity impacts the water availability and soil salinity. Finally, the crop growth was limited directly by the variable water stress and indirectly by the impaired salinity management. It restricts the advancement of saline water drip irrigation technology [
16]. Nonetheless, the current research in this field mainly focuses on the suitable mode of saline water drip irrigation by considering the effects of saline water on the soil environment, crops production, and WUE, while neglecting the issues that are related to emitter clogging that is caused by saline water.
Now, the two basic approaches for controlling emitter clogging have evolved. One is removing the potential source of clogging from the water before it enters the irrigation system, such as with filters [
17]. However, the screen/disc filter has good effects on the physical clogging caused by sands, and the media filter has good effects on the biological clogging caused by colloidal and organic materials. The chemical clogging that is caused by the salts cannot be well controlled by the filter system. Hence, we seek another approach for control chemical clogging that is to prevent or control chemical processes from occurring. The clogging process is affected by irrigation water quality [
18], emitter type [
19], irrigation model [
20], etc. Particularly, the irrigation model could influence the internal medium of drip irrigation systems, thus changing the formation and growth of clogging substances within the emitters, leading to different levels of emitter clogging. The main approaches currently considered to utilize saline water are all saline water irrigation, saline-fresh water mixture irrigation, and saline-fresh water alternating irrigation. The saline-fresh water alternating irrigation model is widely used worldwide, as it could save the fresh water resources when compared to all fresh water irrigation methods, and prevent the damage to crops and soils caused by salt when compared to all of the saline water irrigation models [
21]. The alternating irrigation model could improve crop growth by changing the water-salt distribution in soils. Moreover, it could influence the anti-clogging performance of drip irrigation system by changing clogging substances formation inside the emitters. The existing literature mainly analyzed the impacts of alternating irrigation on the yield and quality of tomatoes, cottons, and lemons, and examined the water-salt movement and distribution in soil under different alternating irrigation models, neglecting its effects on the clogging substances formation inside the emitters and irrigation capacity of drip irrigation systems. The current studies conducted on emitter clogging under saline water drip irrigation focused on investigating the means to control clogging such as adding acids or applying magnetic fields to irrigation water. The relevant experiments usually conducted on bare land with continuous irrigation for a short period, without considering the real irrigation demands of crops. Very limited research has been conducted to examine the effects of saline-fresh alternating irrigation model on emitter clogging. The application of saline water irrigation models to effectively control emitter clogging is a rich study subject. Hence, processing tomato as a high value crop was selected for this research. Processing tomatoes, which grow in areas that receive direct sun and exhibit tolerance to semi-drought and salinity, are widely grown in the arid and semi-arid regions of China. A 2a study of growing processing tomatoes using drip irrigation saline water in the Hetao irrigation district was conducted. The objectives of this study are: (1) to examine the emitter clogging behaviors and clogging substances composition under different fresh-saline alternating irrigation models; and, (2) to evaluate the feasibility of using alternating irrigation models for drip irrigation systems. The results could provide the theoretical basis for agricultural water management using saline water.