**1. Introduction**

Increasing the consumption of water in the agricultural sector, and a lack of preventative measures to permanently conserve water and avoid water shortages, make it vital to manage water resources rather than develop new ways to supply water. Therefore, the need to develop practical and sustainable management systems for water supply has become a subject of intense discussion. Drip irrigation is a promising irrigation strategy that reduces soil evaporation and deep drainage losses, while efficiently delivering water to plant roots [1]. Compared with conventional methods, drip irrigation has shown its utility for water-saving and the efficient use of fertilizers, especially fruit and vegetable crops [2].

Various methods are currently used to increase the efficiency of delivering water to plants. One of these is subsurface drip irrigation (SSDI), which is primarily utilized to decrease water loss during water delivery to plants. Compared with other drip irrigation methods, SSDI has gained more acceptance in the irrigation sector in its ability to increase crop yield and reduce plant diseases and soil erosion [3–5]. Other methods that are used to efficiently managing water irrigation include deficit irrigation (DI) and soil mulching. Ever since the focus of water irrigation shifted from increasing yield per planted area to increasing yield per unit volume of water applied [6], DI has become an important strategy in arid and semi-arid regions where water shortages are a major limitation to farming.

**Citation:** Farah, A.H.; Al-Ghobari, H.M.; Zin El-Abedin, T.K.; Alrasasimah, M.S.; El-Shafei, A.A. Impact of Partial Root Drying and Soil Mulching on Squash Yield and Water Use Efficiency in Arid. *Agronomy* **2021**, *11*, 706. https:// doi.org/10.3390/agronomy11040706

Academic Editor: Aliasghar Montazar

Received: 25 February 2021 Accepted: 4 April 2021 Published: 7 April 2021

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Therefore, the optimal goal of using DI is to save water, either by reducing the number of irrigation cycles or reducing the volume of water applied during each irrigation event [7]. Irrigation water use efficiency (IWUE) has been developed to indicate increasing crop yield while using less water, or maximizing yield in limited water sources [8]. IWUE was defined by the total yield to the total water applied [9,10]. In a physiological perspective, IWUE is used to describe the amount of carbon to the water lost through transpiration [11]. However, agronomists primarily focus on maximizing yield per water applied [12].

Partial root drying (PRD) is an improved form of DI strategy that involves applying water to the sides of a plant root zone, either by irrigating one side of the plant root (fixed PRD) or alternately watering both sides of the root (alternating PRD) [13]. Adequate water and nutrients are delivered to the plant on the wet side of the root, while the dry side is stimulated and releases chemical hormones. These chemical hormones cause stomata to partially close, which increases IWUE [13]. This strategy makes PRD more efficient than DI [13–15]. Barideh et al. [16] reported that alternating PRD saves more water than fixed PRD. Several studies have shown the advantages of DI and PRD over full irrigation (FI), in terms of IWUE without the reduction of yield [17–20]. A number of researchers working on different crops found that the PRD strategy increased IWUE by 38–53% compared with FI without a significant reduction in yield [18,21,22]. Ors et al. [23] reported that deficit irrigation (67%) had significantly reduced chlorophyll index value (7%), leaf water content (42%), stomatal conductance (69%), transpiration (62%), photosynthesis (62%) of squash. Al-Ghobari and Dewidar [24] indicated that deficit irrigation significant affected the fresh leaf, stem weight of tomato, compared with full irrigation. In terms of fruit quality, PRD preserved fruit quality, compared with deficit irrigation. Zhang et al. [25] reported that PRD was not affected by soluble solid contents of strawberry, while deficit irrigation considerably decreased soluble solid contents. Guang-Cheng et al. [26] indicated that both PRD50 and DI50 strategies considerably decreased dry weigh of shoot and root pepper compared with full irrigation. Furthermore, PRD50 reduced photosynthesis 19% while DI50 decreased 22%. In chlorophyll fluorescence (FV/Fm) PRD50 reduced by 9.5% while DI50 decreased 12.0%.

Another method that can increase IWUE is soil mulching, which can be used for many purposes in the agriculture sector. However, preserving soil moisture, improving soil physical properties, and controlling soil erosion are the most significant uses of soil mulching in arid and semi-arid regions [27,28]. Mulching materials positively affect the moisture of the soil by improving soil structure and soil retention, as well as decreasing soil evaporation [27,29–31]. Yaghi et al. [32] reported that combining drip irrigation with plastic mulch increased cucumber yield (45%) and IWUE (72%) compared with the treatment without mulch during two successive growing seasons in the arid region. Abhivyakti et al. [33] found that black plastic mulch increased the tomato yield by 30% compared with bare soil in open field conditions. Abd El-Mageed et al. [34] also reported that soil mulching increased both, the squash yield and IWUE by 26%, compared with the non-mulched treatments. Experimenting on broccoli, Verma et al. [35] observed that mulching increased the photosynthetic rate, stomatal conductance, intercellular CO2 concentration, and transpiration rate. Additionally, Lira-Saldivar et al. [36] found that plastic mulch significantly increased photosynthetic activity in zucchini plants (17.9%) compared with non-mulched treatments.

In addition to water, growing season also influences both crop yield and IWUE. Numerous studies on zucchini squash have reported that growing season has a significant effect on crop yield and IWUE [9,34,37,38].

Despite numerous studies that have been conducted on SSDI, PRD irrigation and soil mulching, as water management strategies, combined with arid regions with different growing seasons, has not been fully investigated. Therefore, this study aimed to investigate the effect of DI levels, associated with PRD strategy and plastic mulch on squash yield and IWUE in winter and spring. This study also examined the combined effects of PRD, soil mulch, and growing season on gas exchanges, chlorophyll fluorescence, and the chlorophyll content index at different plant growth stages.

### **2. Materials and Methods**
