*3.6. Yield and Irrigation Water Use Efficiency (IWUE)*

Statistical analysis of squash yield and IWUE are shown in Table 5. Squash yield was significantly (*p* < 0.05) affected by growing season. The squash yield obtained in the SS was higher (19%) than that in the WS. The reduction of squash yield in the WS could be due to extreme lower temperatures and solar radiations during the WS than SS (Figure 1). Similar results were obtained for cucumber by Wan et al. [79] and for squash by Amer [37], who reported that the different yields, obtained in different growing seasons, were due to

non-favorable weather conditions. Similarly, the higher yield recorded during the SS was due to an increase in physiological properties (gs, Pn, and Tr) and the chlorophyll index, compared with WS (Tables 2 and 3).


**Table 5.** Analysis of variance of squash fresh fruit yield and irrigation water use efficiency (IWUE) for winter (WS) and spring (SS) growing seasons.

ns: not statistically significant, \*\*: significant at the 1% level (*p* < 0.01), \*: significant at the 5% level (*p* < 0.05); different letters indicate significant difference between treatments; Bold letters and words indicate treatments names.

The mulching treatments showed a significant difference (*p* < 0.0001) in squash yield compared with the non-mulched treatments (Table 5). Mulched treatments increased squash yield by 36% compared with non-mulched treatments. However, no statistical difference was observed between mulched treatments (BM and WM). The yield increase observed in the plastic mulch treatment could be attributed to its ability to reduce evaporation, fertilizer leaching, weed accumulation, and soil compaction and increase soil temperature, which enhances root growth [30,31]. These properties led to higher soil moisture and nutrient holding in the root zone, which eventually enhanced squash yield, compared with NM. Many studies have reported that mulch enhances crop yield in squash [34], cucumber [59], chili [80] and broccoli [35].

Squash yield was significantly (*p* < 0.001) affected by irrigation treatments. The highest squash yield was obtained under the PRD70 treatment (82.53 Mg ha−1). Although this yield was not significantly different from that of the FI treatment (80.62 Mg ha−1). This suggests that reducing the irrigation volume perfectly could improve fruit yield. The higher squash yield in the PRD70 treatment than the FI treatment could be partially explained by the PRD having parallel drip lines that irrigate the root zone of the plant interchangeably. This could reduce water losses due to deep percolation in sandy soil, resulting in nutrient availability near the root zone in plants under PRD treatments. Another possible reason for the PRD70 plot having a higher yield than the FI plot is that plastic mulch could prevent soil evaporation to some degree. Therefore, plots under the FI treatment might be over irrigated, and irrigation of 70% of crop water requirement supplies sufficient water for crop growth without stress [81]. Hakim et al. [17] indicate that plants receiving FI could encounter higher soil moisture in the root zone, which reduces root activity, delaying maturity, and lowering yield compared with plants under PRD treatments. This result is consistent with the findings of Qin et al. [20] and Hooshmand et al. [19], who found that the yield of the FI treatment was lower than the deficit treatments, but not significantly different. Howerver,

the squash yield obtained in this study was more than three times higher than the squash yield obtained by Al-Omran et al. [82] under the same environmental conditions. This finding could be attributed to the higher plant density and good fertilization program used in this experiment, resulting in a higher squash yield compared with the mentioned study.

The interaction effects between S × M × I were not statistically significant (*p* > 0.05) for squash yield, while there were strong significant (*p <* 0.001) interactions between S × M and S × I (Table 5). It is worth mension that sowing squash in the SS under non-mulched treatment was almost doubled the squash yield compared to sowing in the WS. The variation of squash yield under mulched treatments in the SS and WS was not considerable. This shows that WM and BM were effective during both growing seasons (Figure 6). The highest squash yield was recorded under SS-BM-PRD70 treatment (95.84 Mg ha<sup>−</sup>1), while the lowest yield (46.06 Mg ha−1) was obtained under WS-NM-PRD50. In the WS, the highest squash yield obtained was 87.9 Mg ha−<sup>1</sup> in WM PRD70, while in the SS, the lowest squash yield obtained was 75.33 Mg ha−<sup>1</sup> in NM PRD50. The Squash yield obtained under SS-NM-FI and WS-NM-FI were 77.4, and 53.1 Mg ha−1, respectively, while in SS-WM-PRD50 and WS-WM-PRD50 were 85.29, and 79.34 Mg ha−1, respectively (Figure 6). This shows that using the PRD strategy and soil mulching technique reduces 50% of applied water, while increasing squash yield in both growing seasons. These results suggest that in arid and semi-arid regions where there are water scarcity problems, soil mulch with PRD50 could be used as a water-saving strategy to maintain the squash yield.

**Figure 6.** Squash yield under irrigation and mulch treatments during the winter and spring seasons.

Data presented in Table 5 and Figure 7 show that the effect of S, M, and I on IWUE was significant (*p* < 0.001). The IWUE in the WS was two times higher than in the SS. This result could be due to the water applied to squash in the SS, which was higher than that applied in the WS. This finding is in line with those recorded by Rouphael and Colla [83], Abd El-Mageed and Semida [9], Abd El-Mageed et al. [34] and Silva et al. [38], who worked on squash and observed that the IWUE was affected by environmental factors under different growing seasons.

**Figure 7.** Squash irrigation water use efficiency (IWUE) during winter (WS) and spring (SS) under mulch treatments (black mulch-BM, transparent mulch-WM and non-mulch- NM) and irrigation treatments (full irrigation-FI, partial root drying with 50% of evapotranspiration- PRD50, partial root drying with 70% of evapotranspiration-PRD70); the data is the mean value ± standard error; different letters indicate significant difference between treatments.

In terms of the mulching treatments, WM increased the IWUE by 48% compared with the NM treatments (Table 5). Soil mulching decreased evaporation and increased the soil moisture content near the root zone, which positively affected the squash yield, and finally, it contributed to higher IWUE. This result is consistent with the findings of Zhang et al. [81], Chen et al. [84], and Yang et al. [61], who found that mulching treatments had higher IWUE than the control treatment (NM).

In terms of irrigation quantities, the highest IWUE was observed under PRD50 treatments (23.90 kg m−3). The corresponding value for the FI treatments was 15.07 kg m−<sup>3</sup> (Table 5). PRD50 and PR70 increased the IWUE by 59%, and 36%, respectively, compared with the FI treatment. These results are in agreement with Amer [37], Abd El-Mageed et al. [34], and Zhang et al. [81], who found that water-stressed treatments increase the IWUE, compared with FI.

Data presented in Table 5 show that the interaction effects of the S×M, S×I, M×I, and S×M×I on IWUE were significant (*<sup>p</sup>* < 0.001). The highest IWUE (38.24 kg m−3) was recorded under WS-WM-PRD50, while the lowest value was 8.82 kg m−<sup>3</sup> under SS-NM-FI (Figure 7). The IWUE in the WS were doubled compared with SS for mulch treatments under same irrigation treatments. It can be seen from Figure 7 that PRD50 obtained higher IWUE in mulch and non-mulched treatments, compared with PRD70 and FI. Overall, Sowing squash in WS, FI-NM obtained squash yield of 53.1 Mg ha−<sup>1</sup> with IWUE 14.42 kg m<sup>−</sup>3, while PRD50-WM obtained 79.34 Mg ha−<sup>1</sup> with IWUE 38.24 kg m<sup>−</sup>3. This result led to conculde that sowing squash in WS using PRD50-WM saves 50% of applied water while increases squash yield by 49%, compared with FI-NM.

#### **4. Conclusions**

The effect of growing season DI integrated with PRD, and soil mulching on the yield and IWUE of squash plants, was studied. The results indicated that plant density postively affected squash yield in both growing seasons for all treatments. The spring growing season positively affected squash yield. In contrast, the SS negatively affected the IWUE, compared with the WS. Moreover, soil mulching enhanced the physiological properties of the squash plants (gs, Pn, and Tr), fruit quality (TSS, TA, and Vc), increasing the squash yield, and IWUE, compared with non-mulched treatments. gs, Pn and Tr were significantly affected by growing season for all measured days. Furthermore, PRD70 and PRD50 reduced the

chlorophyll index at all growth stages. Mulch treatments increased the TSS, TA, and VC, compared with non-mulched treatments. However, growing seasons did not significantly affect fruit quality. In addition, PRD strategy improved both squash yield and IWUE in both growing seasons. This emphasizes that sowing squash plants in the winter season, using PRD50 and plastic mulch as water-saving strategies, could increase the yield and IWUE in arid and semi-arid regions.

**Author Contributions:** Conceptualization, H.M.A.-G., T.K.Z.E.-A. and A.A.E.-S.; methodology, A.A.E.-S., A.H.F. and M.S.A.; software, A.A.E.-S., A.H.F. and M.S.A.; validation, H.M.A.-G., T.K.Z.E.- A. and A.A.E.-S.; formal analysis, A.H.F. and M.S.A.; investigation, A.H.F. and M.S.A.; resources, H.M.A.-G. and T.K.Z.E.-A.; data curation, A.A.E.-S., A.H.F. and M.S.A.; writing—original draft preparation, A.A.E.-S. and A.H.F.; writing—review and editing, H.M.A.-G., T.K.Z.E.-A., A.A.E.-S. and A.H.F.; visualization, T.K.Z.E.-A. and A.A.E.-S.; supervision, H.M.A.-G. and T.K.Z.E.-A.; project administration, H.M.A.-G. and T.K.Z.E.-A.; funding acquisition, H.M.A.-G., T.K.Z.E.-A. and M.S.A. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Deanship of Scientific Research at King Saud University, through research group No. RG-1441-321.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The data presented in this study are available on request from the corresponding author.

**Acknowledgments:** The authors extend their appreciation to the Deanship of Scientific Research at King Saud University for funding this work through research group No. RG-1441-321.

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
