Influence of Irrigation Regime on Total Yield of Tomato Crop and Water Productivity under Drip Irrigation System

Water scarcity remains a significant challenge for global agriculture. Deficit irrigation has emerged as a strategy to optimize water productivity without compromising crop yield. This study aimed to assess the impact of deficit irrigation on tomato yield and water productivity (WP). Two field experiments were conducted over consecutive seasons of 2022 and 2023 using drip irrigation. Three irrigation regimes were employed: 100% (T100), 75% (T75), and 50% (T50) of the full irrigation requirements. Crop stress indicators, including fresh biomass weight (FB), dry-biomass weight (DB), canopy water content (CWC), soil moisture content (SMC), and relative chlorophyll content (SPAD measures) were evaluated. The results showed that the highest values of FB, DB, CWC, SMC, and yield were achieved under T100, followed by T75, while the lowest values were observed at T50. The highest SPAD values were obtained under T75, followed by T100 and T50 for both seasons. The results further showed that the highest WP values were observed with T100 (27.37 kg/m 3 ), followed by T75 (25.96 kg/m 3 ). The lowest WP value was 21.58 kg/m 3 at T50. The application of T75 and T50 led to saving 22.29% and 44.57% of the irrigation water applied compared to T100 in both seasons, respectively. In conclusion, this study proves that applying moderate deficit irrigation at T75 is considered to be a feasible technique for tomato production.


INTRODUCTION
Tomato crop is one of the most commonly grown vegetables worldwide.Global production has increased by roughly 10% in recent years (Shalaby and El-Banna, 2013).Tomatoes are the second most significant crop in terms of cultivated area, after potatoes (Mehdizadeh et al., 2013).Egypt is the world's sixth-largest producer, as the area cultivated with tomatoes amounted to about 143,618 hectares, with a total production of about 6.28 million tons (FAOSTAT, 2022).
Tomato plants are significantly affected by water stress, as there is a strong connection between the water needs of the crops and their overall yield (Zinkernagel et al., 2020).It is imperative to improve water consumption efficiency given Egypt's limited water supply and growing use of irrigation, as revealed by Morillo et al. (2015).In this context, deficit irrigation, in conjunction with effective irrigation techniques like drip irrigation, has drawn interest as a potential strategy to address these challenges.Deficit irrigation is an alternative water conservation strategy without remarkable reductions in crop yield and quality (Afzal et al., 2017).
To accurately determine crop water requirements and establish irrigation schedules, irrigation water management programs can be employed, utilizing weather station data or information from website applications (Gabr, 2022).Khan et al. (2019) found that the CROPWAT program proved to be the most effective for farmers in understanding the optimal timing and amount of water required for their tomato fields, accounting for changes in climatic conditions.
Understanding how plants respond to water stress is crucial for determining the optimal timing and amount of irrigation, as pointed out by Morillo et al. (2015).When soil water content decreases, plants close their stomata to minimize water loss.However, prolonged stomatal closure can lead to a reduction in chlorophyll content, thereby inhibiting photosynthesis Tembe et al. (2017).Crop productivity is significantly influenced by photosynthetic activity.Koech and Langat (2018) emphasized that chlorophyll, the primary pigment responsible for the greenness of leaves, is essential for plant functioning to rapidly and cost-effectively assess chlorophyll regimes.SPAD chlorophyll meters are commonly employed and effectively used to measure chlorophyll (Filek et al. 2015).Ragab et al. (2018) used several deficit irrigation regimes to investigate its effects on tomato plants and found that the maximum FB and DB were found with 100% of the full irrigation treatment (FIT), positively affecting flowering and tomato yield.El-Labad et al. (2019) and Sarker et al. (2020) conducted studies on the impact of varying irrigation regimes (100%, 80%, and 60%) of the FIT on tomato yield and water productivity, considering indicators such as FB, DB, CWC, SMC, and SPAD.Their results showed that applying 80% of the FIT yielded the highest values for all stress indicators, followed by 100% of the FIT.Moderate water deficit application led to increased water productivity without significant reduction in yield, while severe water deficit had a detrimental effect on tomato yield (Zhang et al. 2017 andAbd-Elhakim et al. 2021).These findings point out that moderate deficit irrigation can effectively optimize water productivity in tomato crops.This study's objective is to assess the impacts of three different irrigation regimes (100, 75, and 50% of the full irrigation treatment) on various measured parameters, including fresh biomass weight (FB), dry biomass weight (DB), canopy water content (CWC), soil moisture content (SMC), relative chlorophyll content (SPAD), as well as yield and water productivity (WP) of tomato crop.The study also aimed to determine the optimal irrigation regime for tomato cultivation, balancing water savings and yield.

Study area
Field trials were carried out over two consecutive spring growing seasons of 2022 and 2023 at a private farm located in Talkha, Dakahlia province, Egypt.The precise coordinates of the farm are 31.09°N latitude and 31.38°E longitude, with an elevation of 17 meters.The experimental soil classified as a sandy clay texture, and its maximum rain infiltration rate was determined as 30 mm per day.The daily meteorological parameters, including maximum and minimum temperature, average air humidity, average wind speed, and rainfall, were sourced from the website: https:// power.larc.nasa.gov/data-access-viewer/, according to Power (2022).

Soil and water data analysis
The physical and chemical characteristics of soil samples were taken from various soil profile depths are listed in Table 1.The chemical and hydrophysical characteristics of water samples taken from the irrigation source are displayed in Table 2.These samples were evaluated to assess specific properties.Where, ECe: Electrical conductivity of the irrigation water.

Crop Data
The hybrid tomato seeds 'Gs12 F1' were planted in plastic seedling trays on January 19th, 2022, and January 27th, 2023, for the two respective growing seasons.In the first season, the transplanting process began on February 23rd, followed by a 35-day initial growth stage.The harvest took place on June 17th.For the second season, transplanting commenced on March 3rd, and the harvest was completed on June 25th.The entire growing season for the tomato plants lasted for 150 days, which was divided into four stages: initial (35 days), developmental (39 days), middle (46 days), and late (30 days).According to Noreldin et al. (2014), the crop coefficients (K c ) for different stages were: 0.38 for the initial stage, 1.10 for the developmental stage, 1.10 for the middle stage, and 0.65 for the late stage.

Experimental Design and Procedures Experimental irrigation system
The drip irrigation system's layout is shown in Figure 1.The control head, includes: a centrifugal water pump (diameter: 80 mm; capacity: 1050 L/min; power: 4.8 hp) to supply water; a disk filter to remove impurities; a pressure gauge to monitor the pressure of the system; control valves to control the desired pressure at different parts of the system; and a Venturi-type injector to inject water-soluble fertilizers into the irrigation network.The main line was 75 mm in diameter from polyethylene (P.E.) pipes, and the sub-main line was P.E.pipes with a 63 mm diameter.Laterals with a 16 mm diameter, P.E., a built-in emitters were used with an average discharge rate of 6 lit/h at 1 bar operating pressure.The beginning of each lateral was provided with a T-shaped 16 mm plastic valve to control the irrigation depth at the desired level for each treatment separately.

Fig. 1. The layout of experimental design for the different irrigation treatments
The end of each lateral was closed by an end cap.A drip irrigation system was constructed and tested before being used in the experimental location using equation (1), according to Ella et al. (2013).The distribution uniformity (DU) was estimated to be 92%.

𝐃𝐔 =
* % …………… (1) Planting and water regime treatments Tomato plants were irrigated using a drip irrigation system.In order to reduce the effect of spatial heterogeneity, a randomized complete block with four replicates was used for the experiment.The distance between plants within the same row was 0.4 meters.The spacing between lateral lines was set at 1.2 meters.Each plot had an area of 10.8 m 2 , measuring 9 meters in length and 1.2 meters in width.
Irrigation treatments started after 15 days of transplanting to ensure the survival rate of the seedlings.After that, the irrigation treatments were applied for the rest of the growing season, except for the last 10 days before harvest, when irrigation was stopped.Three irrigation regimes were applied to the tomato plants: 100% (T100), 75% (T75), and 50% (T50) of the full irrigation treatment.
Fertilizer requirements were determined based on the recommendations provided by the Egyptian Ministry of Agriculture.All treatment groups received 357 kg/ha of nitrogen (N) in the form of urea (46.5% N), 60 kg/ha of phosphorus (P) in the form of phosphoric acid (85% P2O5), and 238 kg/ha of potassium (K) in the form of potassium sulphate (50% K2O).These fertilizers were applied through the drip irrigation system using a venturi meter injector throughout the two growing seasons.

Measurements of crop stress indicators
The measurements were conducted on the selected plants under different irrigation treatments at the same time.The following measurements were calculated based on the respective formulas utilized: Soil moisture content (SMC): According to Zotarelli et al. (2009b), the 0-15 cm soil layer contained approximately 70-75% of the root density.Therefore, soil samples were specifically taken within this range.The SMC was determined using the gravimetric method as described by Paltineanu and Starr (1997) and Evett et al. (2002).This method involves drying soil samples for 24 hours at 105 °C in an oven.The laboratory analysis involved weighing the soil samples before and after drying, and the SMC was estimated using equation (2).

Fresh and Dry Biomass Weights
The estimation of FB and DB were evaluated by adopting the procedures outlined by Semananda et al. (2016).Four plants were cut above the ground for each treatment during the flowering stage, 67 days after transplanting (DAT) for the first season and 68 DAT for the second season.The FB was recorded by gram per plant, and after that, the samples were subsequently dried at 105 °C in a forced-air oven for approximately 24 hours.Then, the DB was recorded by gram per plant.

Canopy Water Content (CWC)
The CWC is the percentage of water stored in the plant's canopy, which reflects the plant's water status and transpiration rate.CWC was calculated by adopting the procedures outlined by Semananda et al. (2016)

Relative Chlorophyll Content (SPAD)
The SPAD-502 chlorophyll meter, as explained in Figure 2, was utilized to determine the relative chlorophyll content.This instrument operates by measuring the leaf absorbance in the red and near-infrared regions.It employs two LEDs with peak wavelengths of 650 nm and 940 nm to emit light.The measuring area of the SPAD-502 is 2 x 3 mm, offering a high level of precision with an accuracy of ± 1.0 (Ding and Zhang, 2020).Following the methodology outlined by Bai et al. (2018), the SPAD readings were taken on the newest fully expanded leaf of all plant samples, specifically at a point approximately halfway between the leaf edge and the midpoint of the leaf.To determine the relative chlorophyll content, four leaves were measured for each plant.The values for the four leaves were averaged to represent each plant.Subsequently, for each treatment, the values obtained from the four replicates were averaged to represent each treatment combination.

Crop Evapotranspiration (𝐄𝐓 𝐜 )
Reference evapotranspiration (ET o ) values were calculated on a daily basis using the "FAO Penman-Monteith" equation ( 5) of the CROWAT program, as described by Halimi and Ashebir (2019) and Gabr (2022).Also, the ET c values were calculated by multiplying the ET o by the crop coefficient (K c ) for each growth stage using equation ( 6).

Effective root zone depth (𝐙 𝐫 )
The effective root zone depth (Z r ) was calculated using the equations (7 and 8), according to Salman et al. (2021).The specific values utilized for the following equations in relation to the tomato crop were sourced from Machado and Oliveira (2005).

Net Irrigation Depth (𝐝 𝐧 )
The net depth required through drip irrigation was estimated, according to Allen et al. (1998)

Irrigation Scheduling
The irrigation schedule was determined based on the ET c at different stages of the growing period and the total available water in the soil.The CROPWAT program was utilized for irrigation scheduling, which provides various options for determining when and how much water to apply.In this study, the irrigation scheduling was set at 40% of the critical depletion level.The irrigation application option chosen was to refill the soil to its field capacity, which corresponds to 100% soil moisture level.Furthermore, the efficiency of the drip irrigation system used in the study was reported as 90%.

Irrigation Water Applied (IWA)
The leaching requirement (LR) refers to the quantity of water required to enable the leaching of salts from the root zone.In this work, the LR specifically for a drip irrigation system was determined using equation (10) as described by Doorenbos (1977).However, the leaching requirement was disregarded due to its estimated value being 0.032, which falls below the threshold of 0.1.Therefore, the need for additional water for salt leaching was deemed unnecessary based on the obtained LR value.The irrigation water applied (IWA) is determined as the quantity required to replenish the crop water consumed to reach field capacity.The calculation of IWA for the three treatments (T100, T75, and T50) was conducted using equation ( 11) as specified by Abdulhadi and Alwan (2021).The IWA in the three treatments was based on percentages of the full irrigation treatment, with 100%, 75%, and 50% utilized for T100, T75, and T50, respectively.

Yield and Water Productivity
Eight plants for each treatment were chosen randomly and given labels.The yield from each pick was measured in order to gather yield statistics for these plants.Ripe fruits were manually picked from each replicate.There were two fruit picks, one at 109 and 115 days after transplanting (DAT) and the other at 107 and 115 DAT, in 2022 and 2023, respectively.The average weight of four replicates was used to determine the total fruit production for each treatment, which was then expressed in tons per hectare.
Water productivity (WP) was computed as the ratio of fruit yield to the total amount of IWA during the season.The WP was estimated using equation ( 13), as outlined by Ali and Talukder (2008).

Yield Reduction and Water Saving
The reduction in tomato yield was determined using equation ( 14), according to Ismail (2010).Water saving (WS) was calculated using equation ( 15), according to Ismail (2010).

Statistical Analysis
The experiment was laid out in a randomized complete block design (RCBD) with four replicates.All collected data were subjected to analysis of variance (ANOVA) in order to examine the response of plant stress indicators to different irrigation treatments.SPSS statistical software package version 28.0 was used to analyze the data.Significantly different means were separated using Duncan's multiple range test at the P ≤ 0.05 level of probability.The relationships between plant stress indicators and tomato yield were fitted by linear regression using Excel 2016 (v14.0).

Climatic Data
The climate data collected during the field experiment is presented in Figure 3.The data includes measurements of mean daily maximum and minimum temperatures (°C), humidity (%), and wind speed (m/sec).These data show variations between the two growing seasons.On average, the daily maximum temperature was 46.1 °C and 42.3 °C, while the daily minimum temperature was 7.2 °C and 9.3 °C for both tested seasons, respectively.The mean relative humidity reached its highest values at 79.3% and 68.5% in the two seasons, with the lowest values of 35% and 25.9% respectively.In terms of rainfall, the second growing season had a higher amount of precipitation, with 24.20 mm, compared to the first growing season, which recorded 20.0 mm.

Irrigation water applied
In the two seasons under study, the ET o exhibited a difference, with season 2023 showing a higher value of 789.63 mm compared to season 2022, which recorded 711.79 mm.Regarding the ET c , the second season had the highest value of 841.0 mm, while the first season had the lowest value of 753.1 mm.These results are in close agreement with those published by Kizza et al. (2016) and Çetin and Uygan (2008).Previous researches showed that there was a broad range of ideal irrigation requirements (532 to 905 mm) for having high tomato yields EL-MARAZKY ( 2018) and Attia et al. (2019).These studies demonstrate a diverse array of irrigation requirements to reach optimum yields, and how the irrigation water management is important for enhancing crop productivity.
In this study, the irrigation scheduling for tomato crop in both seasons was calculated by the CROPWAT program, as shown in Figures 4 and 5. Before starting the irrigation treatments, 78.9 and 108.1 mm of water were added equally to each treatment in the first and second seasons, respectively.The total gross irrigation depths during the first season, corresponding to T100, T75, and T50, were recorded as 792.5, 614.1, and 435.7 mm, respectively, with 31 irrigation events.But in the second season, the total gross irrigation depths reached 918.3, 715.75, and 513.2 mm, for T100, T75, and T50, respectively, with 37 irrigation events.These results are close to those of EL-MARAZKY (2018) and Attia et al. (2019).The irrigation water applied for the tomato crop during the 2022 season was 2615.25, 2026.53, and 1437.81m 3 /ha for the T100, T75, and T50, respectively.In season 2023, the values were 3030.39,2361.98, and 1693.56 m 3 /ha for the same treatments.These results are close to those of Soussa (2010).The largest amount of water applied was recorded with T100, while the least amount was observed with T50 in both seasons.The variation in irrigation levels can be attributed to the differences in climatic parameters during both seasons, as depicted in Figure 3.

Effect of Irrigation Regimes on crop stress indicators:
Tomatoes, being one of the most widely cultivated vegetables, exhibit sensitivity to soil moisture stress, primarily due to its shallow root systems (Zotarelli et al., 2009).This characteristic highlights the importance of comprehending the impact of soil moisture on tomato plants.By understanding these effects, effective irrigation management strategies can be developed.Maintaining optimal soil moisture conditions is essential to maximize returns and water productivity in tomato production, particularly when implementing deficit irrigation techniques.

Soil Moisture Content (SMC)
The statistical analysis shows a highly significant impact due to irrigation regimes on soil moisture content (SMC) (p < 0.05), as indicated in Table 3.A comparison of different irrigation regimes with SMC revealed that reducing the amount of applied water leads to a decrease in SMC.These results are in line with Al-Ghobari and Dewidar (2018).Table 3 details the variation in SMC for the different irrigation regimes.The highest and lowest values of SMC in both seasons were observed with T100 and T50, respectively.

Fresh and Dry Biomass Weight
The statistical analysis conducted at different irrigation regimes revealed highly significant effects on the FB and DB of tomatoes throughout both seasons (p < 0.05), as shown in Table 3.For both seasons, T100 has the greatest average FB values (17.59 tons per hectare).These outcomes can be explained by the fact that plants in the T100 received the optimal amount of water.In the T75, the FB decreased by 24.81% and 25.89%, while in the T50, it decreased by 59.94% and 60.61% compared to the T100 during the first and second seasons, respectively.The trend of DB followed a similar pattern as FB, as shown in Table 3.The highest DB, averaging 2.18 tons per hectare, were observed in T100 for both seasons.This outcome can be attributed to the robust vegetative growth, due to good photosynthesis and subsequent accumulation of dry matter.In T75, the DB decreased by 17.57% and 18.78%, while in T50, the decrease was 44.00% and 45.80% compared to T100 in the first and second seasons respectively.These findings suggest that water stress has a highly detrimental effect on both FB and DB.The results concerning FB and DB align with the findings of Zhang et al. (2017), Al-Ghobari and Dewidar (2018), and El-Labad et al. (2019), who reported that the full irrigation treatment produced the greatest FB and DB for tomato crops compared to other deficit irrigation treatments.

Canopy Water Wontent (CWC)
The statistical analysis conducted at different irrigation regimes revealed highly significant effects on the canopy water content (CWC) of tomatoes throughout both seasons (p < 0.05), as shown in Table 3. Comparing different irrigation regimes with canopy water content shows that reducing the amount of irrigation water applied reduces CWC, as shown in Table 3.These findings align with the results obtained by Ihuoma and Madramootoo (2020) and Alordzinu et al. (2021).We observed the highest CWC at T100 during both growing seasons, and the lowest value at T50.While the T75 had a slight reduction compared to the T100, Generally, water-stressed plants within T50 and T75 have a lower CWC than non-stressed plants within T100.So, scientists have used CWC to indicate plant stress and schedule irrigation.

Relative Chlorophyll Content (SPAD)
The numerical SPAD value specifies the relative chlorophyll content within the leaf samples.In this study, a significant variation in SPAD values for tomato plants at different irrigation regimes during both seasons were observed in Table 3.The highest SPAD values were 55. 98 at T75 as a mean for both seasons, followed by 53.87 at T100 and 46.34 at T50. Water stress can affect chlorophyll, the primary pigment responsible for photosynthesis.Stressed plants may experience a decrease in chlorophyll content due to the detrimental effects of severely reduced CWC, as demonstrated by the enigmatic T50.On the other hand, a slight reduction in CWC can make chlorophyll content more concentrated in certain areas of the leaf.These changes in pigment distribution can lead to higher SPAD values, such as T75.These results are consistent with those of Sarker et al. (2020) and Sivakumar and Srividhya (2016).

Effect of Irrigation regimes on Crop yield
The statistical analysis of the tomato yield data demonstrated a highly significant variation due to difference in irrigation regimes (p < 0.05).The tomato yield values for both seasons can be found in Table 4.The highest average tomato yield was 76.83 tons per hectare in T100, followed by T75 with an average yield of 56.44 tons per hectare.However, the lowest average yield of 33.55 tons per hectare was found with T50.T75 resulted in a yield decrease of 23.44% and 29.66% in the two investigated seasons, respectively.Similarly, T50 led to a yield decrease of 56.30% and 56.38% in both seasons, respectively, compared to T100.These results are consistent with those of Etissa et al. (2016), Djurović et al. (2016), andEl-Labad et al. (2019), who observed that increased watering application positively influenced vegetable growth, improved flowering, and ultimately increased tomato yield.

Water productivity and water saving
Water productivity exhibited statistical significance among different irrigation regimes (p < 0.05), except for T75 and T100 during the first season, as indicated in Table 4.The highest and lowest values of WP were observed in tomatoes grown under T100 and T50, with average values of 27.37 kg/m 3 and 21.58 kg/m 3 , respectively.In terms of water saving, T50 and T75 saved approximately 44.57% and 22.29% of the IWA, with average amounts of 1257.14 m 3 /hectare and 628.57m 3 /hectare in both seasons compared to T100.These results align with the Nangare et al. (2016) and Abd-Elhakim et al. (2021).The correlation analysis (R2) conducted on tomato stress indicators, including FB, DB, CWC, and SPAD, revealed a consistent trend across the first and second seasons.Additionally, the combined data from both seasons also displayed the same trend.In the first season, all parameters exhibited a significantly strong correlation with tomato yield (R2 = 0.90, 0.90, 0.78, and 0.63, respectively), as shown in Figure 6.Similarly, during the second season, the correlations remain high and significantly associated with tomato yield (R2 = 0.96, 0.94, 0.88, and 0.76), as shown in Figure 7. Combining data from both seasons, the correlations remain high and significant (R2 = 0.93, 0.92, 0.82, and 0.66), as shown in Figure 8.These relationships might be helpful in predicting and estimating tomato yield.

CONCLUSION
The current research emphasizes the impact of different irrigation regimes on the yield of tomatoes, water productivity, and indicators of crop stress.The findings demonstrated that the highest values of fresh biomass weight, dry biomass weight, canopy water content, soil moisture content, tomato yield, and water productivity (WP) were achieved when irrigation was set at T100, followed by T75, while the lowest values were observed at T50. Regarding relative chlorophyll content, the highest values were recorded under T75, followed by T100 and T50 for both seasons.The highest WP values recorded with T100 (27.37 kg/m3), followed by T75 (25.96 kg/m3), and the lowest WP value at T50 (21.58 kg/m3) on average.In both seasons, implementing T75 and T50 resulted in a 22.29% and 44.57reduction in the irrigation water applied (IWA) while decreasing the total yield by 26.55% and 56.34%, respectively, compared to T100.In conclusion, this study highlights that employing a moderate deficit irrigation strategy at T75 is a viable technique for tomato production, as it achieves a balance between water savings and acceptable yields.
: Weight of container with moist soil, gm.  : Weight of container with oven dry soil, gm.
: Electrical conductivity of irrigation water was measured to be 0.83 ds/m based on the physical and chemical properties of the samples.  : Maximum tolerable electrical conductivity of the soil saturation extract was 13 ds/m for a tomato crop, as mentioned by Savva and Frenken (2002).

Fig. 4 .
Fig. 4. Tomato crop irrigation scheduling for 2022 season at different irrigation treatments

Table 1 . Some physical and chemical properties of soil in the experimental site
Where, F.C: Field Capacity%, P.W.P: Permanent Wilting Point were determined as percentages in weight%, BD: Bulk density.