Effects of Deficit Irrigation on Growth, Yield, and Quality of Tomato Under Semi-Arid Regions ^†

Abstract

This research evaluated deficit irrigation effects on tomato (Solanum lycopersicum L.) growth, yield, and quality in semi-arid Pakistan during 2023–2024. Four treatments were applied: 100% ETc (control), 80% ETc, 60% ETc, and 40% ETc used a randomized complete block design. The treatment with 80% ETc maintained similar yields as full irrigation. It improved water use efficiency from 1.25 kg/m³ to 1.39 kg/m³. Plant height, SPAD values, and leaf area decreased with increasing water stress. Fruit quality parameters, including total soluble solids, improved under moderate deficit conditions. Moderate deficit irrigation (80% ETc) represents an optimal strategy for sustainable tomato production in water-scarce environments.

1. Introduction

Tomato (Solanum lycopersicum L.) ranks among the most economically important vegetable crops in Pakistan, contributing significantly to agricultural GDP and rural livelihoods. The crop occupies approximately 63,000 hectares with annual production exceeding 600,000 tons, making Pakistan the 34th largest tomato producer globally [1]. Conventional irrigation practices in semi-arid regions consume substantial water resources. Tomato cultivation typically requires 400–600 mm of water per season. The Roma VF cultivar requires 450 to 520 mm of water under semi-arid conditions. This requirement varies depending on seasonal climate and irrigation management practices. Water scarcity has emerged as a fundamental challenge for sustainable agricultural development in Pakistan, where agriculture accounts for over 90% of total water consumption [2,3,4,5]. The Indus River system, which supplies irrigation water to major agricultural areas including the Punjab province, faces increasing pressure from competing demands and declining per capita water availability [6]. Deficit irrigation represents a promising water management strategy that involves applying water below full crop evapotranspiration requirements while maintaining acceptable yield levels [7]. This deficit approach has demonstrated potential for enhancing water productivity across various crops, though responses vary significantly based on crop type, growth stage, and environmental conditions [8]. Previous research has shown that controlled water stress can improve certain fruit quality attributes, including soluble solid content and flavor compounds, while potentially reducing production costs [9].

Understanding these relationships is essential for developing sustainable irrigation recommendations that balance water conservation with economic viability for smallholder farmers. This two-year field study evaluated the effects of different deficit irrigation levels on the growth parameters, yield components, and fruit quality of tomatoes under semi-arid conditions. The research aimed to identify optimal irrigation strategies that maximize water use efficiency while maintaining acceptable productivity and fruit quality standards.

2. Materials and Methods

The field experiment was conducted at the Ayub Agricultural Research Institute (AARI), Faisalabad, Pakistan (31.4° N, 73.1° E) during the growing seasons of 2023 and 2024. The experimental site experiences a semi-arid climate characterized by hot, dry summers and mild winters [10]. Mean annual precipitation is 375 mm, predominantly occurring during the monsoon period from July to September. Pre-experimental soil analysis revealed sandy loam texture (sand 65%, silt 20%, clay 15%) with pH 7.8, an electrical conductivity of 1.2 dS/m, an organic matter content of 0.8%, and a field capacity of 28% (w/w). Site preparation involved deep plowing to a 40 cm depth followed by precision land leveling using laser-guided equipment. Soil amendments included incorporation of well-decomposed farmyard manure (20 t ha⁻¹), and basal fertilizer application rates were determined based on soil test recommendations and documented nutrient requirements for the Roma VF cultivar. The nitrogen rate (120 kg N/ha) corresponds to optimal yield response curves established for determinate tomato varieties in Pakistani semi-arid conditions. Phosphorus (80 kg P₂O₅/ha) and potassium (60 kg K₂O/ha) applications were calibrated to soil test indices, and expected nutrient removal rates were applied in split applications at transplanting (40%), flowering (35%), and fruit development (25%) stages.

The tomato cultivar ‘Roma VF’ was selected based on documented adaptability to semi-arid conditions and determinate growth characteristics. Seeds underwent hot water treatment (52 °C for 30 min) followed by fungicide application (Thiram 2 g/kg seed) before establishment in nursery beds during February. Transplanting occurred after 35 days at 60 cm × 40 cm spacing, achieving a plant density of 41,667 plants/ha. Integrated pest management protocols encompassed weekly monitoring for Bemisia tabaci, Helicoverpa armigera, and Tuta absoluta, with targeted interventions based on established economic thresholds. Disease prevention included alternate biweekly applications of copper oxychloride (2 g/L) and mancozeb (2.5 g/L) for early blight (Alternaria solani) and late blight (Phytophthora infestans) control.

Crop evapotranspiration (ETc) calculations were performed using the Penman–Monteith equation [11]:

ETc = ETo × Kc

(1)

where ETo represents reference evapotranspiration derived from meteorological data, and Kc denotes crop coefficients corresponding to growth stages: initial (0.6), development (0.8), mid-season (1.15), and late season (0.8). Crop coefficients were validated against local lysimeter studies conducted at AARI for the Roma VF cultivar and adjusted by ±5% based on regional climatic conditions and cultivar-specific transpiration characteristics [9]. Four irrigation treatments were established: T1 (100% ETc as control), T2 (80% ETc), T3 (60% ETc), and T4 (40% ETc). Water application utilized precision drip irrigation systems featuring pressure-compensating emitters (with a 2 L/h discharge rate) positioned at 30 cm intervals. System uniformity coefficient exceeded 92% based on monthly evaluations across measurement points per treatment block. Operating pressure was maintained at 1.5 bar with automated regulation and filtration systems to prevent emitter clogging. Irrigation scheduling followed cumulative ETc calculations with treatment-specific frequencies: daily applications for 40% ETc, alternate days for 60% ETc, and 2-day intervals for 80–100% ETc treatments.

Soil moisture was monitored using TDR sensors at 15, 30, and 45 cm depths. Buffer zones prevented lateral water movement between plots. Meteorological parameters were recorded using an automated weather station (Campbell Scientific CR1000X; Campbell Scientific, Logan, Utah, USA) positioned within 100 m of experimental plots, measuring air temperature, relative humidity, wind speed, solar radiation, and precipitation at 15-min intervals with real-time irrigation scheduling adjustments.

The experimental design followed a randomized complete block design (RCBD) with three replications. Individual experimental units comprised four rows measuring 10 m in length each, providing a net plot area of 24 m². Growth parameters were measured at 60 days after transplanting, including plant height, SPAD chlorophyll readings, and leaf area determination. Yield components were recorded from ten randomly selected plants per plot, encompassing fruits per plant, fruit length, and fruit diameter measurements. Total yield was calculated by harvesting all fruits from the net plot area and converting them to tons per hectare. Average fruit weight was determined by dividing total yield by fruit number. Water use efficiency (WUE) was calculated as follows:

WUE = Total Yield (kg/ha) / Total Water Applied (m³/ha)

(2)

Fruit quality assessment employed standard analytical procedures. Total soluble solids (TSSs) were measured using a digital refractometer (°Brix); pH determination utilized a calibrated pH meter; titratable acidity was quantified through titration with 0.1 N NaOH solution; and fruit firmness was evaluated using a penetrometer (kg/cm²).

Statistical Analysis

Data were subjected to analysis of variance (ANOVA) using the Statistix 8.1 software. Treatment means were compared using the least significant difference (LSD) test at p < 0.05. Letters were assigned to denote significant differences between treatments.

3. Results

Growth parameters exhibited significant responses to irrigation treatments across both experimental years (

Table 1. Growth parameters of tomato under deficit irrigation (2023–2024).

Treatment (% ETc)		Tomato
	Plant Height (cm)	SPAD Value	Leaf Area (cm2)
100 (Control)	92.5 ± 2.1 a	45.8 ± 1.3 a	1450 ± 35 a
80	90.2 ± 2.5 a	44.7 ± 1.5 a	1420 ± 40 a
60	85.1 ± 1.8 b	42.3 ± 1.2 b	1305 ± 30 b
40	78.3 ± 2.0 c	39.0 ± 1.0 c	1180 ± 25 c

Mean Values Followed by Different Letter(s) Within a Group Differ Significantly at p ≥ 0.05.

). Plant height showed clear water availability responses, with full irrigation (100% ETc) achieving a maximum height of 92.5 cm. The 80% ETc treatment maintained comparable height at 90.2 cm with no statistical difference from control. Moderate water stress (60% ETc) reduced height to 85.1 cm, while severe stress (40% ETc) resulted in a height of 78.3 cm.

SPAD values demonstrated similar response patterns, with control and 80% ETc treatments showing no significant difference (45.8 vs. 44.7). Moderate stress reduced SPAD to 42.3, while severe stress caused a value of 39.0. Leaf area measurements revealed comparable patterns, with 80% ETc maintaining 1420 cm² compared to the control’s 1450 cm². Progressive reductions occurred under 60% ETc (1305 cm²) and 40% ETc (1180 cm²).

Yield components showed threshold responses to water availability (

Table 2. Yield components of tomato under deficit irrigation.

Treatment		Tomato
	Fruits/plant	Fruit Length (cm)	Fruit Diameter (cm)
100	38.6 ± 1.2 a	6.4 ± 0.15 a	5.8 ± 0.10 a
80	37.8 ± 1.4 a	6.2 ± 0.10 a	5.7 ± 0.08 a
60	33.2 ± 1.0 b	5.8 ± 0.12 b	5.3 ± 0.09 b
40	28.5 ± 0.9 c	5.3 ± 0.20 c	4.8 ± 0.11 c

Mean values followed by different letter(s) within a group differ significantly at p ≥ 0.05.

). Fruit number per plant remained statistically similar between control (38.6 fruits) and 80% ETc (37.8 fruits). Significant reductions occurred under 60% ETc (33.2 fruits) and 40% ETc (28.5 fruits).

Length remained comparable between control (6.4 cm) and 80% ETc (6.2 cm), with significant reductions under 60% ETc (5.8 cm) and 40% ETc (5.3 cm). Fruit diameter showed parallel responses, declining from 5.8 cm (control) to 5.7 cm (80% ETc, non-significant), 5.3 cm (60% ETc), and 4.8 cm (40% ETc). Yield and water use efficiency showed clear responses to irrigation treatments across both years (

Table 3. Yield and water use efficiency (WUE) of tomato under deficit irrigation.

Treatment		Tomato
	Yield (t ha−1)	Avg. Fruit Weight (g)	WUE (kg m−3)
100	105.5 ± 2.5 a	90.8 ± 1.8 a	1.25 ± 0.03 b
80	108.3 ± 2.1 a	89.2 ± 1.5 a	1.39 ± 0.04 a
60	92.7 ± 1.9 b	82.5 ± 1.7 b	1.32 ± 0.05 a
40	76.4 ± 2.3 c	75.0 ± 2.0 c	1.22 ± 0.06 b

Mean values followed by different letter(s) within a group differ significantly at p ≥ 0.05.

).

The marginal yield increase under 80% ETc treatment (108.3 vs. 105.5 t/ha) likely resulted from enhanced root development and improved nutrient uptake efficiency under controlled water stress, consistent with hormesis responses documented in deficit irrigation studies. This phenomenon reflects optimal water stress levels that stimulate beneficial physiological adaptations without compromising reproductive capacity. Average fruit weight maintained consistency between control (90.8 g) and 80% ETc (89.2 g), with significant reductions under 60% ETc (82.5 g) and 40% ETc (75.0 g). Water use efficiency achieved maximum values under 80% ETc (1.39 kg m⁻³), representing an improvement over the control (1.25 kg m⁻³). The 60% ETc treatment also showed enhanced WUE (1.32 kg m⁻³), while severe stress reduced WUE to 1.22 kg m⁻³. Quality parameters showed progressive improvements under deficit irrigation (

Table 4. Fruit quality parameters of tomato under deficit irrigation.

Treatment	Tomato
	TSS (°Brix)	pH	Acidity (%)	Firmness (kg/cm2)
100	4.2 ± 0.1 b	4.35 ± 0.05 b	0.35 ± 0.02 b	1.15 ± 0.05 b
80	4.7 ± 0.1 a	4.28 ± 0.04 b	0.40 ± 0.02 a	1.25 ± 0.06 a
60	5.1 ± 0.2 a	4.20 ± 0.05 a	0.45 ± 0.03 a	1.32 ± 0.07 a
40	5.5 ± 0.2 a	4.15 ± 0.06 a	0.50 ± 0.04 a	1.40 ± 0.08 a

Mean values followed by different letter(s) within a group differ significantly at p ≥ 0.05.

). Total soluble solids increased from 4.2 °Brix (control) to 4.7 °Brix (80% ETc), 5.1 °Brix (60% ETc), and 5.5 °Brix (40% ETc).

Fruit pH decreased systematically with water stress intensity, decreasing from 4.35 (control) to 4.28 (80% ETc), 4.20 (60% ETc), and 4.15 (40% ETc). Titratable acidity increased progressively from 0.35% (control) to 0.40% (80% ETc), 0.45% (60% ETc), and 0.50% (40% ETc). Fruit firmness enhanced under water stress, increasing from 1.15 kg/cm² (control) to 1.25 kg/cm² (80% ETc), 1.32 kg/cm² (60% ETc), and 1.40 kg/cm² (40% ETc).

4. Discussion

The observed reduction in plant height, chlorophyll content, and leaf area under water stress conditions aligns with findings from previous studies on tomato response to deficit irrigation. Our findings align well with established research patterns. Patanè et al. [9] reported similar morphological adaptations in Mediterranean tomato cultivars, which supports our observations under Pakistani semi-arid conditions, where plant height decreased by 12–18% under moderate water stress [12]. The decline in SPAD values under severe water stress reflects reduced chlorophyll synthesis, which is consistent with research by Favati et al. [13], who attributed this reduction to impaired nitrogen uptake under limiting soil moisture conditions. Our results showing 14.8% SPAD reduction under 40% ETc treatment demonstrate that tomato possesses inherent mechanisms to maintain functional photosynthetic capacity under moderate stress, as previously documented by Topcu et al. [14] in similar growing conditions. These physiological adaptations suggest that controlled deficit irrigation activates beneficial stress responses without compromising fundamental metabolic processes, particularly when water application exceeds critical threshold levels [15,16].

The enhanced water use efficiency under moderate deficit irrigation represents a significant finding for sustainable water resource management in semi-arid regions. This finding has been observed in other water-limited regions with similar climatic conditions. Research by Sensoy et al. [17] in Turkish tomato production demonstrated that optimized irrigation scheduling can decouple yield from water consumption through improved physiological water utilization. The curvilinear relationship between water application and WUE observed in our study supports previous research by Hartz et al. [18], who identified optimal irrigation thresholds for maximizing resource productivity in California tomato production. These findings have direct implications for irrigation management in water-scarce environments, where economic returns must be balanced against resource conservation objectives, particularly relevant for smallholder farmers in Pakistan’s Punjab province. The 11.2% improvement in water use efficiency at 80% ETc treatment demonstrates that strategic water management can simultaneously achieve conservation goals while maintaining agricultural productivity.

The improvement in fruit quality parameters under deficit irrigation conditions represents a significant finding for commercial tomato production. This quality improvement pattern has been documented across different tomato production systems. The concentration effect results from reduced fruit water content and enhanced synthesis of soluble compounds, as demonstrated by Beckles [19] in controlled environment studies. Enhanced fruit firmness under deficit irrigation improves post-harvest handling characteristics and extends shelf life potential, consistent with findings by Sato et al. [20] in Japanese tomato production systems. The systematic increase in total soluble solids content from 4.2 °Brix under full irrigation to 5.1 °Brix under 60% ETc treatment reflects metabolite concentration processes that enhance flavor characteristics and processing suitability. These quality improvements have particular relevance for processing tomato production, where higher soluble solid content reduces energy requirements for concentrate production and improves final product quality, potentially offsetting yield reductions through premium market pricing.

5. Conclusions

This two-year field investigation demonstrates that moderate deficit irrigation (80% ETc) represents an optimal strategy for tomato production in semi-arid environments, achieving comparable yields to full irrigation while enhancing water use efficiency by 11.2%. The research establishes clear threshold responses, where water stress below 60% ETc significantly compromises productivity, while moderate deficits improve fruit quality parameters, including soluble solid content and firmness. These findings provide evidence-based recommendations for sustainable water management in resource-constrained agricultural systems, particularly relevant for Pakistan’s semi-arid regions facing increasing water scarcity challenges. For practical implementation, farmers can adopt 80% ETc irrigation scheduling to save 20% of water while maintaining productivity. This strategy is particularly beneficial for smallholder farmers facing water constraints in Pakistan’s agricultural regions.