Effect of irrigation stress and phosphorus levels on growth, yield and economics of Wheat (Triticum aestivum L.)

Introduction

Wheat (Triticum aestivum L.) is one of the most important rabi cereal crops in India, occupying more than 33 million ha and contributing substantially to national food security (1). Punjab, Haryana and Uttar Pradesh together account for a major share of production, with wheat forming the dietary staple for millions of people in the form of chapati and bread (2). Inadequate phosphorus (P) nutrition and unscheduled irrigation are considered the two most critical constraints limiting wheat productivity in the Indo-Gangetic plain. Phosphorus is an essential macronutrient involved in energy transfer (ATP), photosynthesis, cell division and root development. Its diffusion in soil is strongly dependent on soil moisture, so moisture deficit directly reduces P availability to plant roots (3,4). Timely irrigation at critical phonological stages, Crown Root Initiation (CRI), Booting and Anthesis is indispensable because water stress at these stages reduces tiller number, spike fertility and grain weight, leading to severe yield penalties (5,6). In Punjab, rapid depletion of groundwater tables has intensified the need for water-efficient irrigation schedules. Research has repeatedly demonstrated a synergistic interaction between P supply and soil moisture: adequate P promotes deeper root systems that exploit residual soil moisture, while sufficient moisture enhances P diffusion and uptake (7,8). Despite this, farmers often apply P fertilizers without matching irrigation, resulting in poor fertilizer-use efficiency (9). The high-yielding variety DBW 222, released for the North-Western Plain Zone, shows a strong positive response to both P nutrition and timely irrigation (10). A systematic evaluation of P × irrigation interactions for this variety under semi-arid Punjab conditions has not been reported. The present study was therefore undertaken with the following objectives: (i) to evaluate the effect of P levels (0, 30, 60 and 90 kg P₂O₅ ha⁻¹) on growth and yield of wheat; (ii) to assess the influence of irrigation timing (CRI, Booting, Anthesis) on yield attributes; (iii) to quantify P and N uptake under different P × irrigation combinations; and (iv) to identify the most economically viable P × irrigation combination for semi-arid wheat production.

Materials and Methods

Experimental site

The field experiment was conducted during rabi 2025-26 at the Agronomy Research Farm, Guru Kashi University, Talwandi Sabo, Bathinda, Punjab, India (lat. 29°57′N; long. 75°7′E; altitude 213 m asl). The climate is semi-arid with extreme summers and cold winters. The experimental period (November 2025 to April 2026) recorded a maximum temperature of 35.0°C in April (maturity stage) and a minimum of 6.0°C in January (tilleringjointing stage). Total rainfall during the crop season was only 3 mm; all crop water requirements were therefore met through scheduled irrigation. Optimum photosynthetic temperatures (20-25 °C) occurred in February-March, coinciding with spikelet development and anthesis.

Soil properties

Composite soil samples were collected from the 0-15 cm layer before sowing and analyzed for physico-chemical properties (Table 2). The soil was sandy loam with neutral to slightly alkaline pH (7.6), low organic carbon (0.42%) and low available P (18.2 kg ha⁻¹).

Observations

Growth observations (plant height, dry matter accumulation and number of effective tillers m⁻²) were recorded on five tagged plants per net plot at 30, 60, 90 DAS and at harvest. Plant height was measured from ground level to spike tip (awns excluded). Dry matter was determined by oven-drying at 65 °C to constant weight and expressed as g m⁻². Yield attributes (spike length cm and 1000-grain weight g) were recorded at harvest. Grain and straw yield were recorded plot-wise and converted to q ha⁻¹. Phosphorus and nitrogen contents in grain and straw were determined by standard analytical methods and uptake calculated as (content × yield).

Economic analysis

Gross returns were calculated as: (grain yield × MSP 2025-26) + (straw yield × market price). Net returns = gross returns -cost of cultivation. Benefit-cost (B:C) ratio = net returns ÷ cost of cultivation.

Statistical analysis

Data were subjected to analysis of variance (ANOVA) for split plot design following Cochran and Cox (1967) and Gomez and Gomez (1984). Treatment means were compared at the 5% level of significance (P = 0.05) using critical difference (CD) values. All statistical computations were done using standard ANOVA procedures.

Results and Discussion

Plant height

Plant height increased progressively and significantly with increasing P levels at all growth stages and at harvest ( (14). Moisture stress at this critical stage prevented adventitious root development and primary tiller differentiation, an injury not fully recoverable in subsequent growth stages (15).

Dry matter accumulation increased steadily from 60 DAS to harvest across all treatments (Table 5). At harvest, P₉₀ recorded 1560 g m⁻², which was 35.6% higher than P₀ (1150 g m⁻²). I₁ recorded 1520 g m⁻² against 1220 g m⁻² under I₃. The interaction P₉₀I₁ produced the highest dry matter (1762 g m⁻²). Higher P availability improved leaf area index (LAI) through greater cell division, thereby enhancing light interception and photosynthetic efficiency. Drought-induced stomatal closure under I₂ and I₃ restricted CO₂ assimilation and reduced overall biomass accumulation (16,17).

Grain and straw yield

Grain and straw yield increased significantly with increasing P levels and were maximum under I₁ irrigation (Table 7). The highest grain yield (51.8 q ha⁻¹) and straw yield (70.4 q ha⁻¹) were recorded under P₉₀, while P₀ produced 32.5 and 48.2 q ha⁻¹, respectively. Among irrigation timings, I₁ produced significantly greater grain (48.6 q ha⁻¹) and straw yield (66.5 q ha⁻¹) than I₂ or I₃. Maximum grain yield (56.4 q ha⁻¹) was obtained under P₉₀I₁. Harvest index was not significantly affected by either P or irrigation, indicating that while total biomass increased, the partitioning ratio (grain: straw) in cv. 'DBW 222' was genetically stable. This is in agreement with Noonari et al (30) who reported a linear increase in grain yield with P application up to 90 kg ha⁻¹, and Kumar et al (22) who documented significant yield losses following delayed early irrigation in northwest India.

Post-harvest soil properties

Soil pH, EC and organic carbon did not differ significantly among treatments (Table 8). Available soil P increased significantly with P level, ranging from 10.5 (P₀) to 24.1 kg ha⁻¹, with irrigation timing also showing a significant effect. Higher residual soil P under I₃ (18.8 kg ha⁻¹) compared to I₁ (15.5 kg ha⁻¹) reflected reduced crop uptake caused by moisture-limited P diffusion and lower biomass production under stressed conditions. Available K was unaffected by treatments.

Phosphorus and nitrogen uptake

Total P uptake increased significantly from 11.00 kg ha⁻¹ (P₀) to 27.13 kg ha⁻¹ (P₉₀) and was highest under I₁ (23.22 kg ha⁻¹; Table 9). The interaction P₉₀I₁ yielded maximum total P uptake (36.08 kg ha⁻¹). Soil moisture at CRI provided a diffusion pathway for basal-applied SSP, delivering P ions to developing crown roots. Under drought conditions (I₂, I₃), diffusion was limited by low soil water potential, effectively starving roots even where fertilizer P was adequate (20). High P application (90 kg ha⁻¹) compensated partially under stress by stimulating root elongation and lateral root formation, enabling P₉₀I₃ plants (21.24 kg ha⁻¹ P uptake) to outperform well-irrigated P₀ plots (12.50 kg ha⁻¹), consistent with Kang et al (19).

Total N uptake followed a similar trend, rising from 76.9 kg ha⁻¹ (P₀) to 134.0 kg ha⁻¹ (P₉₀; Table 10). This synergistic effect of P on N uptake reflects the role of a well-developed root system in mining greater soil volume for nitrate. The interaction P₉₀I₁ produced the highest N uptake (175.4 kg ha⁻¹), demonstrating that adequate P and timely moisture together maximize nutrient-use efficiency.

Economics of wheat production

Economic analysis (Table 11) showed that although cost of cultivation increased marginally with P level (₹41,500 ha⁻¹ for P₀ to ₹46,600 ha⁻¹ for P₉₀), the additional expenditure (~₹5,100 ha⁻¹) was far outweighed by the increase in net returns (₹89,350 ha⁻¹ for P₉₀ vs ₹43,750 ha⁻¹). P₉₀ recorded the highest B:C ratio (2.91), compared with 2.05 for P₀. Among irrigation timings, I₁ yielded maximum net returns (₹79,500 ha⁻¹) and B:C ratio (2.76), while I₃ reduced net returns to ₹53,100 ha⁻¹. The results emphasize that every rupee invested in basal P and timely CRI irrigation generates significantly higher profit, an observation corroborated by Patidar et al (33) and Tiwari et al (48).

Conclusion

Application of 90 kg P₂O₅ ha⁻¹ combined with irrigation at the CRI stage (P₉₀I₁) consistently gave the highest values for all growth parameters (plant height 103.2 cm, effective tillers 447 m⁻², dry matter 1762 g m⁻²), yield attributes (spike length 13.9 cm, 1000-grain weight 45.9 g) and grain yield (56.4 q ha⁻¹) of wheat cv. 'DBW 222' under the semi-arid conditions of Punjab. The interaction between P and irrigation timing was significant for all parameters, confirming that moisture at CRI is essential for effective P diffusion and root development. Even under terminal drought stress (I₃), 90 kg P₂O₅ ha⁻¹ maintained higher yields and nutrient uptake than well-irrigated control plots, demonstrating the buffering role of adequate P nutrition. On economic grounds, P₉₀ with CRI irrigation gave a B:C ratio of 2.91 and net returns of ₹89,350 ha⁻¹, making it the most viable and recommended agronomic practice for semi-arid wheat production in the Indo-Gangetic plain.

Acknowledgement

AcknowledgementsThe authors thank the Dean, Faculty of Agriculture, Guru Kashi University, Talwandi Sabo, for providing the necessary facilities. The technical assistance of field and laboratory staff of the Department of Agronomy is gratefully acknowledged.

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