A field trial was carried out at student farm, University of Agriculture, Faisalabad (31˚25' North latitude and 73˚08' East longitude, with semi-arid environment). Before sowing, soil samples from depth of 0 - 15 and 15 - 30 cm were collected randomly from experimental area for soil analysis. Report of physico-chemical properties of soil was obtained from Soil Fertility Research Institute, Lahore (Table 1). Climatic condition of the experimental site for the duration of study is represented in (Figure 1).

Galaxy-2013 cultivar of wheat was acquired from Ayub Agriculture Research Institute, Faisalabad. Seed bed was prepared by rotavating followed by two ploughings and planking to pulverize the soil. Line sowing was done with hand drill while maintaining 22.5 cm distance between rows using seed rate of 125 kg・ha⁻¹.

Trial was arranged in randomized complete block design (RCBD) with split-plot arrangement and replicated thrice. There were two factors studied in the experiment. Factor which was randomized in main plot comprised of three levels of

potential soil moisture deficit (PSMD), i.e. I₁ = 50 mm PSMD, I₂ = 75 mm PSMD and I₃ = 100 mm PSMD. While, factor randomized in sub plot consist of four levels of nitrogen, i.e. control (No nitrogen), 50, 100 and 150 kg N ha⁻¹ Total number of experimental plots was 36, as set of 12 treatments was replicated thrice.

Canal water as well as tube well water was available to irrigate the experimental unit according to treatment requirement. Soil moisture status was monitored by using tensiometers. Nitrogen fertilizer application was done according to respective treatment in each experimental unit. While recommended dose of Phosphorous (P) and potassium (K) were applied immediately at the time of sowing. The sources of fertilizers were urea, single super phosphate and murate of potash for N, P and K respectively.

A standard model “CROPWAT” was applied to calculate penman potential evapotranspiration (PET). it was developed by Food and Agriculture Organization [45] . It computes the total amount of irrigation water applied to crop is equal to difference between summation of irrigation and precipitation and potential evapotranspiration (PET).

D = ∑ E T o − ∑ ( I + R )

ET_o can be calculated by following formula.

E T o = E p a n × K p

E_pan = mean daily pan evaporation, K_p = pan coefficient.

Water stress was imposed on crop in early, middle and terminal stages of crop development and was continued for varying degree of time. Irrigations were applied at 50, 75 and 100 mm PSMD. Calculation of amount of water per are shown as under.

Irrigation depth = 50 mm = 0.05 m;

Area of net plot = 4.5 m × 1.5 m = 6.75 m²;

As we know that, 1 m³ = 1000 liters;

Irrigation for 50 mm (depth) = 337.5 liters;

Diameter of fountain (d) = 0.24 m;

Radius of fountain (r) = 0.12 m;

Fountain length = 25 cm = 0.25 m;

Fountain total area (π r²) = 0.045 m²;

Fountain total volume = A × L = 0.01125 m³;

Required volume of irrigation water = 0.337 m³;

Total fountain buckets needed for 50 mm PSMD=Required volume of irrigation water/total volume of fountain = 0.337/0.01125 = 30.

To maintain 50 mm PSMD per plot 30 fountain buckets were used.

Similarly, 45 fountain buckets for 75 mm PSMD and 60 buckets for 100 mm PSMD per plot were used.

Soil water content = ( W 1 − W 2 / W 2 ) × 100 where W1 = Mass of soil before drying and W2 = Mass of soil after drying.

Observation regarding productive tillers, plant height, grains・spike⁻¹, test weight, economic yield and total biomass accumulation were recorded according to standard criterion. While radiation using efficiency for total dry matter was computed as (RUE_TDM): TDM/ΣSa, while, for grain yield was calculated as (RUE_GY) = Grain yield/ΣSa.

Here TDM = total dry matter, Sa is equal to amount of intercepted photo synthetically active radiations (PAR) [46] , as it can be calculated by multiplying Fi with Si, where “Fi” is fraction of intercepted radiations and “Si” is daily incident photosynthetically active radiation

S a = F i × S i

here “Fi” can be calculated by Beer’s law

F i = 1 − e x p ( − k × L A I )

K is a coefficient whose value for wheat is 0.4. Furthermore, for calculation of “Si” there is need to calculate solar radiations

S i = Total R s / 2

Rs is equal to solar radiations that can be calculated by

R s = [ a + b ( n / N ) ] × R a

where, a and b are constants and have 0.25 and 0.5 values respectively, n is equal to actual sunshine hours whereas N is maximum possible sunshine hours and Ra is extra-terrestrial radiations. All recorded data was statistically analyzed by using fisher analysis of variance technique and difference among treatment’s means was compared by least significance difference test at 5% level of probability [47] .

The statistical data concerning about the height of plant as affected by different levels of irrigations and different levels of nitrogen is shown in (Table 3). Study has shown that plant height influenced significantly due to different irrigation timing in addition to different delta of water. Moreover, a significant interaction of irrigation levels and Nitrogen application was also observed (Table 4). The results showed that irrigation level 75 mm PSMD and 150 kg N ha⁻¹ gave the maximum 76.27 cm and 82.27 cm plant height respectively and least plant height 68.77 cm was noted in 100 mm PSMD and control N treatments (N₀) gave 59.40 cm plant height. I₂ treated plots gave maximum plant height because effective rainfall was maximum and adequate moisture supply was maintained throughout the all growth stages of crop. The results of our experiment are just like with the study of [48] [49] [50] [51] . High dose application of nitrogenous fertilizer increases the vegetative growth vigorously and our result synchronise with the finding of [52] [53] .

Means sharing same letters did not differ significantly at P = 0.05. I₁: Irrigation at 50 mm potential soil moisture deficit; I₂: Irrigation at 75 mm potential soil moisture deficit; I₃: Irrigation at 100 mm potential soil moisture deficit; N₀: Control (No nitrogen); N₁: 50 kg N ha⁻¹; N₂: 100 kg N ha⁻¹ and N₃: 150 kg N ha⁻¹.

^(b)The data are presented as the means ± SD; Means sharing same letters did not differ significantly at P = 0.05.

Final economic yield is directly influenced by numbers of spike bearing tillers per unit area and its expresses the importance of productive tillers. In Table 3 data indicate that the PSMD and nitrogen levels and in Table 4 interaction of PSMD and nitrogen levels has significant impact (P > 0.05) on the total number of tillers (productive) per unit area. Maximum productive tillers (320.0) were recorded under 75 mm PSMD and 150 kg N ha⁻¹ (I₂ × N₃) treatment while, least (184.59) productive tillers were noted in 100 mm PSMD × control (0 N) (I₃ × N₀) treated plots. Results of our experiment are analogous to those of Nisar et al., [51] (2016). Khaliq, [52] (1999) reported that productive tillers in a unit area increased significantly with the rising application of nitrogen.

Grain per spike were significantly (P ≤ 0.05) affected by PSMD and nitrogen level (Table 3) while their interactive effect was non-significant (Table 4). Maximum (P ≤ 0.05) grains per spike (44.45) were recorded under 75 mm PSMD irrigation treatments (I₂), while, (44.79) when 150 kg N ha⁻¹ treatments (N₃) was applied. Least no of grains per spike (40.29) and (39.23) were recorded in I₁ (50 mm PSMD) and N₀ (0 nitrogen) treated plots. Low level of nitrogen and low PSMD reduced the grains per spike significantly.

In case of 1000 grain test weight PSMD levels and nitrogen level influenced significantly (P ≤ 0.05) (Table 3) but interaction of PSMD levels and nitrogen treatments didn’t affect significantly (Table 4). Highest (45.52 g) 1000 grain weight was recorded under 75 mm PSMD (I₂) treatment, while, I₃ (100 mm PSMD) produced least test weight (37.39 g). Increasing water application increased grain weight [53] [54] , but our result contradicts with these studies, judicial application of irrigation increases the total grain weight. This study has shown the same trend as of [51] . More nitrogen application also increased grain weight significantly and highest test weight (45.67 g) was recorded in N₃ (150 kg N ha⁻¹) and least (36.63 g) was noted in N₀ (control) treatment. These findings are in line with those of [48] . Similar research carried out by Lin et al. [55] and Shao et al. [56] shown that not more than three or four irrigations are necessary for gaining desired outcomes in case of wheat.

Biological yield is defined as “total biomass production per unit area by a crop”. Biological yield depends upon characteristic like plant population in a unit area, height of the plants, total number of grains・spike⁻¹ and test weight of grains. Alteration in any cultural practice, climatic factors or any other factor (fertilization, irrigation and pesticides) reflects alteration in biological produce of crop. The statistical data regarding the influence of irrigation (PSMD) and nitrogen levels on biological yield are presented in Table 3. Data shows that nitrogen levels significantly variate the biological yield as well as irrigation levels also produce significant difference among different treatments, while their interactive effect is non-significant (P ≤ 0.05). Maximum (13.18 t・ha⁻¹) biological yield was attained in the case of I₂ (75 mm PSMD) followed by 9.88 t・ha⁻¹ in case of I₁ (50 mm PSMD) while, minimum (9.15 t・ha⁻¹) biological yield was recorded under I₃ (Irrigation at 100 mm PSMD) treatments. Reasons behind the maximum Biological yield in (I₂) was judicial use of irrigation resulted in better germination, proper stand establishment, maximum numbers of tillers per unit area, more plant height, less water stress to crop and higher water use efficiency [57] . Warraich et al. [50] reported that under water stress plants required more energy to extract water low soil moisture status.

The statistical data regarding impact of different nitrogen levels at total dry matter production of wheat are shown in Table 3. Highest biological yield (13.48 t・ha⁻¹) attained from N₃ (150 kg N per hectare) after that (11.77 tons per hectare) under N₂ (100 kg N per hectare), and least (7.13 t per hectare) biological yield was found in N₀ (control) treatments. Hussain, [49] (2006) and Ali, [58] (2009) observed that total biomass production will increase with increasing nitrogen application. The interaction of two factors was non-significant (P ≤ 0.05) on total biomass production (Table 4).

The pivot point of the research is to maximize the per unit economic yield (grain in case of wheat) to fulfill the human dietary requirement and to ensure food security. That’s why different package of technologies is used to boost the profitability and economics of producers. Economic yield (grain in case of wheat) is product of collective response of yield component (total number of productive tillers unit area⁻¹ × total number of grains・spike⁻¹ × 1000 grain weight). Data about economic yield affected by various PSMD and nitrogen treatments is presented in Table 3. Statistical analysis for grain yield shows that PSMD levels and nitrogen treatment have significant impact. Maximum (5.01 t・ha⁻¹) grain yield was achieved from I₂ (75 mm PSMD) followed by grain yield (3.67 t・ha⁻¹) and least (3.26 t・ha⁻¹) from I₁ (50 mm PSMD) and I₃ (100 mm PSMD), respectively. Appropriate amount and at specific time, application of water increased the yield while un-judicial use or lower use of irrigation both reduced the wheat yield. Excessive irrigation application leads to lodging which ultimately reduced the grain yield. Zhang et al. [59] also declared that judicial application of water is necessary for maximum yield. Bunyolo, [60] stated that wheat yield will increase with increasing irrigation application while Lin, [57] reported that only 4 irrigations at critical growth stages is enough for obtaining economic wheat yield. Mubeen et al. [61] and Zarien et al. [62] findings revealed that judicial application of 4 irrigation at proper time gave maximum yield.

In case of nitrogen application uppermost grain yield (5.50 t・ha⁻¹) was gained from N₃ (150 kg N per hectare), followed by 4.53 t per hectare, 3.50 t per hectare and 2.39 t per hectare from treatments N₂ (100 kg N per hectare), N₁ (50 kg N per hectare) and N₀ (control), in that order (Table 3). Interactive effect of these factors did not affect the economic yield (Table 4). Hussain et al. [49] and Ali et al. [58] noticed that rising nitrogen level increases economic yield significantly.

Agarwal and Sinha, [63] stated the harmful effects of water scarcity on the seed yield of wheat. Drought stress before pollination is negatively correlated with seed yield. Demir and Shaw, [64] described that drought stress at pollination stage of maize plant reduced the seed yield up to half. The economic yield of wheat like other crops has constructive responses as chemical fertilizer application increased. Climatic and management practices (crop rotation, watering and drainage) factors are primarily significance in response of field crops to chemical fertilizers [32] .

RUE for total dry matter was found to be significantly changed with irrigation and nitrogen levels (Table 3), while their interaction found to be non-significant (Table 4). Regarding PSMD levels, RUE for TDM ranged from 1.68 - 1.86 g・MJ⁻¹ and maximum RUE was found in I₂ (50 mm PSMD). Whereas, for nitrogen, it was highest (1. 88 g・MJ⁻¹) in N₃ (150 kg N ha⁻¹) and least (1. 62 g・MJ⁻¹) RUE eas observed in N₀ (control treatmnet). RUE for grain yield was maximum (0.47 g・MJ⁻¹) in case of I₂ (75 mm PSMD) among irrigation regimes and in nitrogen application, RUE_GY found be highest (0.47 g・MJ⁻¹) with 150 kg・ha⁻¹ application of nitrogen, while interaction of irrigation and nitrogen levels effect RUE non-significantly. Whitfield, [65] stated RUE of wheat was reduced due to water stress. Calviglia et al. [42] found that RUE can be increased with higher levels of nitrogen but not significantly (P ≤ 0.05).