Growth and Yield Response of Pea (Pisum sativum L.) Crop to Classical and Regulated Deficit Irrigation along with Nitrogen Fertilization under Drip Irrigation

Pulses are proved as unique jewels of Indian farming. Pulses are an essential part of Indian’s diet. Pulses have the potential to significantly enhance human health, soil health by nitrogen fixation, save the environment and support global food security. The average fresh green pea yield was recorded as 9686.1 kg/ha (FAOSTAT, 2018). Water and nitrogen act as critical factors in green pea production. In Punjab, farmers are using conventional methods for irrigation and fertilizer application which results in more water and nutrient losses (Devi et al., 2021). Improper irrigation scheduling and poor water management under various irrigation methods has led to water stress in pea production. Numerous studies have noted the detrimental impacts of inefficient water management, including over- and under-watering, the impact of water on soil salinity, water stress and a lack of study to determine the ideal amount of water for pea production at different growth stages. The use of modern irrigation methods can improve crop yield and water use efficiency (Jadav et al., 2021; Changade et al., 2023). The upcoming challenge in future agriculture is how to use irrigation water efficiently. Adoption of drip irrigation technique for irrigating crops could overcome this problem. In water scares regions of Punjab, along with drip irrigation; deficit irrigation approach can be a batter option to conserve use of fresh surface and ground water in pea production. Deficit irrigation (DI) refers to the application of irrigation water below the actual crop water requirements, either during the full growing period of crop (Classical deficit irrigation; CDI) or at some specific phonological/growth stages (regulated deficit irrigation; RDI). Crop response to DI varies with the exposure durations and severity of water stress exerted on plants at different growth stages (Chai et al., 2016). DI levels can vary with type of crop so it is crop specific. Therefore, DI involves thorough understanding of how crops respond to water stress in terms of yield and quality. Hence, the appropriate level of deficit irrigation should be ensured for high production of pea crop. Now days, farmers are supplying 100% recommended dose of nitrogen (RDN) through direct soil application (broadcasting) in pea cultivation which results nitrogen losses. So along with water conservation some nitrogen amount can save by drip fertigation which will provide a supply of nitrogen uniformly and timely without polluting the environment by the leaching process. The drip fertigation decreases the requirement of fertilizer by 40-60% and enhances the crop yield by 15-50% over conventional method (Loganathan and Latha, 2016). The integrated application of irrigation water and nutrient (fertigation) to plants boosts the photosynthesis process so they produce new tissues to increase production of biomass. However; there is a gap in the study of integrated water and nitrogen management in the cultivation of green pea. Research works on deficit irrigation along with nitrogen fertilization in green pea are also scant under existing climatic condition of Trans-gangetic region of Punjab. Therefore, the present research work was undertaken.

Study area
 
A field experiment was conducted at research field of Lovely Professional University, Punjab (Plate 1) during rabi 2021-22 (Y1) and 2022-23 (Y2). The site was facilitated with drip irrigation system along with fertigation system.


       
The experimental site is located at latitude 31.25^oN and longitude 75.70^oE along with altitude of 280 m above mean sea level). The region has a humid subtropical climate. The annual mean temperature and precipitation are 23.1^oC and 957 mm. The soil type in study area is sandy loam. The available nitrogen, phosphorus (P) and potassium (K) contents in the 0-20 cm soil layer before transplantation were 256.8, 6.1 and 246.8 kg/ha, respectively.
 
Experimental details
 
The raised beds were prepared with 75 cm width, 15 m long and 30 cm height from ground surface. The total six treatments (including control plot) were arranged in random block design with four replications. As per treatments, full dose of phosphorus and potash (as per recommended dose of fertilizer) were applied as basal dose (prior to sowing of seeds) to the respective plot through soil application (broadcasting). The recommended dose of nitrogen (by urea fertilizer) was supplied to respective plots (as per treatments) in 8 equal splits at 6 day interval through drip fertigation. In control plot, RDF (including nitrogen) was supplied as per farmer’s practice through broadcasting. Pure and healthy seeds of pea were sown in paired row at spacing of 30×15 cm and 4-5 cm depth.
 
Treatments details
 
In this study, the following treatments were taken in random block design with four replications as given in Table 1.
 

 
Calculation of crop water requirement
 
In drip irrigated plots, irrigation water (as per treatments) was given on the basis of following equations. The pan coefficient (K_p) for calculating crop evapotranspiration was taken as 0.7.
   
Where,
IWR = Irrigation water requirement (litre/day/plant).
Epan = Pan evaporation (mm/day).
Kc = Crop factor/coefficient.
Kp = Pan coefficient, m.
Sr = Row spacing, m.
Sp = Plant spacing.
Wp = Percentage wetted area, 90%.
       
In order to calculate the total amount of water supplied, on the monthly basis, the effective rainfall (ER) was calculated by following equation (Sharma et al., 2021):                                                                            
 
Where,
P_t  = Total rainfall, mm.
Standard package of practices (given by Punjab Agricultural University) was followed for rest of the operations to grow the crop. 
 
Crop observation
 
In every plot, five plants were selected. Plant height, number of branches/plant and leaf area index (LAI) were recorded at flowering stage of the crop in both the years. Pods per plant (numbers), grains per pod (numbers), total weight of 100 seeds and yield (kg/ ha) of pea crop were recorded at harvesting. Analysis of variance (ANOVA) procedures were used to statistically analyze the data gathered from the current field experiment, with a 5% threshold of significance.
 
Water use efficiency
 
It is defined as the ratio of yield to the total quantity of irrigation water applied. It was calculated by equation 4.
 

Crop evapotranspiration and irrigation water requirement
 
In study area, the uneven trend of daily pan evaporation was found during year 2021-22 and 2022-23 which varies from 0.1 to 3.1 and 0.4 to 4.2 mm/day, respectively (Fig 1 and 2). This variation emphasis on adoption of modern approaches of irrigation scheduling which is based on daily irrigation water requirement (IWR) of pea crop under drip irrigation. Poor irrigation scheduling results water stress instigating reduction in the growth and pea yield. In case of full irrigation under drip irrigation method, the minimum and maximum IWR were estimated 0.368and 1.8 l/plant during initial and mid stages respectively (Fig 3). It was mainly due to variation in daily weather parameters. In RDI treatments, the total IWR during whole growing period was found 3.2 and 3.3 l/plant/season for T₄ and T₅, respectively. While, the total IWR under CDI treatments i.e T₂ and T₃ were estimated 3 and 2.5 liter/plant/season, respectively (Fig 4) which was slightly lesser than RDI treatments (T₄ andT₅) but it gives continuous water stress for pea plant during whole growing period over full irrigation as well as RDI approaches and consequently affects pea production and water use efficiency. Legume crops are very sensitive to water so in case of DI approach, the over and under irrigation during whole growing period (FI or CDI) will affect crop response so RDI will be a better approach to improve the crop performance under drip irrigation.
 

 

 

 

 
Growth parameters
 
The results showed that the plant growth, yield attributes parameters and pod yield were significantly affected by drip irrigation in combination fetigation over conventional methods of irrigation and fertilizer application. The data given in Table 2 indicated that the plant height was recorded as highest in drip irrigated plot (T₁) and lowest in control plot.  The similar result was reported by Jadhav et al., (2021); Sharma et al., (2021). Among all the drip irrigated treatments, the plant height was highest as 49 cm under treatment T₁ followed by T₅ (45.5 cm). The plant height under treatment T₂ (43 cm) and T₃(42 cm) was recorded at par, which indicates non-significant effect of classical deficit irrigation (CDI) level on plant height. As compared to treatment T₂, the plant height was significantly higher in T₅ which shows that, for same level of deficit irrigation (i.e 85% of daily IWR) the batter plant height was recorded under regulated deficit irrigation (water stress i.e 15% of daily IWR during initial, development and late stage) over CDI (continuous water stress i.e 15% of daily IWR during whole crop period). When nitrogen fertilization strategies and water stress level was same, the plant height under T₄ (43.5 cm) and T₅ (45.5 cm), shows the significant affects of regulated deficit irrigation (RDI) during specific growth stages (Chai et al., 2016). This is clearly indicates that, the water stress during mid growth stage of plant results poor plant growth. Minimum plant height was recorded under T₆ (39 cm) which were significantly less as compared to all other treatments in both the years. It was due to leaching of nitrogen amount through flood irrigation. Better plant height under drip irrigation treatments can be attributed to favorable soil moisture level and minimum losses of nitrogen due to frequent application of irrigation water, nitrogen fertilization and suitable microclimate. This suggests that the seedlings of legumes require a root zone environment that is continually moist and having optimal microclimate. The leaf area index (LAI) was estimated maximum as 1.15 under treatment T₁ followed by T₅ (0.91). The LAI under T₄ (0.88) and T₅ (0.91)indicated the significant effect of same level of RDI during different growth stages. The water stress during mid stage will significantly reduce the LAI. The results are similar with Singhal et al., (2021). Minimum LAI were recorded under control plot (0.71).
 

 
Yield contributing parameters
 
The data related to yield contributing parameters are given in Table 3. The number of branches/plant in all the treatments (except T₅) were not significantly affecting by drip irrigation in combination with nitrogen fertigation over control plot. The significant difference for number of branches/plant was noted between full irrigation treatment T₁ (5) and CDI treatments (T₂ and T₃) under drip irrigation. Which is clearly indicates that, by supplying same dose of nitrogen (through fertigation), the deficit level of water (from full IWR) during whole growing stages (crop period) will reduce the number of branches/plant. In RDI treatments (having same nitrogen fertilization strategies), the number of branches/plant were significantly higher in T₅ (6) as compared to T₄ (4). It is because of change in trend of same water stress during different growth stages. The minimum number of branches/plant was recorded as 4 in T₆ (control plot). In drip irrigated treatments, the significant changes were recorded for number of pods/plant under full irrigation level T₁ (19.5) and CDI levels (T₂ and T₃). In RDI treatments (having same nitrogen fertilization strategies), number of pods/plant was recorded 18.8% higher in T₅ as over T₄. The highest number of pods/plant was recorded as 19.5 in T₁ which were at par with number of pods/plant under T₅. The significant effect of RDI at different growth stages was found on number of pods/plant under drip irrigation. The minimum number of pods/plant was recorded as 13 under control plot. The number of seeds/plant was significantly affected by drip irrigation (except CDI treatments) over flood irrigation method which were found maximum under T₅ (9) followed by T₁ (7.5). At same level of DI (85% of daily IWR) and nitrogen fertilization strategies under drip irrigation, the number of seed/pod was significantly affected by RDI (water stress during different growth stages) in T₄ and T₅ over CDI in T₂. In RDI plots (having same water deficit level and nitrogen fertilization strategies), the number of seeds/pod was recorded significantly lower in T₄ (7) over T₅ (9) which clearly shows that the water stress during mid stage retards the seed formation in pods. The minimum number of seeds/pod was recorded as 6 under control plot. It was due to more water and nutrient losses through leaching, infiltration and surface evaporation. Overall, it can be stated that drip irrigation (which offers a more favorable soil moisture regime than flood irrigation) led to improved grain development. The result is in line with Singhal et al., (2021) for pea performance under drip irrigation. The maximum weight of 100 seeds was measured under T₅ (27 gm) which was at par with weight of 100 seeds measured under T(26 gm). As compared to full irrigation level (T₁) under drip irrigation, the weight of 100 seeds was significantly changes with respect to classical (T₂ and T₃) and regulated deficit irrigation level (T4 and T5). Further, in case of RDI treatments the weight of 100 seeds/plant was significantly (12.5%) higher in T₅ (27) over T₄ (24). It shows the direct impact of water stress on weight of seeds during different growth stages of pea crop. The minimum weight of 100 seeds was recorded under treatment T₆. It is probably due to that under control plot (T₆), the significant amount nitrogen leached downward along with excess volume of irrigation water.
 

 
Crop yield, irrigation water use, irrigation water saving and water use efficiency (WUE)
 
The data in Table 4 shows that, the amount of total irrigation water applied was estimated minimum for T₃ (66.5 cm) and maximum for control plot (120 mm). In same level of DI (85% of daily IWR), 10.2% quantity of irrigation water was saved through CDI (T₂) over RDI (T₅) but it was significant reducing the pod yield and WUE. In comparison of full irrigation (T₁) under drip irrigation, 6.1% amount of irrigation water was saved under RDI (having 15% water stress during initial, development and late growth stages). It was not significantly affecting the pod yield and water use efficiency. The data related to total water use, pod yield and water use efficiency are presented in Table 5. The pod yield and WUE were found maximum under treatment T₁with values of 8.7 t/ha and 0.565 t/ha-cm respectively. The values of pod yield (8.53) and water use efficiency (0.559) under treatment T₅ which were at par with T₁. It clearly stated that, under limited water availability, the significant pod yield can get under drip irrigation by supplying deficit amount of irrigation water (15% less from daily IWR) in combination with deficit nitrogen level (90% RDN by fertigation) through RDI (water stress except mid growth stage) approach over full irrigation and same nitrogen levels.The minimum pod yield and water use efficiency were recorded under control plot (T₆)with values of 5.25 t/ha and 0.283 t/ha-cm respectively. It was because of the wastage of huge amount of water and nitrogen due to infiltration, seepage, evaporation and over wetting. The reduced pod yield in flood irrigated pea over drip irrigated is because of the fact that, the less concentration of oxygen in soil due to over wet conditions leading to stomatal closure of plants, thus decreasing the transpiration rate and later the yield. The water saving techniques can minimize the evaporation loss and can enhance the effective utilization of root zone water towards crop yield. The results of the study were found similar to Ranade et al., (2021). In case of full irrigation, the percentage of increase in yield over conventional irrigation was highest under T₁ (65.8%). The crop yield, water use efficiency and irrigation water saving was significantly higher in drip irrigation treatments as compared to control plot (flood irrigation). Further the increment level for all these parameters was significantly varies with full irrigation, CDI and RDI approaches under drip irrigation.  Among all the drip irrigated treatments (having different water level and trend of water stress in combination with same nitrogen fertilization strategies i.e 90% RDN through fertigation), the increment in crop yield, water use efficiency and irrigation water saving was varies from 27.6 to 65.7%, 63.6 to 99.7% and 26.1 to 44.6% respectively over flood irrigation. The irrigation water saving was highest (44.6%) in T₃ over flood irrigation plot but in this treatment the percentage increase in crop yield and WUE were not significantly higher than other drip irrigation treatments. The increment in crop yield and WUE was highest in a treatment (T₁) where irrigation was done at 100% of daily IWR. Among all the CDI and RDI treatments under drip irrigation, the increment in crop yield, water use efficiency was recorded 58.1% and 97.7% respectively in treatment T₅ over control plot (flood irrigation) which was at par with T₁. The result presented in Fig 5 clearly shows that, the CDI approach for growing pea crop with same nitrogen fertilization strategies under drip irrigation will significantly reduce the crop yield and WUE over RDI. Among both the RDI treatments (T₄ and T₅), the irrigation water saving was higher (34.6%) in T₄ but it was significantly reducing the pod yield and WUE over T₅ which shows that a approach of RDI having water stress (15% less from full IWR) during mid stage of pea crop will retard significant plant growth and pod yield under drip irrigation. Consequently in water scare regions, a approach of RDI i.e irrigation at 85% of IWR (based on daily Epan) during initial, development and late growth stages through drip irrigation will surely enhance pod yield (58.1%), water use efficiency (97.7%) and will save 30.7% irrigation water over flood irrigation (irrigation at 50% depletion in field capacity). Along with above RDI approach, the nitrogen fertilization through drip fertigation can save 10% use of RDN over soil application method which will improve soil health without affecting pod yield and WUE of pea crop.
 

 

 
Correlation between yield and water use
 
There were positive linear co-relations between weight of 100 seeds verses yield (Fig 6a) with R²= 0.815 and between crop water use verses yield (Fig 6b) with R²= 0.942. From all these inter co-relations it can be stated that higher weight of 100 seeds and crop water use has a positive bearing on plant growth and yield.
 

Drip irrigation along with nitrogen fertigation results batter response of pea crop over conventional methods of water and fertilizer application. The classical deficit irrigation (continuous water stress during whole growth period) approach for growing pea crop under drip irrigation was significantly reduces the crop yield and water use efficiency over regulated deficit irrigation (water stress at specific growth stages). Overall results conclude that, among all selected approaches of irrigation scheduling (with same nitrogen fertilization level) under drip irrigation, the regulated deficit irrigation [where irrigation water supplied at 85% of daily irrigation water requirement (based on daily Epan) during initial, development and late growth stages] will surely enhance pod yield (58.1%), water use efficiency (97.7%) and will save 30.7% irrigation water over flood irrigation. In combination with this RDI approach nitrogen fertilization through drip fertigation can save 10% use of recommended dose of nitrogen which will improve soil health with significant plant growth and pod yield over flood irrigation with direct soil application of nitrogen (broadcasting). A cost effective irrigation and fertigation system could be developed as upcoming research for marginal landholdings. For implementation of this approach of irrigation and nitrogen management in pea on farm level, short term training programs and awareness camp for farmers could be conducted.

Authors wish to acknowledge the scientists of MPUAT, Udaipur for his/her immense support for providing guidance, technical support and for analyzing research data during field experiments.

The author(s) declare(s) that there is no conflict of interest.