Impact of Drip Fertigation on Leaf Area Index, Root Biomass and Quality Parameters of Lady’s Finger (Abelmoschus esculentus L.)

Okra (Abelmoschus esculentus L.) is an important vegetable of India occupies 5.90 lakh hectare area with total production of 69.49 lakh tons and productivity of 12.0 t ha^-1 (Horticultural Statistics at a glance, 2018). It is grown throughout the country for its tender green fruits during spring-summer and rainy seasons. okra podsconsist of 81.9 g/100 g water, 8.2 g/100 g total dietary fibre (of which 4.7 g/100 g insoluble fibre and 3.4 g/100 g solublefibre), 4.9 g/100 g carbohydrates, 3.6 g/100 g crude proteins,1.5 g/100 g ash, 0.07 g/100 g fat and 50.6 kcal/100 g ofenergy (Tufaro, 2022). It is one of the popular vegetable crops grown in Telangana with total 13,006-hectare area while, in summer it occupies an area of 810 hectares (Horticulture Department, Telangana State, 2019) with an overall production of 2.60 lakh tons and 20.49 t ha^-1 productivity. Okra is a warm-season vegetable crop requires warm and humid conditions for good growth. Bhendi can be grown in a wide range of soils. However, it grows best in loose, friable, well-drained sandy loam soils rich in organic matter. It also gives good yield in heavy soils with good drainage. A pH range of 6.0-6.8 is considered as optimum. Alkaline, saline soils and soils with poor drainage are not good for this crop, it also requires high amount of organic fertilization (Akanbi et al., 2010 and Akande et al., 2010). It is susceptible to low temperature. Seeds of okra fail to germinate below 20°C temperature. For optimal growth, flowering and fruit initiation, okra requires an average temperature ranging between 25-30°C. The okra plants grow taller in the rainy season than in the warm summer. Okra requires a well distributed moderate rainfall (80-100 cm) for production of its young edible fruits. Increased vigour and high productivity were observed when the crop was grown in rainy season than summer season. Increasing differences between day and night temperatures can reduces seed yield considerably especially during summer season (Dhankhar et al., 2012).
 
For yield enhancement of okra, suitable water supply to maintain sufficient moisture condition in soil throughout the crop growth period is essential especially during summer season. The influence of water deficit on yield in this span is more under surroundings of high temperature and low humidity (Vadar et al., 2019) which is more common during summer season. To meet these optimal conditions, drip irrigation proved to be most effective agronomic management option for enhancement of yield and quality of okra. It was reported that, the drip irrigation alone enhances the crop yield up 40% over conventional irrigation (Lokesh et al., 2024).
 
Use of optimum doses of fertilizer is one of the most important ways to ensure quality of green pod yield production of okra. Nitrogen is an essential macro nutrient which plays crucial role on growth, development and metabolism. Nitrogen application significantly increases pod weight, pod diameter, number of fruits per plant and number of seeds per pod in okra (Moniruzzaman and Quamruzzaman, 2009). Fertilizers applied by traditional methods are generally not effective. In fertigation, nutrients are applied through emitters directly into the zone of maximum root activity and consequently fertilizer-use efficiency can be improved over conventional method of fertilizer application. The drip fertigation in okra offers increased pod yield, pod weight, pod length, root penetration depth and pod quality (Hari and Ramesh, 2017) apart from reducing thecost of weeding and irrigation management and enhances economic returns (Sreeja and Satasiya, 2015). A synergistic method for maximising okra output is the combination of nitrogen fertilization with drip watering. In addition to guarantee effective water management, drip irrigation makes it easier to apply fertilisers precisely.

Keeping in view the opportunity and research gap in okra crop, the investigation on impact of irrigation levels, quantification of water requirement under drip system and N levels for fertigation of summer season okra crop was under the present study.

A field experiment was conducted at Water Technology Centre, College of Agriculture, PJTSAU, Rajendranagar, Hyderabad during 2021-22 (17°19'24.7"N, 78°24"34.0"E) at an altitude of 542.4 m amsl). A total of 12.6 mm of precipitation was received during the crop growing season. The texture of the experimental soil is sandy clay soil and it was low in nitrogen, high in phosphorus and potassium, medium in organic carbon content, alkaline in reactivity and non-saline. Irrigation water was neutral (7.20 pH) and classified as C3 class.Radhika variety was usedfor the experiment. Inline drip system with spacing of 40 cm and discharge rate of 2 L/h was installed. Split-plot design was used to set up the experiment, with 12 treatments and replicated thrice. Thetreatments included drip irrigation scheduled at: 0.75 Epan as I1, 1.0 Epan as I2 and 1.25 Epan as I3 in main plots and four different nitrogen concentrations: 75% RDN (N₁), 100% RDN (N₂), 125% RDN (N₃) and 150% RDN (N₄) in sub plots. Full dose of P₂O₅ and K₂O were applied totally as basal in the form of DAP and MOP. Nitrogen was applied through fertigation in 18 equal, with at 4 days interval gap between each split, starting from 15 days after sowing and ending with the final picking (90 DAS).
 
Leaf area index (LAI)
 
Leaf area index was estimated by taking five randomly selected tagged plants in every treatment at 15 days from sowing to final picking using LI 3100 leaf area meter (LI-COR, INC. Linocoln, Nebraska, U.S.A.).

The leaf area index was calculated by dividing the total leaf area with the corresponding ground area as suggested by Watson (1952). Leaf area index was calculated by using the following formula.
 

 

 
Root biomass studies
 
The effect of irrigation and nitrogen levels on root biomass investigated using a 15 cm³  core sampler at final picking in the wetted zone up to 45 cm depth from surface and from dripper point at 45 cm radial distance was to be active root zone.
 
Quality parameters
 
Total chlorophyll content
 
Total chlorophyll content (mg 100^-1 g F.W.) of pods was recorded by using Delta Absorbance (DA) meter at first picking, fifth picking and final picking.
 
Crude fibre content
 
Crude fibre content was determined by the method suggested by A.O.A.C. (1960). A representative ground fruit sample of 2 g was refluxed with 1.25 per cent H2SO4, washed and again refluxed with 1.25 per cent NaOH for 30 minutes, respectively. The sample was dried out, weighed and ignited in a muffle furnace. Loss in weight was considered as crude fibre content and expressed based on using
following relationship:
 

 

 
Where,
W₁ = Initial weight of sample.
W₂ = Weight of refluxed sample.
W₃ = Weight of ignited sample.

Leaf area index
 
The Leaf Area Index (LAI) of okra as influenced by drip irrigation scheduling, nitrogen levels and their interaction is presented (Table 1). The effect of irrigation scheduling recorded at 15 days interval is depicted in Fig 1 and 2.


 
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Irrigation scheduling
 
The influence of irrigation scheduling on Leaf Area Index (LAI) trend of okra recorded at 15 days interval from 15 days after sowing to final green pod picking is illustrated in Fig 1. Perusal of Leaf Area index indicated that, irrespective of irrigation levels the leaf area index was continuously increasing up to 60 days after sowing and there after decreased gradually towards the final green pod picking stage. The reduction in LAI towards final picking stage was due to leaf detachment (abscission) from plants as the crop reached senescence. Formation of abscisic acid (ABA) in roots and its consequent translocation from root to shoot might have caused reduced stomatal conductance and transpiration rate and there by detachment from the plant at senescence stage of okra (Ahmadi et al., 2010).

Among the irrigation levels, the crop irrigated at 1.0 Epan (I₂) maintained maximum Leaf Area Index (LAI) followed by 1.25 Epan (I₃) and the lowest was at 0.75 Epan (I₁) levels throughout the crop growth period. The higher LAI in I₂ blocks might be due to optimal soil moisture conditions maintained in the rhizosphere throughout the crop growth period. While, the reduced LAI in I₁ and I₃ treatments might be due to deficit and excess soil moisture conditions, respectively prevailed in root zone although the crop growth period.

The influence of irrigation levels on Leaf Area Index of okra recorded at 1^st flower appearance, 1^st green pod picking and final green pod picking stages is analyzed statistically and presented in Table 1. Higher leaf area index of 0.17, 1.10 and 0.51 was recorded with 1.0 Epan (I₂) which was significantly more over 1.25 Epan (I₃) with LAI of 0.16, 0.94 and 0.44 and 0.75 Epan (I₁) with LAI of 0.16, 0.74 and 0.32 at first flower appearance, 1^st picking and final picking stages, respectively. Irrigation scheduled at 0.75 Epan (I₁) remained significantly inferior to I₂ (1.0 Epan) and I3 (1.25 Epan) treatment irrespective of the crop growth stages. 



The reduction in LAI of okra above and below 1.0 Epan levels might be due to deficit and excess soil moisture conditions in the rhizosphere. Similar trend was also reported by Shivaraj et al., (2018). Limited water supply to Okra in deficit irrigation scheduling treatment (I₁) affected the physiological development of the crop, due to sub-optimal supply of required amount of water to the root zone from the pod formation stage to maturity stage of the crop when the crop actually needed sufficient quantity of water to meet its evapotranspiration demand (Konyeha and Alatise, 2013).
 
Nitrogen levels
 
The effect of nitrogen levels on Leaf Area Index of okra is depicted in Fig 2. The data indicated that the crop fertilized with 100% RDN (N₂) produced maximum leaf are index and the lowest underand 75% RDN (N₁) produced throughout the crop growth period respectively. Barring these two extremes the crop fertilized with 125% RDN (N₃) and 150% RDN (N4) remained in intermediate to 100% RDN (N₂) and 75% RDN (N₁). 

The Leaf area Index of okra recorded at 1st flower appearance, 1^st pod picking and final pod picking stages as influenced by nitrogen levels is analyzed statistically and presented in Table 1. At 1^st flower stage the crop nurtured with 100% RDN (N₂) recorded maximum Leaf Area Index (0.17) which was significantly more over its succeeding higher doses of N₃ (125% RDN) and N₄ (150% RDN) and preceding lower dose of N₁ (75% RDN) treatments. However, the N₁ (75% RDN) treatment found significantly inferior to N₂ (100% RDN), N₃ (125% RDN) and N₄ (150% RDN) treatments. Similar trend was also reflected at 1^st green pod picking and final green pod picking stages.

The reduction in LAI under high and low nitrogen levels might be due to general adaptation of okra crop at certain level of nitrogen dose. However, the symptoms of toxicity due to excess of nitrogen (125% RDN or 150% RDN) or symptoms of nitrogen deficiency due to lower dose (75% RDN) with reference to 100% RDN were not observed in plants. These results are in line with the finding of Bhatti et al., (2011) and Chawla et al., (2018) who stated that maximum leaf area index was recorded with 100% RDN significantly enhanced the growth of okra (91.64 q ha^-1) over control and 75 per cent RDN.
 
Interaction effect
 
The interaction effect of irrigation scheduling and nitrogen levels on leaf area index of okra is found significant at first and final picking stages.

At 1^st flower appearance stage under I₂ (1.0 Epan) irrigation scheduling, significantly more LAI of 1.15 was recorded with 100% RDN (N₂) when compared to its preceding lower does [75% RDN (N₁)] and succeeding higher doses [125% RDN(N₃) and 150% RDN(N₄)].  However, the N₁, N₃ and N₄ levels recorded the LAI of 1.08, 1.09 and 1.09 were comparable to each other. At I₁ and I₃ irrigation scheduling, the LAI was not differed significantly with nitrogen levels. Similar trend is also reflected at final picking stage.

Among the different treatment combinations, I₂N₂ recorded more LAI of 1.15 and 0.54 at 1^st and final green pod picking stages, respectively. However, it was significantly more over rest of the treatment combinations at 1st green pod picking stage and comparable with I₂ N₂ (0.52) and significantly more over the rest of the treatment combinations at final green pods picking stage.

Irrigation scheduled at 1.0 Epan had led to efficient use of additional food material synthesized with 100% RDN which clearly indicated that expansion in leaf area responded positively to N availability up to 100% RDN. This could be due to the significant role of N availability in assimilation of photo-assimilates enhancing the period of leaf area expansion by plant. Lower values of leaf area in the N limiting environments were recorded with 75% RDN indicated that depletion and or shortage of N might have adversely affected the ability of N to the crop to sustain its leaf area expansion for longer periods resulting in reduced interception of photosynthetic active radiation (PAR) with overall negative effects on crop growth and yield. Similarly, Venkadeswaran and Sundaram (2016) also documented optimum optimal moisture in the root zone under drip fertigation that reduces the variation in nutrient concentration, thereby enhancing their availability to plantsand reducing the leaching of nutrients beneath the root zone.
 
Root biomass studies
 
The influence of irrigation scheduling and nitrogen levels on root biomass of okra (mg/1cm²) is depicted in Fig 3. Among the irrigation schedules the maximum root biomass (1.41 mg/1cm²) was recordedat 1.0 Epan (I₂) followed by1.25 Epan (I₃). The lowestroot biomass (1.12 mg/1cm²) was recorded under 0.75 Epan and it was inferior to 1.0 Epan and 1.25 Epan treatments. 



Among the nitrogen levels, the maximum root biomass (1.43 mg/1cm²) was recorded with 100% RDN (N₂) which was followed by succeeding higher dose of 125% RDN (N₃) and 150% RDN (N₄) and preceding lower dose of 75% RDN (N₁). The interaction effect of irrigation scheduling and nitrogen levels on root biomass is depicted in Fig 4. The maximum root biomass (1.57 mg/1cm²) was recorded under 1.0 Epan in conjunction with 100 % RDN (I₂F₂).



Whereas, minimum root biomass was recorded (1.24 mg/1cm²) under 0.75 Epan in conjunction with 75% RDN (I₁F₁). Similar results were also reported by Pokhrel et al., (2024) who stated that highest yield which correlates root biomass was obtained with T6 (100 kg N ha^-1) which was comparable with T7 (115 kg N ha^-1) against the minimum was recorded with T₁ (0 kg N ha^-1) in okra. Therefore, it is suggested that root elongation wasinhibited by either excess of deficit N levels. N deficiency can leadto low root activity and water consumption (Zhang et al., 2017) and decrease the production of reactive oxygen species (ROS) in roots, resulting in low root biomassaccumulation. Excess N can increase aboveground organ growth and decrease root growth. Similar results were also reported by Nagegowda and Senthivel, (2021) who recorded higher moisture and nutrient availability in the vicinity of the roots owing to the higher root biomass in okra.
 
Quality parameters
 
Total chlorophyll content of pod (mg 100^-1 g FW)
 
The total chlorophyll content of okra pod was not influenced by drip irrigation scheduling, nitrogen levels and their interactions (Fig 5). However, at first picking the maximum chlorophyll content was recorded under drip irrigation scheduled at 1.0 Epan (I₂) which was followed by 1.25 Epan (I₃) and 0.75 Epan (I₁). While drip irrigation scheduled at 0.75 Epan (I₁) remained inferior to I₂ and I₃ irrigation treatments. Similar trend was also reflected in fifth and final picking. Among the nitrogen levelsmaximum chlorophyll content was recorded under 100% RDN while, the minimum chlorophyll content was recorded under 75% RDN. Similar trend was also reflected in fifth and final picking also.


 
Crude fibre content (%)
 
The crude fibre content of okra as influenced by drip irrigation scheduling, nitrogen levels and their interactions were statistically analysed and presented in Table 2.


 
Irrigation scheduling
 
The influence of irrigation scheduling on crude fibre content of okra pod was significant. Maximum crude fibre content (13.41%) was recorded at 1.0 Epan (I2) which was comparable with 1.25 Epan (13.12%) and significantly higher over 0.75 Epan (I1). Whereas, the lowest crude fibre was recorded with 0.75 Epan treatment. Similar trend was also reflected at fifth andfinal (10^th) picking stages of the okra crop. Rani and Mariappan, (2019) stated that the crop irrigation scheduled at 1.0 Epan has provided optimum soil moisture condition in rhizospherewhich in turn provided higher nutrient uptake by crop. Similar results were also reported by Dhotre et al., (2017) in bell pepper.
 
Nitrogen levels
 
The influence of nitrogen levels on crude fibre content (%) of okra pod was significant. The crop supplied with 100% RDN (N2) recorded more crude fibre content of 13.94% which was significantly higher with its succeeding higher dose of 125% RDN (N₃) and 150% RDN (N₄) and significantly more over preceding lower dose (75% RDN). The crop nurtured with 75% RDN (12.37%) remained inferior to N₂, N₃, N₄ treatments. While the crop supplied with 125% RDN and 150% RDN remained on par with each other. Similar trend was also reflected in fifth and final picking. Crude fibre content (%) decreased due to the increase in succulence by the increased application of nitrogen (kg ha^-1) and with higher levels of potassium due to the involvement of K in strengthening the thickness of the cell wall.Similar results were reported by Kumar et al., (2017) who that maximum crude fibre content was recorded with crop nurtured with 180 kg N ha^-1 which was followed by 120 kg N ha^-1 in okra crop.
 
Interaction effect
 
The interaction effect of irrigation scheduling and nitrogen levels on crude fibre content (%) of okra pod was not significant.

The experiment study concluded that, the crop irrigation scheduled at 1.0 Epan was found outranking in terms of recording maximum LAI across the stages of observations as compared to 0.75 Epan and 1.25 Epan treatments. Among the nitrogen levels, the crop fertilized with 100% RDN recorded maximum LAI, throughout the crop growth period as compared to its preceding lower and succeeding higher levels. The interaction between irrigation scheduling and nitrogen levels was significant in terms of LAI at first and final picking stages. Among the different treatment combinations 1.0 Epan (I₂) in conjunction with 100% RDN (N₂) recorded maximum LAI at first and final green pod picking stages, respectively. The maximum root biomass, pod chlorophyll content and crude fibre was recorded with 1.0 Epan (I₂) treatment. Among the nitrogen levels, the maximum root biomass pod chlorophyll content and crude fibre was recorded with 100% RDN (N₂) were performed better than others.

The authors acknowledge all the staff of the Water Technology Centre for their help during the study period.
 
Disclaimers
 
The views and conclusions expressed in this article are solely those of the authors and do not necessarily represent the views of their affiliated institutions. The authors are responsible for the accuracy and completeness of the information provided, but do not accept any liability for any direct or indirect lossesresulting from the use of this content.
 
Informed consent
 
All procedures for experiments were approved by the Professor Jayashankar Telangana State Agricultural University, Hyderabad.

The authors declare that there are no conflicts of interest regarding the publication of this article. Nofunding or sponsorship influenced the design of the study, data collection, analysis, decision to publish,or preparation of the manuscript.