Agronomic Response of Pole Beans (Phaseolus vulgaris L.) to Drip Fertigation

French bean is an important nutritious vegetable crop widely cultivated in many agro-climatic zones of India.  Pole bean is a type of high yielding French bean with indeterminate growth habit that requires staking.  As the pole beans fetch high prices in the market, the framers are cultivating this crop extensively in open fields as well as in protected conditions. Being leguminous and medium duration crop it fits well in the cropping system under intensive vegetable production system. The green pods of French bean contain 22% protein, 78% carbohydrate, 221 I.U. vitamin A, 11 mg vitamin C and 381 mg calcium per 100 g of edible portion. India occupied an area of 137.54 (000’ha) with annual production of 1370.21 (000’Mt) and an average productivity of 9.96 t ha^-1 of French bean. The major French bean growing states are West Bengal, Andhra Pradesh, Jharkhand, Jammu and Kashmir and Himachal Pradesh in India (Kumar, 2022).
       
Drip irrigation is one of the efficient methods of irrigation having about 90% water application efficiency. Efficient use of water and fertilizer is extremely critical to sustain the agricultural production. The nutrients are applied exactly and uniformly only to the wetted root volume in drip fertigation which increases the application efficiency of the fertilizer (Debbarma and Bhatt, 2022).
       
Application of fertilizers at appropriate stages of crop growth ensures a regular flow of both water and nutrients.  According to Kakade​ et al. (2023) fertigation can enhance the availability of nutrients and their uptake by the plants, if it is done at pre-determined schedule according to the developmental and physiological stage of the crop. However, most of the work on nutrient management in pole beans has been carried out using conventional methods of NPK fertilizer application. Despite the widespread use of high frequency irrigation system and fertigation elsewhere in India, the information on the use of water-soluble fertilizers for fertigation is meager on this crop. Hence, the present study was conducted to study the influence of fertigation, its frequency and the source of nutrients on growth and yield of pole beans.

The experiment was conducted at ICAR-Indian Institute of Horticultural Research, Hessarghatta, Bengaluru, Karnataka, India during consecutive Rabi seasons of 2020-21 and 2021-22. The institute is situated at 13^o7'N latitude, 72^o29'E longitude and an elevation of 890 meters above the mean sea level. The experimental soil was well drained red sandy loam (pH 6.35 and electrical conductivity 0.32 dSm^-1) characterized by medium organic carbon (0.54%), low available nitrogen (168.5 kg ha^-1), high available phosphorus (72.2 kg ha^-1) and medium available potassium (240.2 kg ha^-1). The soil has available water holding capacity of 130 mm in one-meter soil depth. The experiment was laid out in randomized block design with ten nutrient treatments and three replications. Farmyard manure @ 25.0 t ha^-1 was applied as basal dose uniformly to all the treatments as a common practice. The treatment details and quantity of different fertilizers applied are given in Table 1. Sowing was done in the month of November (16.11.2020 and 19.11.2022) at the spacing of 1.2 m x  0.5 m on raised beds. The height and width of the bed was 15.0 cm and 80.0 cm, respectively with a furrow width of 40 cm. The variety used for the experimentation was Arka Sukomal, characterized by yield potential of 24.0 to 26.0 t ha^-1. Fertigation treatments started two weeks after planting and the fertilizers were applied through drip system at weekly and bi-weekly intervals. The treatments were imposed by dissolving the desired amounts of fertilizers and applied via venturi system through drip irrigation to the field. A total of 12 and 24 numbers of fertigation were given for weekly and bi-weekly interval treatments, respectively which were continued up to 15 days before completion of crop growth period. Five plants per replication in each of the treatments were selected randomly for recording growth and yield parameters. Recommended package of practices, including agronomic and plant protection measures were adopted to raise the crop (Prabhakar et al., 2010). Fertilizer use efficiency of pole bean was calculated by using the following formula.
 

 

 
The experimental data were statistically analyzed (Gomez and Gomez, 1984) and compared using critical difference at five per cent probability level.

Effect of fertigation on growth parameters
 
The data pertaining to plant growth and leaf parameters at 60 days after sowing (DAS) are presented in Table 2. Bi-weekly application of 100% nutrient dose of NPK (75:100:75 kg ha^-1) using water soluble fertilizers through drip fertigation (T₇) has resulted in significantly higher vine length (241.67 cm) than bi-weekly application of 75% nutrient dose, where 50 % of N and K given through drip fertigation (T₁₀) in Arka Sukomal at 60 DAS. Soil application of traditional fertilizers (T₁), soil application and drip fertigation with traditional fertilizers (T₂) also recorded higher vine length (226.67 and 229.0 cm) than T₁₀ (215.0 cm). Bi-weekly application of 100% nutrient dose of NPK through water soluble fertilizers (T₇) has resulted in significantly higher number of branches vine^-1 (15.84) than T₁, T₂, T₄, T₅,T₆,T₈ and T₁₀ treatments and remained on par with bi-weekly application of 75% nutrient dose with water soluble fertilizers through drip fertigation  (13.42) and weekly application of 100% nutrient dose  using water soluble fertilizers through drip fertigation (13.84) at 60 days after sowing. The lowest number of branches vine^-1 were recorded with soil application of traditional fertilizers (10.92). Significantly higher number of leaves vine^-1 were recorded with T₇ (102.75) at 60 DAS, which remained on par with rest of the treatments except soil application of traditional fertilizers i.e. T₁ (76.75) and  T₂ i.e application of 100% nutrient dose, where 50% N and K given through drip fertigation using traditional fertilizers (84.25). Dalai et al., (2022) also documented similar findings on improved plant height and branches (primary and secondary) in dolichos bean with higher level of nutrient application. Likewise, Ramesh et al., (2021) also observed higher plant height and number of branches in French bean with the application of 100% RDF given through fertigation with water soluble fertilizers.

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Bi-weekly application of 100% fertilizer dose (75:100:75 kg NPK ha^-1) with water soluble fertilizers through drip fertigation (T₇) has resulted in significantly higher leaf area (283.75 cm²) than soil application of traditional fertilizers (240.55 cm²), application of 100% nutrient dose where 50% N and K given weekly through drip fertigation using traditional fertilizers (253.38 cm²) and application of 75% nutrient dose where 50% N and K given weekly using water soluble fertilizers through drip fertigation (253.20 cm²) at 60 days after sowing. Improved leaf area could be attributed to better availability of nutrients in soluble form at the root zone of the plant. The growth of plants is propelled by nitrogen and phosphorus as nitrogen is an important constituent of protoplasm, cell nucleus, amino acids and chlorophyll. The large size leaves also receive more sunlight for photosynthesis as compared to smaller leaves. Leaf area responded significantly to different levels of NPK at various growth stages (Dalai et al., (2022). Higher leaf area with higher fertilizer application was also reported by Ramesh et al., (2021) in French bean. Significant improvement in growth parameters noticed under higher fertilization dose might be attributed to better utilization of plant nutrients that reflected in luxuriant crop growth owing to enhanced cell division, elongation and differentiation as compared to lower level of fertilizer application. Similar results in  dolichos beans have also been confirmed by Dalai et al., (2022). Improved plant height, number of branches per plant, dry matter weight per plant at 60 days after sowing might be due to enhanced photosynthesis, leaf area and translocation of nutrients to the reproductive parts as compared to conventional method of fertilizer application in few splits through traditional fertilizers. Manikandan et al., (2015) also reported the beneficial effect of higher levels of N, P and K fertigation on growth and yield attributes of pigeon pea.
 
Effect of fertigation on yield attributing characters, yield and fertilizer use efficiency
 
In case of  yield attributing characters like fresh weight of 5 pods, bi-weekly application of 100% nutrient dose of NPK (75:100:75 kg ha^-1) (T₇) through water soluble fertilizers has resulted  in significantly higher pod weight (73.05 g) than other treatments except weekly application of 75% nutrient dose of NPK through water soluble fertilizers (63.42 g), bi-weekly application of 75% nutrient dose of NPK through water soluble fertilizers (64.58 g) and weekly application of 100% nutrient dose  using water soluble fertilizers through drip fertigation (66.23 g). Soil application of traditional fertilizers (T₁) recorded the minimum fresh pod weight (55.33 g). Bi-weekly application of 100% nutrient dose of NPK using water soluble fertilizer through drip fertigation (T₇) has resulted in significantly higher pod length (23.17 cm) than T₁ (21.05 cm), T₂ (21.79 cm), T₄ (21.85 cm), T₆ (21.81 cm) and T₁₀ (21.82 cm). Treatment T₇ maintained its superiority in terms of pod girth (3.26 cm) than rest of the treatments except bi-weekly application of 75% nutrient dose of NPK through water soluble fertilizers (3.19 cm) and weekly application of 100% nutrient dose using water soluble fertilizers through drip fertigation (3.20 cm). Soil application of nutrients through traditional fertilizers (T₁) recorded the minimum pod girth (2.28 cm) followed by application of 100% nutrient dose where 50% N and K given weekly through drip fertigation using traditional fertilizers (2.41 cm).  Improved yield attributes like pod length, pod girth and fresh pods weight with 100% RDF through fertigation could be attributed to adequate and available supply of nutrients through fertigation in the root vicinity of plant coupled with optimum nutrient concentration in the root zone throughout the crop growth period (Udaykumar et al., 2019).
       
With respect to yield, bi-weekly application of 100% nutrient dose of NPK using water soluble fertilizers through drip fertigation (T₇) recorded significantly higher pod yield (34.67 t ha^-1) than soil application of traditional  fertilizers -T₁ (28.82 t ha^-1), soil application and fertigation with traditional fertilizers- T₂ (30.60 t ha^-1) and 75 % of nutrient dose where  50% N and K given using water soluble fertilizers -T₆ (30.54 t ha_-1). The next best treatment with respect to yield was recorded with weekly application of 100% nutrient dose of NPK (T₃) through water soluble fertilizers (34.03 t ha_-1). All the fertigation treatments recorded higher yields to the tune of 6.17 to 20.3 per cent over soil application of traditional fertilizers. Significantly higher pod yield with higher fertilizer dose was due to improved growth parameters and yield attributes. Due to better utilization of NPK, which enhanced photosynthetic activity, accumulation and translocation of assimilates from source to sink.These results are corroborated with the findings of Palankar and Malabasari (2014) in cluster bean and Udaykumar et al., (2019) in French bean. Unlike conventional fertilizer application, fertigation ensures precise application of nutrient solution in the root zone which improves the nutrient uptake and facilitates better translocation of photosynthates from source to sink (Saileela et al., 2017). The fertilizer use efficiency ranged between 122.40 to 179.62 kg kg^-1 across the different fertigation treatments (Table 2). Though bi-weekly application of 100% nutrient dose using water soluble fertilizers through drip fertigation (T₇) recorded the highest yield (34.67 t/ha), but the fertilizer use efficiency was higher (179.62 and 177.76 kg kg_-1) in the treatments consisting of 75 % of nutrient dose applied through fertigation at bi-weekly and weekly intervals. The minimum fertilizer use efficiency was recorded in soil application of traditional fertilizers (115.28 kg kg^-1). Khedkar et al., (2018) also documented higher fertilizer use efficiency at 75% of the recommended dose of NPK through fertigation than 100% recommended NPK fertigation in green chilli and green pea. Liquid as well as water soluble fertilizers used in drip fertigation ensures 80-90% use efficiency, which leads to higher crop yields in vegetables (Sandal and Kapoor, 2015).
 
Effect of fertigation on net income and B-C ratio
 
Economic feasibility of the fertilizer practices should be an essential element of studies aimed at improved crop productivity (Shahid et al., 2015). The average data pertaining to economic returns and B-C ratio of pole bean cv. Arka Sukomal is given in Table 3. The data revealed that fertigation treatments with water soluble fertilizers recorded higher gross income than soil application (T₁) and fertigation with traditional fertilizers (T₂) except T₆, where 50% NK was applied through drip fertigation and only 75% of the nutrient dose was given. Among the fertigation treatments, application of 100% nutrient dose using water soluble fertilizer through drip fertigation on bi-weekly basis (T₇) resulted in highest gross income (x 520050 ha^-1) followed by T₃ (x 510450 ha^-1).  Treatment T₇ maintained its superiority and recorded highest net returns ( x  329690 ha^-1). Soil application of traditional fertilizer (T1) resulted in minimum net income of  x 258640 ha^-1. Irrespective of dosage and frequency, fertigation with water soluble fertilizers resulted in higher B-C ratio (1.61 to 1.75) compared to soil application of traditional fertilizers (1.49). The highest B-C ratio of 1.74 was accrued with bi-weekly application of 75% nutrient dose given through water soluble fertilizers (T₉), which was closely followed by the treatment consisting of 100% nutrient dose given bi-weekly using water soluble fertilizers through drip fertigation. Very marginal difference in yield, coupled with less cost of cultivation resulted in higher B-C ratio in application of 75% fertilizer dose given bi-weekly through water soluble fertilizers (T₉) than application of 100% fertilizer dose given bi-weekly with water soluble fertilizers through drip fertigation (T₇). Kapoor et al., (2014) observed that fertigation through water soluble fertilizers resulted in significant improvement in yield of cauliflower and gross returns, but higher price of water-soluble fertilizers in comparison to conventional fertilizers reduced the net return and B-C ratio. Similarly, Kumar et al., (2017) also reported higher marketable yields in  capsicum with drip fertigation over non-fertigated treatment, whereas reverse trend was observed in B-C ratio owing to higher cost of water-soluble fertilizers  in comparison to conventional fertilizers.

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The emanating results of the present investigation, reveals that the application of water soluble fertilizers @ 75:100:75 kg N: P₂O₅: K2O ha^-1 during the crop period through fertigation at bi-weekly interval resulted in higher yield (34.67 t ha^-1), gross income (x  520050 ha^-1), net income (x 329690 ha^-1)  and B-C ratio (1.73) in  rabi grown pole beans in red sandy loam soil of Eastern dry zone of Karnataka.