Studies on Growth, Yield and Quality of Edible Poded Dolichos Bean As Affected By NPK Fertilization

Dolichos bean (Dolichos lablab L.) is one of the most ancient crop which occupies unique position both as vegetable and pulse purpose, belongs to leguminosae family having chromosome number 2n=22. The fresh green pods are the economic part, the highly nutritive, eaten after cooking and it is the best source of digestible vegetable protein (20 to 25%) required for human health, because of this, this crop is considered as a poor man’s meat (Joshi and Rahevar, 2015). Being a legume, it has ability to fix nitrogen into soil thereby improving soil fertility and crop yields in an economic and environment friendly manner. Hence, it is highly remunerative crop having multiple uses and well suited to all most all agro-climatic regions (Kharbamon et al., 2017). Within India, lablab as an edible poded vegetable crop mostly cultivated in Karnataka and adjoining districts of Tamil Nadu, Andhra Pradesh and Maharashtra. In Karnataka, it is grown mainly in Bengaluru, Dharwad, Belgavi, Bidar and Hassan districts which contributes a major share, accounting for nearly 90 per cent in terms of both area and production in the state but average productivity of lablab bean crop is quite low (12 t/ha of edible green pod yield) due to several production constraints.
       
The major limiting factors, which contribute to the crop yield, include; use of local cultivars, imbalanced nutrition and cultural practices. If the crop is managed properly, green pods are produced continuously for several months. Application of balanced fertilizer increases vegetative growth and improves yield and quality of the produce. Being a leguminous crop, dolichos bean is highly responsive to nitrogenous fertilizer application especially in early stage (Sammauria et al., 2009). Nitrogen promotes the leaf, stem, other vegetative growth and increase the protein content. Application of phosphorus influences symbiotic nitrogen fixation and serves dual purpose in legume by increasing the yield and quality of green pods of current as well as succeeding crop of the dolichos bean (Turuko and Mohammed, 2014). Potassium is often referred as the quality element for crop production due to its positive interaction with other nutrients (especially with nitrogen). Potassium plays a crucial role in legumes by enhancing the production of starch and sugar that benefit the symbiotic bacteria and thus enhances the fixation of nitrogen (Rustamani et al., 1999). Dolichos bean as an edible poded vegetable is growing in a limited area in Karnataka and does not have a separate recommended package of practices, however, farmers are growing this crop by adopting the recommended fertilizers dose used for field type of dolichos bean. Therefore, the present study was undertaken to find out the best level of NPK for optimum growth and higher green pod yield under agro-climatic conditions of Arabhavi in Belgaum district of Karnataka.

The field experiments were carried out to evaluate the effect of different nitrogen, phosphorus and potassium levels on growth, yield and quality of edible poded dolichos bean at experimental field of Department of Vegetable Science, Kittur Rani Channamma College of Horticulture, Arabhavi, Karnataka during the growing period of 2016-17 and 2017-18. The experiments were laid out in factorial randomized complete block design with three replications, measuring a net plot size of 2.7 m × 2.4 m. A composite sample of 30 cm deep soil was used for physical and chemical analysis. The soil of the experimental site was sandy clay loam, having pH (8.22), EC (0.54 dS/m), O.M (0.57%), available N (181.88 kg/ha), available P (62.38 kg/ha) and K (223.31 kg/ha). The healthy and disease free authentic seeds of dolichos bean variety ‘Arka Amogh’ were used for conducting experiments. Two seeds per pit were sown in recommended spacing of 45 cm × 15 cm. The nitrogen (0 and 25 kg/ha), phosphorus (0, 50 and 75 kg/ha) and potassium (0, 25 and 50 kg/ha) were applied in eighteen different combinations. Full dose of fertilizers (nitrogen, phosphorus and potassium) in the form of urea, single super phosphate and muriate of potash, respectively were applied to soil before seed sowing as per the treatment requirements. All other cultural operations were kept normal and uniform for all treatments as per package of practices recommended by University of Horticultural Sciences, Bagalkot (Anonymous, 2015). The observations were recorded by selecting five plants randomly from each plot. Quality parameters like pod protein (The total calorimetric method by Lowry et al., 1951), fibre (Proskey et al., 1988) and sugar (John, 1985) content were assessed from the freshly harvested pods. Two years experimental data as well as pooled data were analyzed statistically with the analysis of variance at 5%  probability level as per the statistical methods i.e. Fisher’s method described by Panse and Sukhatme (1978).

Effect of NPK fertilization on growth parameters of dolichos bean
 
The data regarding on growth parameters of dolichos bean viz., plant height, number of branches per plant, number of leaves per plant at various growth stages, dry matter content at harvest and days taken to crop maturity were significantly influenced by N, P, K and their interaction during both the seasons and in pooled data analysis (Table 1).
 

       
The plant height was maximum (89.65, 91.69 cm and 88.63 cm) when they were applied with higher doses of nitrogen 25 kg N/ha (N₂ level), phosphorus (75 kg P₂O₅/ha) and potassium (50 kg K₂O/ha) respectively than the lower doses of  nitrogen (0 kg N/ha), phosphorus  (50 kg P₂O₅/ha) and potassium (25 kg K₂O/ha) respectively in pooled analysis of 2016-17 and 2017-18 experimental years. Among the different interactions of nitrogen, phosphorous and potassium (N-P₂O₅-K₂O), the plant height at harvest was recorded significantly maximum (98.13, 98.57 and 98.35 cm) in 25-75-50 kg N-P₂O₅-K₂O/ha (T₁₈) which was on par with T₁₇ in 2016-17, 2017-18 and in pooled data respectively. On pooled basis, plant height was significantly varied from 90.95 cm in recommended fertilizer level of 25-50-25 kg N-P₂O₅-K₂O/ha (T₁₄) to 98.35 cm in highest fertilizer level of 25-75-50 kg N-P₂O₅-K₂O/ha. The individual effect of NPK was significantly varied for production of primary branches and recorded more in N₂ (8.19, 8.10 and 8.14) over N₁ level in first (2016-17), second (2017-18) season and in pooled data, respectively. Significantly higher number of primary branches per plant (8.73) was recorded by P₃ (75 kg P2O5/ha) over P₂ (7.92) and P₁ (6.53) level in pooled basis whereas, linear and significant increase in number of primary branches was recorded with increase in potassium level from K₁ (7.57) to K₃ (8.00). Similar trend was also noticed in 2016-17 and 2017-18 successive growing seasons. The marked variations amongst the NPK interaction levels were also noticed for production of primary branches during both the years. Pooled data showed that maximum number of primary branches (9.33) was recorded at highest fertilizer level of 25-75-50 kg N-P₂O₅-K₂O/ha compared to the recommended fertilizer level (25-50-25 kg N-P₂O₅-K₂O/ha) at harvest but it was at par with T₁₇. Similar trend was also noticed in both the growing seasons. Similar results of interaction effect on plant height and number of branches were also noticed by Sammauria et al., (2009) in cluster bean.
       
In indivisual effect of nitrogen, number of leaves (63.04) was recorded maximum in N₂ (25 kg N/ha) over N₁ level in pooled analysis. Likewise, more number of leaves (66.64 and 62.33) were produced in higher level of phosphorus (75 kg P₂O₅/ha) and potassium (50 K₂O/ha) which were significantly superior over lower levels (50 kg P₂O₅/ha and 25 K₂O/ha) in pooled analysis, respectively. The similar trend was also noticed in both the experimental years (2016-17 and 2017-18). There was a gradual increase in number of leaves with the increase of fertilizer doses and the maximum number of leaves (77.30, 75.49 and 76.39) was recorded in higher nutrient level of 25-75-50 kg N-P₂O₅-K₂O/ha (T₁₈) followed by T₁₇ and T₁₆.  The similar trend was also noticed in both the experimental years (2016-17 and 2017-18). The significant increase in growth parameters noticed under higher level of N, P, K and their interaction was attributed by better utilization of plant nutrients and might have resulted in the luxuriant crop growth due to enhanced cell division, elongation and differentiation as compared to lower fertilizer level. Similar results in growth parameters also confirmed by findings of Shrikanth et al., (2008). The total dry matter accumulation in dolichos plant was significantly higher (24.93, 24.15 and 24.54 g) in 25 kg N/ha (N₂) than without nitrogen (N₁) application in 2016-17, 2017-18 growing seasons and in pooled data, respectively. Significantly higher dry matter per plant (27.65 g and 23.99 g) was recorded with higher level of phosphorus (75 kg P₂O₅/ha) and potassium (50 K₂O/ha) which were significantly superior over lower levels of phosphorus (50 kg P₂O₅/ha) and potassium (25 K₂O/ha) levels in pooled analysis, respectively. The similar trend was also noticed in both the experimental years (2016-17 and 2017-18). The NPK interaction has promotive effect on dry biomass and recorded maximum dry weight of plant (35.97 g) in plants supplied with higher dose of fertilizer (25-75-50 kg N-P₂O₅-K₂O/ha) followed by T₁₇ (33.77 g) and T₁₆ (29.67 g) which showed 11 (13.27 g), 9 (11.07 g) and 3 (4.1 g) per cent higher over recommended fertilizer level of 25-50-25 kg N-P₂O₅-K₂O/ha (22.70 g). The interaction effects during 2016-17 and 2017-18 experimental years also followed similar trend as that of pooled analysis. The higher dry matter production with higher level of N, P, K and their interaction was mainly due to higher green biomass and its accumulation in various plant parts. Similar results have also been noticed by Shrikanth et al., (2008). Days to physiological maturity differed significantly with NPK and their interaction levels in 2016-17, 2017-18 growing seasons and pooled data (Table 1). Days increased significantly (75.33, 74.78 and 75.06 days) with increased N levels (25 kg N/ha) in 2016-17, 2017-18 and in pooled data, respectively. Similarly, with increased application of P and K levels, number of days to physiological maturity was significantly recorded maximum in P₃ (75.64 days) and K₃ (75.03 days) level compared to lower levels of phosphorus (50 kg P₂O₅/ha) and potassium (25 K₂O/ha) in pooled analysis, respectively. The similar trend was also noticed in both the experimental years (2016-17 and 2017-18). Among the interaction effects of NPK, significantly maximum days (77.33, 77.00 and 77.17) were recorded in higher fertilizer dose of 25-75-50 kg N-P₂O₅-K₂O/ha (T₁₈) followed by T₁₇ (76.50 days) and T₉ (76.50 days) which confirmed the findings of Shrikanth et al., (2008).
 
Effect of NPK fertilization on yield parameters of dolichos bean
 
The data recorded on yield parameters as significantly influenced by individual NPK and their interactions levels in 2016-17, 2017-18 growing seasons and in pooled analysis which is presented in Table 2. On pooled basis, significantly maximum number of pods per plant (134.18, 142.58 and 134.53) were observed in higher levels of nitrogen (25 kg N/ha), phosphorus (75 kg P₂O₅/ha) and potassium (50 kg K₂O/ha) compared to lower levels. Similar observations were also made during both the years of the study. Among the interaction effect of NPK fertilizers, on pooled basis, significantly more number of pods per plant (148.78) were recorded in higher fertilizer dose of 25-75-50 kg/ha (T₁₈) followed by T₁₇ (146.20) and T₉ (143.35). Similar trend was also noticed during both the years (2016-17 and 2017-18) of experiment. On pooled basis, pod length (11.86 cm, 11.96 cm and 11.86 cm) and pod width (1.62 cm, 1.68 cm and 1.64 cm) were recorded maximum in higher level of nitrogen (25 kg N/ha), phosphorus (75 kg P₂O₅/ha) and potassium (50 kg K₂O/ha) over lower levels. Similar trend was also noticed during both the years (2016-17 and 2017-18) of experiment. However, effect of nitrogen on pod width showed non significant result in first season and in pooled data analysis. Higher yield attributing characters in higher fertilizer dose are mainly due to more number of productive branches by higher level of nitrogen, phosphorus and potassium application thereby increased number of pods per plant and other characters. Likewise, among the interaction effect of NPK, on pooled basis, maximum pod length (12.17 cm) and pod width (1.74 cm) were also recorded under higher fertilizer dose of 25-75-50 kg N-P₂O₅-K₂O/ha (T₁₈) compared to recommended dose. Similar trend was also noticed during both the years of investigation. These results can be due to the fact that better utilization of NPK which enhanced photosynthetic activity, accumulation and translocation of assimilates from source to sink resulting in improved yield attributing characters in higher dose of fertilizers. These results confirmed the finding of Palankar and Malabasari (2014) in cluster bean.
 

       
Pod yield of dolichos bean var. Arka Amogh was significantly influenced by individual NPK and their interaction during both the years of the experiments (Table 2). The nitrogen (N) levels showed a significant effect on pod yield per plant in dolichos bean, which recorded significantly maximum in N₂ (140.20, 138.95 and 139.57 g) than N₁ level in 2016-17, 2017-18 and in pooled data analysis, respectively. Similarly, on pooled basis, the higher level of phosphorus (75 kg P₂O₅/ha) and potassium (50 kg K₂O/ha) produced significantly higher pod yield per plant (154.31 g and 141.21 g) compared to lower levels, respectively. Similar trend was also noticed in 2016-17 and 2017-18 growing seasons. On pooled basis, significantly higher fertilizer dose of 25-75-50 kg N-P₂O₅-K₂O/ha (T₁₈) produced more pod yield per plant (163.95 g) followed by T₁₇ and T₉ treatment combinations which showed maximum improvement of 30.78 g (17%) and 30.79 q (26%) over recommended fertilizer level T₁₄ (25-50-25 kg N-P₂O₅-K₂O/ha). Similarly, T₁₈ also recorded significantly higher pod yield per plant but it was on par with T₁₇ in first season (2016-17) whereas in second season (2017-18) the trend was same as followed in pooled data. Pod yield per hectare of dolichos bean var. Arka Amogh as influenced by NPK individually, their interaction and pooled data are presented in Table 2. On pooled basis, the higher level of nitrogen (25 kg N/ha), phosphorus (75 kg P₂O₅/ha) and potassium (50 kg K₂O/ha) produced significantly higher pod yield per hectare (162.32, 184.14 and 164.75 q) compared to lower levels, respectively. Similar trend was also noticed in 2016-17 and 2017-18 growing seasons. Among the NPK interaction levels, in pooled data, maximum pod yield was recorded at T₁₈ (198.44 q/ha) followed by T₁₇ (193.43q/ha) and T₉ (190.20 q/ha). Similar result trend was also noticed in first (2016-17) and second (2017-18) season of experiments. Maximum pod yield was recorded at T₁₈ which showed maximum improvement of 20.78 g (17%) and 30.79 q (26%) over recommended fertilizer level T₁₄ (25-50-25 kg N-P₂O₅-K₂O/ha). The results of indivisual and interaction effect might be due to increased performance of growth parameters and also complementary effect of optimum combinations of nitrogen, phosphorus and potassium levels. These results confirmed the finding of Shrikanth et al., (2008) in dolichos bean.
 
Effect of NPK fertilization on quality components of dolichos bean
 
Dolichos bean is an important nutritious legume and rich in protein, sugar, fibre and essential amino acid content. The indivisual effect of NPK and their interactions were significantly varied for all pod quality parameters during first, second season and in pooled analysis (Table 3). On pooled basis, fiber (1.71, 1.75 and 1.67 g), protein (3.08, 3.31 and 3.01 g) and sugar content (1.51, 1.56 and 1.51 g) were significantly increased with 25 kg N/ha 75 kg P₂O₅/ha and 50 kg K₂O/ha over other N, P and K levels. Protein content was significantly increased with higher level of nitrogen as it is the structural component of amino acids. Among the interaction levels of NPK, higher fibre content (1.90, 1.87 and 1.88 g) was recorded in 25-75-50 kg N-P₂O₅-K₂O/ha (T₁₈) in 2016-17 and 2017-18 experimental years and in pooled analysis, respectively. These results are in conformity with the findings of Ayub et al., (2012) in cluster bean. In pooled data analysis, significantly maximum protein (3.45 g) and sugar (1.67 g) content were recorded in T₁₈ but it was on par with T₁₇ for protein content. Similar trend of pod protein and sugar content were also noticed during first season (2016-17) and second season (2017-18) of the experiment.
 

From these results of two years experimental study, it can be concluded that significantly higher pod yield coupled with better growth and reproductive parameters could be obtained by growing edible poded dolichos bean with fertilizer dose of 25-75-25 kg N-P₂O₅-K₂O/ha which recorded 18 per cent more yield with better quality pods compared to recommended fertilizer dose (25-50-25 kg N-P₂O₅-K₂O/ha).