Standardization of micronutrient formulation for cowpea
The different concentrations of micronutrient formulation and time required for seed treatment in cowpea was standardized by soaking cowpea seeds with micronutrient mixture at different concentrations (0.25%, 0.50%, 0.75%, 1%, 1.5% and 2%). Seeds were soaked in each of these solutions for seven different durations (1 hr, 2 hrs, 4 hrs, 6 hrs, 8 hrs, 10 hrs and 12 hrs). Observations on seed germination and its emergence showed that the seeds treated with micronutrient mixture for 6 hours showed better shoot and root growth for the different concentration of micronutrient formulation as compared to other duration of seed treatment. Time for seed treatment was standardized in papaya for boron. Seeds treated with 2 ppm boron solution for six hours showed increased germination and growth of seedlings
(Deb et al., 2010).
Seed treatment study
The different concentrations of micronutrient mixture in seed treatment study had no significant influence on germination percentage and days taken for germination whereas seedling length at three leaf stage and seedling vigour index (germination percentage × seedling length) was significantly influenced by the treatments (Table 2). The treatment T
6 showed maximum seedling length at three leaf stage (24.23 cm) and seedling vigour index (2423) which might be due to the beneficial effect of micronutrients in enhancing cell elongation and cell division of meristematic tissues. The increased seedling length of cowpea contributed to considerable increase in seedling vigour index in the treatment receiving 2% concentration of micronutrient mixture. Thus, T
6 was considered as the best concentration for seed treatment study. This treatment was followed by T
5 which recorded the second highest values in seedling length at three leaf stage (22.31) and seedling vigour index (2231). The treatments T
6 (best seed treatment) and T
5 (second best) were selected for the field experiment to evaluate the performance of micronutrient formulation in cowpea.
Masuthi et al., 2009 had reported that cowpea seeds treated with zinc sulphate showed higher vigour index and
Deb et al., 2010 reported that papaya seeds treated with boron at 2 ppm showed better growth of seedlings.
Field experiment
Effect of seed treatment, foliar spray of micronutrient formulation and their interaction on growth attributes
Effect of seed treatment, foliar spray and their interaction on plant height, stem diameter, number of branches and dry matter production is given in the Table 3.
Levels of seed treatment showed significant difference in plant height at flower bud initiation and at harvest. At flower bud initiation S
3 recorded maximum plant height (24.31 cm) which was on par with seed treatment with 1.5% micronutrient formulation, S
4 (23.53 cm). At the time of harvest S
3 recorded maximum height of 39.75 cm which was significantly superior to all other treatments. Levels of foliar spray of micronutrients showed significant difference in plant height at flower bud initiation and at harvest. Maximum height was observed in F
3 treatment both at flower bud initiation (25.98 cm) and at harvest (41.08 cm). In the interaction effect maximum plant height was recorded in the treatment S
3F
3 at both the stages given as 29.80 cm and 44.13 cm, which were significantly different from all other treatments. The beneficial effect of micronutrients in growth and development of plants might be the reason for increase in plant height compared to control treatment receiving no seed treatment and no foliar spray. Micronutrients has the capacity to increase the auxin content and chlorophyll content of tissues thus promoting plant growth and yield. It helps in the growth of cells by promoting cell elongation and cell division of meristematic regions. The micronutrients zinc and boron plays a crucial role in growth and development of new cells in plants. The findings are in accordance with the results obtained by
Suryanarayana and Reddy (1978). They reported that plant height of French bean was increased by the application of 0.01 percent Zn and B. Cowpea seeds treated with borax showed highest plant height at 30 and 60 days after sowing
(Masuthi et al., 2009).
Significant difference was not observed in the number of branches at flower bud initiation and at harvest in seed treatment, foliar spray and their interaction.
Stem diameter showed significant difference with variation in seed treatment. Maximum diameter was observed in treatment S
4 (2.44 cm) at flower bud initiation which was on par with S
3 (2.43 cm) and seed treatment with rhizobium, S
2 (2.35). At the time of harvest treatment S
3 recorded the highest stem diameter (4.65 cm) which was significantly different from all other treatments. Levels of foliar spray showed significant difference in stem diameter at flower bud initiation. F
3 recorded maximum stem diameter (2.54 cm) which was on par with single spray of micronutrient formulation, F
2 (2.40 cm). At the time of harvest, F
3 (4.85 cm) recorded maximum stem diameter which was significantly different from all other treatments. Interaction effect of treatments also showed significant difference among the treatments. At flower bud initiation maximum stem diameter was recorded in S
2F
3 (2.86 cm) which was on par with S
3F
2 (2.66 cm), S
4F
3 (2.64 cm) and S
4F
2 (2.62 cm). At harvest S
2F
3 (5.30 cm) showed maximum stem diameter which showed significant difference from all other treatments. These findings were in accordance with
Mathur (2000) reported that seeds of garden pea inoculated with rhizobium showed enhanced growth characters and yield.
Suryanarayana and Rao (1981) reported that foliar spray of micronutrient solution containing zinc, copper, manganese, magnesium, boron and molybdenum resulted in enhanced growth of okra.
Bukvic et al., (2003) reported the similar increasing trend in stem diameter with zinc application.
Dry matter production recorded was maximum in S
3 (2292.91 kg ha
-1) which was superior over other seed treatments. Dry matter production was lowest in S
1 (2000.06 kg ha
-1). Foliar spray F
3 showed maximum dry matter production per plant (2372.92 kg ha
-1) which was superior over other levels of foliar spray. Interaction of main treatments showed significant difference in dry matter production with S
3F
3 (2613.24 kg ha
-1) produced highest amount which was superior over other interactions. Seed treatment with micronutrients have the capacity to enhance dry matter production. Seed treatment might had resulted in increased seed vigour. Increased seed vigour might be the reason for maximum dry matter production in plants. Similar results were obtained in barley. Seeds of barley treated with micronutrients showed increased dry matter production
(Ajouri et al., 2004).
Effect of seed treatment, foliar spray of micronutrient formulation and their interaction on yield and yield attributes of cowpea
The data on yield and yield attributes are given in Table 3. Levels of seed treatment showed significant difference in the number of pods per plant with maximum number recorded in S
3 (21.02) which was on par with S
4 (19.44). The lowest number of pods per plant was observed in S
1 (16.73). Levels of foliar spray showed significant difference in the number of pods per plant with maximum number recorded in F
3 (20.97). F
1 recorded the lowest number (16.71). The interaction effect also showed significant difference in number of pods per plant with maximum number recorded in S
3F
3 (25.84) which was on par with seed treatment with 1.5% micronutrient formulation + two foliar sprays, S
4F
3 (21.01). S
1F
1 (16) recorded the least value. Treatments did not show any significant difference in the number of seeds per pod.
Levels of seed treatment showed significant difference in pod weight per plant. S
3 recorded highest pod weight per plant (36.14 g) which was on par with S
4 (31.90 g). It was then followed by S
2 (29.73 g) and control recorded the least (24.92 g). Levels of foliar spray showed significant difference in pod weight per plant with F
3 (33.49 g) recorded the highest value which was superior over all other treatments. The treatment F
1 showed lowest value (26.43 g). Interaction effect of seed treatment and foliar spray of micronutrient in pod weight was found to be significant with S
3F
3 (38.11 g) recorded maximum pod weight per plant which was on par with S
4F
3 (31.23 g). Treatment S
1F
1 (24.64 g) recorded the lowest value.
Levels of seed treatment showed significant difference in yield with highest value was obtained in S
3 (2224 kg ha
-1) superior over all other seed treatments. Lowest yield was obtained in S
1 (1969 kg ha
-1). Levels of foliar spray showed significant difference in yield with highest was recorded in F
3 (2173 kg ha
-1) which was superior over all other treatments and the lowest yield was recorded in F
1 (1979 kg ha
-1). Interaction of seed treatment and foliar spray also showed significant difference in the yield with highest was recorded in S3F3 (2320 kg ha
-1) which was superior over other treatment interactions. It was followed by S3F2 (2220 kg ha
-1) which was on par with S
4F
3 (2200 kg ha
-1). Lowest yield was recorded in S
1F
1 (1820 kg ha
-1).
The role of micronutrients in enhancing the yield and its attributes are evident. Seed treatment with micronutrients had positive influence on yield of cowpea. Seed treatment with micronutrients might had increased the seed vigour resulting in better growth and yield of plants. It is also involved in hormonal metabolism, pollination and fertilization and enhancement of cell division which ultimately leads to increase in number and weight of pods. By enhancing the cell division and expansion vegetative growth can also be increased. It also helps in increased production of assimilates and its proper partitioning.
Pranakrishna (1976) reported that pulse crops treated with sodium molybdate increased the seed yield by 45 percentage compared to the control. Common beans treated with zinc increased the yield of crops
(Kaya et al., 2007). Pod yield in pea was found to be higher in seeds treated with 0.5 percent boron solution
(Kumar et al., 2008). Foliar application of micronutrient mixture (zinc, copper, boron and iron) at two percentage resulted in increased yield in okra
(Datire et al., 2010).
Nitrogen, phosphorus, potassium content in grain
Nutrient content in grain is given in the Table 4. S
2 (3.71) recorded highest nitrogen in grain which was superior over other seed treatments. F
3 (3.76) in foliar spray and S
2F
3 (3.91) in interaction were found to be superior over other treatments. Phosphorus content in grain was found to be non significant with respect to treatments and their interactions. S
3 (1.18) in seed treatment and F
3 (1.08) in foliar spray recorded highest potassium content. Interaction effect showed that S
3F
3 (1.25) and S
4F
3 (1.19) were found to be on par with each other.
Nitrogen content in grain was maximum in S
2 (seed treatment with rhizobium). This might be due to the positive effect of rhizobia on increasing the nitrogen content in grain.
Thilakaratna et al., (2019) reported that in common bean, seed treatment with rhizobium showed increased nitrogen content in grain. Considering the potassium concentration in grain, seed treatment with micronutrient mixture at 2% showed highest concentration. The presence of boron in the micronutrient mixture might be the reason for increase in potassium content of grain as it enhances the potassium uptake by plants. The application of micronutrient spray could be beneficial in increasing the grain concentration of nitrogen and potassium. Since it increases the uptake of nutrients, the concentration of nutrients in plant tissues might be increased.
Gad (2012) reported that application of molybdenum increased the concentration of nitrogen and potassium in groundnut seeds. Nitrogen concentration was found to be highest in S
2F
3. Seed treatment with rhizobium might be the reason for increase in nitrogen content which is enhanced by the foliar spray of micronutrient mixture. Potassium content in grain was found to be highest in S
3F
3 which was on par with S
4F
3. Micronutrients, especially boron help in the uptake and translocation of potassium in plants. This might be the reason for increased potassium content in grains supplied with micronutrient seed treatment and foliar spray.
Pattanayak et al., 2000, Thiyageswari and Ramanathan, (2001) and
Hanwate et al., (2018) reported similar results.
Micronutrient content in grain
Seed treatment S
3 (120.91), foliar spray F
3 (117.65) and interaction S
3F
3 (131.96) were found to be superior in the respective treatments and their combinations in iron content of grain. Manganese content in grain was superior in treatments. Among the seed treatments, S
3 (14.30) recorded significantly higher value. F
3 (12.71) and S
3F
3 (17.08) showed superior value in the respective treatments and interaction. Zinc content in grain showed the same trend of iron and manganese with S
3 (56.90), F
3 (53.98) and S
3F
3 (59.21) recorded superior values. Copper content in grain also showed significant difference among treatments with S
3 (6.50), F
3 (6.45) and S
3F
3 (7.02) showed copper content superior over other treatments. S
3 (86.80), F
3 (83.42) and S
3F
3 (89.23) showed highest boron content over other treatments. Molybdenum was found to be non significant with respect to seed treatment, foliar spray and their interaction.
Seed treatment showed significant difference in the concentration of iron, manganese, zinc, copper and boron content in grain and were found to be highest in seeds receiving 2% micronutrient formulation. Hence it is revealed that micronutrient seed treatment has the capacity to increase the nutrient concentration in grain. Similar results were obtained by
Pattanayak et al., 2000. Maize seeds treated with micronutrient increased the concentration of iron, manganese and zinc content in grains
(Harris et al., 2007).
Foliar application of micronutrient mixture also showed significant difference in the amount of iron, manganese, zinc, copper and boron concentration in grain. Treatments receiving foliar spray of micronutrient mixture at 15 and 30 days after sowing showed higher concentration of these micronutrients. Divyasree, 2018 reported that foliar application of micronutrient mixture containing Fe, Mn, Zn, Cu and B significantly increased the respective nutrient concentrations in grains of mung bean.
Similar results were obtained in the interaction effects. Seed treatment with the best micronutrient formulation and two foliar spray recorded highest value of micronutrients in grain except in the case of molybdenum. The combined effect of the individual treatments might be the reason for this. The economic analysis of the field experiment given in Table 5 shows that plants receiving seed treatment with 2 per cent micronutrient formulation and two foliar sprays showed higher benefit cost ratio compared to other treatments.