Influence of Foliar Spray of Nutrients and PGR on Yield and Nutrient Uptake of Blackgram under Partial Shade in Coconut Garden

Blackgram [Vigna mungo (L.) Hepper], also known as urd bean, is a popular short-duration crop among pulses because it thrives in all seasons as a sole crop, intercrop, or catch crop and accounts for 13% of the country’s total pulse area and 10% of its total pulse production (MoA and FW, 2021). 
       
In the era of declining in land area and increasing population, inclusion of pulse crop in the cropping system is essential. The reduction on yield of blackgram may be due to  increased flower drop and poor pod setting caused by floral abscission and lack of nutrients during key stage of crop growth (Mahala et al., 2001). In addition to other climatic and agronomic constraints, a recent literature review by Swaminathan et al., (2021) summarized the varietal constraints causing low blackgram productivity and noted that foliar application of nutrients is an economical yet efficient method of fertilizer application. In order to increase blackgram productivity, they stressed the importance of choosing varieties that are appropriate for the circumstances as well as applying nutrients and/or growth regulators topically. Growth regulators and nutrition foliar spraying have a significant impact on the morphological traits, yield characteristics and yield in pulses (Sridhara et al., 2022).  There is a dearth of research on how foliar application of growth regulators and nutrients can increase the productivity of blackgram intercropped in coconut gardens.
       
Plant growth regulators control plant growth and architecture to promote optimal vegetative development in shady or stressful environments. Additionally, they improve the interaction between sources and sinks and promote photo-assimilate translocation, which aids in the growth of fruit and seeds as well as efficient flower formation, eventually increasing agricultural yield and also will help to improve soil properties. In this backdrop, an investigation was conducted to study the effect of foliar nutrition and plant growth regulators on growth and yield of the identified shade tolerant Blackgram varieties under coconut garden.

At the Instructional Farm of the College of Agriculture at Vellayani, Thiruvananthapuram, Kerala, the field trial was done during Rabi 2020 and summer 2020-21 in partially shaded coconut garden. The field is located 29 meters above mean sea level at latitude 8o 25' 46" N and longitude 76o 59' 24" E. The soil physicochemical properties are given in Table 1.


       
The experiment was laid out in split plot design, replicated four times with five varieties (v₁ - Sumanjana, v₂ - DBGV 5, v₃ - VBN 5, v₄ - VBN 6, v₅ - CO 6) which performed better in terms of yield per unit area under the partial shade in coconut garden (Pooja et al., 2023) were selected as the main plot treatments and six foliar sprays of nutrients and plant growth regulators as subplot treatments (f₁: 19:19:19 (1%) at 45 and 60 DAS, f₂: SOP  (0.5%) at 45 and 60 DAS, f₃: NAA 40 mg L^-1 and salicylic acid 100 mg L^-1 at pre-flowering (30-45 DAS) and 15 days later, f₄: f₃ + f₁, f₅: f₃ + f₂ and f₆: Control - KAU POP).
       
Over-40-year-old coconut gardens with light intensities between 40 and 46.5 klux were chosen, with beds measuring 6 m in length and 3 m in width being taken as the main plots in the spaces between the coconut palms. A two-meter radius was left around the base of each coconut palm. Subplots of 3 m x 1 m were then created by dividing the main plot.
       
Blackgram seeds were added to a Rhizobium culture containing the strain BMBS 47 and sown at a spacing of 25 cm x 15 cm. Urea, rajphos and muriate of potash were used to supply the nutrients (20:30:30 kg N: P₂O₅: K₂O ha^-1) (KAU, 2016). Along with full dosages of P and K, the remaining half of the N dosage was applied as two foliar sprays at 15 and 30 days after sowing (DAS). Weeding was done twice, at 15 and 30 DAS. According to the prescribed treatments, foliar spraying of nutrients and plant growth regulators was carried out.
       
Three pickings were made once the varieties and cultures matured in 80-100 days, depending on the varietal characteristics. The yield was recorded from the net plot area and expressed in kg ha^-1. Soil samples were analysed both before and after the experiments to determine changes in pH, electrical conductivity, organic carbon and available NPK. Plant samples were analysed for NPK content and was multiplied by their total dry matter production and the result was given in kg ha^-1. Statistical analysis was done.

Yield of blackgram as influenced by foliar spray of nutrients and plant growth regulators
 
Significant variation in seed yield ha^-1 was observed during summer and rabi (Table 2). Varieties tested were found to vary significantly with respect to seed yield ha^-1. Among these, Sumanjana recorded higher per hectare seed yield and was on par with DBGV 5 during both the seasons (1530 kg ha^-1 and 1501 kg ha^-1 in summer and 1447 kg ha^-1 and 1446 kg ha^-1 in Rabi respectively). There was significant difference in seed yield ha^-1 due to foliar spray during both the seasons. Foliar application of 19:19:19 (1%) at 45 and 60 DAS + NAA 40 mg L^-1 and SA 100 mg L^-1 at pre-flowering and 15 days later (f₄) recorded the highest seed yield in both the seasons (1536 kg ha^-1 and 1474 kg ha^-1). It was deduced that application of NAA negated flower drop which was manifested as increased seed yield in these two shade adaptive varieties. Salicylic acid foliar spray can improve sink strength by promoting cell division in developing ovaries and it also transports metabolites to growing grains to lower the risk of abortion (Horvath et al., 2007). Increased seed yield of pulse with foliar application of nutrients could be attributed to reduced flower drop and increased pod set percentage (Mamathashree, 2014).


       
Main and subplot effects were reflected in the interaction and higher seed yield ha^-1 was recorded in Sumanjana (v₁) with sub plot treatment f₄ and was on par with DBGV 5 (v₂) with f₄ in the summer season (1750 kg ha^-1 and 1713 kg ha^-1). During Rabi, the highest seed yield was recorded in v1f4 (1700 kg ha^-1). Foliar nutrients often enter the cells through the stomata or cuticle of the leaf, making it easier for nutrients to enter. According to Manonmani and Srimathi (2009), foliar spray is attributed with extremely quick absorption and almost full usage of nutrients, elimination of leaching losses and fixing and aid in controlling the uptake of nutrients by plants.  This may be ascribed to the crop’s demand being provided by greater phosynthate absorption and translocation from source (leaves) to sink (pods) through the provision of necessary nutrients by 19:19:19 foliar spray. These results are in corroboration with the findings of Kuttimani and Velayutham (2011).
       
With seed yields of 1489 kg ha^-1 and 1473 kg ha^-1, respectively, Sumanjana and DBGV 5 were found to perform better under restricted shade in a pooled examination of seed production. With 1505 kg ha^-1, the subplot factor f4 recorded the highest seed output. The largest seed yield was obtained by v1f4 (1725 kg ha^-1) and v2f4 (1626 kg ha^-1). This combination of main and subplot variables is thought to be the result of the above-explained positive interaction of individual effects (Fig 1). On comparison with KAU Package, Sumanjana and DBGV 5 under foliar spray of nutrients and PGR evinced 21.84 and 21.76 per cent increase in seed yield over v1f6 and v2f6 respectively (Fig 2). Higher LAI and chlorophyll concentrations in v1f6 and v2f6 may have enhanced photosynthetic activity, resulting in increased carbohydrate synthesis and assimilate translocation from source to sink, both of which ultimately helped to increase seed output. Also, higher number of nodules and nodule mass might have enhanced the assimilation, production of proteins and translocation of carbohydrate from source to sink which might have led to higher seed yield ha^-1. Better crop growth enhanced the absorption of nutrients through root and enhanced the synthesis of IAA, carbohydrate and N metabolism which ultimately led to higher economic yield. The fact that plants treated with macronutrients and growth regulators continued to be physiologically more active to accumulate adequate food reserves for the developing flowers and seeds may be the cause of the greater seed output produced as a result of the nutrients and growth regulators.





NPK uptake of blackgram
 
The data on the effect of varieties, foliar spray and their interaction on NPK uptake of Blackgram during the both the seasons are given in Table 3a and 3b. There was significant variation in NPK uptake due to treatments.

a

b
       
Crop nutrient uptake is correlated with plant nutrient content and dry matter production, which in turn is correlated with plant photosynthetic capacity. During both the seasons, comparatively higher NPK uptake was observed in the varieties Sumanjana and DBGV 5. This might be attributed to higher content of N, P, K and increased morphological attributes and LAI which resulted in higher dry matter production in the respective varieties. Increased N, P and K levels in plants may be attributed to water soluble fertilizers with greater concentrations that plants have directly absorbed through leaves. The findings of Tohamy et al., (2011) and the results are in accord.
       
Regarding the subplot factor f₄ recorded higher NPK uptake and was on par with f₃ and f₅ in summer season and the highest NPK uptake was recorded in f₄ during Rabi. Nutrients and PGRs given via foliage aided with improved nutrient uptake and effective photoassimilates translocation to all regions of the plant, which in turn led to enhanced activity of functional root nodules and increased dry matter production. More flower production, followed by pod development and other yield-attributing traits, may have resulted from this. Fritz (1978) shown that tiny amounts of foliar fertilizers applied during crucial plant growth phases boosted nutrient absorption and promoted plant metabolism.
       
During Rabi,  v1f4  recorded the highest NPK uptake due to the higher yield and dry matter accumulation. According to Tabassum et al., (2013), increasing nutritional availability accelerate physiological processes, which in turn affect the formation of dry matter and nutrient absorption. The absorption of N and K was much greater, which may have contributed to the higher yield. According to Sangwan and Raj (2004) report on chickpea and Anitha et al. (2005) research on cowpea, the results are consistent. Amjad et al., (2004) and Calhor (2006) showed increased photosynthetic efficiency, assimilation and dry matter production as a result of enhanced nutrient availability and absorption.

Soil properties
 
Perusal of the data revealed that the varieties, foliar spray and their interaction did not exert any substantial influence on soil pH and electrical conductivity during both the seasons (Table 4). Nevertheless an increase in the soil pH status from initial value (5.9) was recorded with the cultivation of different Blackgram varieties with foliar spray during both the seasons. This could be attributed to the effect of liming done before sowing. Liming can raise the soil pH (Goulding, 2016) as a result of desorption of the Al3+ and H+ ions from the exchange sites to soil solution.


       
There was no significant variation in organic carbon solely due to varieties and foliar spray and their interaction in the summer season. During the Rabi season, the plots grown with the varieties, Sumanjana and DBGV 5 showed higher organic carbon contents. Wani et al., (2003) and Jensen et al., (2012), found that the addition of legumes to the rotation greatly increased the soil’s organic carbon content and nutritional availability. There was significant variation in organic carbon due to foliar spray in Rabi and the treatment f4 recorded highest organic carbon. The enhancement in organic carbon content observed in all the treatments might be due to the decomposition of farmyard manure (20 t ha^-1) coupled with the left over residues of the previous crop after summer. According to Lynch and Whips (1990), root exudates made up roughly 40% of the dry matter the plant accumulated and was discharged into the rhizosphere. Hasanuzzaman et al., (2019), reported that the release of organic compounds (organic acids, amino acids, sugars, vitamins, mucilage, etc.) into the rhizosphere during crop growth as well as owing to the addition of organic matter in the form of FYM may have increased the soil’s organic carbon content. Bochalya et al., (2021) reported improved organic carbon status due to the foliar spray of 19:19:19 at flowering stage in wheat. The treatment combinations v1f4, v2f4 and v5f4 recorded higher organic carbon content and were on par with v2f5. Organic carbon was observed to have increased from the initial status (0.93) after the harvest of Blackgram. There was significant improvement in the organic carbon status in the Rabi compared to the summer season. The probable reason of higher organic carbon in the Rabi might be due to the residue decomposition of summer crop in the next Kharif season and also due to the addition of organic manures to the Rabi crop.
       
There was an improvement in the N, P and K status compared to the initial status (Table 5). Legumes in rotation boosted the NPK content of soil (Thamburaj, 1991). The crop was able to get nutrients from the deeper strata thanks to enhanced crop establishment and roots. The availability of N was shown to be higher in treatments with higher levels of organic carbon, which may be the result of symbiotic N-fixing bacteria in the nodule fixing ambient N. The outcome is consistent with Sakin’s (2012) findings, who claimed that high soil organic carbon improved the soil’s N content. After the trial, it was discovered that all of the treatments had significant levels of available P in the soil. Increased soil organic carbon content maintained soil fertility by preventing nutrient leakage. Similar observation was also made by Suman (2018).


       
The varieties Sumanjana and DBGV 5 recorded higher available N compared to other varieties which might be due to comparatively higher root nodulation, which is expected to have contributed more N in soil. In the case of subplot factor, f₄ recorded higher N during both the seasons and the highest P status in Rabi season. This can be correlated with the higher nodules number and dry weight of nodules per plant observed in f₄ which might have contributed more biological N fixation and rhizo-deposition. This will mobilize the fixed P in the soil and make it in the available form. The interaction effect was a reflection of main and subplot effects and the treatment combination v1f4 and v2f4 recorded comparatively higher N status after the experiment during both the seasons. Even though, the uptake of N was higher in Sumanjana and DBGV 5, the greater contribution of N by fixation recorded increment in soil available N status. Exploration of the effect of legumes on soil enrichment have shown that nitrogen fixation and rhizodeposition of N from legumes increased the available N status in soil (Zhang et al., 2015).

The varieties performed differently under partial shade and responded to nutrient application in varied manner. Sumanjana or DBGV 5 raised under partial shade in coconut garden with recommended dose of nutrients supplemented with foliar application of 19:19:19 (1%) at 45 and 60 DAS + NAA 40 mg L^-1 and SA 100 mg L^-1 at pre-flowering and 15 days later (f₄) realized higher yield, nutrient uptake and improved soil nutrient status.

All authors declared that there is no conflict of interest.