Pulses are a global staple, crucial for nutritional diets. In India, pulses are vital for nutritional security, contributing to the national food basket and addressing environmental challenges. The UN declared 2016 as the International Year of Pulses to highlight their significance. India leads globally in pulse area (34%), production (26%), and consumption (30%). Pulses are the second most important food source after cereals, containing 22-34.6% protein, which is 2 to 3 times more than cereals. They are key dietary protein sources and contribute to atmospheric nitrogen fixation (Mandi et al., 2017). Pulses enhance soil fertility, improve soil physical condition, and increase water retention. They also provide health benefits by producing flavonoids, phytosterols, and polyphenols, reducing the risk of diseases like colon cancer and cardiovascular diseases (Jukanti et al., 2012). The lentil is a "clean plant", relatively free of antinutritive factors, low in flatulence and has a low post-prandial glycemic index, which is good for diabetic patient (Singh et al., 2023).

Lentil (Lens culinaris Medik), commonly known as 'Masoor,' is a highly nutritious winter pulse crop widely grown in India, particularly in temperate regions, often cultivated alongside chickpea. This versatile crop can be grown as a mixed, single, or relay crop and is used for pulse production, forage, and green manure. Lentil seeds are an excellent source of protein (340-346 g), calories (340-346 g), and carbohydrates (65%), surpassing many other legumes in nutritional value. They are rich in essential nutrients, including calcium, fiber, iron, phosphorus, thiamine, sodium, potassium, niacin, and riboflavin. Additionally, lentils provide high levels of vital amino acids such as leucine, arginine, lysine, and sulfur-containing amino acids (Kumar and Gupta 2019). 

In India, lentils are cultivated on 1.51 million ha, producing 1.22 million tonnes with an average yield of 1032 kg/ha. In Bihar, they occupy 0.15 million ha, yielding 0.148 million tonnes at 985 kg/ha (MoA & FW 2018-19). As an annual crop, lentils are often grown as a relay or paira crop, utilizing residual soil moisture on marginal lands. Relay cropping with rice expands lentil cultivation by leveraging residual fertility and moisture. This practice, termed Utera cropping in West Bengal and Paira cropping in Chhattisgarh and Bihar, involves broadcasting lentil seeds 15-20 days before rice harvest to optimize moisture use and ensure timely establishment.

The need for the present study emerged from several key research gaps in the field of lentil production within the rice-lentil relay cropping system. Despite the recognized importance of lentil as a nutrient-rich pulse crop, its productivity remains suboptimal due to various agronomic and nutritional limitations. The following research gaps were identified, necessitating the current study.

In India yield of lentil in rice-based relay cropping system remains below its potential due to poor management, nutrient deficiencies, and water stress (Ali et al., 2012). Traditional fertilization often fails to meet nutrient demands at critical stages, and farmers rely on residual soil fertility from rice, which is insufficient. Limited research exists on foliar nutrient application as an alternative strategy to enhance yield (Sharma et al., 2012). Conventional soil fertilization in lentils has limitations like low nutrient-use efficiency due to fixation, leaching, and volatilization. Nutrient uptake is often delayed, making them unavailable at critical growth stages. Additionally, soil-applied fertilizers may not meet micronutrient demands, particularly zinc, which is essential for plant metabolism and protein synthesis (Kumar et al., 2015; Hegazy et al., 1990). Nutrient deficiency during pre-flowering and pod initiation stages hampers lentil productivity. Poor soil fertility and inefficient root absorption limit nitrogen, phosphorus, and potassium uptake, while zinc deficiency affects enzyme activation, hormonal balance, and protein synthesis (Thakur et al., 2017). Apart from that lentil depends on biological nitrogen fixation (BNF) via Rhizobium bacteria, but poor nodulation due to low phosphorus and micronutrient deficiencies limits nitrogen fixation (Singh et al., 2020). Protein content, a key quality trait, is influenced by zinc and nitrogen, though soil-applied nitrogen is often lost through leaching. Foliar-applied nitrogen ensures better absorption, enhancing amino acid synthesis and protein accumulation in seeds (Gowda et al., 2014).

Nutrient foliar spray is the easiest way to boost crop growth (Kuttimani, 2012).  During flowering and pod development, foliar spray of nutrients showed positive impact on increasing the no. of pods per plant which ultimately increased the lentil yield (Shankarappa et al., 2020; Reid et al., 2011). Foliar spraying efficiently delivers water and nutrients to the plant's active food synthesis sites with minimal waste, quickly supplying the necessary nutrients (Nayak et al., 2020; Kannan, 2010). This helps regulate the plant's source-sink relationships, especially under adverse or stress conditions (Premaradhya et al., 2018). Using microelements through foliar application is more beneficial than soil application (Darwesh, 2011).

Based on the provided research context, the present study titled "Optimizing Growth and Yield of Lentil (Lens culinaris Medik) via Foliar Nutrient Application in Rice-Lentil Relay Cropping System" was conducted during the rabi season of 2020-21. Given the limitations of conventional soil fertilization, foliar application of NPK and Zinc Sulphate was explored as an alternative strategy. Limited research existed on its effectiveness in improving plant height, dry matter accumulation, seed yield, nodulation, and nitrogen fixation in relay-cropped lentils. Additionally, the study aimed to assess the role of foliar fertilization in enhancing protein content, addressing a key gap in existing research.

A. Field layout and experimental conditions

In this experiment, lentils were sown in a standing paddy crop as a paira/utera crop, eliminating the need for preparatory tillage. The layout was designed to meet experimental requirements, and the trial was conducted using a Randomized Block Design (RBD) with three replications and a net plot size of 12.6 m² (4.2 m x 3.0 m). Treatments were randomized according to the procedure provided by Cochran and Cox (1957). The detailed description of the treatments was given in below; T1- Water Spray at pre-flowering and pod initiation, T2- 2% Urea spray at pre-flowering and pod initiation, T3- 2% DAP  spray at pre-flowering and pod initiation, T4- 0.5% Potassium nitrate spray at pre-flowering and pod initiation, T5- 0.5% NPK@ 19:19:19 spray at pre-flowering  and pod initiation, T6- 0.5% Zinc sulphate spray at pre-flowering  and pod initiation, T7- 2% Urea + 0.5% Zinc sulphate spray at pre-flowering and pod initiation, T8- 2% DAP + 0.5% Zinc sulphate spray at pre-flowering and pod initiation, T9- 0.5% Potassium nitrate + 0.5% Zinc sulphate spray at pre-flowering and pod initiation and T10- 0.5% NPK@ 19:19:19 + 0.5% Zinc sulphate spray at pre-flowering and pod initiation.

Meteorological parameters (morning & evening relative humidity, maximum & minimum temperature etc.) were recorded as standard meteorological week during the period of experimentation is mentioned in Fig. 1.

Fig. 1. Meteorological parameters observed during the period of experimentation (Standard meteorological week).

B. Varietal details, seed treatment and sowing

The HUL-57 lentil variety, developed by the Institute of Agricultural Sciences, BHU as Malaviya Jankalyani, is recommended for the North Eastern Plain Zone (NEPZ) including U.P., West Bengal, Assam, and Bihar. It is a short-duration, rust-resistant, moderately wilt-resistant, and yellow mosaic virus-resistant variety with a yield potential of 1800 kg ha-1. Pure and healthy seeds were used, treated with Bavistin at 2g kg-1 and sown at a rate of 30 kg ha-1. A basal dose of 20 kg N, 40 kg P2O5, and 20 kg K2O per hectare was applied 10-15 days after sowing.

C. Foliar application of treatments

For each experimental treatment, the appropriate amounts of foliar nutrients/chemicals and water were measured and mixed to prepare a uniform solution. This solution was then evenly sprayed using conical-shaped nozzles with a knapsack sprayer. The first foliar application was carried out 74 days after sowing (DAS) at the pre-flowering stage, and the second application was given at the pod initiation stage, coinciding with 99 DAS of the crop under study.

D. Observation recorded

Representative sampling was used to record observations of different agronomic parameters of lentil plants at various growth stages. Five plants per plot were randomly chosen and marked for measurement. Plant height was recorded at 30, 60, 90 DAS, and at harvest. These plants were labeled and measured from base to tip, then averaged. Additionally, five random plant samples were collected at these intervals, washed, sun-dried, and oven-dried at 70°C to a constant weight to determine the final dry weight.

E. Nodulation studies and yield attributes

Nodule counts per plot were taken at 30 and 60 DAS by randomly selecting and carefully uprooting five plants per plot, followed by washing and counting nodules on the roots. The total number of pods on five sampled plants was averaged. A sample of 100 lentil seeds per plot was sun-dried to 12% moisture and weighed. The plot-wise grain weight was recorded in kg/ha after threshing, winnowing, and sun-drying. The stover yield was calculated after completely drying the crop residues. Harvest Index (H.I.), the ratio of economic yield (seed) to biological yield (seed + stover), was expressed as a percentage.

F. Qualitative Analysis

(i) Protein content in seed (%). Samples from various experimental plots were dried, crushed into powder, and analyzed for nitrogen content using the micro Kjeldahl technique. The protein content of the seeds was then calculated by multiplying the percentage of nitrogen in the seeds by a constant factor of 6.25.

G. Statistical analysis

The data for growth, yield, and other characteristics were analyzed using the Variance Analysis technique and tested for significance with the "F" test at a 5% significance level, as proposed by Cochran and Cox (1957). Critical difference values at the 5% probability level were used to compare treatments.

A. Growth attributes

(i) Plant height (cm) & dry matter accumulation (g plant^-1). Plant height is a critical growth parameter that reflects the overall vigor and development of plants. The results indicate significant differences among the treatments at later stages of growth (90 DAS and harvest), while the differences were non-significant at earlier stages (30 and 60 DAS). At 30 DAS, the tallest plants of 11.7 cm were observed in T5 and T3 (11.6 cm), while T6 (0.5% Zinc Sulphate) exhibited the least plant height (10.6 cm). Similarly, at 60 DAS, T4 (20.6 cm) and T2 (20.5 cm) recorded higher plant heights, whereas the lowest plant height was recorded in T9 (19.2 cm). At 90 DAS, T10 (41.3 cm) recorded the maximum plant height, followed by T8 (39.7 cm), while the lowest height was recorded in T1 (31.2 cm). At harvest, T10 (46.7 cm) continued to show superior performance, followed by T8 (43.4 cm), whereas the minimum plant height was recorded in T1 (33.5 cm). Foliar-applied fertilizers increase nutrient applications efficiency, reduce leaching losses, and provide a consistent supply of important nutrients for growth and development, as indicated by the increased plant height with nutrient-rich treatments. Similar results regarding plant height were reported by Thakur et al. (2017), who found that foliar sprays of 19:19:19 (N:P:K) during flowering and also during the pod development stage in chickpea resulted in a notable increase in plant height.

Plant dry matter accumulation is an important indicator of biomass accumulation and overall plant health. The data revealed non-significant differences at 30 DAS and 60 DAS, but significant differences at 90 DAS and harvest. At 30 DAS, the dry matter accumulation ranged from 0.36 g (T9) to 0.44 g (T5), indicating marginal variations. At 60 DAS, the highest dry weight was observed in T2 (3.17 g), followed by T4 (3.14 g), while the lowest was recorded in T9 (2.94 g). At 90 DAS, T10 (9.47 g) recorded the highest dry matter accumulation, followed by T8 (8.94 g), whereas the lowest was found in T1 (5.62 g). At harvest, T10 (14.02 g) again showed the maximum biomass accumulation, followed by T8 (13.21 g), while the lowest dry matter accumulation was observed in T1 (8.87 g). Nutritional uptake and nutritional status in plant elements are improved by foliar spraying. The leaves will sustain an increased rate of photosynthesis as a result, increasing their dry weight. These results are similar to those of Muthal et al. (2016); Singh et al. (2014).

Table 1: Impact of foliar application of nutrients on plant height (cm) and dry weight (g plant-1) of lentil plant.

The increase in branch number in T10 and T8 can be attributed to the combined effect of macronutrients (NPK and DAP) and micronutrients (Zinc Sulphate). Nitrogen plays a crucial role in vegetative growth, promoting cell division and expansion, while phosphorus is essential for root development and energy transfer (Sharma et al., 2017). Zinc further enhances enzyme activity and hormonal balance, particularly auxin synthesis, which promotes lateral branching (Alloway, 2008). The higher branch number in T10 (NPK + Zinc Sulphate) indicates that a balanced foliar application of macro and micronutrients optimizes shoot growth and branching potential (Ali et al., 2017). Similar result also found by Krishnan et al. (2014).

Fig. 2. Impact of foliar application of nutrients on No. of branches plant-1 of lentil.

(iii) Number of nodules plant-1. Nodule formation is a key parameter in leguminous crops as it determines biological nitrogen fixation (BNF). The results show a moderate variation in nodule count at 30 DAS and 60 DAS, with the highest number of nodules at 60 DAS in T9 (9.94 nodules), followed closely by T3 (9.87 nodules) and T8 (9.67 nodules). It is happened because of nodulation started much before the application of foliar nutrition. For those causes there was no greater influenced root growth and plant development, as well as prolific nodulation. There was whatever variation found only due to difference in soil physical conditions. 

Fig. 3. Impact of foliar application of nutrients on No. of nodules plant-1 of lentil.

B. Yield attributes and yield

Seed yield is a crucial agronomic parameter that determines the economic viability of a crop. The results indicate significant differences among the treatments. The highest seed yield (1477 kg/ha) was recorded in T10 (0.5% NPK @ 19:19:19 + 0.5% Zinc Sulphate), followed by T8 (2% DAP + 0.5% Zinc Sulphate with 1411 kg ha-1), whereas the lowest yield (976 kg ha-1) was observed in T1 (Water Spray control). It is mainly due to reduced nutrient losses and enhanced nutrient supply. During the reproductive period, when nutrient demand is at its highest, the lentil plant's indeterminate growth habit could promote quick nitrogen absorption. It might have been owing to increased nitrogen availability throughout crop season due to basal application N, N-fixation, and NPK@ 19-19-19 spray. As a result, flower drop or abortion were decreased, which ultimately increased pod setting and resulted in a higher seed yield. These findings are in close conformity with Hoque et al. (2022).

Table 2: Impact of foliar application of nutrients on seed, stover yield (t ha-1) and harvest index of lentil plant.

Harvest index (HI) is the ratio of economic yield (seed yield) to biological yield (total biomass). The values in the study ranged from 32.07% (T1) to 34.23% (T10), indicating non-significant differences among treatments. Although T10 and T8 had the highest harvest indices, the lack of significant differences suggests that nutrient management primarily influenced total biomass production rather than the partitioning efficiency between grain and stover. This aligns with previous findings that higher nutrient availability enhances both seed and stover yield (t ha-1) without significantly altering the HI (Singh et al., 2020).

C. Quality Parameters

(i) Protein content in seeds (%). The highest protein content (24.23%) was recorded in T10, while the lowest (21.06%) was in T1. The increased protein content in T10 (24.23%) compared to T1 (21.06%) can be attributed to the synergistic effects of combined nitrogen and zinc applications. Nitrogen is a fundamental component of amino acids, the building blocks of proteins, and plays a critical role in nitrogen metabolism. Enhanced nitrogen availability, provided by nitrogen fertilization, leads to increased amino acid synthesis and subsequently higher protein content in the seeds (Kumar et al., 2015). Zinc, on the other hand, is crucial for several enzymatic reactions involved in protein synthesis. It acts as a cofactor for various enzymes that catalyze the synthesis of amino acids and proteins, ensuring efficient metabolic processes (Cakmak, 2008). The application of zinc improves the functionality of these enzymes, resulting in better protein formation, Boonchuay et al. (2013); Gowda et al. (2014).

Therefore, the combined application of nitrogen and zinc enhances the overall protein metabolism in lentil plants, leading to a significant increase in protein content. This highlights the importance of balanced nutrient management in optimizing crop nutritional quality and yield.

Fig. 4. Impact of foliar application of nutrients on seed protein content (%) of lentil plant.

Further long-term field experiments are needed to evaluate the cumulative effects of foliar nutrient applications on soil health, sustainability, and overall cropping system productivity. Detailed investigation into the physiological and biochemical mechanisms underlying nutrient uptake and assimilation in relay cropping systems can provide deeper insights into optimizing foliar fertilization strategies. Additional studies can focus on refining nutrient concentrations, combinations, and the best application timing to maximize efficiency under different agro-climatic conditions. Apart from that, cost-benefit analysis of foliar nutrient applications can provide farmers with practical recommendations on the economic feasibility and profitability of adopting these practices. Exploring the impact of foliar nutrient applications under different climatic stress conditions, such as drought and excessive moisture, can help in developing climate-smart nutrient management strategies. The effectiveness of foliar nutrition in improving productivity can be tested in other pulse crops grown in relay systems to broaden the applicability of the findings.