Effect of integrated nutrient management on nodulation, nutrient uptake and residual soil fertility in rice fallow green gram (Vigna radiata L.) ecosystems of Eastern India

Introduction

Medicinal plants have greatly gained importance in the management and treatment of human diseases, globally [1] . It constitutes the main source of primary healthcare in most rural populations, especially in many African countries, due to its affordability and availability. However, as the usage of these medicinal plants becomes more widespread around the world, there are questions and misgivings about the quality, efficacy, and safety of the products utilized in the health sector [2, 3, 4] . These concerns have hampered the sensible use and validation of bio-products derived from these herbs for the treatment and management of disorders [5] . The validation and quality assurance of medicinal plant products has been hampered by a lack of or incorrect plant identification. The correct identification of the starting material is a must for assuring the reproducible quality of herbal medicine, which is imPulses hold an important position in India, especially for people who follow a vegetarian diet, as they are an excellent source of protein. Their lysine-rich protein helps compensate for the amino acid deficiency commonly found in cereal-based diets, making their nutritional quality comparable to that of milk protein.

Because of their high protein value, pulses are often referred to as the "poor man's meat." fixation, making them critical for sustainable agriculture (Kanniyan, 1999). In India, pulse crops are mainly cultivated under rainfed conditions on low-fertility soils. Considering the growing population and widespread malnutrition, pulse yields need substantial improvement. A balanced diet requires the inclusion of all essential food groups. According to FAO/WHO, an adult needs about 85 grams of pulses per day to meet basic protein requirements. However, per capita availability of pulses in India has fluctuated, dropping from 70.3 g/day in 1956 to 37.5 g/day in 1981, and further to 29.1 g/day in 2003. Due to improved production, government support, and increased imports, availability has gradually risen to 47.2 g/day (GoI, 2016), though it still falls short of the recommended 50 g/day. The Indian Institute of Pulses Research (IIPR), Kanpur, estimates that national pulse demand will reach 39 million tonnes by 2050, requiring a 2.2% annual growth rate in production (IIPR, 2015). Meeting this demand will require both higher productivity and expansion of pulse cultivation through improved technologies. One promising approach is the effective use of rice fallows to grow short-duration pulses such as green gram, black gram, and cowpea. Odisha falls under a low-productivity zone (<600 kg/ha), where yields could be significantly enhanced by addressing major production challenges. Since green gram grown in rice fallows must rely on residual soil moisture and nutrients and complete its life cycle within 60-70 days, yields are often low and variable (300-500 kg/ha). Major constraints include poor seed quality, low germination, moisture stress during flowering, lack of fertilizer use, absence of foliar sprays, and inadequate weed management. Of these, insufficient nutrient application is a key factor limiting yields. Although nutrient management has been well studied under irrigated conditions, research on nutrient management in rice fallow green gram remains limited. Currently, foliar spraying is the most effective method to overcome nutrient stress and improve yields in rice fallow ecosystems. Foliar nutrition allows for rapid and efficient nutrient uptake, minimizes nutrient losses, and helps regulate plant nutrient absorption (Manonmani & Srimathi, 2009). Applying essential nutrients through foliar sprays promotes root growth, nodulation, energy transfer, metabolic activity, nutrient translocation, pod formation, and early maturity, ultimately contributing to higher pulse productivity.

Materials and Methods

Experimental Site and Design

The experiment was conducted during the rabi season of 2017-18 at the Instructional Farm, College of Agriculture, Orissa University of Agriculture and Technology, Bhubaneswar. The site is located at 20°15' N latitude and 85°52' E longitude, 25.9 m above mean sea level, and approximately 64 km from the Bay of Bengal. It falls under the East and Southeastern Coastal Plain Agroclimatic Zone of Odisha. A randomized block design with three replications and twelve treatments was used for the study. Each gross plot measured 5.65 m × 5.3 m, while the net plot area was 5.0 m × 5.0 m, with a plant spacing of 30 cm × 10 cm.

Soil Characteristics

The soil at the experimental site was sandy loam with a slightly acidic pH of 5 The green gram variety IPM 02-14 was planted on December 17, 2017, using a seed rate of 20 kg ha⁻¹. Basal nutrients were supplied according to the treatments using urea, di-ammonium phosphate (DAP), and muriate of potash (MOP). Foliar sprays were applied with a hand sprayer fitted with a conical nozzle at the pre-flowering stage (26 DAS) and again 10 days later (36 DAS).

In each plot, root nodules were counted on five randomly selected plants at 15, 30, and 45 DAS. The plants were carefully uprooted, the roots were washed, and the nodules were separated, counted, weighed, and recorded.

Soil analysis

Soil samples from each treatment were collected at a depth of 0-15 cm. Samples from the corresponding treatments in each replication were combined to form composite samples, which were then shade-dried, finely ground, and sieved through a 2 mm mesh for chemical analysis.

Plant analysis 2.3.1 Nutrient content

At harvest, plant samples were randomly collected and analyzed for nitrogen, phosphorus, and potassium content in both the seed and haulm. For each treatment, a composite sample was prepared from the three replications. The ovendried samples were finely ground and subjected to nutrient analysis using standard procedures. Total nitrogen was estimated using the modified Micro-Kjeldahl distillation method (Jackson, 1973) after digesting 0.1 g of oven-dried (70 °C) haulm and 0.2 g of dried seed. Phosphorus and potassium contents were determined by digesting 0.1 g of straw and 0.2 g of grain with nitric acid (HNO₃) and perchloric acid (HClO₃), filtering, and diluting the digest to a standard volume. Phosphorus was measured using a spectrophotometer, while potassium was estimated with a flame photometer (Jackson, 1973).

Nutrient uptake

The nutrient concentrations in the seed and haulm, determined from plant analysis, were multiplied by their respective yields to calculate nutrient uptake expressed in kg ha⁻¹.

Uptake (kg ha -1 ) = Nutrient content (%) X Yield (kgha - 1 )/100

Statistical analysis

All biometric observations recorded before and after harvest were tabulated and analyzed statistically following the standard procedures for a Randomized Block Design (RBD). Analysis of variance (ANOVA) was performed, and treatment differences were tested for significance using the F-test. The standard error of the mean [SE(m) ± ] and the critical difference (CD) at the 5% level of probability were calculated using the methods outlined by Gomez and Gomez (1984) for result interpretation.

Experimental Findings 3.1 Root nodules plant -1

The number of root nodules per plant was measured at each growth stage, and the pattern of nodule formation is presented in Table 1.

Fresh weight of root nodules was measured at 15, 30, and 45 DAS, and the corresponding data are presented in Table 2.

Nutrient content and up take

The nutrient content and uptake data are presented in Tables 3.1, 3.2, and 3.3.

Nitrogen

The statistically comparable with T 9 and T 8 for seed uptake, T 9 , T 8 , and T 7 for haulm uptake, and T 9 for total nitrogen uptake. The lowest nitrogen uptake was observed in the control (T 12 ), with 9.43 kg ha⁻¹ in seed, 20.52 kg ha⁻¹ in haulm, and 29.95 kg ha⁻¹ for the total plant.

Phosphorous

The highest phosphorus content in both seed (0.39%) and haulm (0.17%) was observed in the treatment with RDF as basal and 2% NPK (19:19:19) foliar sprays at 26 and 36 DAS (T 10 ), which was superior to all other treatments except T 9 and T 8 . The lowest phosphorus content in seed (0.33%) and haulm (0.14%) was recorded in the control treatment (T 12 ). treatment was statistically at par with T 9 for seed uptake, T 9 and T 8 for haulm uptake, and T 9 for total potassium uptake. The lowest uptake was recorded in the control (T 12 ), with 9.43 kg ha⁻¹ in seed, 20.52 kg ha⁻¹ in haulm, and 29.95 kg ha⁻¹ for the total plant.

The highest number of root nodules and fresh weight per plant were recorded at 45 DAS. Root nodule development was significantly influenced by different foliar nutrient treatments. The maximum number of nodules was observed with the application of RDF as basal combined with 2% NPK (19:19:19) sprays at 26 and 36 DAS. This effect is likely due to the improved root growth and enhanced rhizobial activity in the rhizosphere stimulated by nitrogen, phosphorus, and potassium supplied through basal and foliar nutrition, leading to the formation of a greater number of active nodules. These findings are consistent with the observations of Kumar et al. (2018).

Nutrient content and uptake

The application of foliar nutrients along with RDF as basal significantly enhanced nitrogen, phosphorus, and potassium content in both seed and haulm compared to the control, likely due to more efficient nutrient absorption through the foliage than the roots. In this study, nitrogen content in both seed and haulm was highest with RDF as basal combined with 2% NPK (19:19:19) sprays at 26 and 36 DAS, followed closely by RDF as basal with two foliar sprays of 2% DAP or urea. The increased nitrogen uptake may be attributed to greater nitrogen availability, higher biomass production, increased nodule formation, enhanced yield, and delayed chlorophyll and leaf nitrogen loss, which promoted photosynthesis. Similarly, phosphorus and potassium content in seed and haulm were generally highest under the treatment with RDF as basal plus two 2% NPK foliar sprays at 26 and 36 DAS, and were at par with RDF as basal combined with two 2% DAP foliar sprays. The improved P and K uptake may be due to greater dry matter accumulation and increased availability of soil nutrients supplemented by foliar feeding. These results are in agreement with the findings of Suhathiya and Ravichandran (2017), Shashikumar et al. (2013), and Geetha and Velayutham (2009).

Residual soil fertility status

The data on residual soil fertility indicated that the highest residual nitrogen and potassium (195.8 and 303.8 kg ha⁻¹, respectively) were recorded in the treatment receiving RDF as basal along with 2% NPK (19:19:19) sprays at 26 and 36 DAS. This was statistically at par with treatments receiving RDF plus two sprays of 2% DAP or urea, as well as RDF combined with a single spray of 2% NPK or DAP. The highest residual phosphorus (P₂O₅) was observed in the treatment with RDF as basal and two 2% DAP foliar sprays at 26 and 36 DAS, closely followed by RDF with 2% NPK or urea sprays at the same stages. The increased residual nitrogen in the soil may be attributed to enhanced nodule formation. Higher levels of available N, P₂O₅, and K₂O could be due to greater nutrient application and the increased number of nodules per plant, which fixed more nitrogen. These findings are consistent with those reported by Bansal and Ahmad (2015)

Suggestions for further work

It is recommended that this experiment be conducted for at least three years to validate and confirm the present findings.

References

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