Effects of Organic Manure and Recommended Dosage of Fertilizer on Nodulation, Chlorophyll Content of leaves, Availability of Nutrients and Soil Properties Under Greengram [Vigna radiata (L.) Wilczek] Cultivation

In India, pulses are commonly known as food legumes and hold the second position in both production and consumption, after cereals. Greengram, being a vital pulse crop, is rich in carbohydrates-51%, vitamins-3% and minerals. It also provides a significant source of protein content of 25-26%. Being a resilient pulse crop, it contributes approximately 10-12% to the overall pulse production in the country. However low productivity of greengram can be attributed to its cultivation in marginal and sub-marginal soils with poor soil fertility in agro-managements (Saravanan et al., 2013). It is often cultivated as an intercrop and suited for dryland farming. Studies have reported that neglecting fertilizers can have a substantial negative impact on green gram yield (Singh and Sekhon, 2008). Further, the continuous depletion of nutrients poses a significant challenge in achieving sustainable production of crops and greengram is not an exception. In order to promote the growth and yield of greengram, the application of a starter dose of nitrogen is crucial along with bio-organics. Excessive and imbalanced nutrient use has led to nutrient depletion in the soil, decreased crop productivity and ultimately impair soil health (Sachan and Deeksha, 2021). By ensuring an adequate nitrogen supply, the plant’s protein synthesis, chlorophyll production and enzymatic activities can be effectively supported, leading to improved growth and ultimately higher yields in greengram. Organic manures serve as an excellent medium for microbial growth and help sustain an optional nutrient balance, supporting a healthy and productive soil ecosystem (Shariff et al., 2016). Organic manures such as farmyard manure and vermicompost aid in enhancing soil structure, aeration and water retention capacity (Rambuatsaiha et al., 2017). Considering the above facts, the present study was undertaken to evaluate the usage of different organic manures and RDF in greengram for their effects on root nodules, chlorophyll content, availability of nutrients and their uptakes and soil chemical properties.

The field experiment was conducted during rabi and kharif (2022- 23) at the south farm field No. R15, Karunya Institute of Technology and Sciences, Coimbatore. The farm is situated in Western Agro-Climatic zone of Tamil Nadu (10° 56'N and 76°44'E) at an elevation of 474 m above mean sea level. The Greengram variety ‘CO 8’ with a seed rate of 25 kg ha^-1 was sown at a 30 cmx10 cm spacing following pre-sowing irrigation. The experiment was laid out in randomized block design with three replications having nine treatments i.e., T₁: Absolute control, T₂: Vermicompost 100% on N equivalent basis (4 t ha^-1), T₃: Farmyard manure 100% on N equivalent basis (12.5 t ha^-1), T₄: Vermicompost 50% (2 t ha^-1)+Farmyard manure 50% (6.25 t ha^-1), T₅: Vermicompost 75% (3 t ha^-1)+Farmyard manure 25% (3.125 t ha^-1), T₆: Vermicompost 25% (1 t ha^-1)+Farmyard manure 75% (9.375 t ha^-1), T₇: RDF 100% (inorganic) (25:50:25 of N, P₂O₅ and K₂O kg ha^-1), T₈: RDF 50% (inorganic) (12.5:25:12.5 of N, P₂O₅ and K₂O kg ha^-1)+Vermicompost 50% (4 t ha^-1), T₉: RDF 50% (inorganic) (12.5:25:12.5 of N, P₂O₅ and K₂O kg ha^-1)+Farmyard manure 50% (6.25  t ha^-1). Organic manures and RDF were applied as basal in soil (Sand 43.20%, Clay 38.10% and Clay 18.17%). The root nodulation was recorded at 30 and 45 DAS. The total chlorophyll content of leaves was estimated by SPAD chlorophyll meter at 30, 40 and 50 DAS using physiologically active leaves randomly selected from five plants. The estimation of soil pH and EC at 25°C (1:2.5) was estimated by the potentiometric method by Jackson (1973). The pH of the experimental field was 7.6, EC 0.40 dSm^-1 and the organic carbon content was 7.96%. The wet oxidation method by Walkley and Black (1934) was used to estimate the organic carbon. The soil available nitrogen was estimated by the Alkaline Permanganate method as outlined by Subbiah and Asija (1956). The soil available phosphorus was estimated by the method proposed by Olsen et al., (1954). The available potassium content was determined by neutral ammonium acetate extraction method using flame photometer by Stanford and English (1949). The online computer program “OPSTAT,” created by Sheoran et al., (1998) was employed for statistical analysis.
 

Impact of different sources of organic manures and RDF on nutrient uptake of greengram at harvest

The recommended dose of fertilizer (T₇) had the highest uptake of N,P and K and the least was registered in absolute control (Table 1).



Treatment T₇ was at par with T₂ and T₈ and was significantly superior over other treatments for the uptake of nitrogen and potassium. In the case of phosphorous uptake, the treatment T₇ was at par with T₂, T₄ and T₈ and was significantly superior over other treatments. In general, a balanced uptake of NPK nutrients leads to higher plant height, better nodulation, improved growth and yield characteristics and higher-quality greengram harvests (Meena and Varma, 2016).

Impact of different sources of organic manures and RDF on chlorophyll content of leaves
 
Application of vermicompost 100% on N equivalent basis (T2) significantly improved the chlorophyll content of the leaf (Table 2).



The chlorophyll content of the leaves showed a progressive increase from 30 DAS to 50 DAS during both seasons. During the Kharif season chlorophyll content in T₂ was significantly superior over all the other treatments at 30, 40 and 50 DAS, which was on par with T₄, T₅, T₆ and T₈. During rabi season, T₂ recorded higher chlorophyll content at all the stages. At 30 DAS, T₂ was at par with T₃, T₄ and T₅. At 40 and 50 DAS T₂ was at par with T₃, T₄, T₅, T₆ and T₈ treatments. Prasad and Ram (1984) observed that even basal doses of recommendation of fertilizers and seed inoculation with single or multiple strains of rhizobia increased the chlorophyll content of green gram. It is widely accepted that vermicompost enhances the physical, chemical and biological properties of the soil, besides supplying nearly all the necessary nutrients for plant growth and development. Similar results were also reported (Sitaram et al., 2014; Vaithiyanathan and Sundaramoorthy, 2016).
 
Impact of different organic manures and RDF on root nodules
 
The nodule number per plant was significantly influenced by the treatments at 30 and 40 DAS in both seasons. The highest number of nodules per plant were observed in T₂ (19.89 and 19.72 nodules per plant at 30 DAS during rabi and kharif season respectively) which received vermicompost 100% on an N equivalent basis. At 45 DAS, T₂ had about 22.88 (rabi) and 22.71 (kharif) nodules per plant (Table 3).



The use of vermicompost enhanced the production of metabolites and enzymes which might have favored root nodulation. The phosphorus supply from vermicompost and FYM increased root development and increased root nodulation. Singh et al., (2017) and Singh et al., (2022) reported similar findings.

Impact of various sources of organic manures and RDF on soil pH, EC and organic carbon
 
The application of various combinations of vermicompost, farmyard manure and RDF did not influence the soil pH and EC at harvest during kharif and rabi seasons of 2022 (Table 4).



The highest soil pH was under absolute control in both the seasons. The pH was generally low in all the organic treatments though not significantly.
 
The retention of soil pH in plots receiving vermicompost might be attributed to the soil’s improved buffering capacity by the organic matter. In the present study, adding organic manures alone or in combination with the fertilizers brought the pH closer to neutral, but use of organic fertilizers slightly increased soil pH. These results are supported by Kharadi and Bhuriya (2020).
 
Vermicompost 100% on N equivalent basis (T₂) recorded higher soil organic carbon in both seasons (Table 4) followed by T₅. The treatment T₂ was at par with T₄, T₅ and T₆ in both the seasons. The absolute control had the lowest soil organic carbon. The addition of vermicompost alone or in combination with farmyard manure contributed to the improved organic carbon content of soil.
 
Impact of vermicompost, FYM and RDF on soil available nutrients (kg ha^-1) at harvest stage of greengram
 
At harvest, an improved nutritional status was observed in RDF 100% (inorganic) treated plots. Available N, P₂O₅ and K₂O were highest in T₇ (RDF 100% inorganic). In the case of K₂O, T₇ was at par with other treatments barring T₁. The highest nitrogen content (287 kg ha^-1) in the soil after the experiment was observed in T₇ was at par with T₂ and T₈ (Table 5).



The highest P₂O₅ content (19.21kg ha^-1) was observed with T₇ which was at par with T₂ and T₈. The highest available potassium (505 kg ha^-1) was observed in T₇ which was at par with other treatments except the absolute control (T₁). Kharadi and Bhuriya (2020) reported comparable results in their study.
 

A significant increase in the uptake of N, P and K and availability of soil N, P and K after harvest were observed with 100% RDF treatment followed by T₂ (vermicompost 100% on N equivalent basis). The application of vermicompost 100% on N equivalent basis (T₂) enhanced the root nodulation, chlorophyll content and soil organic carbon. However, the treatments could not significantly alter the electrical conductivity and pH of the soil.
 

I hereby certify that none of the authors of the manuscript have any conflicts of interest.