Impact of pigeon pea substrate on physico-chemical properties of vermicompost

Introduction

Pigeon pea (Cajanus cajan L. Millsp.), commonly known as red gram, arhar, or tur, is a major legume crop in the tropics, particularly in India. It is predominantly grown during the kharif season, both as a sole crop and as an intercrop, across diverse agroecological conditions. The seeds of pigeon pea contain 21% dietary protein (Sharma et al., 2015) [15] and are rich in essential minerals like phosphorus, magnesium, iron, calcium, sulphur, and potassium (Kunyanga et al., 2013). [9] India ranks first globally, contributing to 82% of the total area and 78% of the total production of pigeon pea. Among Indian states, Maharashtra leads in pigeon pea production with 7 lakh tonnes, followed by Uttar Pradesh, Madhya Pradesh, Karnataka, and Gujarat (Anonymous, 2017) [2] . Pigeon pea's deep root system and drought tolerance make it suitable for areas with low and erratic rainfall. As a leguminous plant, it plays a role in nitrogen fixation, enhancing soil fertility (Cardoen et al., 2015) [3] . However, the common practice of burning pigeon pea stalks for firewood not only affects the environment negatively but also degrades soil quality. Approximately 10.5 million tonnes of pigeon pea stalks could be efficiently utilized for producing organic manure like vermicompost (Sahoo et al., 2021) [14] . The green revolution led to intensive cropping systems that depleted soil organic matter, necessitating increased fertilizer use and resulting in the loss of beneficial soil microorganisms (Singh and Benbi, 2016) [17] . Vermicomposting has been recognized as a rapid, efficient, and cost-effective method to convert crop residues into organic manure. Earthworms act as mechanical mixers, breaking down organic matter, reducing the C:N ratio, and promoting microbial activity (Thakur et al., 2021) [20] . Vermicompost produced through this process contains plant growth regulators, high microbial activity, and pest-repellent properties, making it an environmentally friendly alternative to chemical fertilizers.

Adopting vermicomposting techniques can help farmers manage agricultural costs and reduce reliance on chemical inputs, promoting a greener agricultural practice (Kaplan, 2016) [8] . Epigeic earthworm species, such as Eisenia fetida, are particularly suited for vermicomposting due to their surface activity and ability to decompose organic matter rapidly (Hartenstein and Bisesi, 1989; Viljoen and Reinecke, 1992) [6,22] . This study, conducted at the College of Agriculture, Navsari Agricultural University, Bharuch, aims to evaluate the capacity of pigeon pea stalks for vermicomposting and assess physicochemical properties like pH, EC, Total organic carbon and Moisture content.

Materials and Methods

The study "Impact of pigeon pea substrate on physico-chemical properties of vermicompost" was conducted from May, 2023 to January, 2024 at the College of Agriculture, Navsari Agricultural University, Bharuch, Gujarat, India. The experiment involved various treatments combining cattle dung (CD), pigeon pea stalk (PPS), bacterial biodecomposer consortium (BBC), and the earthworm species Eisenia fetida.

Location and Experimental Site:

The study took place at Bharuch (21°42' N, 72°59' E, elevation 18m), specifically at the Farm Shed of the College of Agriculture.

Materials

Pigeon Pea Stalks and Cattle Dung were sourced from the college farm, dried, chopped, and analyzed for chemical properties. Plastic tubs (50 cm diameter, 30 cm height) were used as vermireactors. Each reactor was layered with cattle dung as bedding, topped with a mix of cattle dung and pigeon pea stalks, reaching a total of 6 kg. Eisenia fetida were collected from vermicomposting unit, college farm. Liquid BBC was bought from Pathology Lab, NMCA, Navsari Agricultural University.

Experimental Procedure

Once the substrate temperature fell below 35 C, 50 adult earthworms were introduced in each of 6 out of 9 treatments. 10 gm/l BBC was applied in each of 6 out of 9 treatments as per experiment. Optimal moisture (70-80%) was maintained, and the reactors were covered with wet jute bags. Manual turning was performed every 15 days, and watering was adjusted to maintain 60-70% moisture after the first month. After 150 days, vermicompost was harvested by stopping watering and separating earthworms. The compost was then sieved and stored. Initial chemical properties of the materials were measured, including pH, EC, organic carbon, CN ratio, and nutrient content as displayed in Table 1. Quality of water used in the experiment was also analyzed as shown in Table 2.

Results and Discussion

Changes in Physico-Chemical Properties 1. pH

The pH ranged from 8.24 to 7.14, with the lowest pH observed in the 50% CD + 50% PPS + 10 g BBC + EE (T8) treatment at both 120 and 150 days. As depicted in figure 1, the highest pH was recorded in the 60% CD + 40% PPS + 10 g BBC (T4) treatment at 30 and 60 days. The decline in pH over time is attributed to the breakdown of organic compounds and the release of humic acids, along with the mineralization of nitrogen and phosphorus into nitrates and orthophosphates. Microbial metabolism likely produced CO2 and organic acids, further lowering the pH, as supported by Haimi and Huhta (1986), Albanell et al., (1988) [1] Elvira et al., (1998) [4] . Furthermore, the pH of feedstocks may have decreased as a result of the bioconversion of organic material into organic acids and intermediates reported by Ndegwa and Thompson (2001) [10] and Patel (2023) [12] . During vermicomposting earthworms maintain the pH in the neutral range by secretion of intestinal calcium and ammonia which neutralizes carboxylic and phenolic groups of humic acids produced during the process reported by Pramanik et al. (2007) [13] . Reduced pH may also result from the addition of H+ ions by microorganisms during the transformation of NH4+-N into NO --N in waste mixtures. (Rai and Suthar, 2020) [19] .

[10] , the precipitation of dissolved salts and the synthesis of soluble metabolites like ammonium (NH +) were the primary causes of the decrease in electrical conductivity. The initial salt content in the wastes was reduced by vermicomposting, when soluble elements were leached out by the excess of water applied reported by Fernández-Gómez et al. (2013) [5] . Similar results were also reported by using biosludge from a beverage industry by Singh et al. (2010) [16] and by using cotton stalk residues by Patel (2023) [12] . In the present experiment, all the treatment showed lowest EC from the threshold value of safer application for soil which was 3.0 dS/m (Soumare et al., 2002) [18] .

TOC

Total organic carbon (TOC) content decreased over time, ranging from 48.13% to 30.28%, as depicted in figure 3. The most significant reduction occurred in the 60% CD + 40% PPS + 10 g BBC + EE (T7) treatment, which decreased to 30.28% at 150 days. The reduction in TOC suggests extensive mineralization of the organic matter, CO2 release, and conversion into more stable humic substances. These findings align with previous research by Viji and Neelanarayanan (2015) [21] on the role of earthworms in enhancing organic matter decomposition. The differences in amount of carbon loss may be attributed to rapid respiration rate of microbes as stated by Suthar (2008) [19] .

Moisture content

Moisture content varied significantly across treatments, influenced by the frequency of watering and the physical activity of earthworms. It is demonstrated in figure 4 that higher moisture content was recorded during the initial stages (30 and 60 days) due to more frequent watering, with levels ranging from 77.94% to 34.68%. The 50% CD + 50% PPS + EE (T2) treatment had the highest moisture content at 30 days, while the lowest was in the 40% CD + 60% PPS + 10 g BBC (T6) treatment at 150 days. Reduced moisture content over time is linked to decreased watering frequency as the compost stabilized. Hossen et al. (2022) [7] stated that cattle manure containing 70% initial moisture would be a good option for vermicomposting.

Conclusion

The study demonstrated that the treatment of 60% CD + 40% PPS + 10 g BBC + EE (T7) significantly improved the organic carbon reduction and maintained favorable moisture levels, reflecting its effectiveness in the vermicomposting process. At 150 days, the lowest electrical conductivity was achieved in the 40% CD + 60% PPS + 10 g BBC (T6) treatment, while the 50% CD + 50% PPS + 10 g BBC + EE (T8) treatment exhibited the lowest pH. The findings indicate that incorporating bacterial biodecomposer consortium and earthworms into specific ratios of cattle dung and pigeon pea stalks enhances the quality and stability of vermicompost. This approach holds promise for sustainable waste management and improved soil amendment practices.

References

1. Albanell E, Plaixats J, Cabrero T. Chemical changes during vermicomposting (Eisenia fetida) of sheep manure mixed with cotton industrial wastes. Biol Fertil Soils. 1988;6:266269.
2. Anonymous. Annual Report 2016-17, Ministry of Agriculture and Farmers Welfare. Available from: agriwelfare.gov.in/Documents/Annual_rpt_201617.pdf. [Accessed on 3rd July, 2023].
3. Cardoen D, Joshi P, Diels L, Sarma P, Pant D. Agriculture biomass in India: Part 1 Estimation and characterization. Resour Conserv Recycl. 2015;102:39-48.
4. Elvira C, Sampedro L, Benitez E, Nogales R. Vermicomposting of sludges from paper mill and dairy industries with Eisenia andrei: a pilot-scale study. Bioresour Technol. 1998;63(3):205-211.
5. Fernández-Gómez M, Díaz-Raviña M, Romero E, Nogales R. Recycling of environmentally problematic plant wastes generated from greenhouse tomato crops through vermicomposting. Int J Environ Sci Technol. 2013;10:697708.
6. Hartenstein R, Bisesi M. Use of earthworm biotechnology for the management of effluents from intensively housed livestock. Outlook Agric. 1989;18:72-76.
7. Hossen M, Khan M, Azad M, Hashem M, Bhuiyan M, Raman M. Effects of moisture content on the quality of vermicompost produced from cattle manure. Bangladesh J Animal Sci. 2022;51(2):40-46.
8. Kaplan M. The National Master Plan for Agricultural Development in Suriname. Final Report. Kaplan Planners Ltd. Regional and Environmental Planning. 2016. p. 255.
9. Kunyanga C, Imungi J, Vellingiri V. Nutritional evaluation of indigenous foods with potential food-based solutions to alleviate hunger and malnutrition. Kenya J Appl Biosci. 2013;67:5277-5288.
10. Lim S, Wu T, Sim E, Lim P, Clarke C. Biotransformation of rice husk into organic fertilizer through vermicomposting. Ecol Eng. 2012;41:60-64.
11. Ndegwa P, Thompson S. Integrating composting and vermicomposting in the treatment and bioconversion of biosolids. Bioresour Technol. 2001;76(2):107-112.
12. Patel S. Management of cotton stalk residues through vermicomposting using the epigeic earthworm. MSc thesis (Unpublished), College of Agriculture, Navsari Agricultural University, Bharuch, Gujarat, India. 2023.
13. Pramanik P, Ghosh G, Ghosal P, Banik P. Changes in organic-C, N, P and K and enzyme activities in vermicompost of biodegradable organic wastes under liming and microbial inoculants. Bioresour Technol. 2007;98(13):2485-2494.
14. Sahoo S, Vijay V, Chandra R, Kumar H. Production and characterization of biochar produced from slow pyrolysis of pigeon pea stalk and bamboo. Cleaner Eng Technol. 2021;3:100101.
15. Sharma S, Gupta R, Bisaria VS. Effect of agricultural amendments on Cajanus cajan (pigeon pea) and its rhizospheric microbial communities-a comparison between chemical fertilizers and bioinoculants. PLoS One. 2015;10(7):e0132770.
16. Singh J, Kaur A, Vig A, Rup P. Role of Eisenia fetida in rapid recycling of nutrients from bio sludge of beverage industry. Ecotoxicol Environ Saf. 2010;73(3):430-435.
17. Singh S, Benbi D. Punjab-soil health and green revolution: a quantitative analysis of major soil parameters. J Crop Improvement. 2016;30:323-340.
18. Soumaré M, Demeyer A, Tack F, Verloo M. Chemical characteristics of Malian and Belgian solid waste composts. Bioresour Technol. 2002;81:97-101.
19. Suthar S. Microbial and decomposition efficiencies of monoculture and polyculture vermireactors based on epigeic and anecic earthworms. World J Microbiol Biotechnol. 2008;24(8):1471-1479.
20. Thakur A, Kumar A, Kumar C, Kiran B, Kumar S, Athokpam V. A review on vermicomposting: By-products and its importance. Plant Cell Biotechnol Mol Biol. 2021;22:156-164.
21. Viji J, Neelanarayanan P. Effect of different animal manure on vermicomposting of mixed leaves litter by utilizing an exotic earthworm. Int J Adv Res. 2015;3(7):1360-1376.
22. Viljoen S, Reinecke A. The temperature requirements of the epigeic earthworm species Eudrilus eugeniae (Oligochaeta) -a laboratory study. Soil Biol Biochem. 1992;24(12):13451350.