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Vermicompost is obtained by a simple process of decomposition and low-cost ecotechnological transformation (Khatua et al. 2018). It is efficient and can convert organic wastes into value-added products for soil restoration practices (Muñoz-Rojas et al. 2021). Vermicomposting is a viable alternative for the treatment and management of different organic wastes from agricultural and agroindustrial activities (Velasco-Velasco 2018). In the vermicomposting process, the detritivorous capacities of worms are used, as well as the action of their digestive enzymes and the aerobic and anaerobic microflora present in their intestine, which allows the biodegradation of organic wastes (Yuvaraj et al. 2021).
Farm animals produce large amounts of manure, depending on their storage and dispersal. This waste in the soil can cause contamination of the atmosphere and water, so it is necessary to undergo stabilization processes for its agronomic use (Colín-Navarro et al. 2018). The livestock area highlighted for the livestock production of importance in the economy of Putumayo (Urquijo-Pineda 2020 and Riascos-Vallejos et al. 2020). However, the establishment of livestock in the Colombian territory and in the Amazon has a high environmental cost. The loss of natural habitats, the fragmentation of ecosystems and the decrease in soil productivity are among the consequences of the livestock model that currently prosper in Colombia, which contributes to soil degradation and loss of organic matter (Alkharabsheh et al. 2021).
In the Putumayo department, in the agricultural sector, a large amount of waste is generated. The main crops per sown area are banana (Musa paradisiaca), corn (Zea mays), sugarcane (Saccharum officinarum), cassava (Manihot esculenta), peach palm (Bactris gasipaes), cocoa (Theobroma cacao), rainfed rice (Oryza sativa), rubber tree (Hevea brasiliensis), banana (Musa paradisiaca) and beans (Phaseolus vulgaris).
The accelerated growth of the population in urban and peri-urban areas, industrial activity and the intake increase contribute to the important problem of solid waste generation, which are those materials generated in production and intake activities that have not reached economic value (Palomino and Huisa 2021). The management of organic waste through vermicomposting is a biotechnology with great environmental benefits and low cost (Huaccha et al. 2018). In addition, it is an alternative that is framed between the processes of recycling and recovery of organic waste that generates an effect for the environment, and that allows improving the physical, chemical and biological conditions of the soil (Dada et al. 2021).
Composting technologies have been poorly developed on a small scale, and even less under adverse climatic conditions, in terms of moisture, temperature, and excessive rainfall (Nguyen et al. 2022). Make a quality organic fertilizer based on organic waste will allow the farmer to have a more attractive proposal to improve yields, with options for reincorporating organic matter into degraded soils and reducing costs (Martins et al. 2022).
Due to the mentioned, there is also a need to propose solutions to support the comprehensive management of biodegradable solid waste, by proposing treatment methods such as vermicomposting, which allows the transformation of solid waste by biological means under controlled conditions and into products such as fertilizer and substrate. It also takes part in amendments applied in agriculture and in soil bioremediation (Bowman et al. 2021).
The objective of this study was to evaluate in an area of the Amazonian plain the effect of food source on the chemical composition of Californian red worm (Eisenia foetida) vermicompost, in terms of its nutrient composition.
Materials and Methods
This research was developed in “El mochilo” farm, from Centro Agroforestal and Acuícola “Arapaima” SENA. This facility is located in Puerto Asís municipality, Putumayo department, Colombia. It is at an altitude of 256 m o s. l., with an average temperature of 25.3 °C, relative humidity of 85 % and annual rainfall between 3,520 and 4932.8 mm, and corresponds to the tropical humid forest life zone (IDEAM 2020).
Three treatments with three repetitions were established, for a total of 9 experimental units, distributed in random blocks (DRB). Three compost piles corresponded to a block with all treatments: T1) homogeneous mixture (100 %) of fruit and vegetable waste (FV), composed of orange peel, table tomato, long onion, plantain and banana peels in equal proportions; T2) chicken manure (CM) at 100 %; T3) 30 % bovine manure (BM), 35 % chicken manure and 35% FV. Once the normality of data was verified, analysis of variance was performed. To compare the means, Duncan’s (1955) (P<0.05) test was applied. The results were analyzed using the InfoStat statistical package (Di Rienzo et al. 2012).
Precomposting process. A total of 6000 kg of each of the food sources for the worm (fruit and vegetable waste, chicken manure and bovine manure) were collected. They were distributed in piles of 600 kg, which were daily watered with the help of an aerial irrigation system at 1 m from the ground, four times a week. In addition, a weekly turning with a shovel was carried out.
Vermicomposting process. It was carried out in a greenhouse, where nine wooden containers were installed, lined with polyethylene canvas, with dimensions of 1 m long, 0.50 m wide and 0.25 m deep. From each source of the precomposted material, 60 kg were taken, and 20 were placed in each of the boxes destined for each previously randomized treatment. After, the Californian red worm (Eisenia foetida), order: Haplotaxida, family: Lumbricidae) was supplied. Approximately 200 specimens per box were used (Canales-Gutiérrez et al. 2021) for a total of 9 experimental units. The wooden boxes were kept covered with 65 % black polyshade, which made it possible to control high temperatures and protect the red worm from sun exposure.
The pH and temperature were daily measured, which allowed for better control during the process. All the sources were allowed to mature for 21 d, to avoid the presence of pathogens and insect pests. The variables organic matter (OM), carbon-nitrogen ratio (C/N), pH, electrical conductivity (EC), nitrogen (N), phosphorus (P) and potassium (K) were evaluated. According to the chemical analysis methodology, proposed by the soil quality analysis laboratory of "Jorge Tadeo Lozano" University from the biosystems center, N was determined according to Kjeldahl, P by colorimetry, K by atomic absorption; organic carbon by calcination, pH and EC in saturation extract, and the percentage of major elements according to weight to weight ratio.
Results and Discussion
When analyzing the OM, the values for T1, T2 and T3 were 35.61 %, 49.66 % and 42.01%, respectively (table 1). As reported by Trinidad (2018), the percentage of OM obtained through vermicomposting is 40 %, similar to what was recorded in this study for T2 and T3, with the highest values compared to T3, which is probably due to due to the amount of N provided by the manure in the substrates (Fernando and Arunakumara 2021).
The treatment that achieved the highest OM content was T2, since unmixed manure possibly increased OM levels in vermicomposting (Lammertyn et al. 2021b), since it works as a conditioner that protects the soil from erosion, improving its physicochemical characteristics, which allows its structure to be repaired, by increasing water retention, regulating the activity of nitrites and the ability to store and release the nutrients required by plants in a balanced way, such as N, P, K, S and B (Ghorbani and Sabour 2021).
The OM is low in the soils of the Amazonian plain, so when transformed plant waste are applied, such as vermicompost, its fertility increases, by increasing the OM content, in the medium and long term and, with it, the availability of nutrients (González García and Godoy Ponce 2021).
Table 1 Chemical composition of vermicomposting, %
| Treatments | OM | N | P | K |
|---|---|---|---|---|
|
|
35.61b | 1.27 | 0.52b | 1.23a |
|
|
49.66a | 1.43 | 1.10a | 0.55b |
|
|
42.01ab | 1.60 | 0.55b | 1.20a |
| Standard error Significance |
± 2.62 P = 0.0470 | ± 0.16 P = 0.4198 | ± 0.04 P = 0.0005 | ± 0.03 P = 0.0001 |
FV: fruit and vegetable waste
BM: bovine manure
CM: chicken manure
Different letters by columns indicate significant differences (P < 0.05)
For the percentage of phosphorus, T2 obtained significant differences, with a value of 1.10 % with respect to T1 and T3, with figures of 0.52 % and 0.55 %, respectively. Font-Palma (2019) estimates that, on average, the manure contains 0.25 % phosphorus, so possibly the contribution of chicken manure favored the content of this element in T2.
Because it has a higher percentage of P, T2 could become a source for worm feeding, since it acts as a soil conditioner and allows the P content to increase in the final product. This generates an additional value, since this element is in low contents or is little available in the soil (Coban et al. 2022).
Studies conducted by Benjawan et al. (2015) report lower values in P content. According to what they refer, in week 12, for example, they have 0.36 % and they increase in week 16, with 3.06 %. It is used as a base dry garbage, manure, lime, charcoal, green manure and rice husk. The cited authors also obtained K contents of 0.5 % at week 24, lower than those achieved in this study at T1 and T3.
For the percentage of potassium, in T1 and T3, values of 1.23 and 1.20 % were obtained, respectively, with differences with respect to T2, with 0.55 %. Similar studies estimate that, on average, manure contains 0.5 % K (Sepúlveda Casadiego and Mosquera 2021). Other studies show higher values for this element, with the use of cattle manure as a substrate for worm feeding (Ahmad et al. 2021a).
It could be deduced that the content of K decreases, while P increases. The K is higher when the source has fruit and vegetable waste (Lachica et al. 2020) for T1 and T3, whose contents were mostly orange peel, table tomato, long onion, plantain and banana. These last two are in greater proportion.
The amount of K also depends on the interaction between factors, such as added moisture and the amount of waste (Bin Dohaish 2020). Possibly, the amount of fruits and vegetables waste in the sources of treatments T1 and T3, allowed the increase in potassium content. Therefore, the unmixed harvest waste allow obtaining a higher K content, which is why it is possible that T1 obtained significant differences for this variable, compared to the other treatments.
Table 2 shows the indicators that must be additionally measured when vemicomposting is made. When analyzing the C/N ratio, there were no differences in the evaluated treatments. Indeed, Singh et al. (2020) highlight the importance of the C/N ratio, since it is one of the indices that allow studying the speed of decomposition of the substrate during the vermicomposting process. And this is because it represents the loss of organic carbon, as a consequence of the mineralization of its components, and because it measures the increase in the concentration of N, due to weight loss. Values similar to those reported here were obtained by Gudeta et al. (2022), who refer to a C/N ratio of 10.77. Figures below 15 show that it is a stable and mature vermicompost (Nazeri et al. 2021).
Table 2 Indicators of carbon: nitrogen ratio, pH and electrical conductivity in vermicomposting
| Treatments | C/N | pH | EC (dS.m) |
|---|---|---|---|
|
|
13.13 | 8.57 a | 12.72 a |
|
|
16.53 | 7.23 c | 7.03 b |
|
|
12.09 | 8.33 b | 14.47 a |
| Standard error Significance |
± 1.15 P = 0.1071 | ± 0.06 P = 0.0002 | ± 115 P = 0.0221 |
FV: fruit and vegetable waste
BM: bovine manure
CM: chicken manure
Different letters by columns indicate significant differences (P < 0.05)
According to Xavier et al. (2022), microbial activity soon reaches its maximum due to the rapid release of energy and the release of carbon dioxide. Under these conditions, N quickly disappears from the soil, due to the insistent demand by microorganisms to synthesize their tissues, and after a while there is no longer any of this element.Therefore, when degradation occurs in T3, the C/N ratio was the lowest and the N content was the highest, with a value of 1.60 %. This shows that there is possibly an influence of the mixtures from the different sources to obtain a greater amount of N in the vermicompost content (Ferreira et al. 2018).
Table 2 shows the pH values, where it is evident that there were differences between the treatments: T1) 8.57, T2) 7.23 and T3) 8.33. These values agree with those obtained by Vukovi et al. (2021), who affirm that the parameters of a stable vermicompost are between 4.5 and 8.5, it is advisable to keep them above 7 for the control of predators and pests. Also during the process there is a succession with a predominance of different microorganisms, influenced by different factors. One of these is the chemical nature of the substrate, which is digested with greater intensity, according to moisture content, oxygen availability, temperature, C/N ratio and pH. That is why some microorganisms multiply more quickly than others, and predominate in the fermentation medium (Palacios Valenzuela et al. 2021).
The electrical conductivity values presented in table 2 show differences between treatments. It can be said that the chemical properties of vermicompost can be variable, depending on the type, state of decomposition and storage time of the by-products used for its manufacture (Durán and Henríquez 2009 and Ahmad et al. 2021b), which is why, possibly , the values may change depending on the substrate used. From the above, it should be taken into account that one of the product quality criteria is related to the stability of the material, which is determined from the variables pH and electrical conductivity (Santos et al. 2021).
However, the addition of manure increases the pH value, by mixing it with fruit and vegetable waste (Mendez et al. 2018). On the contrary, in this case, the pH was lower in the treatments where animal manure was used. Although possibly this stabilizes during the sanitation process, and it will depend on the type of plant waste that is mixed with the manure.
As mentioned above, the application of organic fertilizers produces an interaction of several microorganisms that biosynthesize different intermediate substances and generate a multienzymatic process that breaks the chains and rings of hydrocarbons, which favors the biorecovery of contaminated soils (Chilon and Chilon 2016).
Not using compost reveals greater environmental impacts, associated with the generation of greenhouse gases (Bernstad-Saraiva-Schott et al. 2016). Vermicomposting is one of the most widely applied technologies for managing biowaste in developing countries, due to its low investment cost, simple operation, and generation of a value-added product (Peralta et al. 2019). Vermicomposting, produced from vegetable waste, bovine manure and chicken manure, has physicochemical and microbiological characteristics that appear in quality standards (Da Costa et al. 2018).
The vermicomposting must have good characteristics, in terms of nutrients richness, as well as it must also inhibit the germination of pathogens. It is an alternative to recycle biodegradable organic solid waste (Suárez-Tapia et al. 2018), transform it into fertilizers for agriculture and avoid its improper disposal. Thus, it becomes a viable alternative for farmers in Colombia and, especially, in Putumayo department (Galindo 2018 and Gunya and Masika 2022).
Conclusions
According to the chemical characterization of the vermicompost obtained in this research from different substrates, it is concluded that it has adequate quality, which could be an alternative for soil improvement.
The research showed that the food source affects the final composition of the vermicompost. A source with a higher content of fruits and vegetables obtained a higher amount of K. On the contrary, higher contents of P and OM were obtained from a source that contained chicken manure.
