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Tuesday, 29 May 2007

Chemical Characteristics Of Several Vermicomposts In Mexico

March 4, 2007

By Hernndez, Rufo Snchez; Chaparro, Vctor M Ordaz; Valdes, Gerardo Sergio Benedicto; Lpez, David J Palma; Boln, Judith Snchez

Wastes were collected (cocoa husk, sugarcane bagasse, sugarcane filter cake and bovine manure) in Tabasco State, Mexico. These were vermicomposted, mixed and pretreated for temperature stabilization. The wastes were then vermicomposted with earthworms of the specie Eisenia andrei. Data were collected 60 days after the earthworms were inoculated. The vermicompost obtained was also chemically characterized. The objectives of this study were to evaluate the survival of earthworms (Sv) in several wastes and to assess the capacity of the earthworms to produce vermicompost (Vp). Waste with high C/N ratio had lower Vp, although the Sv was not affected. The C/ N ratio was closely associated with the quality of organic matter (OM); when wastes had high content of nitrogen compounds, the C/N ratio decreased. The integration of cocoa husk in the treatment improved Sv, while the mixture of filter cake and bovine manure (1:1) was the optimum treatment for Vp. Important changes concerning the chemical characteristics of the vermicompost due to the influence of earthworms were not observed.

Introduction

In the region of the Chontalpa, Tabasco, Mexico, the cultivation of cocoa and sugarcane, along with cattle breeding, generate wastes that can be biodegraded through the vermicompost process. This facilitates reincorporation of the wastes into the soil, reducing environmental pollution and providing a benefit.

Earthworms have an important role since they consume these wastes. After digestion, they excrete terricolous worms, characterized by their high microbial load. The total mass of excretions is known as vermicompost. The most prevalent species of earthworms for vermicomposting are Eisenia foetida (tiger earthworm), Eudrilus eugeniae (African earthworm), and Perionyx excavatus (oriental earthworm), and Eisenia andrie. However, Eisenia andrei (red earthworm of California) is the most widely used earthworm due to its efficiency in this process (Capistrn et al. 2001). According to Quintero et al. (1998) and Santamara-Romero and Ferrera-Cerrato (2002), the species of the earthworm, chemical and physical characteristics of wastes and environmental conditions should be considered in a vermicompost system.

The use of earthworms in the compost process has been a controversial issue. The transformation of organic matter (OM) (mineralization and humification) occurs through processes integrating the uninterrupted action of insects, annelids, fungi, actinomicets, and bacteria. Therefore, earthworms are considered to be the organisms attributed to the transformation of OM by physically and chemically changing the wastes which they consume (Kulhnelt and Walker 1961; Haynes et al. 2003). However, the addition of earthworms does not accelerate OM mineralization. The chemical and microbiological characteristics of the compost and vermicompost are also considered similar (Faras et al. 1999; Santamara-Romero et al. 2001).

Faras et al. (1999) recommended the measurement of the cation exchange capacity (CEC) and hydrosoluble ashes to measure maturity. Venegas et al. (2004) reported that CEC and pH indicate the humification degree of compost.

The purpose of this study is to evaluate the performance of Eisenia andrei as a compost-promoting organism in wastes from the southeast of Mexico, as well as to chemically characterize the vermicompost.

Materials and Methods

The most abundant wastes were collected from the agricultural region of Chontalpa, Tabasco, Mexico. The wastes were placed individually and mixed using a precompost process which was divided into two phases. In the first phase, the treatments were placed in 2x15x0.30 m piles. Although the volumes in all the piles were the same, weights were variable since the densities differed among wastes (Table 1). The compost was established in its thermophilic phase where the temperature of the wastes was stabilized at 202C, after having increased to 70C. As part of the control, the moisture was adjusted permanently to 80% by adding water as needed. Samples were taken every third day, oven-dried to 110C for 24 hours, and then gravimetric moisture calculated.

TABLE 1.

Wastes compositions in each mixture.

Aeration was conducted every 8 days and temperature was monitored every third day until the thermal stability of the piles was reached which occurred two months after the precompost preparation (temperature decreased and stabilized). The product obtained was placed in 30x50x15 cm plastic containers and inoculated with 100 adult earthworms of the species Eisenia andrei. This was considered the second phase of the precompost process. As in the first phase, the temperature was monitored and moisture was adjusted to 80%.

The survival of the adult earthworms, 60 days after inoculation in the containers, were quantified and were related to the total worms initially inoculated. The aggressiveness of the materials on the earthworms was verified by a biological test that was conducted on the four wastes used as a base in the formulation of the treatments (Fc for filter cake; Bm for bovine manure; Sb for sugarcane bagasse; and Ch for cocoa husk), assuming that the aggressiveness of every waste was equal or less in the treatments generated from them. This test consisted of filling 247 cm^sup 3^ buckets with the selected wastes and inoculated with 30 worms. Three days after sowing, the live organisms were quantified.

Production of Vermicompost (Vp)

To evaluate Vp, the water supply to the substrate of the containers was suspended until the level of moisture descended to 50% (Caizares et al. 2004). Then, the entire content of the containers was passed through a 2-mm mesh sieve. To determine the compost quantity produced by vermicomposting, treatments (controls where earthworms were not inoculated) were established to identify the amount of material passing through the 2-mm sieve but not corresponding to vermicompost.

Vermicompost Analyses

Cocoa husk (Ch), sugarcane bagasse (Sb), filter cake (Fc) and bovine manure (Bm), were chemically characterized to compare its characteristics at the initiation and at the end of the vermicompost production. At the end of study, the chemical variables were measured in all treatments. The total C contents were measured through analyzer automatic (TOC-5050A C-Analyzer). Total N was determined by Semi-microkjeldahl (Bremmer 1965); pH through suspensions of vermicompost in distilled water (1:1 ratio) (Venegas et al. 2004); Electric conductivity (EC) was measured from suspensions of vermicompost in distilled water (1:4 ratio) (Santamaria-Romero et al. 2001); cation exchange capacity (CEC) in extractions of Ba(Oac)^sub 2^ solutions (Harada and Inoko 1980); and humic and fulvic acids contents in extractions of acids solutions (Kononova 1982). C/N ratio was calculated, Humic acid/fulvic Acid ratio (HA/FA), which Kononova (1982) suggests as an indicator of the humus quality, was determined. Based on each waste dry weight and volume, bulk density was estimated. The experimental design was a completely randomized block, with three replications. The data were subjected to an analysis of variances (ANOVA), and comparison of treatment means by Tukey, using the statistical package SAS for Windows version 6.12.

Results And Discussion

Survival of Earthworms (Sv) and Production of Vermicompost (Vp)

The biological test conducted on filter cake, bovine manure, sugarcane bagasse and cocoa husk indicated that 100% of the inoculated earthworms can survive at least three days after the inoculation. However, after 10 days, the earthworms in this treatment did not survive in the 100% sugarcane bagasse. Therefore, this treatment was excluded from the second phase of this study.

The calculation of the Vp percentage was corrected through a correction factor, according to the following equation:

Vp= ((Mtdv-Mttc)/Tmi)*100

Where:

Vp= Percentage of Vermicompost Production 

Mtdv= Sifted material derived from the vermicompost

Mttc= Sifted material obtained from treatment-control (without earthworms)

Tmi= Total initial material

In 60% of the treatments, the population of earthworms did not increase after 60 days, except in treatments 1 (Fc+Ch), 5 (Sb+Ch), 8 (Fc), and 9 (Ch). In these treatments, the population of earthworms increased in number than the initially 100 inoculated (Figure 1).

In treatments containing some proportion of bovine manure (25%- 100%), the earthworm population was affected negatively whereas treatments where cocoa husk or filter cake was included, the number of earthworms increased, although Vp in the same treatments was low.

FIGURE 1.

Vermicompost production (Vp) and earthworms survival (Sv) during the vermicomposting process. Columns with different letters are statistically different (Tukey &8804;.05). 60 days after of the establishment the earthworms populations.

Increase of bovine manure in the mixtures resulted in Sv decrease, whereas increase in filter cake or cocoa husk had increased Sv (Figure 1). Vp decreased when cocoa husk proportion was increased with the gradual increase of filter cake. When 100% bovine manure was used, Sv and Vp were adversely affected. However, if mixed proportionally (1:1) with filter cake or sugarcane bagasse, the results of Vp were improved (Table 2). These observations \reinforce the investigation of Santamaria-Romero and Ferrera- Cerrato (2002). They reported that the conditions of the substrates determine the appropriate conditions for the survival of earthworms. They also indicate that when the substrates are not favorable, the earthworms suspend the Vp as a survival strategy. Vp was correlated negatively (r=-0.64) by a high total C, whereas the Sv correlated negatively (r=-0.83**) with the increase in electrical conductivity (EC).

TABLE 2.

Vermicompost production (Vp) and earthworms survival (Sv) associated with gradual increase of Filter cake (Fc), Cocoa husk (Ch) and Bovine manure (Bm).

Chemical Characterization of the Vermicompost

According to Edwards and Bater (1992) and Dalzell et al. (1987), the production of vermicompost depends on the enzymatic activity of the organisms present in the feedstock. Many factors affect the biological activity, although the C/N ratio is the most important factor that controls the process rate since the microorganisms demand carbon (C) and nitrogen (N) energy sources to grow and multiply. This C/N ratio should be about 30. If the ratio is higher, the process will require more time for decomposition. If the ratio is lower, mineralization is faster, and nutrients eventually become available, a large amount of N is lost (Capistran et al. 2001).

In this study, the treatment 5 (Sh+Ch) exceeded the limits of C/ N ratio of 30. Treatment 9 (Ch) had the lowest ratio (19.82) (Figure 2). The highest C/N ratio ocurred in treatments derived from Sb, as in the case of treatments 4 (Fc+Sb), 5 (Sb+Ch), and 6 (Bm+Sb), perhaps due to its low N content and its high fiber content. Similar information was reported by Santamara-Romero and Ferrera-Cerrato (2002) with hay, manure, and market waste vermicompost. They indicate that the lack of nitrogenous material, accompanied by the abundance of lignin or cellulose in a waste, causes slow decomposition and limited growth in the population of earthworms.

FIGURE 2.

C/N ratio and HA/FA ratio of several treatments (Columns with different letters are statistically different, Tukey P<0.05).

The treatments with high C/N ratio were also the treatments with the highest total C values, except in treatment 9 (Ch), where a high total C value occurred with a low C/N ratio. This occurred since the treatment had the highest Total-N (Table 3).

According to Fassbender (1982), OM is composed of compounds of biological origin which can be carbohydrates, proteins, and others. When OM is dominated by nitrogenous compounds, the C/N ratio is lower. Therefore, mineralization rate generally increases. However, if carbonate compounds such as the lignin and the celluloses dominate the OM composition, the C/N ratio is higher and it is possible that humification is increased. The humics substances (HS) are the result of compounds from the resynthesis or polymerization of the proteins or carbohydrates which were not mineralized (Veeken et al. 2000). It is the most resistant compound that remains after mineralization. This explains why the treatments, mainly constituted of lignin and cellulose - as in the case of the sugarcane bagasse and cocoa husk - were those which had the highest amount of HS. The HA/FA ratio is an indicator of the quality of humus and waste's humification rate (Kononova 1982). Labrador (1996) suggests that generally, in the compost final phase, the HA/FA ratio value is 1. Therefore, the treatments derived from more resistant materials (for example sugarcane bagasse), had the highest values of the HA/FA ratio (Figure 2). In addition, this index correlates with Nt (r=- 0.63**) and with CEC (r=0.62**), which confirms that the lack of nitrogenous compounds favors polymerization or humification of the wastes and reaffirms, as indicated by Venegas et al. (2004), that humification is a natural process through which SH are formed, and where the reactive functional groups are responsible for the CEC of the compost.

TABLE 3.

Chemical characteristics of feedstock

Treatments with high EC were those derived from wastes with high EC, particularly from bovine manure. The wastes that initially had a high percentage of total C produced treatments with a high total-C content. These were evident from sugarcane bagasse and cocoa husk. The treatments with higher CEC were those which contained cocoa husk.

Bovine manure, in spite of initially highest pH value, had decreased to 5.63. Epstein et al. (1997) attribute this phenomenon to the formation of organic acids with low molecular weight during humification. However, filter cake had a stable pH. According to Stevenson (1994), the pH level can be altered during humification since the abundance of phenolic OH functional and OH alcoholic groups are a source of sites negatively charged to pH>7.0. pH and EC were negatively correlated (r =-0.47^sup **^), for this reason when the organic material is acidic, EC tends to increase, allowing an increase of basic cations such as the Ca^sup 2+^, Mg^sup 2+^, and K^sup +^ (Wolf 1999).

A slight OM decrease occurred in all the wastes (Table 4), which suggests a low rate of decomposition. The decomposition of OM promotes the production of some organic acids which results in decreases in pH. This is observed in both cocoa husk and bovine manure whereas in the case of filter cake, the pH level was maintained.

TABLE 4.

Initial and final chemical characteristics of wastes under vermicomposting.

Except for filter cake, the treatments derived from cocoa husk and bovine manure, had a low EC. This can be due to the solubilization and leaching of some salts as a result of the slight acidification of the wastes for the decrease in the pH. The changes in total-N, C/N ratio, and CEC were as slight as for total C, pH, and EC since the time between the compilation of the wastes and their compilation as vermicompost (3 months), is still insufficient to observe changes in the chemical characteristics of the wastes, regardless of the changes in their physical aspect (size of the particles). Faras et al. (1999) reported that 150 days after an organic material is subjected to decomposition via vermicompost, the activity of earthworms was not evident in the decomposition of OM. Consequently, the microorganisms play an important role in the degradation processes.

Total N is a very important indicator of the resistance degree in a waste degradation, especially since total-N content generally stems from proteins, which are more susceptible to decomposition than carbonated compounds. Total N content resulted in the differences in C/N ratio of the treatments. For cocoa husk, in spite of having high content total C, the C/N ratio was low.

The initial characterization of the wastes indicated that cocoa husk and sugarcane bagasse had the highest C/N ratio. Among the selected wastes, filter cake had the highest CEC, whereas sugarcane bagasse had the lowest value. Venegas et al. (2004) reported that CEC is an evolving indicator due to the OM humification. As for the bulk density of the materials, Sb registered 0.422 Mg m^sup -3^, whereas filter cake had a 1.203 Mg m^sup -3^ density.

EC and pH affect the optimum development of the earthworms. In general, the wastes selected for this study did not affect earthworm development, except bovine manure had pH and EC over 8, which can be harmful to the oligochaeta population growth (Santamara-Romero and Ferrera-Cerrato 2002).

The use of manures in the vermicompost can be variable. Labrador (1996), clarifies that manures are very heterogeneous materials due to the influence of the decomposition degree of the material, type of cattle which they come from, as well as the management provided to the animals and to the manure itself. Therefore, the manure pH heterogeneity allows approximate prediction of the vermicompost pH, only if the manure pH from which it is derived from is known.

Acknowledgements

We thank Fundacin Produce-Tabasco (FUPROTAB) for financing this research. We are also grateful to the Consejo de Ciencia y Tecnologa del Estado de Tabasco (CCYTET) for supporting the publication of this article.

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Rufo Snchez Hernndez1, Vctor M. Ordaz Chaparro1, Gerardo Sergio Benedicto Valdes1, David J. Palma Lpez2 and Judith Snchez Boln3

1. Programa de Edafologa, Campus Montecillo, Colegio de Postgraduados, Edo. de Mxico, Mxico

2. Campus Tabasco, Colegio de Postgraduados, Tabasco, Mxico

3. Instituto Tecnolgico Agropecuario, Tabasco, Mxico

 
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