RESEARCH WORK

Behavior of earthworm communities in two livestock production systems

Saray Sánchez y Marta Hernández

Estación Experimental de Pastos y Forrajes «Indio Hatuey» Central España Republicana, CP 44280, Matanzas, Cuba
E-mail: saray.sanchez@indio.atenas.inf.cu

ABSTRACT

In order to evaluate the behavior of earthworm communities in two livestock production systems (grassland and silvopastoral system), which were managed for cattle fattening and seed production, a study was conducted at the Experimental Station of Pastures and Forages «Indio Hatuey», Matanzas. For the study of the earthworm communities six collections were made. In each of the described areas 40 soil samples were taken, according to the Methodology of the International Research Program «Tropical Soil Biology and Fertility». In the grassland and the silvopastoral system, 297 and 740 organisms were found, respectively. The species Onychochaeta elegans showed higher proportional abundance in the grassland; while in the silvopastoral system three species were found, two of them typical of forest areas: Polypheretima elongata and Onychochaeta windlei; the former showed a higher value, with significant differences as compared to the species found of the Onychochaeta genus. It is concluded that the presence of trees in grasslands contributes to stimulate edaphic organisms, especially earthworms, which play an important role not only by improving soil physical and chemical indicators, but also as stimulators of other organisms.

Key words: Lumbricidae, grasslands, silvopastoral systems.

INTRODUCTION

In recent years the importance of the diversity of the soil biota in the global functioning of the ecosystem has been revalued. In this sense, there are many studies which clearly show the sensitivity of the communities of edaphic organisms to soil management, changes
in cover and vegetation transformation, as well as the deeply negative effect of the disturbances imposed by cultivation systems (De Aquino et al., 2008).

As a result of the above-mentioned facts, certain organisms are considered bioindicators of soil stability and fertility, especially earthworms (George, 2006), and even establish soil status in different land uses.

Earthworms represent the highest animal biomass in most land ecosystems, and where they are abundant they can process through their bodies up to 250 tons of soil per year, per hectare. This enormous work significantly influences the soil physical, chemical and biological properties, and provides these organisms with an essential role in the modification of its structure, in the acceleration of organic matter decomposition and nutrient recycling, which has in turn important effects on the plant communities that live on the soil surface (Domínguez et al., 2009).

Due to the above-expressed elements, the objective of this work was to evaluate the behavior of earthworm communities in two livestock production systems (grassland and silvopastoral system), on a lixiviated Ferralitic Red soil.

MATERIALS AND METHODS

The studies were conducted at the Experimental Station of Pastures and Forages «Indio Hatuey», located between 22º, 48' and 7" latitude north and 81º and 2' longitude west, at 19,01 masl, in the Perico municipality, Matanzas province, Cuba.

The soil on which the experimental stage was conducted is classified as lixiviated Ferralitic Red (Hernández et al., 1999).

Two livestock production systems were evaluated: a conventional system (grass monocrop) and a silvopastoral system, which were under continuous exploitation (ten years) and during that time no cultural works were performed. Each one had its own characteristics, determined by prevailing vegetation, stocking rate and management. Both were managed for cattle fattening and seed production. The main features of each pastureland are indicated below:

- Conventional system (grass monocrop). The floristic composition of this pastureland indicated 80% Panicum maximum; 9,6% natural pastures (Paspalum notatum and Sporobolus indicus); 6% Cynodon nlemfuensis; 2,5% herbaceous legumes and 1,9% uncovered soil.

- Silvopastoral systems with P. maximum cv. Likoni and Leucaena leucocephala cv. Cunningham. In this system P. maximum represented 79,9% of the botanical composition, followed by 8,9% natural pastures (S. indicus and P. notatum); 7,6% C. nlemfuensis and 3,4% herbaceous legumes. The L. leucocephala population was 595 plants ha-1.

The animal stock in both systems was integrated by Zebu cattle in the growth-fattening stage. During the evaluated period the average global stocking rate was 1,2 animal ha-1, with grazing intensities of 50 and 83 animals ha-1 day-1, and pastureland rotations of 54-63 days and 36-45 days in the dry and rainy seasons, respectively.

For the study of the earthworm communities six collections were made, in the two systems, during three years. In each collection 40 25 x 25 x 30 cm monoliths were made, for a total of 240 in each system, according to the Methodology of the International Research Program «Tropical Soils Biology and Fertility» (Anderson and Ingram, 1993), which consisted in the extraction of a transept, which origin spot and direction were randomly determined. The specimens were manually collected in situ in three soil depths (0-10, 10-20 and 20-30 cm) and they were preserved in solution of 4% formalin and 70% alcohol.

The organisms were identified down to the lowest possible level, and the keys proposed by Brinkhurst and Jamieson (1971) and Sims (1980) were used. The classification from the functional point of view (epigeous, anecic and endogeous) was made according to the recommendations made by Lavelle (1997). The proportional abundance (%) was calculated for each taxon, by means of the relationship between the quantity of individuals that belonged to a taxonomic group and the total of individuals of all the taxonomic groups.

In each sampling spot soil samples were taken in each depth. After being air-dried, they were passed through a 0,5 mm-mesh sieve and the OM and N content was determined through techniques of the AOAC (1995), phosphorus was found by means of the method proposed by Oniani (1964); Ca and Mg were determined by the techniques suggested by Paneque (1965) and the pH was found through the potentiometric method.

For the information processing a simple classification lineal model was used according to the statistical program INFOSTAT 2001, version 1.

RESULTS AND DISCUSSION

In the studied systems a total of 1 037 organisms were found (297 in the grassland and 740 in the silvopastoral system), belonging to the phylum Annelida, class Oligochaeta (table 1).

The three species found corresponded to endogenous organisms and 100% are mesohumic, that is, they live in the soil and feed from organic matter or (dead or live) roots. Due to the low amount and quality of nutritional resources, they must select particles richer in C and have to ingest higher soil quantities to feed, for which they produce wide galleries and abundant excreta of different size and physical-chemical and biological composition. The galleries can be very deep and represent an important part of macroporosity, which causes them to be acknowledged as active excavators, which can enhance the formation of biopores and stable aggregates (Anderson and Ingram, 1993).

Earthworms have been reported by many authors as the prevailing group within the edaphic macrofauna in most livestock production ecosystems, and especially the most humid ecosystems and in pasturelands (Jiménez and Decaëns, 2004; Suthar, 2009).

These organisms, classified by their ecological and functional role as ecosystem engineers, according to Lavelle et al. (1994), make physical changes in the soil which control the availability of resources for other edaphic organisms, including plants and their roots. With their activity engineers create biogenic physical structures that exert a regulating effect on smaller organisms, through: 1) competition for resources, mainly organic matter; 2) activation of the edaphic microflora, through mutualism and the priming effect; 3) their influence on the carbon cycle and nutrient availability; and 4) changes in the rizosphere activity, such as the growth of roots and populations of rizosphere organisms (Lavelle, 1997; Brown et al., 2001).

The different earthworm species respond differently to the system used. Figure 1 shows the proportional abundance of the species found in the grassland. The species Onychochaeta elegans had higher proportional abundance, and highly significant differences with regards to Polypheretima elongata.

This species was also found by several authors in grass monocrop (Cabrera, 2006; Feijoo et al., 2007), and they say it is an indicator of highly disturbed environments, for example, of crops with use of chemical inputs or pasturelands without shade.

On the other hand, in the silvopastoral system (fig. 2) three species were found, from them two were typical of forest zones: P. elongata and Onychochaeta windlei; the former showed a higher value, with significant differences as compared to the species found from the genus Onychochaeta.

According to Fragoso et al. (1999), the structure of earthworm communities is determined by several hierarchical factors, such as temperature in the higher level, followed by edaphic (nutritional status, texture, etc.) and environmental factors (seasonal variation).

In this study, the differences between systems could have been related to the best environmental conditions, mainly temperature and humidity, which is favored by the presence of trees in the silvopastoral system, the quantity of litter accumulated on the soil, as well as its nutritional status.

When analyzing the chemical composition of the soil in both systems (tables 2 and 3) a more favorable behavior of the indicators was found in favor of the silvopastoral system, with an organic matter content between 4,06 and 4,53%; because of a higher nutrient recycling, characteristic of such system.

Calzadilla et al. (1993) stated that as a result of seven years of reforestation and natural regeneration in the silvopastoral system paddocks, the soils improved remarkably and the organic matter content increased from 3,4 to 4,19%, which was similar to what happened in this study.

It is concluded that the presence of trees in pasturelands contributes to stimulate soil organisms, especially earthworms, which play an important role, not only by improving physical and chemical indicators, but also as stimulators of other edaphic organisms.