Abstract
Earthworm biomass and production in savannas are limited by seasonal precipitation and the lack of organic and nutrient resources; I hypothesize that after a long-term protection of savanna from fire and agricultural activities drastic changes in the physical and chemical characteristics of the soil occur with a concomitant increase in earthworm abundance and activities. Similar changes might occur after a long-term fertilization of savannas with manure. This review article considers the earthworm communities and other soil quality indices in Trachypogon savannas of the Orinoco Basin in an organic agricultural forestal savanna (OAFS) amended with compost over forty years in Puerto Ayacucho, Venezuela, and in an Experimental Station long-term protected (PS) from fire and cattle raising from more than four decades in Central Llanos, Venezuela, comparison is made with results from similar savannas. Long-term additions of organic manure or a long protection have induced significant changes in the soil physical and chemical properties of the natural savanna (NS) soils that induce a significant increase in the density and biomass of earthworm populations. On the other hand, the protection of the savanna promotes an improvement in the physical and chemical properties of the soil, which favors an increase in the density and biomass of earthworms in the PS compared with the NS subjected to recurrent burning and grazing. The results emphasize the importance of appropriate organic matter management and the relevance of earthworms in such agroecosystems.
Highlights
The results showed that the earthworm communities had an aggregated dispersion in space, since the ratios obtained were 11, in the case of the members of the Glossoscolecidae located in the organic agricultural forestal savanna (OAFS)
In the case of the protected savanna (PS), the biomass of earthworms registered exceeded the values reported by Decaëns et al [53], Jiménez et al (1998) [4] and Araujo & López-Hernández [5,6] in neotropical savannas, whereas the density of earthworms had a maximum value greater than the results reported by Jiménez et al [4] and Araujo and López-Hernández [6], but lower than the presented by Decaëns et al [53] in a savanna of Carimagua, Colombia
This review article has considered information on the changes in earthworm communities and other soil quality indices in Trachypogon savannas of the Orinoco Basin managed under long-term fertilization and/or protection
Summary
A very important extension of savannas in the north of South America (Llanos of Colombia and Venezuela) are located in dystrophic and well drained soils dominated by grasses such as Trachypogon plumosus Ness., Andropogon sp., and Axonopus sp., locally known as Trachypogon savannas [1]. The information regarding pedofauna communities from tropical savannas is very scarce, we know that their earthworm biomass and production are limited by the seasonal precipitation and the lack of organic and nutrient resources [4,5,6] Despite their predominance on nutrient poor soils, savannas are key production areas in Venezuela, Colombia and Brazil, where agricultural activities have been established and represent a substantial income for their economies. Since earthworm biomass and production in savannas are limited by seasonal precipitation and the lack of organic and nutrient resources, it must be hypothesized that after a long-term protection of savanna from fire and agricultural activities a drastic change in the physical and chemical characteristics of the soil occur with a concomitant increase in biological activity, in earthworm abundance and activities. Venezuela, and in an Experimental Station long-term protected (PS) from fire and cattle raising from more than four decades in Central Llanos, Venezuela, a comparison is made with results from similar savannas, with the earthworm populations of Eastern Llanos in Carimagua, Colombia
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