RESEARH WORK
Characterization of the edaphic mesofauna under different land uses on Ferralitic Red soil of Mayabeque and Artemisa
Ana A. Socarrás1 y N. Robaina2
1Instituto de Ecología y Sistemática.
Carretera de Varona km 3½, Capdevila, Boyeros, C.P. 10800. La Habana, Cuba
E-mail: anameri@ecologia.cu
2Estación Experimental de Plantas Medicinales, Güira de Melena, La Habana, Cuba
ABSTRACT
The study was conducted during October, 2009, in 11 sites of two provinces of the country (Mayabeque and Artemisa), in order to characterize the edaphic mesofauna in different land uses: regenerated forests, pasturelands, sugarcane and crops on Ferralitic Red soil. Three soil samples were taken in each replication of land use, at only one depth level (0-10 cm), following a completely randomized sampling design. For their extraction, Berlese-Tullgren funnels were used, with a light and heat source, for seven days. The highest density values (ind.m-2) for the mesofauna and detritivorous groups were recorded in the forest, followed by varied crops, pastureland and sugarcane. The oribatides/astigmates balance was higher than one in the forest and the pastureland, which indicated soil stability and fertility; while in varied crops the balance was very close to one and it revealed the need of a management change in the agricultural exploitation. In the use sugarcane this ratio was lower than one, which showed disturbance and unbalance of the edaphic environment produced by agricultural practices.
Key words: Indicator organisms, land use.
INTRODUCTION
The intensive exploitation (high input technologies) to which agricultural soils have been subject in Cuba (especially those of ferralitic red composition of the Havana plain) in order to increase the yields and commercial quality of their productions, has caused the loss of their fertility, shown in a high acidity, a remarkable loss of organic matter and a reduction of their structural stability and soil microorganisms which produce the OM transformation. All this indicates that there is great deterioration of the edaphic system, which is manifested in a decrease of agricultural yields, the soil physical, chemical and nutritional properties, the regulation of resources for other organisms and the activation of the edaphic microfauna through mutualist interactions with the rest of the biota.
The mesofauna, as part of the edaphic biota, participates in the decomposition of organic matter, in nutrient acceleration and recycling and in the process of phosphorus and nitrogen mineralization, decisive factors for the maintenance of soil productivity (Usher et al., 2006). Many of the groups that integrate it function as bioindicators of the stability and fertility of the edaphic environment, because they are highly sensitive to climate changes and anthropic disturbances, which cause variations in their density and diversity.
Precisely, due to the ecological role played by the groups of the edaphic biota, as well as the susceptibility they have before changes of their environment and their relation to some physical and chemical features, they are considered bioindicators of soil stability and fertility, even establishing soil status in different land uses (Chocobar, 2010).
The objective of this work was to characterize, through the variation of the edaphic mesofauna components, the conservation status of Ferralitic soils of the Mayabeque and Artemisa provinces with different uses.
MATERIALS AND METHODS
The study was conducted in October, 2009 in the Mayabeque and Artemisa provinces, in four land uses on Ferralitic Red soils (Hernández et al., 1999) following a stratified random sampling protocol. Eleven reference sites were selected in the sampled areas. The studied uses were:
1. Forest or forest vegetation: Three sites were chosen: two semi-deciduous located in Managua (22º56'44.80" N, 82º16'11.07" W) and Nazareno (22º58'05.40" N, 82º14'02.72" W) where timber species prevailed, such as Cordia gerascanthus, Calophyllum inophyllum, Swietenia mahagoni and Cedrela odorata, which herbaceous and shrubby strata allowed the soil to be completely covered; and the other site in Aguacate (22º59'17.90" N, 81º50'01.03" W), with high anthropization and predominance of fruit trees. The herbaceous and shrubby stratum was dispersed.
2. Pasturelands: Two pasturelands were selected. The first one was located in the dairy unit 3 of the Institute of Animal Science (23º00'01.50" N, 82º09'49.10" W), Güines municipality, where the Voisin Rational Grazing system was applied and the prevailing grass was Guinea grass (Panicum maximum) with a 70% soil cover; in addition, large proportions of cattle manure from the stock were incorporated to the soil. The other chosen dairy unit was 025 from Guayabal (22º53'52.10" N, 82º02'08.12" W), San José municipality, without a defined grazing system. The prevailing species were star grass (Cynodon nlemfuensis) and Guinea grass (P. maximum) with 90% soil cover. This area was not subject to any type of additional organic input, except the litter from pastures and the direct contribution of cattle manure.
3. Varied crops: Three areas were selected located in the Güines (22º47'43.60" N, 82º02'31.46" W), Batabanó (22º46'42.40" N, 82º15'08.27" W) and Güira de Melena (22º45'40.50" N, 82º29'21.71" W) municipalities, with a traditional tillage system and electrical spray irrigation, of central pivot. In addition, the full NPK formula with a dose of 1 490 kg/ha and 224 kg of urea/ha were applied, as well as fertigation in three or four applications. The main crop of these areas was potato, which was rotated with sweet potato (Ipomoea batatas), beans (Phaseolus vulgaris) and corn (Zea mays). Weeds were represented by Sorghum halepense and Cyperus rotundus.
4. Sugarcane: Three sugarcane units were sampled, from the Güira de Melena (22º50'24.80" N, 82º26'50.56" W), San Nicolás de Bari (22º46'32.60" N, 81º55'05.90" W) and Madruga (22º58'47.00" N, 81º50'49.24" W) municipalities. The sugarcane varieties used were CP 52-43, C 86-12,
C 323-68 and C 86-56. Gravity irrigation was used, with an adequate land leveling, and the following inorganic fertilization doses were used: N (62,13 kg/ha), P2O5 (25,73 kg/ha) and K2O (82,78 kg/ha). The main weeds were Rottoboellia conchinchinesis and P. maximum.
Sampling of edaphic mesofauna
Three soil samples were taken in each land use replication, at only one depth level (0-10 cm), with a cylinder of 5 cm diameter and 10 cm of depth, following a completely randomized design.
For the extraction of the edaphic fauna, the Berlese-Tullgren funnels were used, with a light and heat source, through the direct action of 40-W fluorescent lamps, for seven days. The individuals were counted and separated under the stereoscope, with the aid of a teasing needle. The collected specimens were preserved in alcohol at 70% and they were identified, by means of the key suggested by Krantz (2009) for mites, up to the order category: Cryptostigmata,or Oribatida, Astigmata, Prostigmata and Mesostigmata. For the Collembola identification the key proposed by Palacios-Vargas (1991) was used, and in the case of Psocoptera, the work of Brusca and Brusca (2003). From the number of individuals the average density values (ind.m-2) were calculated for each taxon in every area. The applied balance or ratio was oribatides/astigmates proposed by Karg (1963), taking into consideration ecological and functioning criteria of the groups involved in such balance.
Statistical data processing
The fauna data were subject to the Bartlet and Kolmogorov-Smirnov tests to prove whether they fulfilled variance homogeneity and normality, respectively. As they did not fulfill these requisites, non parametric analyses were used.
In order to learn if there were differences in the density of the edaphic communities among the areas and determine its variation among the diverse uses, the Kruskal-Wallis test was used; in the cases in which the differences were significant, the Student-Newman-Keuls (SNK) test was used. The statistical processing was made using the package of the automated program TONYSTAT (Sigarroa, 1987).
RESULTS AND DISCUSSION
The average density values of the microinvertebrates oscillated between 28 843 (± 5 019) ind.m-2 in the forest, 19 173 (± 2 987) ind.m-2 in varied crops and up to 10 943 (±4 472) and 9162 (± 3 468) ind.m-2 in the pastureland and sugarcane, respectively. According to the Kruskal-Wallis test, the communities showed highly significant differences (p<0,05) among the studied uses, regarding this indicator. The SNK showed that the mesofauna was more abundant in the forest, followed by varied crops. The lowest abundance was observed in the pastureland and sugarcane, although these uses did not differ among themselves (fig. 1).
In the forest, the communities of edaphic invertebrates were 1,5 times higher as compared to the varied crop use and 2,6 and 3,1 times higher than in the pastureland and the sugarcane, respectively, in terms of density. This behavior could have been due to the predominance of timber and fruit tree species and the quality of the litter produced by them, which shows a lower C/N ratio than other plants, such as grasses (Rodríguez et al., 2002). On the other hand, Marsi and Ryan (2005) stated that an ecosystem is more mature when there is an increase in the values of diversity, richness and percentage of rare taxa. In different studies conducted in Cuba and Mexico, a higher abundance of the components of the soil mesofauna is reported in forest and agroforestry ecosystems than in agricultural ones (Prieto et al., 2005; Socarrás, 2006).
The pastureland showed lower density estimates than the ones reported for the forest and varied crops (fig. 1), but very similar to those of other pasturelands subject to grazing in Cuba, in an agroecosystem of Havana province (Izquierdo et al., 2004). Cole et al. (2006) observed lower densities, which confirm that the higher taxa richness and density depends on the behavior of the species in this medium.
The values reached in the pastureland could have been influenced by the continuous trampling of the animals, because this system had more than half a century of exploitation and 70% of soil cover, with isolated fruit and agroforestry trees which provide shade and a better litter quality. In this study the pasturelands did not have any type of additional organic input, except pasture litter and the direct contribution of cattle manure. This contribution of more stable dead biomass provides a better function in the arrangement of the physical and chemical soil properties, as well as in the establishment and functioning of the edaphic biota in these areas. Organic matter is known to represent the most important quality feature of the soil and influences almost all its properties, and can be disturbed by the use of different agricultural methods (Marsi and Ryan, 2005).
In varied crops there were intermediate values of average mesofauna density, as compared to the other uses (fig. 1). With more than 12 years of agricultural exploitation, these soils were subject to a tillage technique highly aggressive and degrading for the edaphic environment, which had a negative repercussion in its conservation and caused a fast physical, chemical and biological deterioration; in addition, chemical fertilization and noxious products were used to eliminate weeds.
In spite of such situation, generalist taxa were found which developed strategies that allowed them to be present in this adverse environment. The presence of weeds in this use provides a soil cover which decreases the negative effect of agricultural practices, improves the humidity and temperature values in the edaphic environment, besides guaranteeing an additional feeding source to microarthropods produced by the root exudates of weeds. This set of soil improvements accounts for the mesofauna density values reported for this use.
The results were higher than those of other areas with crop rotation practices established in the country, in different agroecosystems (Izquierdo et al., 2004); in this sense, Franklin and Morais (2008) in Brazil and Gizzi et al. (2006) in Argentina found lower values in a study in which conventional and non-conventional methods in corn, soybean, beet, flax and bean crops were compared.
In sugarcane the minimum values of average mesofauna density were observed (fig. 1). These soils received a high rate of chemical fertilizers and intensive tillage for more than 50 years since the species was established; in addition, there was not enough accumulation of a litter and crop residue layer deposited in the field that would guarantee an adequate soil cover.
González et al. (2003) reported higher values than the ones found in this study, in plots with or without plant cover (23 216 and 7 853 ind.m-2, respectively). These results are ascribed to the gradual accumulation of plant remains combined with favorable abiotic factors. In Matanzas, in a study conducted on the same soil type in experimental plots with more than 20 years without agronomic intervention, Robaina (2009) found values three times higher (30 880 ind.m-2) than the ones in this research (9 162 ind.m-2).
The prevailing groups of the pedofauna in the samplìngs made were mites and among them oribatides stood out, followed by gamasines and astigmates; collemboles also reached good representativeness.
The density values calculated for oribatides obtained their maximum in the forest (16 627 ± 1 891 ind.m-2) and differed significantly (p<0,05) from the other land uses. The SNK proved that this group of mites was more abundant in the forest, followed by varied crops (10 349 ± 3 485 ind.m-2) and the pastureland (7 804 ± 451 ind.m-2).The lowest abundance was observed in sugarcane (2 036 ± 509 ind.m-2) (fig. 2).
The conditions for the establishment of these edaphic populations in the forest are guaranteed with higher cover, litter contribution and root exudates, as well as higher humidity, lower temperature, absence of agricultural practices, fertilization and lower anthropic activity.
In Cuba Reyes (2004) reported similar values as the ones found in this study for this group of mites; while Socarrás (2006) reported lower values. The oribatide density constitutes a good indicator, because their different taxa show diverse sensitivity degrees to the disturbances of the edaphic environment (Morais et al., 2010).
Astigmata showed their maximum average density values in the uses destined to varied crops and sugarcane (6 277 ± 2 059 and 3 732,6 ± 378 ind.m-2) (fig. 2), although no significant differences were found among the uses. All of them are subject to the alterations produced in the edaphic environment, due to the continuous and deep cultural practice and the addition of inorganic compounds. According to Vásquez et al. (2007), the high abundance of Astigmata in the soil is interpreted as an indication of low fertility, because they are specific of disturbed soils and behave favorably to disturbance. Prieto et al. (2005) and Socarrás (2006) found lower density values of these mites in plots cultivated in the same soil type.
There was a close relation between the density of oribatides and astigmates, because as one group increased the other decreased (fig. 3). In this study the oribatides/astigmates ratio remarkably favored oribatides in the land uses forest and pastureland, for which these sustained ratios constitute an indicator of balance in the edaphic communities and the surrounding environment. In varied crops the presence of astigmates was close to that of oribatides, and although the latter constituted majority, this warns about the real situation of this land use and allows aiming at more soil-fertility preserving methods. In the use destined for sugarcane the ratio was lower than one, that is, Astigmates prevailed, which indicated a disturbance and unbalance of the edaphic environment and, thus, a decrease of soil fertility produced by agricultural practices.
Another group that is present in all land uses is gamasines, egg predators, immature and adult stages of oribatides, collemboles and other edaphic invertebrates (Salmane and Brumelis, 2010). According to the Kruskal-Wallis test there were no significant differences among them, taking density into consideration. In general, there were similarities in the behavior of this group among uses and its average density values stood out for the forest (2 714 ± 2 227 ind.m-2), because they are active predators of oribatides (fig. 2).
Battera et al. (2006) state that the fluctuations of oribatides and gamasines are in correspondence with the generalized model of interaction between predator and prey. In Cuba in a pastureland and an agroforestry system similar results were found; while in the area destined to crops the values were lower (Socarrás, 2006).
Collembola showed its highest values in the use forest, followed by the pastureland, sugarcane and varied crops (fig. 2). The Kruskal-Wallis test showed significant differences (p<0,001) among the studied uses, regarding density. The SNK indicated that collemboles were more abundant in the forest, which guaranteed the necessary conditions for their establishment. Likewise, those differences were not found among the pastureland, varied crops and sugarcane, which densities were very low and similar.
The average density values of this group found in the forest (5 090 ± 2 059 ind.m-2) doubled those of the pastureland (1 187 ± 545 ind.m-2), were 10 times higher than in sugarcane (509 ± 294 ind.m-2), and 30 times higher as compared to varied crops (170 ± 169 ind.m-2). Díaz et al. (2003) and Guillén et al. (2006) found higher values in the forest in Cuba and Costa Rica, respectively. The average density of collemboles depends, to a large extent, on the conjugation of the factors organic matter and humidity (Karyanto et al., 2008). The existence of abundant vegetation produces high humidity, which is positive for the development of the pedofauna and especially for this group.
In varied crops, sugarcane and pasturelands, González et al. (2003) in Cuba and Guillén et al. (2006) in Costa Rica found higher values than the ones reported in this study; while in the United States, Cole et al. (2006) obtained negative changes in the densities of this taxon in the areas destined to agriculture, due to the loss of niches, lower humidity and tillage. These authors stated that the use of insecticides did not cause the same effect on all Collembola groups.
These apterygotes are known as good indicators of stable areas and with minimum alteration of the edaphon, as they are highly susceptible to the changes in the OM quality and quantity, humidity, temperature and pH; in addition, they have different sensitivity degrees to insecticides and inorganic fertilization (Gulvik, 2007).
When making an analysis of the variation of the mesofauna components in the four land uses, in general, an affectation was observed in the following order: forest, varied crops, pastureland and sugarcane, given by the decrease of their densities. The zoological category indicated the degradation status of Ferralitic Red soils in the different land uses; the best behavior was shown in the forest, followed by pasturelands and, finally, crops.
CONCLUSIONS
