Pampas Region Of Argentina Research Articles

Effect of indigenous mycorrhizal colonization on phosphorus‐acquisition efficiency in soybean and sunflower

AbstractDespite a general consent about the beneficial contribution of arbuscular mycorrhizal fungi (AMF) on natural ecosystems, there is an intense debate about their role in agricultural systems. In this work, soybean (Glycine max L.) and sunflower (Helianthus annuus L.) field plots with different P availabilities were sampled across the Pampean Region of Argentina (> 150 samples from Mollisols) to characterize the relationship between available soil P and indigenous mycorrhizal colonization. A subsequent pot experiment with soybean and sunflower was carried out to evaluate the effect of P supply (0, 12, and 52 mg P kg–1) and AMF inoculation on AMF colonization and crop responsiveness to P in a Mollisol. Both crops showed high AMF colonization in the field (average: 55% for soybean and 44% for sunflower). While mycorrhizal colonization in soybean was significantly and negatively related to available soil P, no such trends were apparent in sunflower. Also, total biomass was 3.5 and 2.0 times higher in mycorrhizal than in nonmycorrhizal pot‐grown soybean under low‐ and medium‐P conditions, respectively. Sunflower, on the other hand, did not benefit from AMF symbiosis under medium and high P supply. While mycorrhization stimulated P‐uptake efficiency in soybean, the generally high P efficiency in sunflower was not associated with AMF symbiosis.

Performance of Sulfur Diagnostic Methods for Corn

Sulfur availability indicators are necessary for rational use of S fertilizers. There are disagreements, however, about which S diagnostic method provides the best results for many crops. This work evaluates the performance of different S diagnostic methods for corn (Zea mays L.). Five field experiments with different rates of S and sufficiency of other nutrients were conducted in two contrasting areas in the Argentinean Pampas region. Measurements of some soil properties, grain yield, N and S concentration in total biomass, and chlorophyll meter readings (CMR) at upper and middle layers of the canopy were performed. Sulfur application significantly increased grain yield in four of the five experiments. Fertilization with S also increased total biomass, S concentration, and CMR depending on the experiment and crop stage, but rarely N concentration in total biomass. Soil indicators (especially sulfate‐S availability) did not perform well as predictors of S response. Total S concentration and N/S ratio in biomass could be used to help characterize the S nutritional status at physiological maturity, since 89 and 72% of the samples were correctly characterized considering thresholds of 0.0095 g kg−1 and 11:1, respectively. Leaf greenness intensity could have a high potential as a predicting/characterization methodology of corn S status since acceptable linear relationships were found between corn relative yield (RY) and a new sulfur sufficiency index (SSI), based on CMR (R2 = 0.56 and 0.75 for the middle and the upper crop layer, respectively). Further research in areas with high levels of S deficiency will have to be done to validate the findings presented in this study.

Pedotransfer functions to estimate proctor test parameters under different tillage systems

The Proctor test is time-consuming and requires sampling of several kilograms of soil. Proctor test parameters were predicted in Mollisols, Entisols and Vertisols of the Pampean region of Argentina under different management systems. They were estimated from a minimum number of readily available soil properties (soil texture, total organic C) and management (training data set; n = 73). The results were used to generate a soil compaction susceptibility model, which was subsequently validated using a second group of independent data (test data set; n = 24). Soil maximum bulk density was estimated as follows: Maximum bulk density (Mg m-3) = 1.4756 - 0.00599 total organic C (g kg-1) + 0.0000275 sand (g kg-1) + 0.0539 management. Management was equal to 0 for uncropped and untilled soils and 1 for conventionally tilled soils. The established models predicted the Proctor test parameters reasonably well, based on readily available soil properties. Tillage systems induced changes in the maximum bulk density regardless of total organic matter content or soil texture. The lower maximum apparent bulk density values under no-tillage require a revision of the relative compaction thresholds for different no-tillage crops.

Orientation mechanisms and sensory organs involved in host location in a dipteran parasitoid larva

The robber fly Mallophora ruficauda is one of the principal pests of apiculture in the Pampas region of Argentina. Larvae are solitary ectoparasitoids of third-instar scarab beetle larvae. Females of M. ruficauda do not lay eggs on or near the hosts, but on tall grasses. After hatching, larvae are dispersed by the wind and drop to the ground, where they dig and search for potential hosts. It is known that second-instar larvae of M. ruficauda exhibit active host-searching behaviour towards their preferred hosts, i.e., third-instar larvae of Cyclocephala signaticollis. Although host-location seems to be mediated by chemical cues, the mechanism of orientation and the sensory organs involved in host location remain unknown. We carried out behavioural experiments in the laboratory to address these questions. We also tested whether the orientation behaviour is exclusively based on the use of chemical cues. We found that larvae of M. ruficauda detect the chemicals with chemosensilla on the maxillary palps. Only one maxillary palp suffices for orientation, but their bilateral ablation abolishes orientation. Besides, an hexane extract of the host body was as attractive as a live host. Our results support that M. ruficauda larvae find their hosts underground by means of chemoklinotaxis.

A discrete model for estimating the development time from egg to infecting larva of Ostertagia ostertagi parametrized using a fuzzy rule-based system

Ostertagia ostertagi is a nematode, predominantly affecting cattle in the Pampean region of Argentina. A mathematical model parametrized using fuzzy rule-based systems of the Takagi-Sugeno-Kant type (FTSK) for estimating the development time from egg to infecting larval stage L3 of the gastrointestinal parasite O. ostertagi is here proposed. The estimation of development time of O. ostertagi is essential for the generation of appropriate control mechanisms, since this provides information about the time when parasites are ready to migrate to pastures. For the purpose of reflecting the natural environmental conditions, the mean daily temperature is taken as the main and only regulator of the development time. Humidity conditions are considered to be sufficient for the normal development of the larvae. Hence the individual's daily growth is a function of its length and the mean temperature recorded on the previous day. It is expressed in terms of a difference equation with fuzzy parameters, which are defined using laboratory data. Model outputs are tested against results of field experiments. Simulation results are very satisfactory, yielding a mean estimation error (MEE) of 0.64 weeks, with variance 0.34, and a determination coefficient R 2 = 0.74. The model clearly exhibits an inverse relationship between development time and temperature both in controlled and in field conditions. It also exhibits a very sensitive response both to the order in which the temperature sequence occurs, – reproducing the differences observed between spring and autumn – and to the amplitude of the temperature range.

Ethnobotanical study of the rural population in the limits of the Pampa plain (Argentina)

This paper is an ethnobotanical study of cattle farming in the western Pampa region of Argentina, an arid region with very scarce rainfall and a population consisting mainly of Criollo farmers. A total of 68 rural settlers were interviewed, providing information on 69 specific and infraspecific taxa. Plants were classified into the following categories according to use: forage, toxic species or species with adverse effects on animals, use in rural constructions, tools, and those with veterinary applications. Data include native, naturalized and cultivated species. They revealed a diverse group of forage plants, according to the type of livestock, and very few toxic plants. Veterinary applications were related to first aid cases. In rural construction, plants were mostly used for fencing paddocks and corrals. The results of this study show the acute level of perception and detailed knowledge of the plant environment held by this farming community in relation to their main economic activity.

Changes in topsoil bulk density after grazing crop residues under no-till farming

The grazing of crop residues during the winter in integrated crop–livestock systems can either increase soil bulk density (BD) by compaction or decrease BD by swelling, as a function of gravimetric soil water content (GW) during grazing. A field experiment was conducted from 2005 to 2008 to evaluate the BD response to grazing in a no-till silty loam soil (Typic Argiudoll) of the Pampas region of Argentina. Soil BD (core method), GW data and the calculated air volume (AV) were obtained from the 0–50 mm and 50–100 mm layers at different sampling times from ungrazed and grazed treatments. Over most of the study period (2006 through 2008) soil BD showed little impact from grazing, with minimal temporal variation (1.32–1.46 Mg m − 3). This stable behavior was ascribed to low rainfall and relatively low GW values at the time when soil was trampled by livestock and routinely trafficked by machinery. Soil BD in the upper (0–50 mm) layer was significantly (p < 0.001) lower at the beginning of the study (2005 to early 2006), when the rainfall was higher (as was soil GW) during transit periods. Lower BD was not due to soil swelling but to air that was trapped by kneading in response to transit of livestock and machinery. Fitted straight lines indicated that this process became particularly prominent when GW was > 330 g kg − 1 in the ungrazed treatment and GW was > 240 g kg − 1 in the grazed treatments. Grazing accentuated the soil kneading process that promoted air entrapment. Our results suggest in this no-tilled silt loam soil that winter grazing of crop residues caused no deterioration of topsoil porosity in the no-tilled silty loam soil.

Tillage system does not affect soil macrofauna in southeastern Buenos Aires province, Argentina

Soil degradation increased incessantly in the Pampas region of Argentina, due to the intensification of agricultural activities, when carried out with conventional tillage (CT) systems. No-tillage system was adopted as conservation practices by the farmers. The objectives of this study were: a) to determine the macrofauna taxa and their relative abundance under CT and NT in two different seasons; and b) to evaluate soil tillage and seasonal effects on the density of the main macrofauna taxa. The study was conducted from 2002 to 2004 in 46 production farms, in Balcarce, Argentina. Ten soil monoliths (25.2 cm side; 30 cm depth) ramdomly directed field at July-August; and at October-November to determine the number of individuals of macrofauna and Enchytraeidae. Soil macrofauna density did not differ between tillage systems. Oligochaeta Megadrilli density was generally not affected by the tillage system (P&gt;0.05) except in 2004 when it was greater under CT in July-August (P=0.0002). Chilopoda density was greater in soils under NT, with significant differences in 2002 in October-November (P=0.0070). In July-August of 2003 it was higher in CT (P=0.0109). Diplopoda were more abundant only under NT in July-August 2004 (P=0.0010). In July-August a significantly (P

Ecological differences between two sympatric species of armadillos (Xenarthra, Mammalia) in a temperate region of Argentina

Morpho-physiological specialization related to foraging can act as constraints on behaviour and ecological patterns of abundance and distribution. We tested this prediction in two species (weeping or screaming hairy armadillos Chaetophractus vellerosus Gray, 1865 and mulitas Dasypus hybridus Desmarest, 1804) that represent the two subfamilies of armadillos (Dasypodidae, Xenarthra): Euphractinae and Dasypodinae. The first subfamily possesses a well-developed masticatory apparatus that is considered primitive within the Xenarthra, while Dasypodinae show reductions in various aspects of cranial morphology. We sampled signs (burrows and foraging holes) and captured both species on 34 farms randomly selected in the north-eastern Pampas region of Argentina. We analyzed several niche dimensions. The two species showed significant differences in habitat use, seasonal patterns and diet. Weeping armadillos were generalists in their diet and active throughout the year. They were associated with calcareous-sand soil, as expected for a burrowing animal of the deserts. They tolerated a wide range of environmental conditions. We found that mulitas are myrmecophagous, and that they demonstrated a reduction in body temperature and activity during the cold season. As expected from their geographical distribution, mulitas used mainly vegetation with high cover and were associated with humic soils. Niche segregation between the two species of armadillos appeared to originate from different degrees of dietary specialization.

Evaluation of the toxicity of a propolis extract on Varroa destructor (Acari: Varroidae) and Apis mellifera (Hymenoptera: Apidae)

SummaryThe effects of a propolis extract on Varroa destructor and Apis mellifera were evaluated by three different application methods: topical, spraying and oral. A propolis sample was extracted and its organoleptic and physic-chemically traits characterized. These analyses showed that it was a typical propolis from the Pampean region in Argentina, with elevated contents of biologically active compounds. Topical application was carried out by subjecting mites to contact with various propolis concentrations for different periods of time, which resulted in mortality and narcosis. Acaricidal effects were stronger with increasing concentrations of the propolis extracts. Spraying infested bees with a 10% propolis solution was harmless for bees but killed 78% of mites. Feeding infested bees with propolis extract in sugar syrup was not toxic to the mites but caused the death of bees treated with the highest concentration. Our results suggest that the propolis extracts from the Pampean Region could be incorporated into bee colonies by spraying, although the appropriate doses and concentrations to be administered, and the mechanism of action of the extracts on the mites are still to be elucidated.

Dinámicas territoriales pampeanas y microemprendimientos agrarios en sujetos vulnerables

Este trabajo analiza la incidencia de las transformaciones productivas en la región pampeana argentina y, en particular, la provincia de Buenos Aires, en el desarrollo de microemprendimientos agrarios por parte de sujetos sociales vulnerables. La consideración en el interjuego de los factores macro y micro permite extraer conclusiones en relación con ciertos factores que inciden en la viabilidad de dichas iniciativas en los contextos peculiares en que se insertan. Desde otra perspectiva, los procesos de amplio alcance que están influyendo en las áreas estudiadas permiten plantear la limitada capacidad de inclusión del agro pampeano en el contexto de la globalización, en tanto la expulsión de pequeños productores se combina con canales reducidos para posibilitar el ingreso “desde abajo” al sector, como opción ocupacional para quienes experimentan dificultades de inserción en el mercado de trabajo.

Insights to host discrimination and host acceptance behaviour in a parasitoid (Diptera: Asilidae): Implications for fitness

The robber fly Mallophora ruficauda is one of the principal pests of apiculture in the Pampas region of Argentina. As adults they prey on honey bees and other insects, while as larvae they are solitary ectoparasitoids of third instar scarab beetle larvae. Females of M. ruficauda lay eggs away from the host in tall grasses. After being dispersed by the wind, larvae drop to the ground, where they dig in search of their hosts. It is known that second instar larvae of M. ruficauda exhibit active host searching behaviour towards its preferred host, third instar larva of Cyclocephala signaticollis. Although the means by which host location occurs has been studied and since superparasitism is a frequent scenario in the field, no information about host discrimination and host acceptance is available. We carried out studies in the field and behavioural experiments in the laboratory to determine if M. ruficauda is capable of quality host discrimination. We also studied if this parasitoid is capable of conspecific detection in order to avoid superparasitism. Finally, we analyzed the conditions under which superparasitism occurs in the field. We report here that the second instar larva of M. ruficauda is able to discriminate the parasitism status of the host by means of chemical cues, but is not capable of detecting conspecifics prior to attacking a host. We also found that the host cannot detect the presence of the parasitoid by means of chemical cues, so that no counter-defense against parasitism occurs. Furthermore, we determined that superparasitism occurs on the heavier hosts, i.e. those with more abundant resources which could harbor several parasitoid individuals. Finally, we discuss the possible implications of larval host location and host discrimination decisions on the fitness of this parasitoid.

Topsoil Properties as Affected by Tillage Systems in the Rolling Pampa Region of Argentina

Improved topsoil structural quality is expected under no‐till farming, but soil physical constraints can develop under continuous no‐till. Our objectives were: to evaluate the properties of loam, silty loam, and silty clay loam soils under various management practices on a regional scale; to clarify the relationship between soil organic matter pools and soil physical properties; and to find a minimum set of topsoil properties to characterize trends established by tillage. Thirty‐nine loam, silty loam, and silty clay loam soils were sampled from cropped fields managed using conventional tillage (CT) and no‐till (NT) as well as six undisturbed soils (uncropped). The A horizon thickness did not differ among soil textural groups and was 4 cm thicker in uncropped soils. Total and particulate organic C were significantly affected by management (uncropped &gt; CT = NT, P &lt; 0.001). Soil structural instability of uncropped soils (0.317 mm) differed from CT soils (0.723 mm) but not from NT soils (0.573 mm). Soil structural instability was negatively related to total and particulate organic C, and no relation was found with the resistant organic C pool. Water infiltration rate was the only topsoil property affected by a significant texture × management interaction. Lower infiltration rates in NT silty soils were caused by platy structural forms with horizontal pores. Soil penetration resistance (0–5 cm) was 0.77 MPa higher in NT than in CT soils. A minimum set of topsoil properties to evaluate tillage management includes structural instability, total or particulate organic C, infiltration rate, and penetration resistance.

Dipsacus fullonum: an Alternative Host of Sunflower chlorotic mottle virus in Argentina

Abstract Dipsacus fullonum L. is a biennial weed that is widely spread in the Pampean region of Argentina. Plants of this species showing leaf mosaic symptoms were collected near sunflower (Helianthus annuus L.) crops infected with Sunflower chlorotic mottle virus (SuCMoV). Symptomatic plants were tested by biological, serological and molecular assays. Sunflower and Nicotiana occidentalis L. plants mechanically inoculated with extracts from symptomatic D. fullonum leaves developed typical SuCMoV symptoms. Samples were DAS‐ELISA positive when probed with a SuCMoV antiserum. RT‐PCR was used to amplify the whole coat protein gene of the infecting virus. An 807 bp fragment was amplified, cloned and sequenced. The deduced amino acid sequence (EU606023) shared 96% amino acid identity with the SuCMoV sequence (AF255677). These results indicate that D. fullonum mosaic is caused by an isolate of SuCMoV. Thus, this finding has epidemiological relevance as the weed may act as a natural virus reservoir.

Quaternary mammalian faunas of the Pampean Region

Knowledge of the fossil mammals from the Pampean Region of Argentina has greatly increased in recent years. To analyze the patterns of change in regional climates and environments through the Quaternary, the fossil record of land-mammals was used. Two principal factors affected mammalian diversity in the Pampean Region during the Pleistocene: glaciations and the climatic, environmental, and sea-level changes associated with them; and the large numbers of North American taxa that immigrated to South America. From the Pliocene, the regional climatic conditions changed from being warm and wet to being colder, drier, and more seasonal. During the Pleistocene, as a consequence of glacial cycles, cold and dry conditions were interrupted by relatively short warmer and wetter periods. Several pulses of expansion and contraction of steppes and subtropical forests are recorded. This change in habitat produced the provincialism that has characterized the mammal faunas from the Pampean Region. Finally, the most notable characteristic of the Quaternary mammal fauna of South America is the almost complete extinction of large mammals during the latest Pleistocene–earliest Holocene. The evidence presented here is most consistent with a model that explains megafaunal extinction through climatic fluctuations, as it appears that only a few species of large mammals survived until the Holocene. Nevertheless, a human presence could have accelerated the process of extinction.

The earliest record of Neuryurus Ameghino (Mammalia, Glyptodontidae, Hoplophorinae)

Zurita, A.E., Soibelzon, E., Scillato-Yané, G.J. & Cenizo, M., March, 2009. The earliest record of Neuryurus Ameghino (Mammalia, Glyptodontidae, Hoplophorinae). Alcheringa 33, 49–57. ISSN 0311-5518. Among the Pleistocene Cingulata (Glyptodontidae), Neuryurus Ameghino is poorly documented; the only well-characterized species being N. rudis (Gervais), limited to the Ensenadan Age/Stage (early-middle Pleistocene) of the Pampean region in Argentina. The genus is characterized by dorsal carapace osteoderms with uniformly punctate exposed surfaces giving them a rugose, almost spongy aspect; sutures between the osteoderms are loose. Outside Argentina, Neuryurus has been recorded in western Uruguay and southern Brazil. Until now, its temporal range was restricted to the Ensenadan-Lujanian (early Pleistocene–early Holocene). In this context, we present the earliest record of the genus from the San Andrés Formation (Sanandresian Substage; late Pliocene), consisting of dorsal carapace osteoderms and caudal rings and sheath. Most of the associated fauna indicates a dry climate and the assemblage probably characterizes a cold arid event detected at around 2.5 Ma.

Sowing date and nitrogen supply determine the outcome of competition between dallisgrass (Paspalum dilatatum Poir.) and tall fescue (Festuca arundinacea Schreb.) in the Pampas region of Argentina

AbstractThe effects of sowing date and nitrogen (N) fertilizer on the inter‐specific competition between dallisgrass (Paspalum dilatatum Poir.) and tall fescue (Festuca arundinacea Schreb.) in the humid Pampas of Argentina were investigated in two pot experiments where a constant soil moisture content was maintained. Tall fescue and dallisgrass seeds were sown either in the spring (October 2000) or in the autumn (March 2001) in mixed and mono‐specific stands with 0 or 100 kg N ha−1. In the spring, competition from tall fescue depressed dry‐matter (DM) yield of dallisgrass from 1·53 to 0·36 g DM per plant and tiller number from 9·4 to 3·7 tillers per plant in mixed and in mono‐specific stands, respectively, while tall fescue had 3–4 times higher DM yields in mixed stands. Leaf extension rate (LER) of tall fescue was higher (1·3 mm d−1) than that of dallisgrass (0·53 mm d−1). In the autumn, inter‐specific competition did not affect DM yield of dallisgrass and N fertilizer increased DM yield from 0·53 to 2·07 g DM per plant, tiller number from 6·8 to 14·2 tillers per plant and LER at the beginning of autumn from 1·2 to 2·12 mm d−1 in both species. As temperature decreased, LER was reduced in both species to 0·31 mm d−1 by late autumn. The number of leaves per tiller was not affected by treatment. Nitrogen fertilizer increased N concentration of above‐ground tissues of both species (18 g kg−1 DM in autumn and 20 g kg−1 DM in spring). It was concluded that a productive mixed pasture of dallisgrass and tall fescue can be obtained by sowing early in the autumn. The application of N fertilizer in this season is essential to ensure a high herbage yield and quality.

Climate change and wheat production in Argentina

The aim of this work is to assess the impact of past and future climate changes on wheat productivity in the Pampas region of Argentina. The study was based on long-term climatic and crop productivity data, regional climatic scenarios and a crop simulation model. Our results demonstrate that the potential wheat yield has been declining at increasing rates since 1930 mainly due to minimum temperature increases. Further increases in temperature could lead to potential wheat yield reductions of 7.5% for each °C of temperature rise. If the expected effects of CO2 really do occur, the decline of the potential wheat yields due to temperatures that are 2.5°C warmer could be entirely offset by a CO2 concentration of 550 ppm. If the CO2 effects are not considered, rainfed wheat yields could be reduced by 4% by the end of the 21st century (2080), the northern part of the Pampas region being the most affected zone. Inversely, if the CO2 effects are considered, rainfed wheat yield could increase by 14%. Advancing planting dates could be a good strategy to take advantage of new environmental conditions with prolonged frost-free periods.

Bird community responses along urban–rural gradients: Does the size of the urbanized area matter?

Human settlements have a strong influence on bird communities. To explore the size effect of the urbanized area in avian community structure, we examined changes in species richness, composition and abundance along urban–rural gradients of different extensions. We measured land-cover variables and surveyed birds along nine urban–rural gradients in the Pampean region of Argentina. In towns over 7000 inh, increasing constructed area was negatively related to species richness. In towns over 13 000 inh, the abundance of native species decreased towards the urban core whereas total abundance increased, decreased or remained constant depending on town characteristics. In villages (<2000 inh), small (2000–14000 inh) and large towns (>60000 inh), there was a constant representation of the rural community composition along gradients. In towns of intermediate sizes (>14 000–60 000 inh), species composition was more similar to that from the rural zone as this zone was approached. Similarity between both urban-core and peripheral points and the rural zone decreased with increasing gradient extension. It appears to be a size threshold for community sensitivity to urbanization below which the impact on community attributes is insignificant; increasing urbanization above the threshold level had pronounced effects on bird assemblages. Research approaches separating responses of native and exotic species to urbanization enhance our understanding to favor native birds and quality of urban bird communities. The size of the urbanized area is a key factor in policies designed to improve ecosystem health and human interactions with nature.

Growth of individual tillers and tillering rate of Lolium perenne and Bromus stamineus subjected to two defoliation frequencies in winter in Argentina

AbstractThe aims of the experiment were to (i) test whether the higher leaf elongation rate per tiller (LERT) of Bromus stamineus D. than Lolium perenne L. at moderately low temperatures was maintained at high defoliation frequencies and (ii) explore responses in tiller dynamics during the onset of the cool season in the south‐east of the humid Pampas region in Argentina. The following treatments were applied: defoliation frequency at the 3·0‐leaf stage (i.e. one‐leaf lifespan), which is considered optimal, and higher defoliation frequency at the 1·5‐leaf stage (i.e. half‐of‐a‐leaf lifespan). The higher defoliation frequency reduced leaf elongation rate in both the species but it did not affect the leaf appearance rate. This confirms previous studies on several C3 grasses, suggesting a similar pattern of response. Changes in tiller size are proposed as a possible mechanism to explain such long‐term defoliation effects on leaf elongation rates. Responses in tiller production depended on the species considered. The higher defoliation frequency caused a reduction in site‐filling which led to lower tiller production rates in L. perenne but not in B. stamineus. Thus, B. stamineus maintained the advantage in LERT over L. perenne and its tiller production was not affected when defoliated at frequencies higher than those considered optimal.