Pampean Region Research Articles

SELECTING THE TIME OF CONCENTRATION CONSIDERING GROUNDWATER DEPTH AND RUNOFF COEFFICIENT IN THE ARGENTINIAN PAMPA REGION

The time of concentration (Tc) is one of the most sensitive parameters for calculating the maximum runoff in a basin and plays a key role in the determination of design flows. In this work, the consistency of the equations that make up the analytical methods used to estimate the Tc is evaluated through the contrast of observed events from the application of the graphical method in a plain basin located in the Pampa region, Argentina. The methodology used considers the complexity of the runoff generation process and of the water dynamics of the region taking into account the analysis of the groundwater depth and the runoff coefficient. This study shows that the equations available may generate Tc predictions with errors by up to 95% in plain basins. The results indicated that Ventura’s and Pasini’s equations are suitable to determine Tc under water deficit, while Izzard’s and Kinematic Wave equations are appropriate for saturated conditions of the system.

Shallow lakes under alternative states differ in the dominant greenhouse gas emission pathways

AbstractOver the past decades, shallow lakes of the Pampean Plain, Argentina, have been shifting from clear vegetated to turbid phytoplanktonic states due to anthropic pressures. It is not clear, though, if this change in state also involves a change in the overall CO2 and CH4 balance of these lakes. Therefore, the main objective of this work was to assess potential differences in the C gas (CH4 and CO2) balance of shallow lakes under contrasting states—clear vegetated and turbid phytoplanktonic. We sampled two clear and two turbid shallow lakes in the Pampean region along an annual cycle and we measured all of the major C gas emission pathways: diffusive and ebullitive fluxes and also emissions from emergent vegetated habitats. CO2 and CH4 diffusive, ebullitive and vegetated habitat fluxes were comparable between states, but they differed in their relative contribution to the C gas balance because of differences in the coverage of the habitats associated to these pathways. Mean annual, area‐weighted CO2 and CH4 fluxes of clear lakes were 41.9 ± 19.0 and 15.4 ± 18.5 mmol m−2 d−1, respectively, and 7.7 ± 7.3 and 17.9 ± 19.8 mmol m−2 d−1 for CO2 and CH4 fluxes, respectively, for turbid lakes. Despite major differences in the relative contribution of the emission pathways between states, there was a remarkable convergence between states in total greenhouse gas emissions when expressed in terms of mean annual CO2 equivalent greenhouse gas flux.

Direct and indirect nutritional factors that determine reproductive performance of heifer and primiparous cows.

Pregnancy rate is a major determinant of population dynamics of wild ungulates and of productivity of livestock systems. Allocation of feeding resources, including stocking rates, prior to and during the breeding season is a crucial determinant of this vital rate. Thus, quantification of effects and interaction among multiple factors that affect pregnancy rate is essential for management and conservation of pasture-based systems. Pregnancy rate of 2982 heifers and primiparous cows was studied as a function of animal category, average daily gain during the breeding season, stocking rate, pasture type and body weight at the beginning of the breeding season. Data were obtained from 43 experiments conducted in commercial ranches and research stations in the Pampas region between 1976 and 2015. Stocking rate ranged from 200 to 464 kg live weight ha-1, which brackets values for most of the grazinglands in similar regions. Age at breeding was 14-36 months (24.6±7.5 months); initial breeding weights were 129-506 kg and 194-570 kg for heifers and primiparous cows. Pregnancy rate was modeled with an apriori set of explanatory variables where proximate variables (breed, body weight at start of breeding, weight gain during breeding and category) were included first and subsequently modeled as functions of other variables (pasture type, supplementation and stocking rate). This modeling approach allowed detection of direct and indirect effects (through nutrition and body weight) of factors that affect pregnancy rate. Bos taurus breeds (N = 1058) had higher pregnancy rate than B. Taurus x B. indicus crossbreed (N = 1924) females. Pregnancy rate of heifers and primiparous cows grazing in natural grasslands decreased with increasing stocking rate, but no effect of stocking rate was detected in cultivated and improved pastures. Pregnancy rate increased with increasing average daily gain during the breeding season. Use of cultivated or improved natural pastures promotes higher pregnancy rate, as well as allows an increase in stocking rate at the regional level. Body weight at the start of the breeding season is the primary determinant of pregnancy rates in heifer and primiparous cows.

Impact of exposure to arsenic on the bacterial microbiota associated with river biofilms in the Pampas region

Freshwater contamination by arsenic (As) is a worldwide problem. It may be found in Pampean streams of Argentina at concentrations higher than those recommended by international organizations and stipulated by national regulations. Exposure to high As concentrations causes serious consequences to both human health and the environment. The general objective of this work was to evaluate the effect of As on the biofilm microbiota structure from Naveira stream, Luján, Province of Buenos Aires (Coordinates: 34º34′02″ S 59º03′51″ W). The biofilm collected was cultivated in glass aquaria at different As III concentrations (0, 0.2 and 20 mg / L), inside incubation chambers under controlled conditions (16 h light: 8 h dark and 24 ± 1 °C) and constant aeration for 31 d, with partial water renewal every 9 d. We amplified the hypervariable regions V3 and V4 of the bacterial 16S rRNA gene from biofilm bacterial community samples to determine the diversity and abundance of the different taxa. The taxonomic composition of each sample, the alpha diversity of each treatment and the main metabolic pathways were analyzed. Principal Component Analysis of the present phyla and a Linear Discriminant Analysis of the metabolic pathways was also performed. Significant changes were observed in relation to the taxonomic composition of the bacterial community after exposure to the metalloid. However, this effect was not observed at the low concentration used (0.2 mg / L), which is the one that corresponds to ecologically relevant levels. The significantly affected phyla were Verrucomicrobiota, Acidobacteriota, Patescibacteria, Hydrogenedentes and WPS-2. The relative abundances of the Verrucomicrobiota, WPS-2 and Patescibacteria groups were notably decreased in the treatment with high As, while the Acidobacteria group was increased in both treatments with As. The stream samples showed greater bacterial diversity than those grown in the laboratory without As. Finally, it was possible to characterize the metabolic profile of the biofilm developed under natural conditions in the leaves of the aquatic plant Elodea canadensis in the Naveira stream. In addition, results showed that biosynthesis-related pathways were more abundant at the high As concentration treatment (20 mg / L).

Modeling drought stress impacts under current and future climate for peanut in the semiarid pampas region of Argentina

In the semiarid pampas region of Argentina, peanut ( Arachis hypogaea L.) crop undergoes frequent and unpredictable drought stress periods, with high probability of occurrence under future climate change projections. However, the overall frequency of occurrence and timing of different drought stress patterns under current and future climates has not been well investigated for the main peanut region in central Argentina. The aims of this study were to: (i) define the main peanut drought stress patterns and their occurrence (frequency) during the peanut growing season, via a crop growth modeling approach, (ii) test seed yield stability of the formerly defined (in i) drought stress patterns under future climate scenarios, and (iii) analyze the effect of sowing dates on peanut seed yield as a management strategy to mitigate the impact of future climate scenarios for peanut seed yield in the semiarid pampas region of Argentina. The APSIM-peanut growth model was calibrated and validated for local genotypes and production environments. Our study simulated seasonal drought stress patterns at five representative locations across the region under current and future climate scenarios, and tested six sowing dates as a practice to mitigate the impact of climate change. Clustering analysis identified two contrasting environment types (ETs). The high stress ET showed greater frequency of occurrence (>50%) at the southern locations. Future climate conditions increased the frequency of high stress ET by roughly 6% and reduced peanut seed yield by 12%, as average across locations. For both current and future climates, earlier sowing dates maximized peanut seed yield, regardless the locations. Changing sowing date was not an effective practice to mitigate the negative impact of climate change on peanut seed yield. The defined ETs allowed identifying a target population of environments (TPE) having implications for optimizing peanut breeding and management strategies. The projected increase in the frequency of drought stress for all tested locations provides a challenging scenario for sustaining peanut productivity in this region. • The aims were to determine drought patterns under current and future climate, and to test sowing date as a mitigation tool • The defined drought stress patterns changed the frequency across locations, identifying a target population of environments • ·Future climate increased the frequency of drought stress by ~6% and reduced peanut seed yield by ~12% • Sowing date did not mitigate climate change impact. • This study provides insights to optimize breeding and management, and assists policy makers to address climate change.

A New Species of Sprentascaris (Nematoda: Raphidascarididae) in Hypostomus commersoni (Pisces: Loricariidae) from Argentina.

To report a new species: Sprentascaris pampayensis, a Raphidascarididae parasite from the Neotropical region. During a parasitological survey, specimens were collected of a new species of Sprentascaris from Hypostomus commersoni Valenciennes from urban lakes in Santa Fe City, Santa Fe Province, in the Pampean region of Argentina. Morphological and morphometric descriptions, and molecular analyses were performed. The new species, S. pampayensis n. sp., is characterized by having slightly extended lateral wings in both sexes, oral structure with three well-developed lips with double papillae, ventrolateral lips with an amphidial pore. Triangular buccal opening with three well-developed lips with flattened extensions at their bases, which end in a pointed manner towards the back. Males have 17 pairs of preanal papillae, 1 pair of adanal papillae, 3 pairs of postanal papillae and 1odd median postanal papilla located between the first and second pairs, unusual shape of caudal papillae with the central tubular part conspicuously elevated. Females have pre-equatorial vulva, smooth-shelled eggs, and mature embryonated eggs. Sprentascaris pampayensis n. sp. differs morphologically and genetically from S. manherti Petter and Cassone, 1984, S. lanfrediae Melo, Santos, Giese, Santos and Santos, 2011 and S. andersoni Malta, Paiva, Elisei, Tavares and Pereira, 2018. Morphological and morphometric comparison also distinguishes it from S. pimelodi Petter and Cassone, 1984, S. hypostomi Petter and Cassone, 1984, S. marano Ramallo, 2009, and S. saltaensis Ailán-Choke, Ramallo and Davies, 2017. Sprentascaris pampayensis n. sp. is a new parasitic nematode of Hypostomus commersoni.

Coupled socio-ecological changes in response to soybean expansion along the 2001–2010 decade in Argentina

The socio-economic benefits and environmental spillover effects of the international soybean trade have commanded scientific attention in recent years. This is particularly true for exporting countries, where soybean has promoted the replacement of other agricultural productions and also the an also the transformation of native ecosystems. Better understanding of the problem requires spatially disaggregated analysis of these dimensions, with focus on their interactions. This study assessed socio-ecological trends at county scale during the 2001–2010 growing expansion period of soybean cultivation in Argentina. The study sample comprised 126 counties within (1) the Chaco region, one of the largest natural forest regions until the expansion of the agricultural frontier; and (2) the Pampa region, the largest agricultural production area in the country. The relative variation of socio-economic, ecological and agricultural indicators was calculated for examination of patterns of variation and interrelation through uni- and multivariate analyses. Results indicate different patterns and trade-offs among soybean expansion, socio-economic and ecological indicators of soybean expansion, socio-economic and ecological. Soybean expansion, which mainly occurred in the Pampa region, was based on the replacement of other crops and pastures as well as the loss of livestock and ecosystem services provision. At the same time, the expansion of soybean promoted immigration and unemployment, and reduced improvements in alphabetization and growth in economically active population density. The pattern of soybean expansion triggered notable trends, mostly in the Chaco region where they were related to deforestation and rangeland loss. Findings of the study highlight the utility of a coupled approach in revealing socio-ecological patterns that may not be possible through more fragmentary analyses. • Spillover effects of global soybean trade were examined for the Argentine case. • Socio-ecological changes were related to soybean expansion at the county level. • Land use changes triggered indirect effects on social indicators. • Partially coupled socio-ecological changes varied between agricultural regions.

Application of hydrological and hydraulic models to quantify surface runoff in the endorheic system of the La Picasa Lagoon basin

The basins in the plain present particularities from the approach of the hydrological processes that take place there. They are characterized by presenting a predominance of vertical water movements (evapotranspiration-infiltration) over horizontal movements (runoff), showing a strong interrelation between surface and underground water. The La Picasa Lagoon basin is defined as a naturally depressed humid pampa region with an undulating plain relief that has low sectors of temporary flooding and permanent lagoons without a defined drainage network. It is an inter-jurisdictional endorheic basin between the provinces of Córdoba, Santa Fe, and Buenos Aires (Argentina) that has suffered recurrent floods between 2014 and 2017 caused by an increase in the average level of the lagoon reaching historical maximums, producing floods, and affecting infrastructure, transport, and agricultural activity. Due to these problems, through the application of hydrological and hydraulic models, the behavior of La Picasa basin system is quantified and evaluated to avoid future floods. In the present work, a hydrological model is applied using the HEC-HMS free tool and a 1D/2D hydraulic model using the HEC-RAS free tool, where the system of channels and reservoirs that make up the system is considered. The flood marks in reservoirs and La Picasa Lagoon are analyzed, and it is defined as regulating the variation of levels in the different reservoirs within permitted ranges. These models are a useful tool for studying future hydrological situations that may occur around the study area.

New well-preserved materials of Glossotherium chapadmalense (Xenarthra, Mylodontidae) from the Pliocene of Argentina shed light on the origin and evolution of the genus

ABSTRACT Fossil remains of extinct mylodontine sloths have been discovered in numerous localities throughout the American supercontinent, but knowledge of them is still mainly centered on the Pleistocene forms rather than their Neogene relatives. In this contribution, previously unpublished cranial and postcranial materials herein ascribed to Glossotherium chapadmalense (Kraglievich), coming from the Pliocene Chapadmalal Formation (Province of Buenos Aires, Argentina), are presented. These remains are described and compared with those of other mylodontine species from South and North America, providing an exhaustive characterization of cranial morphology in G. chapadmalense and some preliminary insights into its postcranial anatomy. The results have revealed a unique combination of differences and similarities of this enigmatic species with the larger-sized representatives of Glossotherium. In addition, these materials allowed shedding light on the long-standing uncertainties regarding its taxonomic status, as this form has been alternately considered to belong to the genera Glossotherium or Glossotheridium over the last century. As a result, the genus Glossotherium was present, at least, at the Early–Late Pliocene transition in the Pampean region of Argentina, and is recorded by the Upper Pleistocene throughout the entire South American continent. The radiation of the Pleistocene species is associated with a consistent body mass increase that was probably a response to the cooling temperatures and higher predation pressure in South America during the Late Pliocene–Early Pleistocene. These phenomena were probably driven by the stable emergence of the Panamanian Isthmus around 3 Ma and the successive faunal turnover pulses of the Great American Biotic Interchange.

Location matters: survival of artificial nests is higher in small grassland patches and near the patch edge

Nest survival is an important part of breeding success in grassland ecosystems, and the location of nests can determine vulnerability to different predators. We conducted an experiment with artificial nests to evaluate jointly the predation rate on nests at different spatial scales (landscape, patch and tussock) and the relative abundance of potential nest predators (small mammals and birds) in a temperate grassland area. In November 2014 and 2016, we installed 288 artificial nests in Common Pampas Grass Cortaderia selloana grasslands in the southeastern Pampas region, Argentina. The nests were placed in two 10‐ha plots in a continuous grassland patch (c. 900 ha) within a reserve and in two small grassland patches (1.5 and 1.8 ha) in an agricultural matrix (landscape‐scale), at the patch edge and inside the patches (patch‐scale), and at two heights within the tussock grass (tussock‐scale). In 2016, we also conducted live trapping of small mammals and surveyed birds along strip transects at the sampling sites. Nests located in patches within an agricultural matrix and near the edge had greater relative survival than those set in the reserve and inside the patches, respectively. This might be explained by the lower relative abundance of small mammals that we found outside the reserve. Artificial nest survival values recorded at the landscape‐scale contrasted with those previously observed for natural nests. Our results could be partly explained by differences in nest density between agro‐patches and those within the reserve. Future studies could also evaluate the role of parental nest defence on nest survival.

Cropping and livestock impacts on surface waters in the Pampas region (Argentina)

The rivers and streams of the cropping and livestock regions of Buenos Aires province (Argentina) contain variable concentrations of pollutants and high concentrations of nutrients that simultaneously affect aquatic ecosystem communities. In the present study, we evaluated the water quality of the Burgos stream and El Tala river (San Pedro, Buenos Aires province) by analyzing chemical contaminants (As, Cu, Pb, Zn, and glyphosate), nutrients (ammonium, nitrate, and phosphate), and algal toxicity bioassays. Surface water was collected at six sampling stations in three months (April and September 2019, and February 2020). By taking into account the percentages of algal growth inhibition (%I), the standard species Raphidocelis subcapitata and a species isolated from the study area, Scendesmus acutus, showed different sensitivities to the water samples, with a maximum %I of 70.64% and 34.62%, respectively. Moreover, algal growth stimulation was observed due to the high nutrient concentrations. A risk quotient (RQ) was applied to evaluate the environmental hazards of the chemical contaminants Cu, Pb, Zn, and glyphosate on the algal populations. According to the RQ values obtained for Pb (1.20 and 3.30) and Zn (1.17 and 2.12), the growth of algal populations could be at risk due to the maximum environmental concentrations measured of Pb (132 µg L-1) and Zn 106 µg L-1). The present study showed the first approach of an environmental risk analysis based on simultaneous determinations of chemical contaminants and laboratory bioassays with algae, using a strain of alga isolated from the aquatic ecosystems studied.

Is Dairy Effluent an Alternative for Maize Crop Fertigation in Semiarid Regions? An Approach to Agronomic and Environmental Effects.

Simple SummaryDairy effluent can be an environmental problem if it is not properly managed. Several application technologies exist for its reuse as a source of nutrients in agricultural crops. Our study provides new information on GHG emissions after the application of dairy effluent through a subsurface drip irrigation system on a semiarid soil of the southern Pampean Region (Argentina). In addition, some edaphic properties are compared with conventional chemical fertilization on the yield of a corn crop, contributing as a proposal for an improvement in agricultural sustainability.The reuse of effluents from intensive dairy farms combined with localized irrigation techniques (fertigation) has become a promising alternative to increase crop productivity while reducing the environmental impact of waste accumulation and industrial fertilizers production. Currently, the reuse of dairy effluents through fertigation by subsurface drip irrigation (SDI) systems is of vital importance for arid regions but it has been poorly studied. The present study aimed to assess the greenhouse gas (GHG) emissions, soil properties, and crop yield of a maize crop fertigated with either treated dairy effluent or dissolved granulated urea applied through an SDI system at a normalized N application rate of 200 kg N ha−1. Fertilizer application was divided into six fertigation events. GHG fluxes were measured during fertigation (62-day) using static chambers. Soil properties were measured previous to fertilizer applications and at the harvest coinciding with crop yield estimation. A slight increase in soil organic matter was observed in both treatments for the 20–60 cm soil depth. Both treatments also showed similar maize yields, but the dairy effluent increased net GHG emissions more than urea during the fertigation period. Nevertheless, the net GHG emissions from the dairy effluent were lower than the theoretical CO2eq emission that would have been emitted during urea manufacturing or the longer storage of the effluent if it had not been used, showing the need for life-cycle assessments. Local-specific emission factors for N2O were determined (0.07%), which were substantially lower than the default value (0.5%) of IPCC 2019. Thus, the subsurface drip irrigation systems can lead to low GHG emissions, although further studies are needed.

A POSSIBLESMILODON(MAMMALIA, FELIDAE) COPROLITE FROM THE PLEISTOCENE OF ARGENTINA

ABSTRACTPleistocene large carnivores from the Pampean Region have been studied almost always based on bone remains. Here we report the first coprolite of a large carnivore from the Late Pleistocene of the Pampean Region, Argentina. The coprolite was found associated with megafauna bone remains and it shows the typical shape and size of a carnivorous mammal, with a length of 240 mm and a maximum diameter of 39.59 mm. The coprolite contains two bones of the autopodium of an artiodactyl, and numerous dermal ossicles of giant terrestrial sloths. The coprolite's composition, size, and shape allow us to discard ursids, canids, and small felids. Ursid and canid feces contain abundant plant remains, which are absent in the coprolite described here. Feces of extant felids are smaller than the coprolite here as they do not exceed 130 mm in length and 30 mm in diameter. Based on size, shape, and bone inclusions, the discovered coprolite may be attributed to the Machairodontinae saber-toothed felid Smilodon. If correctly identified, this coprolite sheds light on predatory habits of Smilodon.

Statistically based soil-climate exposure scenarios for aquatic pesticide fate modeling and exposure assessment in the Pampa Region of Argentina.

Although pesticides are used intensively in Argentina's Pampa region, the possibility of performing an environmental risk assessment (ERA) remains limited due to the absence of readily available databases to run pesticide fate models and the lack of standardized realistic worst-case scenarios. The aim of the present study was to further advance capacities for performing probabilistic ERAs in the Pampa region by dividing and parameterizing the region into functional soil-climate mapping units (SCU) and defining statistically based, worst-case soil-climate exposure scenarios. Results obtained demonstrate that the SCU selected for a specific modeling exercise should depend on the dissociation constant (Kd ) of the pesticide evaluated and whether short- or long-term pesticide fate modeling and risk assessment are needed. Four regionally representative SCUs were specifically identified for modeling the fate of pesticides with low, high, and intermediate values of Kd . Fate modeling of pesticides with an intermediate Kd requires the use of a different SCU for short- versus long-term pesticide modeling, whereas this distinction is not necessary for pesticides with both low and high Kd . The current definition of realistic, worst-case, soil-climate scenarios represents a crucial step toward better pesticide fate modeling and exposure assessment in Argentina's Pampa region. Integr Environ Assess Manag 2023;19:626-637. © 2022 SETAC.

Avian Biodiversity and Frugivory in an Agroecological Cherry Orchard in The Pampas Region of Argentina

La agroecología tiende a beneficiar a la biodiversidad mientras que toma provecho de algunos de los servicios ecosistémicos, como por ejemplo el control natural de plagas. Sin embargo, cuando la biodiversidad y la producción agrícola entran en conflicto, es necesario determinar las causas de las pérdidas previo a tomar medidas de control. Nuestro estudio tuvo como objetivo evaluar la diversidad de aves en un cultivo de cerezas ubicado en Argentina, y analizar las tasas de consumo de frutos de las diferentes especies de aves. Se realizó un total de 82 horas de observación en 35 cuadrantes de 3 m × 3 m durante las cuales se registró la riqueza de aves, el número de individuos por especie y el total de cerezas consumidas por especie. Se consideró la posición de los cuadrantes dentro del cultivo, la forma del árbol y la hora del día. Además, se contabilizó el número total de cerezas en cada cuadrante de 3 m × 3 m y se las clasificó en cerezas con marcas de agua, atacadas por hongos, dañadas por pájaros o sanas. Se observaron un total de 21 especies de aves. El consumo de cerezas fue mayor durante la mañana y en el borde del cultivo. La proporción de cerezas afectadas por hongos fue mayor que la cantidad afectada por aves y agua. Nuestros hallazgos respaldan la idea de que los sistemas agroecológicos brindan refugio a muchas especies de aves con costos bajos para el productor. —O'Connor, T., García, G.Ó. e Isacch, J.P. (2022). Biodiversidad de aves y eventos de frugivoría en un cultivo agroecológico de cerezas en la región Pampeana de Argentina.

Soil structure and glyphosate fate under no-till management in the Pampa region. II. Glyphosate and AMPA persistence and spatial distribution in the long-term. A conceptual model

Glyphosate and AMPA were measured in a no-tilled (NT) soil and in the runoff resulting from the rain simulation carried out after 270 days of the application of the herbicide. Glyphosate concentration was in low values in runoff water but was not detected in the soil. In contrast, AMPA was found only in soil samples (same LOD/LOQ for both molecules). These intriguing results, on the one hand have led us to develop a conceptual model explaining the dynamics of glyphosate in NT soils with strongly developed platy structures resulting from this soil management, and, on the other hand, to underline the requirement of certain methodological precautions when analyzing properties of such stratified surface horizons. In our model, glyphosate was mostly degraded into AMPA although a small part remained adsorbed and trapped in the plates in the upper soil layer. In the field test, platy aggregates were destroyed by the raindrop impacts, glyphosate was washed off and transported in solution or bound to eroded soil particles. Glyphosate was not detected in soil analysis mainly due to the reduced volume of the surface plates in the total sample and, to a lesser extent, some loss of surface soil material during samples preparation due to its high content of roots and plant debris. In contrast, AMPA leached preferentially and became trapped in the micropores of the dense layer. Therefore, its absence in the runoff and its relatively high proportion in the soil would be due to its accumulation and preservation in the lower portion of the A horizon. The long persistence of AMPA would be explained not only by its physical occlusion in small pores preventing microbial accessibility, but also by a low diffusivity of oxygen and water restricting biotic and abiotic degradation processes. It is suggested that an integrative approach considering both the physical behaviour and the architecture of the soil at different scales in the laboratory and in the field, can contribute to understanding the fate of glyphosate and other agrochemicals in NT soils.

Superabsorbent Polyacrylamide Effects on Hydrophysical Soil Properties and Plant Biomass in a Sandy Loam soil

ABSTRACT There is a complicated relationship between land degradation, water efficiency, and crop yield in arid and semiarid regions. In the Semiarid Pampa region, Argentina, land use changes that affected fragile lands (high content of fine sands plus silt and low organic carbon) have decreased soil quality, thus endangering agricultural activities. The use of polyacrylamide (PAM) is an option for increasing productivity and protecting soil resources. However, there is scarce information about superabsorbent PAM on water storage linked to aggregate stability mechanisms in this fragile land. Hydrophysical variables and plant biomass were evaluated in a greenhouse pot experiment. Three factors were analyzed: 1) PAM rates (doses): D0 = 0%, D1 = 0.04%, and D2 = 0.08%; 2) vegetation presence (Festuca arundinacea ssp.): vegetation (+) and vegetation (–) and; 3) water regime: field capacity (FC) and half field capacity (FC/2). After 5 months, the incorporation of superabsorbent PAM had a strong effect on most hydrophysical variables. Storage variables (available water content and easily available water content) were improved mainly by increasing water retention at lower suctions (i.e. large pores). Dose increments regardless of the water regime led to higher plant biomass (P < .05). PAM incorporation enhanced abiotic mechanisms (swelling–shrinkage, cracks formation) and biotic mechanisms (root activity – direct, increment water retention – indirect) acting synergically to increase aggregate stability and water storage. Aggregate stability tests (fast wetting test – FW, slow wetting test – SW, and stirring aggregates after ethanol submersion – Stir) proved to be useful in discriminating stabilization mechanisms of soils, highlighting the effect of PAM incorporation on soil cohesion (Stir). Finally, superabsorbent PAM may contribute to maintain crop yields, leading to soil quality amelioration.

Infectividad micorrícica nativa en suelos de la Región Pampeana con cultivo de soja, diferentes historiales y características edáficas

The expansion of soybean crop in Argentina replaced other crops, extensive livestock and forest ecosystems. It’s unclear whether this has altered native microbial communities that could supply ecosystem services, such as arbuscular mycorrhizal fungi (AMF), symbionts of the roots of most higher plants and known to promote host nutrition and growth, and soil sustainability. However, the magnitude of the contribution by the AMFs depends, in part, on maintaining its abundance in the soil and their potential to form mycorrhizae with roots. Our objective was to analyze variations in mycorrhizal infectivity (IMS50) and in spontaneous arbuscular mycorrhizal colonization (AM) of soybean crops cropped at three agricultural sites from the north of the Pampean Region (Córdoba), in relation to the historical land use (Agricultural [soybeans for more than 60 years], Mixed agricultural-livestock [A-G, soybean in the last 35 years], and Sierras [soybean in the last 20 years]). An in vivo bioassay revealed that the highest IMS50 occurred at the Agricultural and Sierras sites, in relation to the Mixed A-G one, the site with the highest available soil P content. Both the IMS50 and AM negatively correlated with soil P, while IMS50 was negatively associated with sand content, and positively with water, carbon and clay content. A high degree of infective potential by native AMF was detected in soils destined for soybean crop at the Pampean Region with different historical land use. The IMS50 was a more sensitive detection method than the determination of AM colonization in the field. It is concluded that IMS 50 could be used to define agricultural management strategies to maintain/favor native AMF communities.

Assessment of the distribution of Pseudoryzomys simplex (Cricetidae, Sigmodontinae) in the Pampean region, central-east Argentina, in the late-Holocene

Pseudoryzomys simplex (Winge 1887) is a small to medium sized terrestrial oryzomyine rodent (Cricetidae, Sigmodontinae) widely distributed in humid environments of tropical and subtropical lowlands of South America with a marked rainy season. The occurrence of this species in the south-central Pampean region between 4700 and 200 ka cal BP was originally associated with some warm climatic episodes. A later hypothesis points out that P. simplex was a typical element of the Humid Pampa subregion during this period, whose distribution was retracted to the north due to the strong anthropic modifications in the area. To corroborate these hypotheses, the niche of occurrence of P. simplex was calculated to analyse the preferred climatic conditions of contemporaneous and fossil record of the species since 4700 ka cal BP. The derived climatic niche of P. simplex shows a marked preference for areas with seasonality precipitation patterns and tropical/subtropical conditions. Geographical estimations and climatic niches derived revealed a moderate overlapping between contemporaneous and Pampean late-Holocene projection, which in no case includes the localities where fossil data were found. Although a better comprehension of the ecological requirements of the species is necessary to discard a shift in its realized climatic niche, it is probable that P. simplex is able to maintain stable populations under similar conditions to the ones represented by fossil occurrences. The distribution of the species in the Humid Pampa subregion is probably affected by non-climatic factors today which are reducing its contemporaneous realized climatic niche and distorting the derived climatic niches obtained. These results support that this species cannot be considered a reliable palaeoclimatic indicator of more Brazilian conditions in the Humid Pampean subregion during the past.

Cropland Net Ecosystem Exchange Estimation for the Inland Pampas (Argentina) Using EVI, Land Cover Maps, and Eddy Covariance Fluxes

Estimations of Net Ecosystem Exchange (NEE) are crucial to assess the carbon sequestration/carbon source capacity of agricultural systems. Although several global models have been built to describe carbon flux patterns based on flux tower data, South American ecosystems (and croplands in particular) are underrepresented in the databases used to calibrate these models, leading to large uncertainties in regional and global NEE estimation. Despite the fact that almost half of the land surface is used worldwide for agricultural activities, these models still do not include variables related to cropland management. Using enhanced vegetation index (EVI) derived from MODIS imagery (250 m) and monthly CO2 exchange from a 9-year record of an eddy covariance (EC) flux tower in a crop field in the Inland Pampas region, we developed regression models to predict monthly NEE. We tested whether including a term for crop identity/land cover as a categorical variable (maize, soybean, wheat, and fallow) could improve model capability in capturing monthly NEE dynamics. NEE measured at the flux tower site was scaled to croplands across the Inland Pampa using crop-type maps, from which annual NEE maps were generated for the 2018–2019, 2019–2020, and 2020–2021 agricultural campaigns. The model based solely on EVI showed to be a good predictor of monthly NEE for the study region (r2 = 0.78), but model adjustment was improved by including a term for crop identity (r2 = 0.83). A second set of maps was generated taking into account carbon exports during harvest to estimate Net Biome Productivity (NBP) at the county level. Crops across the region as a whole acted as a carbon sink during the three studied campaigns, although with highly heterogeneous spatial and temporal patterns. Between 60% and 80% of the carbon sequestered was exported during harvest, a large decrease from the carbon sequestration capacity estimated using just NEE, which further decreased if fossil carbon emissions from agricultural supplies are taken into account. Estimates presented in this study are a first step towards upscaling carbon fluxes at the regional scale in a South American cropland area, and could help to improve regional to global estimations of carbon fluxes and refine national greenhouse gas (GHG) inventories.