Rolling Pampas Of Argentina Research Articles

Physical properties and organic carbon in no-tilled agricultural systems in silty Pampas soils of Argentina

Context Under continuous long-term no-till farming, many silty soils develop platey and massive compacted structures in topsoil, ascribed to low crop diversification and intense agricultural traffic. Aims We hypothesise that agricultural scenarios of greater diversification and cropping intensity should increase carbon (C) inputs and total and particulate organic C, resulting in the disappearance of these platey and massive compacted structures and soil compaction. Methods The hypothesis was tested in 55 selected production fields (lots or macro-plots of trials with a cultivated area greater than 15 ha) and five non-cultivated sites across the Rolling Pampas of Argentina. The whole area was covered by fine, illitic, thermal, silty loams (Typic Argiudolls, US Soil Taxonomy; Typic Phaeozems, FAO Soil Map). Based on estimations of the crop intensity index (CII; proportion of days in the year with active crop growth) and recent agricultural history of crop sequences, sampled fields were grouped into five categories: soybean (Glycine max) monoculture (CII < 0.45; mean CII = 0.39); low intensity cropping sequence (CII = 0.45–0.60; mean CII = 0.50); high intensity cropping sequence (CII = 0.60–0.80; mean CII = 0.66); pastures for hay bale production (CII = 1.0); and quasi-pristine situations (areas with non-implanted and non-grazed grass vegetation or with negligible stocking rate, CII = 1.0). Key results Total C inputs to soil varied within ~1400–7800 kg C ha−1 year−1 and were significantly and positively related to crop intensity index (P < 0.0001, r = 0.83). The highest (P < 0.05) soil organic C levels were observed in the first 0.05 m of soil and quasi-pristine conditions (even higher than under pasture), and the lowest (P < 0.05) under soybean monoculture. In the 0.05–0.20 m soil layer, quasi-pristine conditions had significantly (P < 0.05) higher soil organic C levels; the other situations did not differ. Soil organic C and particulate organic C levels (0–0.05 m layer) were related to both CII and annual C input. Platey structures and clods >0.1 m (0–0.2 m layer) were negatively related to CII (r = −0.59 and −0.45, respectively; P < 0.0001) and C inputs from crops (r = −0.60 and −0.29, respectively; P < 0.01). Nevertheless, this did not result in soil compaction alleviation, as shown by soil bulk density, maximum penetration resistance and water infiltration variations. About 92% of the samples with soil bulk density above the threshold (1.35 Mg m−3), and about 32% of the total records, presented levels of maximum penetration resistance, aeration porosity and/or water infiltration beyond the values suggested as critical. Conclusions Although soil organic C in topsoil varied as hypothesised, the studied soil physical properties did not. This partially rejects our hypothesis. Implications This study underscores the intricate interplay between crop intensity, SOC enhancement, soil structure improvement and the persistent challenge of subsoil compaction.

Short‐term effects of a severe drought on avian diversity and abundance in a Pampas Agroecosystem

AbstractAgroecosystems are naturally variable at different scales showing strong environmental variations through time and in space. Therefore, temporal dynamics should be taken into account to understand the species‐habitat relationship and provide information for biodiversity management. Droughts are climatic events that introduce variations in environmental conditions by reducing food resources and are increasing in severity and frequency due to global climate change. In 2008, a severe drought occurred in the argentine Pampas, which allowed us to test its short‐term effect on avian diversity patterns according to different land uses. Also, we could test how variations in net primary productivity affected bird populations and explore the usefulness of this ecological process as an indicator of ecosystem service supply applicable to different ecological contexts. We surveyed bird diversity in two consecutive years (2007–2008) in the Rolling Pampas of Argentina, and we assessed environmental attributes at two spatial scales. We explored the relationship between bird diversity and an ecosystem services provision index (ESPI) that uses a proxy of net primary productivity and its intra‐annual variation to test its adequacy in the changing conditions, we conducted our surveys. Results showed that drought affected negatively both species richness and abundance as a consequence of net primary productivity reductions. There was not a clear association of diversity changes with land use, and it is probable that the effect of drought is a complex combination of productivity, land use and spatial scale. ESPI proved robust in front of the environmental changes, and its predictive capacity was better at larger scales. These results are promising for the assessment of ecosystem services provision in a context of global climate changes.Abstract in Spanish is available with online material.

Land use intensification in the Rolling Pampa, Argentina: Diversifying crop sequences to increase yields and resource use

Abstract Increasing and maintaining high productivity levels presents a major challenge facing farmers today and will continue into the near future. More integrative and complex approaches to decision-making, besides adopting new technologies, are necessary for redesigning more productive, stable, and sustainable farming systems. Thus, novel crop sequences should be implemented to improve these properties of farming systems. The aim of our research was to characterize how different preceding crops that open recurrent sequences will impact on the productivity and resource use of the following crops, in order to determine the possibilities of increasing the frequency of double crops in rotations. Three field experiments were conducted under rainfed conditions at three sites in the Rolling Pampas of Argentina. The effects of seven cropping systems on the productivity of succeeding crops were evaluated at each location. The seven cropping systems included five double crops (rapeseed/soybean, wheat/soybean, barley/soybean, field pea/soybean, and field pea/maize) and two single crops (maize and soybean). The seven cropping systems were followed by the same crop sequence: wheat/soybean double crop and maize single crop in the first and second growing seasons, respectively. Radiation use and grain yield, water use and nitrogen uptake were evaluated for each crop in the sequence. Results indicate that repeating cereal crops in the cropping sequence reduces their productivities, while well balanced sequences that include legumes resulted in the highest productivities of cereal crops. Our findings highlight that diversifying cropping systems by adopting different double crops are practical options that can contribute to a more sustainable intensification of cropping systems specialized for grain crops. Increasing crop diversity in sequence influenced nitrogen uptake, among other factors, and may explain the enhanced crop yield in such systems. Our research highlights that crop diversification is critical in designing efficient and sustainable intensified crop sequences.

Rolling Pampas agroecosystem: which landscape attributes are relevant for determining bird distributions?

Agricultural intensification is among the main factors affecting biodiversity. The Rolling Pampas of Argentina have undergone through a process of landscape transformation and agricultural intensification that altered avian diversity patterns. Grassland area loss is argued to be the main reason for grassland bird species declines, but there is a lack of studies that compare cropland vs. pastures including other landscape features as determinants of species richness and distribution. Also, it is needed to understand how these relations are modified at different spatial scales. In this study, we explored how species are associated to different landscape attributes and elements like land use, roadside vegetation, trees, homesteads, and water bodies. Our aim was to explore how bird species are associated to the new elements of the Pampas agroecosystem at different spatial scales to reveal which are important for avian management. We ran field surveys covering a range of land use and landscape complexity, defined by the variety of component features. We performed canonical correspondence and diversity partition analyses to determine the association of species with land use, landscape complexity, and particular anthropogenic elements. Our results show that land use type is an important driver of bird species distributions, but it is also controlled by the presence of trees, houses, and water bodies that provide nesting and food resources. Simple landscapes have higher species turnover rates (beta diversity) than complex ones with similar gamma diversity, demonstrating that the effect of landscape simplification on bird diversity differs across spatial scales, leading to different possible management and conservation strategies. New approaches are needed to manage agroecosystems for avian conservation. We need to take pragmatic approaches, and in highly disturbed ecosystems, anthropic elements have to be included as constituent parts of the system.

A fuzzy logic method to assess the relationship between landscape patterns and bird richness of the Rolling Pampas

The loss of biodiversity in productive ecosystems is a global concern of the last decades. The Rolling Pampas of Argentina is an intensively cropped region that underwent important land use and landscape change, with different impacts on biodiversity of both plants and animals. Land use type and habitat complexity are hypothesized to be the most important factors determining species richness in agro-ecosystems. But it is not easy to define these attributes in an unambiguous fashion, or determine their interactions at different spatial scales. A fuzzy logic approach allows overcoming some of these problems by using linguistic variables and logic rules to relate them and formulate hypothesis. We constructed fuzzy logic models to study how bird species richness in the Rolling Pampas is related to land use and habitat complexity, and how these variables interact at two spatial scales. Results showed that at the local scale, landscape complexity is the most important factor determining species numbers; trees and bodies of water are the most influential complexities. The effect of local scale landscape attributes was modified depending on the context at broader scales, so that agricultural sites were enriched when surrounded by more favorable landscapes. There was a high dispersion in the predicted/observed value relationship, indicating that landscape factors interact in more complex ways than those captured by the models we used. We suggest that the fuzzy logic approach is suitable for working with biological systems, and we discuss the advantages and disadvantages of its use.

The arable plant diversity of intensively managed farmland: Effects of field position and crop type at local and landscape scales

Agro-ecosystem biodiversity is threatened by increasing spatial homogenisation of intensively managed farmland. Yet current understanding of patterns of arable plant diversity at various scales remains limited. We evaluated the extent to which species richness of arable plants in the Rolling Pampas of Argentina is determined by field position (fencerow, edge and centre) and crop type, at both field (local) and landscape scales. Plant richness was assessed in maize, soybean and wheat–soybean fields across four landscape types differing in spatial complexity, as defined by percentage area devoted to cropland. Species richness was hierarchically nested within landscape types, field positions and crop types. Landscape richness (γ-diversity, the cumulative number of species in a set of fields) was additively partitioned into two components, one for local richness (α-diversity, the mean number of species per field) and one denoting differences in species composition among fields (β-diversity, where β=γ−α). Field position was the main determinant of landscape-scale plant richness. Overall, γ-diversity declined from fencerows, through field edges to field centres, but was unaffected by crop type. Spatial variation in species composition (β-diversity), rather than species packing within fields (α-diversity), accounted for most of the variation in arable γ-diversity. Higher β-diversity in field edges than in field centres suggested that propagule dispersal from fencerow vegetation may create a ‘mass effect’ onto certain crop types. Shifts in γ-diversity of major perennial life-forms (chamaeophytes and phanerophytes) between field positions and crop types reflected the contrasting disturbance regimes affecting plant communities of fencerows and cultivated fields. Our results indicate that preserving coherent and extensive fencerow networks is essential to conserve farmland biodiversity. Moreover, maintaining landscape heterogeneity to support elevated β-diversities of arable plants requires cropping systems that promote crop diversity in both space and time.

Landscape complexity differentially affects alpha, beta, and gamma diversities of plants occurring in fencerows and crop fields

Agro-ecosystems still retain part of the original biodiversity, although agricultural intensification threatens to eliminate refuge patches from farmland mosaics. Landscape complexity resulting from networks of uncultivated corridors associated with fencerows may play a key role in sustaining biodiversity across scales, and may further influence diversity in adjacent, cultivated fields. We evaluated the relationship between farmland complexity and plant diversity of fencerows and crop fields at local and landscape scales in the Rolling Pampas of Argentina. We surveyed 222 fencerows and fields cultivated with winter or summer crops, and characterised farmland complexity by the perimeter/area ratio of cropland in 2-km diameter circles surrounding each field. Plant diversity was additively partitioned into alpha, beta, and gamma components. Fencerows had noticeably higher richness than cropped fields at local and landscape scales. Gamma and beta diversities of fencerows and fields were positively related to farmland complexity, supporting the role of spatial heterogeneity in maintaining plant diversity in agro-ecosystems. Landscape complexity did not influence alpha diversity of fencerows but significantly increased diversity within fields, a likely result of enhanced mass effects from uncultivated habitats in more varied farmland. More complex landscapes contained greater gamma diversity of exotic perennials in fencerows, and of exotic and native annuals within fields. Importantly, alpha and gamma diversities of native perennials from the pristine Pampa grassland increased with landscape complexity within cropped fields. In the face of ongoing landscape homogenisation under agricultural intensification, maintaining fencerow networks may become critical for conserving habitat heterogeneity and farmland biodiversity.

Seedbed compaction produced by traffic on four tillage regimes in the rolling Pampas of Argentina

The main function of primary tillage is to increase the soil's structural macro-porosity, but during secondary tillage operations over these freshly tilled soils, traffic causes significant soil compaction. In terms of soil conservation however, there is evidence that direct sowing is a more sustainable system, even though there is still insufficient information about the rheology of a non-tilled soil under traffic. The objective of this study was to compare the traffic intensity and soil compaction caused by four different tillage regimes currently used by Argentinean farmers (1 direct sowing with a tractor and planter weighing 127 kN and 3 conventional tillage systems with equipment weighing 55.2 kN). The work was performed in the east of the Rolling Pampa region, Buenos Aires State, Argentina at 34°25′S, 59°15′W. Variables measured were: (1) cone index in the 0–450 mm depth profile; (2) bulk density; (3) total soil porosity; and (4) rut depth. (a) Results indicated that in the depth range 0–150 mm with all tillage treatments, bulk density and cone index values generated by tractor traffic were greater than the 1.3 Mg m −3 and 1400 kPa respectively. Similarly in deeper layers these parameters were greater than 1.45 Mg m −3 and 2000 kPa respectively. Measurements revealed that traffic reduced topsoil porosity under direct sowing by an average of 7% and under conventional tillage by 7.6–14.8% confirming that both systems cause both topsoil and subsoil compaction.

Foliar diseases affect the eco-physiological attributes linked with yield and biomass in wheat ( Triticum aestivum L .)

Foliar diseases are the main biotic cause of yield loss in wheat crops ( Triticum aestivum L.) in Argentina and other regions around the world. Most of the studies on foliar diseases take a phytopathological perspective, but few studies have analyzed the problem with an eco-physiological approach aimed at the understanding of which crop traits are affected by foliar diseases. The present study was designed to determine the effects of a foliar disease complex (including leaf rust, Septoria leaf blotch and tan spot), on (i) grain yield and (ii) the physiological components of biomass production; intercepted radiation (RI) and radiation use efficiency (RUE), in bread wheat crops growing under contrasting agronomic and environmental conditions (i.e. different cultivars, years, location and nitrogen supply). The experiments were carried out during 4 years in different locations (three in the rolling pampas of Argentina and one in northern of France). Five different commercial wheat cultivars were sown on early (E) and late (L) sowing dates (SD); and two contrasting nitrogen availability and two fungicide treatments (protected and unprotected) were applied. Foliar diseases appeared during the grain filling period and affected both, leaf area duration (LAD) and healthy area duration (HAD) during that period. Foliar diseases reduced both, above-ground biomass at harvest (1533 and 1703 g m −2 for unprotected and protected treatments, respectively) and grain yield (646 and 748 g m −2 for unprotected and protected treatments, respectively) without important effects on harvest index. Biomass reductions after anthesis, due to the effects of foliar diseases, were associated with a reduced capacity of the canopy to absorb solar radiation more than any effect on RUE. However, RUE was consistently lower—when leaf rust was the predominant disease in the crop, suggesting that this biotrophic pathogen could affect the photosynthetic activity at the leaf or canopy level.

Insect communities related to wheat and coriander cropping histories and essential oils in the Rolling Pampa, Argentina

Intensive land use in the Rolling Pampa of Argentina have resulted in a mosaic of fields with different cultural histories creating different soil environments, which interact with crops and cropping activities producing a wide range of habitats for insects. Species and functions in canopy structure, food quality and essential oils of the crop–weed associations may vary depending on the field's cropping history and management (i.e. crops, soil degradation, weeding and fertilization). Species composition and functional structure of insect communities may respond to these changes. We studied insect communities in wheat and coriander crops that differed in their canopy structures, essential oil production, and the cropping histories of the fields on which they grew. For this purpose we planted wheat ( Triticum aestivum L.), and two coriander ( Coriandrum sativum L.) landraces in plots with two levels of weeding and fertilization. The crops were grown in two consecutive years at two locations differing in cropping history and related to this in level of soil degradation. Insects were sampled in all plots at crop full flowering, and were classified and related to agronomic variables and to essential oils using multivariate techniques. Among all the environmental factors tested in this study, year and soil degradation were the main factors explaining insect community structure; and also weed community structure in unweeded plots. The proportion of essential oil components varied with cropping history, suggesting an association among soil properties indicative of soil degradation, plant chemical signals and insect distribution. Although insect community composition varied widely, functional structure was very similar among crop–weed communities. Soil degradation appeared to have affected directly crop–weed communities and insects’ assemblages, since no consistent relationship was found between plant composition and insect community structure. It can be hypothesized that soil degradation might have affected the amount of volatiles produced especially by coriander, generating a “soil degradation scent” that determined the structure in the insect community, and/or the soil itself emitted different signals, in relation to changes in its physical, chemical and biological characteristics.

Emergy analysis of one century of agricultural production in the Rolling Pampas of Argentina

Historically, agricultural production in the Rolling Pampas of Argentina was characterised by low use of synthetic inputs. This changed during the 1990s, with the widespread adoption of technology privileged by neoclassical macroeconomic policies implemented in the same decade. In this paper, Emergy Accounting is used to quantitatively assess the ecological sustainability of agricultural systems in the region throughout the 20th century. Economic deregulation and trade liberalisation have led to an increase in productivity, but have also increased dependency on non-renewable resources. As the ecological and socioeconomic implications of intensification become more controversial, there is an urgent need for integrated, multiscale and multi-disciplinary monitoring and research. Moreover, there is a greater need for a broader, critical and inclusive debate to redefine the role and shape of sustainable agriculture in the Rolling Pampas. Emergy accounting, an evolving methodology that brings ecological imperatives to the forefront of evaluation, constitutes a valuable tool for such a debate.

Analysis of Soil Fertility and Management Effects on Yields of Wheat and Corn in the Rolling Pampa of Argentina

AbstractThe Rolling Pampa is the most productive region of the Argentine Humid Pampa comprising around 10 Mha. Wheat (Triticum aestivum L.), corn (Zea mays L.), and soya bean [Glycine max (L.) Merr.] are the main grain crops produced. To develop sound cropping strategies, a better understanding of the impact of soil fertility and management on crops is needed. The objective of this study was to develop models for estimating the effects of growing season precipitation, soil fertility and management on wheat and corn yields. Data from 347 wheat and 323 corn field experiments and production fields over six growing seasons were used. Soil, management and weather characteristics were determined and yields were then evaluated. Data were analysed using linear and quadratic models and a quadratic polynomial surface model. Soil fertility, management and rainfall and interactions were analysed. Growing season precipitation correlated with wheat (R2 = 0.42) and corn (R2 = 0.25) yield. Maximum wheat yield was achieved with 350–400 mm rainfall and corn yield reached a plateau around 700 mm. Soil fertility accounted for 33 % of wheat yield variability and 5 % of corn yield variability. Management accounted for 48 and 9 % respectively. Whole polynomial models integrating rainfall, fertilizer N and P rates, soil N and P, previous crop and tillage system accounted for 67 % of wheat yield variability and 51 % of corn yield variability. Soil organic matter was not included in the models but an indirect effect on yield was detected as organic matter correlated with initial soil N levels for both crops. Soya bean as a previous crop had a positive effect on wheat and corn yields. Wheat was insensitive to tillage system but corn yield was higher under no till. N and P fertilization had a two‐ to three‐fold greater impact on yield than soil nutrient levels. As this region is considered to be of high soil fertility and has a history of very low fertilizer consumption, adequate use of N and P fertilization will be essential to maintaining high wheat and corn yields.

Long‐Term Cropping Effects on Maize

Long‐term cropping in the Rolling Pampa of Argentina may reduce available soil water for maize (Zea mays L.) production. Grain yield, however, has not decreased possibly because of genetic improvement. Our objectives were to: (i) evaluate root and shoot growth and its relation to crop evapotranspiration (ETa), (ii) analyze interactions among hybrids and length of the cropping period on grain yield and its components, and (iii) establish functional relations between grain yield components and their determinant processes. Three hybrids with contrasting production stability coefficients and representing different eras of maize breeding were grown at three farms in 1994 to 1996 in fields with short (S) and long (L) cropping periods on silty clay loam soils (fine, illitic, thermic Typic Argiudolls). Silking took place 5 to 6 d later in L than in S and a significant (P < 0.05) reduction (21–36%) of ETa was observed in L vs. S around this stage. Lower root abundance (reduction of 60%) and canopy size (reduction of 6–13%) in L have probably contributed to less ETa. In addition, the ontogenic delay exposed crops grown in L to more stressful meteorological conditions around silking. Kernel number (KN), closely related to grain yield (r2 > 0.65), was significantly associated with daily ETa around silking. The modern hybrid established a greater KN mm−1 d of ETa (853 kernels m−2 mm−1 d) compared with the older ones (386 kernels m−2 mm−1 d). This characteristic may mask the deleterious effects of long‐term cropping on maize grain yield.

Assessing Soil Quality in the Rolling Pampa, Using Soil Properties and Maize Characteristics

AbstractIntensive land use in the Rolling Pampa of Argentina appears to be reducing soil quality for crop production. Our objective was to establish the best edaphic and/or plant indicators for assessing soil quality with regard to functioning as a medium for crop production. Nine fields with Typic Argiudoll soils were selected for evaluation based on agriculture history and apparent soil structural stability. Soil chemical and physical properties and maize (Zea mays L.) vegetative and reproductive characteristics were measured. Multivariate statistical analyses were applied to the data to determine potential indicators of soil quality. Soil and crop variables explained more than 70% of the variance in soil quality among agricultural histories. The edaphic indicators that showed the greatest change from pristine conditions were organic C, total N, P, Mg, K, B, Ca, and Zn contents and cation exchange capacity. Using crop variables, leaf length, maximum fraction of intercepted photosynthetically active radiation, grain yield, kernel number, prolificacy, and total dry matter at physiological maturity, served to establish a soil quality gradient. Variation of maize growth was associated with edaphic indicators of soil quality and revealed the importance of soil aggregate stability in determine changes in soil quality for crop production.