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The objective of the study was to assess the effect of soil type, land-use and -management on root-C inputs and soil carbon storage in the central semiarid pampa region, Argentina. Twenty-one sites were assessed with different land uses (agriculture, natural grassland and pasture) and textures (sand, loamy sand, sandy loam and loam). Root and shoot biomass, and soil properties including texture, total C and N, particulate C, mineral associated C, pH, bulk density and available phosphorus were determined. Results showed that land use conditioned the magnitude of C input in the system while texture limited C storage. Higher root to shoot ratio (5.1–7.6:1) was observed in natural grassland than in pasture (2–4.2:1) and agriculture (0.6−1:1). Positive linear relationships were found between soil C and silt plus clay content with increments of C storage of 4, 2 and 1% under natural grassland, pasture and agriculture respectively. Linear and saturation models were performed for the relationship between soil organic matter and root-C for each soil type and the first 0.20 m depth. Sandy loam soils achieved C saturation level at 65 Mg C ha−1 defined by maximum values under natural grasslands with C storage capacity of 34 Mg C ha−1. Soils with silt plus clay content lower than 20% (sand and loamy sand textures) also showed an upper limit of 16.6 Mg ha−1 (equivalent to 0.6% C). In contrast, loam soils showed no -saturating behavior (linear response) with increments of 14 Mg C ha−1 per unit of root-C input. Particulate C increased with increasing root-C inputs in loam and sandy loam soils with no change in mineral associated C. The rate at which root-C was transformed to particulate C was 11.8 and 7.3 Mg Cp Mg root-C−1 for loam and sandy loam soils respectively. Our results showed that soil type and climate are crucial for determining C sequestration capacity of soils, and root inputs, more than aboveground biomass, should be considered when deciding appropriate soil management for enhanced C storage.

In order to obtain baseline values for the evaluation of soil degradation, the biological and physical quality of petrocalcic Paleustolls, of the calcrete plains of the Semiarid Region Pampa of Argentina, soils under agricultural (Ag) and native vegetation (NV) were selected, with the same clay content, in which three depth layers (upper, middle and lower) were sampled. Total organic carbon and its fractions, total nitrogen, soil texture, aggregate size distribution, mean weight diameter, aggregate volumetric weight, maximum bulk density, susceptibility to compaction, critical moisture content, hydraulic conductivity, infiltration, penetration resistance were determined. In addition, the size, distribution and shape of the macropores were measured through image analysis of thin sections. As biological indicators, respiration, microbial biomass carbon and nitrogen were determined. Soils under Ag use had lower carbon and nitrogen content, they also had lower total porosity and macroporosity compared to the NV soils, and the predominant shape of macropores was round. This change in the distribution and shape of the pores led to lower rates of infiltration and lower hydraulic conductivity, higher bulk density and greater resistance to penetration. The round macropores were found to be negatively correlated with organic carbon, total porosity and macroporosity and positively with indicators associated with compaction (maximum bulk density, susceptibility to compaction and bulk density). Compacted soils with lower total porosity and higher proportion of round macropores presented higher volumetric weight of the aggregates. The Ag soils with lower carbon and nitrogen content also had lower microbial biomass carbon and respiration, compared to the soils under natural vegetation, and the variables associated with compaction were negatively related to biological properties. The suggested minimum set of indicators included organic carbon, total porosity, mean weight diameter, macropores, penetration resistance, aggregates volumetric weight of 2–3-mm, elongated macropores, respiration and microbial biomass carbon. All of them were strongly related to indicators that reflect the physical, chemical and biological functionality of the soil that sustain soil-based ecosystem services. Degradation and rehabilitation processes might be governed by the feedback between pore formation and microbial activity, underpinning the importance of perennial crops and cover crops for providing substrate supply to the soil biota for sustainable agricultural systems.

En la región semiárida pampeana aún no se han usado indicadores biológicos para valorar cambios en la calidad del suelo relacionados con el uso de la tierra. El objetivo de este trabajo fue caracterizar, evaluar y obtener valores de línea de base de respiración de suelo, biomasa microbiana y cociente metabólico en suelos de la región semiárida pampeana bajo vegetación natural y agricultura. El estudio se desarrolló en Paleustoles petrocálcicos de la planicie con tosca de la región semiárida pampeana central. Determinamos los contenidos de arcilla y limo, la porosidad total, el contenido de carbono y nitrógeno, la respiración y la biomasa microbiana, la relación hongo/bacteria y el cociente metabólico en los estratos superior, medio e inferior de dos suelos con vegetación natural y otros dos bajo uso agrícola. El tipo de uso del suelo influyó significativamente sobre la actividad y el tamaño de la biota, de manera tal que los suelos agrícolas, con menores contenidos de carbono y nitrógeno, tuvieron una menor respiración y menores contenidos de carbono y nitrógeno en la biomasa microbiana, en relación con los suelos bajo vegetación natural. El cociente metabólico no presentó diferencias entre suelos bajo distinto uso, por lo que no fue de utilidad para indicar el estado de degradación edáfico, en comparación con la biomasa microbiana y la respiración. El uso del suelo también afectó la relación hongo/bacteria, ya que la participación de hongos en la biomasa microbiana de los suelos bajo uso agrícola fue considerablemente menor que la de los suelos bajo vegetación natural. Estos resultados nos permitieron establecer valores umbrales y de línea de base para la respiración del suelo y el carbono de la biomasa microbiana. In the semiarid Pampa, biological indicators have not yet been used to evaluate the effect of land-use on soil quality. Our objective was to characterize, evaluate and obtain base-line values for soil respiration, microbial biomass and metabolic quotient in agricultural and native vegetation soils of the central semiarid Pampa region. In two natural vegetation and two agricultural soils, we determined clay, silt, total porosity, total carbon and nitrogen contents, microbial respiration and biomass, fungi-bacteria ratio and metabolic quotient in the upper, middle and lower profile layers. Soil use significantly affected the activity and the size of soil biota, in the sense that the agricultural soils, with lower carbon and nitrogen contents, showed lower respiration and microbial biomass carbon and nitrogen contents compared to the natural vegetation. Microbial biomass and respiration were better indicators for soil degradation than the metabolic quotient. Soil use also had an effect on the fungi/bacteria ratio since agricultural soils had a lower proportion of fungi than soils under natural vegetation. These results enable us to establish baseline and threshold values for respiration and microbial biomass carbon contents.

Identification of areas with similar restrictions to crop productivity could improve the efficiency to manage agricultural systems, guarantee stable yields, and reduce the effect of droughts in rainfed systems. The ability of any vegetation index to discriminate N and moisture-related changes in leaf reflectance would present an important advantage over the present diagnostic system which involves soil-testing for moisture and available N. The purpose of the study was to calibrate different vegetation indices regarding their capacity to identify water and nitrogen availability for rainfed corn crops in the semiarid Pampas of Argentina. A field experiment with corn with a control without fertilization (N0), and fertilized with 120 kg ha−1 of nitrogen (N120) was used. Two sites, Low (L) and High (H), were identified within the field, according to their altimetry, a multi-spectral aerial photography was taken from a manned airplane during flowering stage of the corn crop, and four spectral indices were calculated (NDVI, green NDVI, NGRDI, (NIR/GREEN)-1). At six georeferenced points at each site soil texture, organic matter, available phosphorus, nitrogen and moisture contents as well as corn aerial biomass and grain yield were determined. The two sites differed in most of the evaluated soil properties, crop biomass and grain yield. The spectral information obtained at crop flowering showed clear differences between sites H and L for all four indices, indicating that any of these would be able to detect the differences in soil moisture and fertility among these environments. Both (NIR/GREEN)-1 and green NDVI had the best correlation with crop yield determined in the field, and therefore could be considered most appropriate for estimating corn yields from images taken at flowering. For estimation of N requirements, green NDVI differentiated best between fertilized and non-fertilized crop in the moisture limited environment (H), while (NIR/GREEN)-1 performed better in the site where soil moisture was non-limiting (L).

The reliance of current farming systems on synthetic fertilizers caused concerns about their sustainability, and alternatives to supply nitrogen through biological processes have to be adapted to practical conditions. The present study compared a pure legume and legume-grass biculture as cover crops for sorghum in their supply of nitrogen (N) to the cash crop and their N leaching losses during fallow. A three-year field experiment under no-till with sorghum (Sorghum bicolor Moench.) as main crop and cover crop treatments (C- control = bare fallow; R-rye Secale cereale L.; V-vetch Vicia villosa sp dasycarpa; VR-vetch-rye biculture) was established with a completely randomized block design (four replicates) in semiarid central Argentina. Aerial biomass (AB) and N contents were determined for all crops. Soil moisture to 1 m and nitrate-N to 0.60 m depth were determined. Water use- and nitrogen use efficiencies (WUE and NUE) were calculated and biological nitrogen fixation (BNF) estimated. BNF depended on nitrate-N contents of the soils; highest values (11 and 10 g BNF m−2 for V and VR respectively) were reached at 1.3 g N m−2. Sorghum responded to higher N availability with an average of +299 and +512 g AB m−2 for V and VR compared to C, with higher WUE. The relationship between WUE and nitrate-N was positive with an optimum of 0.048 g N m−2 mm −1 where WUE reached a maximum of 4.9 g AB m−2 mm−1. Potential N losses by leaching were highest in control, while all cover crop treatments had lower losses. Our results support the hypothesis that a legume-grass biculture was more efficient in the trade-off between nitrogen provision to the cash crop and prevention of N losses by leaching. Although the amount of BNF was lower in the biculture than in pure vetch, it covered sorghum N requirements with less potential leaching losses even in high rainfall fallows.

The growing global demand for food, fibers and energy has triggered a scientific and political debate on how to attain increasing land productivity without further degrading soils. The objective of this study was to quantify the effect of long-term no-till cultivation with light grazing on soil quality, land productivity, and resource use efficiency. The experiment was established in 1993 with two main treatments, no-till (NT) and conventional tillage (CT), sub-divided into grazed and ungrazed subplots, in a paired strip design with three repetitions. Crops included sunflower, corn, soy and wheat, and stubbles were grazed for at 3 months with young animals. Soil samples were collected in 2015 and determinations included total carbon and its fractions, total nitrogen, microbial biomass carbon, soil moisture contents, aggregate size class distribution, volumetric aggregate weight, mean weight diameter change, maximum bulk density, total infiltration, and saturated hydraulic conductivity. Crop production was on average 13% higher in NT than in CT, and grazing had no effect on yields. NT increased organic matter contents by 6% and CT diminished it by 1.7% in the top 0.10 m compared to the original value in 1993, and showed no significant variation at 0.10–0.20 m depth. The labile C fractions and microbial biomass carbon showed a similar trend with highest values in the non-grazed NT topsoil. We found positive relationships between microbial biomass and labile carbon and nitrogen fractions only for the NT soils. All soil physical quality indicators had better values for NT compared to CT soils, and grazing had no effect. The results of this long-term experiment gave evidence that a NT system with light grazing was a feasible land management that increased land productivity in a semiarid environment.

The objective of the present study was to describe the relationships between soil physical properties and to identify variables that determine the pore system and hydrological functions which are specifically important in drought prone semiarid marginal croplands. We compared Mollisols under natural vegetation (NV) with their agriculture (AG) pairs in the central Argentinean Dry Pampas to obtain the range of values for variables that characterize the soil pore system. These were total carbon (OC), bulk density (BD), structural instability index (SII), volumetric weight of aggregates (VAW), total porosity (TP), macropores (Ma), saturated hydraulic conductivity (K), infiltration rate (IR), Dexter's S index (S), and least limiting water range (LLWR). To a depth of more than 23 cm, TP and Ma were considerably lower (~ 35% and 50% less, respectively) in AG versus NV. The changes in porosity and pore size resulted in 74% smaller IR and 65% lower K. The S index had mean values of 0.16 and 0.14 for the upper and middle layer respectively in NV; while for AG, these values were significantly lower (0.09 and 0.10, respectively). The LLWR was also lower in AG (21 and 59% less in the upper and middle layer, respectively), due to high soil resistance even at non-limiting BDs (1.17 and 1.32 g cm−3 for AG2 and AG1, respectively). Soil OC was positively correlated with TP, Ma, and S, and negatively correlated with BD and SII. Multiple regression models for S included SII, TP, and clay contents, while for LLWR the variables were OC, TP, and clay plus silt. Thus, these complex soil quality indices can be predicted by using simpler physical parameters, but texture and organic matter also have a strong effect on them. Moreover, our results contribute to a better understanding of the role of texture and organic matter in controlling soil physical quality and for maintaining soil-based ecosystem services.

The goal of this study was to evaluate different strategies for defining homogeneous zones, and to verify their usefulness by comparing soil moisture contents and crop yields. Data were obtained from a field experiment near General Pico, La Pampa, Argentina, with a sampling grid of 598 points. Soil texture, organic matter, available phosphorus, pH, and electrical conductivity were determined. Altimetry was obtained by a GPS (Garmin 19X). Corn yields and available soil moisture contents were determined in a 184 point grid. Treatments were early and late planting date, and control and 100 kg N ha −1 . MULTISPATI-PCA was used to carry out for multivariate spatial analyses of soil attributes. The synthetic variables (sPC) were analyzed, mapped and used for determination of homogeneous zones by three strategies: S1-natural rupture method on sPC1, S2-Fuzzy k-means cluster analysis on soil variables and S3-Fuzzy k - means cluster analysis on all sPC. Zones were compared for means of soil variables, available soil water and maize yields. The three tested statistical strategies divided the field in a very similar manner when the minimum number of zones was considered, with coincidence in the classification of 98% of the sampled grid points. The different strategies resulted in different number of zones with different characteristics. The choice of the method depends on the objectives for determination of management zones. In our case, for fertilization management zonification might prioritize the differentiation of OM and available P contents and use S3, while if water was the main limiting factor, the management zones would be two according to S1 or S2, responding to textural and altimetry differences.

The objective of the study was to evaluate the effect of a change in management on the soil microbial community and C sequestration. We conducted a 3-year field study in La Pampa (Argentina) with rotation of sorghum (Sorghum bicolor) in zero tillage alternating with rye (Secale cereale) and vetch (Vicia villosa ssp. dasycarpa). Soil was sampled once a year at two depths. Soil organic matter fractions, dissolved organic matter, microbial biomass (MBC) and community composition (DNA extraction, qPCR, and phospholipid FAME profiles) were determined. Litter, aerial- and root biomass were collected and all material was analyzed for C and N. Results showed a rapid response of microbial biomass to a bacterial dominance independent of residue quality. Vetch had the highest diversity index, while the fertilized treatment had the lowest one. Vetch–sorghum rotation with high N mineralization rates and diverse microbial community sequestered more C and N in stable soil organic matter fractions than no-till sorghum alone or with rye, which had lower N turnover rates. These results reaffirm the importance of enhanced soil biodiversity for maintaining soil ecosystem functioning and services. The supply of high amounts of N-rich residues as provided by grass–legume cover crops could fulfill this objective. EEA Anguil Fil: Frasier, Ileana. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Anguil; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de La Pampa. Facultad de Agronomía; Argentina Fil: Noellemeyer, Elke. Universidad Nacional de La Pampa. Facultad de Agronomía; Argentina Fil: Figuerola, Eva Lucia Margarita. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular; Argentina Fil: Erijman, Leonardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular; Argentina Fil: Permingeat, Hugo. Universidad Nacional de Rosario. Facultad de Ciencias Agrarias; Argentina Fil: Quiroga, Alberto Raul. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Anguil; Argentina. Universidad Nacional de La Pampa. Facultad de Agronomía; Argentina

Semiarid grasslands are still managed without considering site-specific differences in productivity. A better understanding of spatial heterogeneity would improve land management and might avoid desertification in semiarid systems. We studied a toposequence in the semiarid savanna of central Argentina. By using Shuttle Radar Topography Mission (SRTM) for toposequence characterization, and radar images to identify a site with small area, we differentiated four ecological sites (ESs): valley floor, slope, plateau and deflation pits. Plateau presented the shallowest soil because of caliche layer present, while valley floor and deflation pit had the deepest CaCO3 accumulation. Moreover, valley floor had the thinnest A horizon (6.7 cm) while deflation pit had the thickest one (26.3 cm). Slope and deflation pit showed the highest organic matter (OM) contents (about 32 g kg−1). Total woody plant density was greater in slope and lower in valley floor. Plateau had higher shrubby Prosopis spp. density, and deflation pits higher tree Prosopis spp. density. Besides, we found a positive linear regression between OM content and woody plant cover, and an exponential relation between CaCO3 depth and shrub density. Chosen indicators explained ES variation, and the methodology allows to create ES maps and prescribe management strategies according to site limitations.

In many no-till (NT) systems, residue input is low and fallow periods excessive, for which reasons soil degradation occurs. Cover crops could improve organic matter, biological activity, and soil structure. In order to study changes in soil carbon, nitrogen and microbial biomass a field experiment (2010-2012) was set up with sorghum (Sorghum bicolor Moench.) monoculture and with cover crops. Treatments were control (NT with bare fallow), rye (Secale cereale L.) (R), rye with nitrogen fertilization (R+N), vetch (Vicia villosa Roth.) (V), and rye-vetch mixture (VR) cover crops. A completely randomized block design with 4 replicates was used. Soil was sampled once a year at 0.06 and 0.12m depth for total C, microbial biomass carbon (MBC) and-nitrogen (MBN) determinations. Shoot and root biomass of sorghum and cover crops, litter biomass, and their respective carbon and nitrogen contents were determined. Soil temperatures at 0.06 and 0.12m depth, volumetric water contents and nitrate concentrations were determined at sowing, and harvest of each crop, and during sorghum's vegetative phase. NT led to a small increase in MBC and MBN, despite low litter and root biomass residue. Cover crops increased litter, root biomass, total C, MBC, and MBN. Relationships between MBC, MBN, and root-C and -N adjusted to logistic models (R(2)=0.61 and 0.43 for C and N respectively). Litter cover improved soil moisture to 45-50% water filled pore space and soil temperatures not exceeding 25°C during the warmest month. Microbial biomass stabilized at 20.1gCm(-2) and 1.9gNm(-2) in the upper 0.06m. Soil litter disappearance was a good indicator of mineral N availability. These findings support the view that cover crops, specifically legumes in NT systems can increase soil ecosystem services related to water and carbon storage, habitat for biodiversity, and nutrient availability.

Graphical abstract, The present article describes a field auger sampling method for row-crop root measurements. In agroecosystems where crops are planted in a specific design (row crops), sampling procedures for root biomass quantification need to consider the spatial variability of the root system. This article explains in detail how to sample and calculate root biomass considering the sampling position in the field and the differential weight of the root biomass in the inter-row compared to the crop row when expressing data per area unit. This method is highly reproducible in the field and requires no expensive equipment and/or special skills. It proposes to use a narrow auger thus reducing field labor with less destructive sampling, and decreases laboratory time because samples are smaller. The small sample size also facilitates the washing and root separation with tweezers. This method is suitable for either winter- or summer crop roots. • Description of a direct field method for row-crop root measurements. • Description of data calculation for total root-biomass estimation per unit area. • The proposed method is simple, less labor- and less time consuming.

The issue of variances of different soil variables prevailing at different sampling scales is addressed. This topic is relevant for soil science, agronomy and landscape ecology. In multi-stage sampling there are randomness components in each stage of sampling which can be taken into account by introducing random effects in analysis through the use of hierarchical linear mixed models (HLMM). Due to the nested sampling scheme, there are several hierarchical sub-models. The selection of the best model can be carried out through likelihood ratio tests (LRTs) or Wald tests, which are asymptotically equivalent under standard conditions. However, when the comparison leads to a restricted hypothesis of variance components, standard conditions are not maintained, which leads to more elaborated versions of LRTs. These versions are not disseminated among environmental scientists. The present study shows the modeling of soil data from a sampling where sites, fields within sites, transects within fields, and sampling points within transects were selected in order to take samples from different vegetation types (open and shade). For soil data, several sub-models were compared using Wald tests, classic LRTs and adjusted LRTs where the distribution of the test statistic under the null hypothesis is the Chi-square mixture of Chi-square distributions. The inclusion of random effects via HLMM and suggested by the latest version of LRT allowed us to detect effects of vegetation type on soil properties that were not detected under a classical ANOVA. Fil: Gili, Adriana Anahi. Universidad Nacional de La Pampa. Facultad de Agronomía; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Noellemeyer, Elke Johanna. Universidad Nacional de La Pampa. Facultad de Agronomía; Argentina Fil: Balzarini, Monica Graciela. Universidad Nacional de Córdoba. Facultad de Ciencias Agropecuarias; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

The objective of the present study was to evaluate the effect of afforestation of degraded agricultural soils on soil organic carbon (OC) stocks and related soil physical properties. We assumed that forest species and soil texture would have a strong effect on C stabilization and thus would also affect some physical properties. The study was composed of two experiments to evaluate (i) the effect of different tree species and (ii) the effect of soil texture on OC and physical properties. In the first case, soil samples were taken in 40-year-old plantations of Pinus haleppensis, P. haleppensis inoculated with ectomycorrhiza at planting, Pinus pinea, Eucalyptus spp., and Gleditsia triacanthos. For the second experiment, soils under three land-use types, namely, agriculture, P. haleppensis forest, and native savanna virgin were sampled at seven different sites in La Pampa, Argentina, that represented a climatic gradient from 850- to 600-mm annual rainfall and a textural gradient ranging from loam, sandy loam, to sand. The measured variables were bulk density, particle density, water retention at field capacity water content, structural stability index, total OC, large-aggregate C, intermediate-aggregate C, and small-aggregate C. Forest species had a differential effect on physical properties, especially bulk density, and OC contents. The forest species with the most favorable effects were P. haleppensis inoculated with ectomycorrhiza and G. triacanthos, whereas P. pinea and Eucalyptus were least effective, confirming the beneficial role of mycorrhizal fungi and symbiotic N fixation for restoring C stocks in a semiarid temperate environment. In all sites, we found significant differences in total OC and large-aggregate C contents between agriculture and forest treatments, thus indicating that afforestation with P. haleppensis would favor C sequestration in any of the three textural classes.

Silvopasture systems combine trees, forage, and livestock in a variety of different species and management regimes, depending on the biophysical, economic, cultural, and market factors in a region. We describe and compare actual farm practices and current research trials of silvopastoral systems in eight regions within seven countries of the world: Misiones and Corrientes provinces, Argentina; La Pampa province, Argentina; northwestern Minas Gerais, Brazil; the Aysén region of Patagonia, Chile; the North Island of New Zealand; the Southeast United States; Paraguay; and Uruguay. Some countries use native trees and existing forests; some use plantations, particularly of exotic species. Natural forest silvopasture systems generally add livestock in extensive systems, to capture the benefits of shade, forage, and income diversification without much added inputs. Plantation forest systems are more purposive and intensive, with more focus on joint production and profits, for small owners, large ranches, and timber companies. Trends suggest that more active management of both natural and planted silvopastoral systems will be required to enhance joint production of timber and livestock, achieve income diversification and reduce financial risk, make more profit, improve environmental benefits, and realize more resilience to adapt to climate change.

In a cultivation experiment 18 different Amaranthus genotypes were cultivated in parallel in Argentina, Mexico, Spain and two different locations in the Czech Republic. The ripe seeds were analysed for their content of 11 polyphenols and the variations among genotype, species and location were analysed by principal component analysis (PCA). The flavonoid, rutin, exhibited large variations with varying environmental conditions whereas the flavonoid, nicotiflorin, was affected less. Amaranthus hypochondriacus displayed the most stable content of polyphenols with a high end content of flavonoids. The variations between location/environmental condition were primarily described by the variations in the content of p-coumaric acid and protocatechuic acid in the seed samples.

The purpose of the present study was to evaluate the long-term (14 yr) effect of no-till (NT) compared with conventional tillage (CT) on the distribution of dry sieved aggregate size fractions, their carbon (C) and nitrogen (N) contents and respiration activity. Soil samples were taken from a long-term (14 years) tillage experiment with a rotation of 6 cash crops, 4 years pasture and another 6 cash crops in the sandy plains region of semiarid central Argentina, on an Entic Haplustoll. Sampling was carried out at 0.06 m intervals to 0.18 m depth, with 4 replicates per tillage treatment. Bulk density (BD), C and N were determined on air dried samples. Dry aggregate size distribution (fractions: >4, 1–4, and 4 and

Diversification of production is a concern for farmers in many regions of the world, raising a renewed interest in crop-animal rotations. However little information is available on whether the introduction of grazing animals in a no-till system could be a sustainable practice. The present long-term study was carried out in the semiarid region of Argentina, on an Entic Haplustoll (A, AC, C and C k profile). The experimental plots were established in August 1993, with two treatments, no-till (NT) and conventional tillage (CT). Stubble was regularly used for grazing until 2002, when plots were divided into grazed (G) and non-grazed (NG) sub-treatments. Soil samples were taken at 0–0.10 and 0.10–0.20 m depth at the beginning of the experiment (1993) and during 2007, with the following determinations: clay + silt contents, bulk density (BD), total carbon (C), total nitrogen (N), available P, C contents of aggregate fractions of 2000–100 (POC), 100–50 (IOC) and −1 vs. CT 13.2 Mg ha −1 ) and higher amounts in all C fractions, even in FOC (11.3 Mg ha −1 vs. 9.2 Mg ha −1 ). For BD, we found no difference between NT and CT at the surface and an even lower value for NT at 0.10–0.20 m depth. Under NT no depletion of available P occurred, while CT lost about 23 kg ha −1 . Grazing had a negative effect on BD when averaging BD data across tillage systems, while there was no effect on aggregate stability, and a positive one on the proportion of >8 mm aggregates (23.3% vs. 11.7% for CT G and CT NG, respectively). C stratification showed a differential effect of grazing: NT G had the highest index (1.31) and CT G the lowest one (0.98). Our results indicated that the introduction of grazing animals in NT crop systems would not be detrimental to soil conditions and quality, at least in semiarid conditions of Argentina.

Land-use change affects vast areas of the semiarid region of central Argentina, where agriculture becomes predominant over mixed farming systems, and large areas of permanent pastures (PAS) are being converted to agricultural land. This land-use change causes loss of soil structure, but very little is known about the effect of changes in aggregate size distribution on soil physical, chemical and biological properties. We decided to use dry sieved aggregates since this technique is commonly used in semiarid regions. The study was carried out at Anguil, La Pampa, Argentina. The soil was a sandy loam Entic Haplustoll with a carbonate-free A-horizon. The PAS site had been under weeping love grass for more than 40 years. Parts of this PAS were turned to cultivation in 1989 (CULT14) and in 2001 (CULT2). Sampling was carried out at 0.6 m intervals to 0.18 m depth. Bulk density (BD), organic carbon (OC), and water holding capacity and infiltration were determined on these samples. Dry aggregate size distribution and OC content of the size fractions were determined on large undisturbed samples. Samples of pooled aggregate size fractions >4, 1–4, and 2 evolved. The soil of CULT2 had 29% lower contents of large (>4 mm) and 37% higher contents of very small ( 2 evolved was related to OC contents of fractions; however, PAS respired more from its small aggregates than expected from their OC content. The results showed that OC turnover and loss of aggregation was very fast in this soil, but soil hydraulic properties were affected in the longer term. Dry aggregates were found to useful for studying soil degradation, and they showed similar trends as those indicated in the literature for water stable aggregates.

Soil organic matter (SOM) is known to play a major role in soil fertility due to its influence on physical, chemical and biological properties of soil; and it is closely related to particle size distribution. The ratio of SOM (g kg−1) to clay + silt content (g kg−1) was evaluated as an indicator of soil quality for barley (Hordeum vulgare) grain yield, reflecting N availability and soil physical conditions to which crop development is sensitive. Thirty-eight sites in the semiarid Pampa region of Argentina with a wide range of SOM and texture were evaluated for malting barley yield during three growing seasons. In control plots, 51% of grain yield could be explained by this indicator. The threshold value between high and low N-fertilization response was 4.4. Better yield prediction to almost 68% was achieved by combining the SOM to clay + silt indicator with initial nitrate content of the soil at seeding. This combined indicator was also able to explain a high proportion of water use efficiency, particularly in the early growth stages. The ratio of SOM to clay + silt content provided a better tool for estimating grain yield than nutrient availability or SOM alone.

Half-lives of 50 to 100 yr have been reported for native soil C in temperate Mollisols taken under cultivation, whereas some C fractions have shown mean residence times of hundreds of years. In the Tropics, C turnover is much more rapid. This lower C stability may be attributable to climate or to a mineral suite with low C stabilization potential typical of many tropical soils. We present data on the mineralization and accretion pattern of organic C under land use conversion in illitic loessial loams of the semiarid, warm temperate Province of La Pampa, Argentina. These soils should have a low C stabilization potential, and the semiarid temperate climate should provide for relatively slow turnover compared with tropical conditions. Using 13 C-natural abundance and soil fractionation, we determined soil C derived from C3 and C4 plants under land use changes between native Calden savannah, pastures, and arable fields, specifically: (i) the conversion of C3 natural savannah to agriculture that includes (C4) maize in the rotation, (ii) the conversion of a 40-yr-old C4 pasture into arable land under C3 crops, and (iii) the reclamation of highly degraded C3 cultivated land with C4 pastures. Although none of the land cover changes represented 100% conversions between plants of C4 and C3 metabolism, C turnover could still be determined. All sites provided evidence for rapid C losses with C half-lives just above 10 yr and no evidence for long-term stabilized C in any soil fractions. Soil under long-term pasture or the natural vegetation of the region, with initial C contents between 24 and 33 mg C g -1 bulk soil, lost 33 to 57% of this original bulk soil C within 12 to 18 yr of continuous cultivation. On degraded soils under restoration with C4 pasture, C accretion was also rapid but leveled off well below the original C levels. Theses results provide evidence for potentially irreversible soil degradation and corroborate local practical experience that these temperate, coarse-textured, illitic soils are highly susceptible to degradation and should be managed carefully.

Degradation of semi-arid rangelands in the Argentinean Pampa due to increasing grazing intensity has been a growing concern among ecologist. Many studies document the impact of grazing on vegetation structure but little information is available on soil properties in these environments. The present study aims to establish some terms of reference for these range soils. Field studies were carried out to test the validity of selected soil chemical, physical and biological parameters for their capacity to discriminate soils according to quality under rangeland use. The selected data set includes total soil organic carbon (SOC), particulate organic carbon (POC), total N and P contents, dry aggregate size distribution, water stable aggregates and proctor maximum bulk density. Three soils (sand, sandy loam and loam) corresponding to different topographical situations and natural vegetation structure were sampled in 6 cm depth intervals up to 18 cm in bulk density cylinders, with six replicates in each site. Sun and shade vegetation communities were sampled separately. Standing biomass was determined and dry matter was analysed for N, P, Ca and Mg content. A positive significant relation between clay+silt content and SOC was found ( R 2 = 0.53 ) in the 0–6 cm depth. Topsoil SOC was related to standing biomass ( R 2 = 0.21 ) , and POC showed a strong correlation with SOC ( R 2 = 0.94 ) . The highest values of SOC and POC were found in the sandy loam, while the loam had the highest POC/SOC ratio. Aggregate size distribution especially of >8 and 8 and

Soil carbon in the form of organic matter is a key component of the soil ecosystem structure. The soil carbon content is an important contributing factor in the many flows and transformations of matter, energy and biodiversity – the essential soil functions that provide ecosystem services and life-sustaining benefits from soil. These goods and services include food production, water storage and filtration, car bon storage, nutrient supply to plants, habitat and biodiversity. Soil functions provide natural capital as a means of production for the ongoing supply of the essential goods and services. Soil carbon content and soil functions are under threat worldwide due to resource demands and the increasing intensification of land use. Land degradation is characterized by soil carbon losses, loss of soil structure and associated loss of fertility, and the physical loss of bulk soil by erosion. Soil carbon accumulation is associated with plant productivity, wet conditions that ensure water supply to vegetation and lack of physical disturbance to the soil. Carbon accumulation is also associated with decreased organic matter decomposition in the soil, created by cool conditions that reduce the rate of microbial activity and wet conditions that create an O 2 diffusion barrier from the atmosphere and reduced aerobic microbial respiration during organic matter decomposition. The environmental conditions for the accumulation of soil carbon also provide important clues to management approaches to reverse soil carbon losses and to increase soil carbon content under widely different environmental conditions around the world. Soil management strategies can be developed from the natural cycling of soil carbon, by reducing physical disturbances to soil, enhancing vegetation cover and productivity and through improved water management. These approaches are essential in order to prevent and reverse the loss of soil functions where land is degraded and to enhance soil functions where actively managed land is undergoing intensification of use. Improved soil carbon management provides an important opportunity in land management worldwide, to meet increasing resource demands and to create resilience in soil functions that arise from the intense pressures of land use and climate change.

Land-use changes (LUC) are one of most significant global change processes of the current era, with noticeable consequences on habitat loss, due mainly to agricultural expansion and urbanization. The carbon cycle dynamics can be affected significantly by LUC, with impacts on carbon sequestration and emission rates. Considering the direct effect of carbon gases enrichment of the atmosphere on climate change, it is of utmost importance to improve the knowledge base on the impacts of agricultural-based LUC on carbon sinks, such as soils. This chapter reviews the available data on the effects of LUC on soil carbon stocks in three major biomes of the southern portion of the South American continent (the Cerrado, the Southern Grasslands and the Atlantic Forest). The area of soybean crops has expanded almost four times in the La Plata Basin Grasslands of Argentina over the past decade, and near ten times in the Brazilian Cerrado since the mid-1980s. The area under sugarcane crops in Brazil has almost doubled since the mid-1990s, occupying approximately 8.5 million ha (Mha) in 2009. In 2011, forestry plantations occupied 28% more land in Brazil than in 2005, with a total area of 6.5 Mha (75% with Eucalyptus and 25% with Pinus). In general, all conversions of natural vegetation to agricultural land-use systems in the different biomes have resulted in significant losses of soil carbon stocks. The conversion of pastures and grasslands to annual croplands in the Rolling Pampas grasslands has decreased C stocks by 50% over the last century. This represents a much faster loss rate than the loss triggered by the introduction of domestic herbivores over the course of the previous nearly four centuries (22%). These results imply that soil degradation caused by annual crops is very rapid and results in a strong decrease in carbon stocks. However, adopting soil and water conservation management strategies and increasing the complexity of the cropping systems - through adoption of no-tillage (NT) agriculture, well-managed pasture systems, integrated crop-livestock-forestry systems, multiple cropping and crop rotation with legume cover species, for example, can improve soil carbon sequestration rates by up to nearly 2.0 Mg C ha-1 year-1. The elimination of preharvest burning practices in sugarcane crops alone can result in gains of up to 0.93 t C year-1 ha-1. Improving soil and crop management to boost carbon sequestration in agricultural systems, while at the same time increasing resilience by improving soil quality, is a potential climate change mitigation option for farmers in South America.

The dendrochronological characteristics of 52 tree species from the semi-tropical forests of the Yucatan Peninsula were opportunistically explored in a salvage dendrochronological study. The existence of clear growth rings in these trees is a key prerequisite for further studies and a convincing demonstration of the dendrochronological potential of tropical tree species will allow the development of future research programs concerning the ecology of the species and inferences about past environmental changes detected from tree rings. Many aspects of the conservation and management of Yucatec forests should be urgently addressed to aid in the development of improved strategies beyond the scope of more traditional agricultural uses. Development of tree-ring analyses from selected local species can be of substantial assistance in these initiatives.