Search

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.

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.

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 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.

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

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.