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The objectives were to quantify its effect on the yield of the successor summer crop, to evaluate the dynamics of the decomposition of rye residues from a fertilized and unfertilized cover crop (CC), and to evaluate the cumulative effect of 5 years of rye CC in a rotation with a high incidence of soybean on the soil organic matter contents. The study was carried out on a petrocalcic Paleustoll, located in the Southern Plain of the Semiarid Pampa Region. The experiment was part of a long-term trial where in 2010 two treatments for soybean management were installed, continuous soybean without CC and soybeans in rotation with CC. In 2018 an experimental design was established where plots were arranged in completely randomized blocks and 4 management treatments for soybean cultivation were established: continuous soybean without CC, soybean in rotation with CC without fertilization, fertilized with 60 kg N .ha-1, and with 120 kg N.ha-1. Nitrogen fertilization in the CC improved the capture rate of both carbon, nitrogen and phosphorus. The results showed that 40% carbon, 60% nitrogen, and 61% phosphorus contained in above-ground biomass were lost from the CC from drying to soybean harvest. The highest soybean yields were recorded in the rotation with fertilized CC, due to a positive effect between the higher soil water content in the early stages of cultivation due to a greater amount of residues, and also by the contribution of different nutrients during the soybean crop-cycle. The long-term trial showed that after 5 years of cover crops in the soybean rotation there was no effect on the organic matter contents.

El objetivo de este trabajo fue evaluar la influencia de la fertilizacion nitrogenada en la expresion del rendimiento y el contenido de proteina en grano de trigo en distintos ambientes de la regionsemiarida pampeana. Los ensayos se realizaron en las localidades de Embajador Martini, Macachin y Anguil. Los tratamientos fueron: Testigo; fertilizacion a la siembra con 40 kg N.ha -1 y 80 kg N.ha -1 , fertilizacion postergada con 40 kg N.ha -1 , fertilizacion dividida a la siembra con 40 kg N.ha -1 y postergada con 40 kg N.ha -1 . El diseno experimental fue en bloques completamente aleatorizados con cuatro replicas. En cada localidad se realizaron cinco ensayos y se determino el rendimiento, el contenido de proteina en grano, la eficiencia en el uso del agua (EUA) y eficiencia de uso de nitrogeno (EUN). Los sitios con un IMO>4,5% tuvieron mayores respuestas al rendimiento respecto del testigo que los suelos con un IMO 50% de A+L presentaron mayor fertilidad potencial del suelo, y tuvieron diferencias significativas respecto del testigo ante el agregado de 80 kg.ha -1 de nitrogeno a la siembra o dividida. En cambio, suelos con

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.

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 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

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.

Sulfur (S) fertilization has increasingly become an important issue in crop management. In Argentina S deficiencies have been reported, but there has been no success in finding soil tests for predicting soybean response to S fertilization. The objectives of this study were to: (i) evaluate seed S and N:S ratio as a tool for identifying S deficient soybean crops in field conditions and (ii) determine shifts in stoichiometric relationships among nitrogen (N), phosphorus (P) and S in soybean seeds which can be used for identifying S responsive sites under field conditions. Seed samples from 20 field experiments designed to explore response to S fertilization in soybean were collected in a large area in the Argentinean Pampas region. Seed yield (SY) and P (%P), S (%S) and N (%N) concentration in seeds were determined. Different data analyses were tested in order to find an S deficiency index. Moderate SY responses to S fertilization were observed in the present study (i.e. relative SY was never below 75%). seed S concentration increased in response to S fertilization in most responsive sites, and N:S ratio was governed by variations in seed S concentration. Stoichiometric relationships were more accurate for identifying S responsive sites than using single variables (e.g. seed S concentration or N:S). The isometric variations among N, P and S suggest that the accumulation of these nutrients is proportional in seed tissue. A significant increase in the intercept of the stoichiometric relationship between N and S in S deficient crops was observed. An S deficient index (SDI) was calculated based on this difference that can be used as a diagnostic tool for identifying S responsive sites in soybean. The present study shows a novel approach for using stoichiometric concepts in fertilizer management in soybean. Fil: Salvagiotti, Fernando. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Santa Fe. Estación Experimental Agropecuaria Oliveros; Argentina Fil: Ferraris, Gustavo Nestor. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Norte. Estación Experimental Agropecuaria Pergamino; Argentina Fil: Quiroga, Alberto Raul. Instituto Nacional de Tecnología Agropecuaria. Centro Regional La Pampa-San Luis. Estación Experimental Agropecuaria Anguil; Argentina Fil: Barraco, Mirian Raquel. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires. Estación Experimental General Villegas; Argentina Fil: Vivas, Hugo. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Santa Fe. Estación Experimental Agropecuaria Rafaela; Argentina Fil: Prystupa, Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales; Argentina Fil: Echeverria, Hernan Eduardo. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Sur. Estación Experimental Agropecuaria Balcarce; Argentina Fil: Gutiérrez Boem, Flavio Hernán. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales; 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.

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

This study was intended to contribute information on the relation between soil texture and plant community composition, and the effect of interactions between texture and vegetation patch on soil C dynamics. Six sampling sites were chosen and a vegetation census and soil sampling were performed for between-canopy (BC) and under-canopy (UC) patches at each site, Shannon-Weaver diversity index (DI) was determined for herbaceous species, an relative abundance of forage species and avoided grasses were calculated. Soil data included texture, bulk density, total organic C (TOC), particulate organic C (POC), intermediate organic C (IOC), and fine organic C (FOC). Correspondence analysis showed that sandy and loamy sites did not share the same herbaceous species. We also found an interaction between vegetation patches and texture, with distinct vegetation composition in the same type of patch in different textures. The DI was lower in UC than BC patches (0.86 vs. 1.7), but no effect of texture was found. The TOC showed a positive relation with texture; the extremes were 9.0 vs. 16.3 g kg -1 for a loamy sand and loam, respectively. Carbon fractions varied in their response to texture: while POC and IOC showed no clear trend with texture, FOC contents followed a textural gradient. Particulate organic C showed higher values in UC than BC (10.8 vs. 4.0 g kg -1 ). Differences between patches diminished with increasing clay contents. Intermediate organic C was similar to POC, while FOC showed no effect of patch but was related to texture. The high proportion of POC in sandy soils (50 vs. 35% in a loam) makes these more susceptible to changes in C balance and might thus render them less resilient under grazing.

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.

In the semiarid central region of Argentina the probability that rainfall meets crop requirements during growing season is less than 10%, therefore fallowing has been the most important practice to assure water availability during the growing season. Various site-specific and management factors have been identified as crucial for defining fallow efficiency (FE) and final available water contents (AW). The objective of the present study was to improve our knowledge about the interactions between residue cover, weed control, soil profile depth and water storage capacity (WSC) on FE. In 10 sites covering the environments of calcareous plains and sandy plains of the semiarid central region of Argentina and with different WSC, experiments with 3 different levels of residue cover (H, M, L) and with and without weed control (C and W respectively) during fallow were set up. A completely randomized block design with four repetitions and splits plots to consider weed control was used. Soil texture and organic matter were determined in samples of the A horizon (0.20 m). Bulk density, field capacity, permanent wilting point and soil water contents (monthly frequency) were measured at depth intervals of 0.20 m to the depth of the calcite layer or to 2.00 m depth. Soil temperature was taken in weekly intervals at 0.05 m depth and weed plants, separated by species, were counted at the end of fallow in 4 repetitions of 0.25 m2 in each treatment. An empirical model was developed to predict final AW under these experimental conditions. Model parameters were: Residue level, weed control, WSC, profile depth, and rainfall during fallow. Site-specific conditions (WSC and profile depth) affected water storage during fallow; soils with highest values for both parameters showed highest final AW. Weed density was the most important factor that controlled AW, with on average 35 mm less AW in W than in C treatments. Residue level had a positive effect on final AW in both C and W treatments, with a difference of 18.5 mm between H and L. An interaction between residue level and weed density was observed, indicating weed suppression in H treatments. This was also confirmed by correspondence analysis between residue level and weed species which revealed that different species were related to each level. High residue levels also decreased soil temperature, thus affecting germination of post-fallow crops. The empirical model had an overall average prediction error of 13.7% and the regression between measured and predicted values showed a determination coefficient of 0.77

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 physical properties of coarse-textured soils in semi-arid regions often deteriorate with use. We hypothesize that compaction is related to the cropping systems employed in accordance with the different water balances of the soils. Surface samples of 52 Entic Haplustolls under three different regimes (24 under continuous cultivation, 18 under rotation with grass leys and 10 virgin soils) were analysed for clay, silt, organic matter and water content, bulk density, resistance to penetration, hydraulic conductivity and susceptibility to compaction. Data were statistically analysed using regression equations and soils were distinguished on the basis of organic matter content and susceptibility to compaction. In soils of similar texture we found resistance to penetration and susceptibility to compaction to be inversely related to organic matter content and therefore higher under continuous cultivation. Hydraulic conductivity was lower in cultivated soils, especially those with a fine texture. The results show that in sandy to loam soils an increase of about 5 g kg −1 organic matter is required to achieve a 0.06 Mg m −3 decrease in bulk density at the proctor optimum. The results also indicate that the loss of organic matter occurring in the cultivated soils of the study region makes them more susceptible to compaction, which not only has adverse mechanical effects on plants but also gives rise to a considerable reduction in hydraulic conductivity.

The physical properties of coarse-textured soils in semiarid regions often deteriorate with use. We hypothesized that the changes in the physical properties of the soil were related to the cropping systems employed. Surface samples of 52 Entic Haplustolls under three different uses (24 under continuous cultivation (C), 18 under rotation with grass leys (R), and 10 virgin soils (V)) were analyzed for clay, silt, organic matter and water content, bulk density, compaction and aggregate stability. Data were analyzed statistically using principal components, canonical variables, and discriminant functions. A satisfactory segregation of the soils according to discriminant properties (coarse organic matter, aggregate stability, and susceptibility to compaction) was obtained. The model developed satisfactorily classified the soils under different uses (100% R, 83% C and 88% V). Principal component analysis also showed that bulk density, compaction, and wet aggregate stability are related to organic matter content. We conclude that, in the studied region, the lower the ratio of organic matter to clay + silt content, the more severe the physical deterioration of the soils.

Rising demands for food and uncertainties about climate change call for a paradigm shift in water management with a stronger focus on rainfed agriculture. The objective here was to estimate water productivity of different crops under no-till (NT) and conventional till (CT), in order to identify rotations that improve the water productivity of dryland agriculture. We hypothesized that NT and cereal crops would have a positive effect on overall water productivity. Crop yield and water use data were obtained from a 15 year experiment (1993 to 2008) on an entic Haplustoll in the semiarid Pampa, Argentina, with a rotation of wheat (Triticum aestivum L.), corn (Zea mays L.), sunflower (Helianthus annus), and soybean (Glycine max L. Merr.). The results indicated an improved water productivity of all crops under NT compared with that of CT; however, the response of cereals (corn +1.0 kg ha−1 mm−1, wheat +1.3 kg ha−1 mm−1) was higher than that of sunflower (+0.3 kg ha−1 mm−1) and soybean (+0.5 kg ha−1 mm−1). Crop type had a higher impact on water productivity than did tillage system. In agreement with our hypothesis, cereal crops were more efficient (corn 9.8 and wheat 6.9 kg ha−1 mm−1) compared with soybean 2.4 and sunflower 3.9 kg mm−1, but the economic water productivity of sunflower (0.9 US$ ha−1 mm−1) almost equaled that of wheat (1.1 US$ ha−1mm−1) and corn (1.2 US$ ha−1 mm−1). We concluded that the use of the synergy between NT and water efficient crops could be a promising step towards improving food production in semiarid regions. View Full-Text Fil: Noellemeyer, Elke. Universidad Nacional de La Pampa. Facultad de Agronomía; Argentina Fil: Fernandez, Romina. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Anguil; Argentina. Universidad Nacional de La Pampa. Facultad de Agronomía; 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

Because the level of organic matter in soils can reflect the intensity of soil utilization, the present study was carried out with the aim of elucidating the precise effects of different soil management practices on total organic matter and its particle size fractions in soils of the semiarid pampa region. Surface samples of 52 entic Haplustolls under three different uses (24 under continuous cropping, 18 under rotation with grass leys and 10 virgin soils) were analyzed in terms of clay, total organic matter content and organic matter particle size fractions. The obtained data show that organic matter fractions differ according to particle size distribution and the prevailing soil management system. Stable organic matter content ( 100 μm) is strongly influenced by the type of soil management utilized.

A-horizons of 48 Haplic Phaeozems and Kastanozems in plain sites of the Semiarid Argentinian Pampas under three contrasting management systems (virgin bushland, permanent pasture and continuous agriculture) were studied. Morphological characteristics, organic carbon and total nitrogen levels and E4:E6 ratios were determined on the assumption that both quantity and quality of organic matter should be related to soil texture of parent materials in this region since other soil forming factors are uniform. The more intensive land use produced an averaged decrease of 7 cm in A-horizon thickness and degradation of soil structure, but little changes in color and properties of boundaries to AC horizons. In virgin soils organic carbon and nitrogen contents correlate with silt + clay fractions (r = 0,92 and 0,99, respectively), while E4:E6-ratios are related to clay contents (r = −0.69*) confirming the strong influence of soil texture. Agricultural-management and pasture use of soils lead to dispersion of these correlations probably because of differential influence of varying intensities of land use within each management system. Soils under continuous agriculture show lower organic carbon contents than virgin soils only at clay + silt > 40%. Eragrostis curvula-pastures seems to be more effective in restoring organic matter and nitrogen levels in sandy but not in loamy soils with respect to virgin soils. This may be due to a better efficiency of E. curvula-roots in coarse than in fine textured soils to produce humificable residues than the autochthonous grass species. Humusverteilung in Boden der semiariden argentinischen Pampas Die A-Horizonte von 48 Haplic Phaeozems und Kastanozems in ebener Lage der semiariden argentinischen Pampas wurden untersucht. Sie verteilten sich unter die drei unterschiedlichen Landnutzungssysteme naturliches Buschland, Dauerweide und permanenter Ackerbau. Die morphologischen Eigenschaften, die organischen Kohlenstoff- und Gesamtstickstoffgehalte sowie die E4:E6-Verhaltnisse wurden bestimmt unter der Annahme, das sowohl Quantitat wie auch Qualitat der organischen Substanz zur Bodenart des Ausgangssubstrats und Bodennutzung in diesem Gebiet in Beziehung stehen, alle anderen bodenbildenden Faktoren konnen als einheitlich betrachtet werden. Die intensivere Landnutzung erzeugte im Durchschnitt eine Abnahme der Machtigkeit der A-Horizonte von 7 cm und eine Degradierung der Bodenstruktur, aber nur geringe Veranderungen der Bodenfarbe und der Ausbildung der Grenze zu den AC-Horizonten. Die org. Kohlenstoff- und Stickstoffgehalte korrelieren mit den Schluff + Tongehalten (r = 0,92 bzw. 0,99), wahrend die E4:E6-Quotienten nur mit der Tonfraktion in den jungfraulichen Boden in Beziehung stehen (r = −0,69). Dies bestatigt die Eingangshypothese. In ackerbaulich und weidewirtschaftlich genutzten Boden nimmt die Straffheit dieser Korrelationen ab; wahrscheinlich, weil der Einflus verschiedener Intensitaten der Landnutzung innerhalb eines Landnutzungssystems differenzierend wirkt. Die Eragrostis curvula-Weiden waren effektiv im Erhalten der organischen Substanz und des Stickstoffniveaus in sandigen aber nicht in lehmigen Boden, wiederum bezogen auf die jungfraulichen Boden. Wahrscheinlich sind Eragrostis curvula-Wurzeln in groberen eher als in feineren Boden in der Lage, mehr humifizierbare Ruckstande zu bilden als die autochthonen Graser.