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Nitrous oxide (N2O) emission estimation derived from the application of synthetic fertilizers using default emission factors and in a homogeneous way throughout the country for the Inventories of Greenhouse Gases of Argentina do not reflect local productive characteristics and the regional differences. The objectives of this study were a) to disaggregate synthetic nitrogen (N) data by region, crop and weather, b) to analyze and synthesize the state of the art of research in Argentina about the development of local N2O emission factors (FE) for synthetic fertilizers application. For the first objective, a methodology was developed that consists of multiplying the average N dose applied per region by the area sown per crop. For the second, a compilation of scientific papers published in national and international journals was carried out. It was possible to disaggregate the N application data by district and crop by crossing different sources of information: 36.7% of N at country level is applied in the Province of Buenos Aires, 26.3% in Córdoba, 12% in Santa Fe and 7.3% in Entre Ríos. Corn (Zea mays L.) and wheat (Triticum aestivum L.) are the crops with the highest application of N (33.9 and 23.3% respectively). Concerning the state of the art of local research, we found 11 papers that allow us to propose FE for direct N2O emissions, and 15 that allow us to estimate volatilization or leaching fractions that result in indirect N2O emissions. The average values estimated and reported from the literature were 0.0124 kg N2O-N (kg N)-1(direct N2O emission factors), 0.081 kg N volatilized (kg N)-1(volatilization fraction) and 0.244 kg N (kg N)-1 (leaching fraction). Compared to the values used in the National Inventory, the difference is up to 25%. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to explore turbulence-ease in integral human-environment field patterning. This is significant for nursing theory, research and practice given that turbulenceease is a pervasive experience in the life process. Existing literature on the rhythm of turbulenceease within unitary science is summarized. For a more robust understanding of turbulence-ease, the concept is explored through personal, empiric and aesthetic patterns of knowing. Insights from these areas inform an enhanced perspective of the rhythm of turbulence-ease within the Science of Unitary Human Beings (SUHB). Possibilities for wellbecoming in the patterning of turbulence-ease are offered as implications for nursing practice. [ABSTRACT FROM AUTHOR]

In Argentina and particularly in the Pampa region, no-tillage (NT) is the main cropping system. Within this framework, in recent years two situations have characterized NT: one with low crop sequence intensification and thus high soybean participation, and another with greater crop diversity. In this work two treatments represent these situations, referred herein as poor (MP) and good agricultural practices (BP) respectively, together with a reference situation (AN - natural environment) have been evaluated through micromorphological and micromorphometric methods. The presence of a larger crop proportion during the year and shorter winter fallow periods favored the development of the surface (0-6 cm) macroporosity (> 50 µm) in BP (13%) compared to MP (8.8%) while in the 6-12 cm layer, BP macroporosity decreased to 10% and MP maintained its percentage respect to the topsoil layer. AN presented a surface porosity similar to BP (12%). Porosity differences between treatments were associated with the relative proportion of macropores> 1000 µm which corresponded mainly to the elongated pores. Higher frequency of rounded pores in MP respect to BP and AN was observed; in MP their origin would be related to compaction of microaggregates and individual particles, while rounded pores in BP and AN would be associated with biological channels. In turn, and although macropores with vertical orientation where more frequent in BP respect to MP, elongated pores showed a strong tendency to horizontal orientation in both agricultural managements. Although horizontal planes, associated with platy structures were notorious in both agricultural treatments, some of their features appeared clearly different between treatments at the microscopic level. This paper highlights the value of coupling micromorphological and micromorphometric analyses as a tool to characterize the porosity and structural features in soils under NT, and highlights the morphological heterogeneity of the platy structures found in this cultivation system. [ABSTRACT FROM AUTHOR]

In this paper, our objectives were a) to test the utility of biological and biochemical variables to separate degraded areas from soils with minimal human disturbance of Mollisol and Vertisol soil orders and to select the most suitable ones to use as soil quality indicators; b) to generate information to establish reference levels of these variables, and c) to use them in the construction of an index to classify soils with different management history, according to their biological and biochemical quality. We took samples from Mollisol and Vertisol soils from Entre Ríos, corresponding to three soil subgroups. Samples were taken from areas with minimal human disturbance (PD), degraded areas (D), and areas with an intermediate degradation degree (I). Measured variables were: C and N in the microbial biomass (CBM and NBM), potential N mineralization (PMN-IA), organic carbon (Corg) and total N (Ntot). We analyzed the PD, D, and I zone separation by using discriminant analysis applied per soil order independently. Afterwards we built an index with four indicators selected with a prioritization matrix (CBM, PMN-IA, Corg and Ntot). We tested this index on soil samples whose quality we knew in advance. In Mollisols, the total misclassification rate was of 11.1%, while in Vertisols it was of 12.8%. We consider that these results show acceptable errors as the grouped soil series show a high variability. The PMN-IA was the most sensitive variable, reflecting the management effect on both soils. In degraded areas PMN-IA decreased by 60%, while CBM decreased between 30 and 35%. The biological quality index properly classified Aquic Argiudolls and a Typic Hapludert. [ABSTRACT FROM AUTHOR]

The development of precise and accurate methods to determine carbon (C) in soils has currently a strong motivation due to agricultural and environmental importance of this element. In calcareous soils, the total C (CT) consists of sources of organic (Corg) and inorganic (Cinorg) C. When are realized dynamics studies of soil Corg, a method to quantify it without interference from the inorganic fraction is required. In this paper, it was used the dry combustion method by the TruSpec CN (LECO) instrument for analysis of CT, Corg and Cinorg and compared the results obtained with the classical method of wet oxidation for Corg and the titration method for Cinorg. The results indicate a low ratio (R² = 0.62) between the wet oxidation and dry combustion methods with all samples analyzed under study. However, this relationship improves when considering only samples with no carbonates (R² = 0.95). Thus Estimating Corg as the difference between CT and Cinorg it could be an option in calcareous soils. Furthermore we evaluated simple titration and dry combustion method for determining Cinorg obtaining a high determination coefficient (R² = 0.99). Dry combustion method is not suitable for direct determination of Corg in soil samples with presence of Cinorg, being necessary the application of methods to differentiate carbon sources. [ABSTRACT FROM AUTHOR]

Concepts behind the best management practices of crop nutrition include production, economics, as well as social and environmental aspects. All of these should be considered in the development process of fertilizer recommendations. This paper is a study of some of the economic aspects related to the N, P and S fertilization in corn (Zea mays L.), wheat (Triticum aestivum L.) and soybean [Glycine max (L.) Merr.] crops. For this purpose, a series of data, gathered from five on-farm experiments in the north-central pampas region of Argentina between cropping seasons 2000/01 and 2013/14 cropping seasons, were analyzed. Treatments consisted of four nutrient combinations (PS, NS, NP, and NPS) and a Check treatment. The economic performance indices were EAP (kg grain kg applied nutrient-1), MBP (US$ ha-1) and RI (US$ US$-1). The soil fertility level, cropping history, rotation and yield level determined site-specific responses, efficiencies and economic performances. The most profitable was the NPS treatment, except in cases with high initial soil P level, where the NS treatment was the best option. These treatments generated profits from 77 (NS, RI=1,64) to 392 US$ ha-1 y-1 (NPS, RI=2,38). On average, nutrients with a larger cumulative economic impact were N (MBP=1365 US$ ha-1, RI=1,8), and S (MBP=1282 US$ ha-1, RI=4,6), compared to P fertilization (MBP=642 US$ ha-1, RI=1,3). However, P fertilization generated residual effects on the soil P level whose estimated value ranged from +255 to +418 US$ ha-1. Under a long term approach, these results highlight the profitability of fertilization management under a build-up and maintenance criterion. [ABSTRACT FROM AUTHOR]

Site-specific management demands the identification of small areas within fields with homogeneous characteristics (management zones). However, determination of these homogeneous sub-fields is difficult because of complex relationships and spatial variability of soil properties, which affect spatial patterns of yield crop. In this paper, we evaluated apparent electrical conductivity (ECa) functions as potential estimators of soil properties and nutrients, and their possible use as tools for the delimitation of homogeneous areas. ECa mapping of a total of 58 ha was performed on two Haplustoll production fields, located south of the province of Cordoba, near the town of Canals. Soil, nutrients and ECa were analyzed using descriptive statistics, simple correlations and ANOVA. Fine particles (clay, silt), coarse sand and soil organic matter (OM) content exhibited higher correlation with ECa (r>0,6; p≤0,001), whereas P content and pH were lower (r= -0,47 and 0,42, respectively). The correlation among ECa and extract electrical conductivity (ECext), N-NO3 - and S-SO4 -2 were weak or inconsistent. ECa measurements successfully delimited three homogeneous soil zones associated to spatial distribution of fine particles (clay and silt), sand and OM content. However, it would not be advisable to differentiate management zones based on N-NO3 -, SSO4 -2 content and ECext because the values were very low and there was little variation between ECa classes. These results suggest that field-scale ECa maps have may be a useful tool for site-specific crop management (SSCM). [ABSTRACT FROM AUTHOR]

Soil moisture is one of the major factors affecting rainfall-runoff response. The objectives of this paper are to discuss the effect of antecedent moisture condition on surface runoff calculated by Curve Number (CN) method on a gauged basin of Tandilia hills, Buenos Aires province, and to estimate this moisture condition by an alternative method employing a soil water balance calibrated for the study area. The limit set between antecedent moisture conditions I and II was 87,5 mm of soil water reserve at the rainfall previous day. This variable was estimated by water balance adjustment. The relationship between observed and estimated runoff by CN method and 5-day antecedent rainfall had a coefficient of determination that only explained 28% of the variability and overestimated predicted values. The same relationship but adjusting antecedent moisture using soil water reserve at the rainfall previous day showed an R2 of 0.48, with less overestimation of runoff depths than the first method. It follows that new runoff estimations were improved compared to those obtained by the original Soil Conservation Service CN method. This shows that the water balance procedure can be useful to evaluate antecedent moisture conditions for the study region. According to the present results and others from local and international sources, initial moisture condition proved to be a highly sensitive variable for runoff estimation. This highlights the need to carry on further studies to improve the prediction of this soil water variable. [ABSTRACT FROM AUTHOR]

The Optimal Hydric Interval ( IHO IHO) is the interval of easily available soil water for the crops, during which soil resistance and aeration do not limit root growth. In this paper, the upper and lower limits of the IHO are discussed. The upper limit is θCC (soil water content at field capacity) when air capacity ( θa) is not restrictive for root respiration; otherwise, the limit is θa. The lower limit is determined by the variable of greater value between θRP (soil water content at which soil resistance reduces root elongation) and θFU (soil water easily available by crops below which water stress begins). The validity of the limits is analyzed, and methodological problems for their determination are discussed. Values of the IHO obtained by other authors with different critical limits are compared with those obtained using the values proposed in this study. Each agronomic situation (soil, climate, crops) requires specific values of the IHO that should be calculated for each region. For the northern Pampean Region (Argentina) and the usual crops, the following critical values are proposed: θCC = soil water content at -10 kPa, θa = 15%; θRP = 2,5 to 6 MPa (according to the clay content) and θFU = -0,17 MPa . [ABSTRACT FROM AUTHOR]

Entre Ríos soils have been developed on different materials and in a varied topography, which has resulted in a variety of soils. The objectives of this paper were to characterize and establish relationships between biological and biochemical indicators of soil quality in areas of minimum disturbance in Mollisols, Vertisols and Alfisols of Entre Ríos and to analyze their similarities and differences. Soil samples were taken in areas with minimal disturbance and biological and biochemical indicators were measured: organic C (Corg), total N (Ntot), microbial biomass C and N (CBM and NBM), N mineralized in 7 days anaerobic incubations (N-IA) and respiration. Metabolic quotient ( qCO2) and relationships between these variables were estimated. Results showed a wide range of extreme values of biological indicators. The differences found between extreme values were: 16% for Corg, 16.5% for Ntot, 33% for CBM, 46% for NBM and 62% for N-IA. The variables that were highlighted were: N-IA, CBM and CBM/Corg. In relation to the evaluated variables, soils belonging to the order Vertisol could be grouped first, followed by vertic Argiudoll. To establish critical levels of soil quality indicators, reference values will be required for each soil subgroup, while subgroups belonging to Vertisols may be grouped. [ABSTRACT FROM AUTHOR]

The fertilization efficiency program in pasture systems for improving livestock feeding is very important for for farmers in southern Chile. This paper reformulates a mathematical simulation model proposed to describe the concentration of total nitrogen (NT) in soil, in order to fit real experimental data. The objective was to determine the appropriate fertilization strategies in pastures and their direct use by livestock. Critical assumptions consisted, first, in that the concentration of TN in the soil depends on the concentration of its three major components: organic nitrogen (N-NO), nitrate nitrogen (N-NO3 and ammonium nitrogen (NNH4+) and second, that the behavior of the concentration of these components depends strongly on the season of the year and, therefore, the coefficients in the model must be different for each season and third, that only the first 10 cm of the soil profile are meaningful for pasture growth. The modified model consists of a system of partial differential equations (PDE), which consists of EDP's for N-NO and N-NO3, while N-NH4+ was interpolated by a polynomial with the degree varying with the season. The model parameters were calculated solving a functional least squares sum of residuals, using the experimental data. We used optimization methods to solve the problem of least squares. The model used initial data and boundaries approximated by polynomials for each season of the year. The resulting parameters were two: A Quasi-Newton (BFGS) and a Genetic Algorithm (GA). The combination of these algorithms was used to avoid possible local minima and to find a global minimum. The GA was used systematically to find good reference points, which gave BFGS as the initial solution. This combination worked well as all the parameters found globally minimized the residual sum of squares. The results showed that the proposed model was significantly adapted to the data (with a 3% maximum error); therefore, the parameters obtained can be considered for the model for the soil type and season accordingly. [ABSTRACT FROM AUTHOR]

Data on the total nutrient content of soils is essential for assessing potential fertility and is fundamental to environmental and edaphogenetic studies. The aim of this paper was to measure Cu, Zn, Fe y Mn in soils of the Chaco Pampean Plain in Argentina using the simultaneous acid nitric (HNO3 4 M) extraction procedure (called pseudototal) to infer geochemical background and geochemical baseline data by analysing surface and subsurface samples. The results can be related with other edaphic features such as organic carbon, acidity, salinity and carbonates. Average values of 11.3 to 19.2 mg Cu kg-1, 29.4 to 61.5 mg Zn kg-1, 285 to 626 mg Mn kg-1 g-1 and 9 to 19.9 g Fe kg-1 were found at a soil depth of 0-60 cm, falling within the range reported in worldwide literature. The lowest values were found in sandy soils. The values at a soil depth of 0-20 cm were 17 mg Cu kg-1, 55 mg Zn kg-1, 562 mg Mn kg-1 and 16 g Fe kg-1 in loessic and loam loessic soils and 12 Cu kg-1, 36 mg Zn kg-1, 347 mg Mn kg-1 and 11 g Fe kg-1 in loam sandy soils. The textural difference between loessic and sandy soils reflects different background values for the four elements studied, the lowest values corresponding to sandy soils. Multiple regression analysis included Fe and Mn as the main variables to explain the amounts found for each of the four elements at each depth which is related to the high affinity between transition metals and their tendency to co-precipitate as low cristallinity oxides.The second variable in most of the models for the studied elements was organic carbon, confirming the importance of organic matter as a primary source of these micronutrients. [ABSTRACT FROM AUTHOR]

Accelerated soil erosion is, at present, one of the most widespread environmental problems in the world. Geographic Information Systems (GIS) have become an essential tool in soil erosion studies and consequently in the development of appropriate soil conservation strategies. The objective of this paper was to assess the degree of soil erosion associated with land cover dynamics through GIS analysis and to validate the modeling with indicators of soil erosion. Universal Soil Loss Equation (USLE) model, GIS technology and ground-truth dataset (erosion indicators) were employed to elaborate the soil loss maps for four dates at Sorocaba Municipality (SP, Brazil). It was verified that, although the predicted soil loss rate is normally small along the study area, such rate is significantly greater than the soil formation rate. This shows a non-sustainable situation of soil and land cover management. Unplanned urban expansion seems be the main driving force that acts in increasing the erosion risk/occurrence along the study area. [ABSTRACT FROM AUTHOR]

Phosphorus is a nutrient with low soil solubility and mobility and may present limited availability for plant growth. One way to increase phosphorus availability in soil is by fertilization. Due to the variability in the evaluation of phosphorus availability in soil, the study was carried out with the following objectives: a) to compare two of the most common soil available P methods (Bray I and Olsen), and the iron oxide impregnated filter paper method (Strip); b) to evaluate which of the methods is better related to some plant variables under different managements and soil conditions. The soils selected from Corrientes Province were: 1) Entisol: natural soil as a control and cultivated with Citrus, 2) Alfisol: control and cultivated with rice, 3) Vertisol: control and cultivated with pastures. Physical and chemical soil properties indicated that soils from the same order differed in the textural composition, despite having similar chemical properties, suggesting that the differences among soils can be ascribed to cultivation. In addition, a greenhouse pot trial was conducted.Six soils were fertilized with eleven levels of P (0-200 mg P kg-1) and then incubated during 25 days at 28 °C. After incubation, soil samples were analyzed for P by the Olsen, Bray I and Strip methods. Rye grass was grown in pots during 45 days and the shoot dry matter was harvested and its P content analyzed. The results obtained in this work suggest that the three studied methods of P availability in soils described adequately and significantly the relationship between extracted P and dry matter yield (R² between 0.35 for the Vertisol and 0.95, for the Entisol), % P (R² between 0.92 and 0.95) and absorbed P (R² between 0.93 and 0.96). Nevertheless, the adjustments were different between soils, extractants and crop managements, suggesting the existence of a three-way interaction that determines different results in the final value of P availability in soil. Finally, we can conclude that the simplest method may not be the one that is most positively related to dry matter production or the concentration of the P in plant tissue. [ABSTRACT FROM AUTHOR]

The aim of this paper was to study the applicability of the Curve Number method (CN, USDA) for a small arable watershed of 300 ha belonging to the Rolling Pampa under conventional tillage from 1994 to 1998 and subsequently under no tillage until 2004. This analysis was performed by studying rainfall and runoff paired data recorded in situ. Land use consisted mainly of annual crops, particularly soybean. Considering a data pool of 583 rainfall events, only 11% produced appreciable surface runoff. Most of the runoff occurred under antecedent moisture condition I (AMC I). This condition was defined according to the amount of rainfall corresponding to the previous 5 days, thereby opening a critical argumentation for the use of this methodology in the Rolling Pampa. The analysis of the ordered paired data series showed similar CN values under no-tillage and conventional tillage for AMC II (CN 82) and AMC III (CN 96), respectively. However, considering the AMC I condition which corresponds to the lower 10% of the ordered paired data series, the watershed under conventional tillage showed a tendency to produce lower runoff volumes compared to the same catchment area under no-tillage (CN 56 and 68, respectively). This was particularly appreciable for the autumn and winter periods, in which primary tillage operations under conventional tillage produced surface roughness resulting in high infiltration rates. [ABSTRACT FROM AUTHOR]

The expansion of agriculture in areas with a certain degree of fragility, make it necessary to evaluate the state of soil system by means of indicators. The aim of this paper was to develop and apply a minimum set of indicators of the state of the resource to assess soil quality in agroecosystems with low to moderate development Mollisols. The methodology was tested in a homogeneous environmental unit (with Typic Hapludolls) under different uses and management systems in a piedmont basin in SW Córdoba province. Quality ranges were established for the measured properties (organic carbon, pH, base saturation, water stable aggregates, infiltration rate, bulk density, A horizon depth) to normalize the indicators. Selected indicators constitute a minimum number of variables with a high aggregation degree, easy to measure and repeatable, representing the local conditions. These soil resource state indicators are not universal since they were selected in function of the environment and soil type in the studied region. [ABSTRACT FROM AUTHOR]

Copper, iron, manganese and zinc are among the essential elements for plant growth. Despite the small amounts required by plants, agricultural soils are usually deficient in one or more of these micronutrients. Therefore, their concentration in plant tissues falls below the optimum levels. Soil nature plays a fundamental role in the availability of micronutrients and their behavior at a soil-plant level. The aims of this paper were: a) to establish the relationship between soil properties and micronutrient dynamics within the soil profile and b) to determine the plant availability and areas of deficiency in agricultural soils with risk of salinization. The percentage of organic matter was the determining factor in the presence and distribution of the available metals in the soils of the studied area, being the top horizon the one of greatest accumulation. CUDTPA, FeDPTA and MnDPTA were mobile within the profile, whereas ZnDPTA remained adsorbed without vertical displacement. ZnDTPA was the only available metal which also showed differences due to the soil salinity and textural classes. However, soil geochemical conditions imply low extractability and a certain difficulty for micronutrient absorption by plants. [ABSTRACT FROM AUTHOR]

Soils with shallow water table have greater probability of being affected by waterlogging. The prediction of the water table depth temporal oscillation is an important tool to assess the risk of occurrence of such processes. The goal of this paper is to present the theoretical foundations, operative structure and predictive capacity of the water balance simulation model Freat. 1. This model is based on the calculus of water transference between atmosphere, soil profile, vegetation and water table. The simulated processes are: outgoing runoff, water table level rise due to net rainfall values and the incoming underground runoff water table level descent due to underground outgoing runoff, evaporation, capillary rise from the water table and vegetation transpiration. We present the results of its application on Udortenthic Haplustoll and Typic Natralboll soils with a water table oscillating above three meters depth. The prediction error when indicated as the root of the quadratic error between observed and simulated watertable records reached values minor of 15 cm for both soils. The simulation model turns out to be appropriate to predict temporal oscillations of the water table depth and to evaluate the risk of soil waterlogging. [ABSTRACT FROM AUTHOR]

Information about the effects of crop residues on soil parameters in no-tillage systems is not abundant in Argentina because the relative recent adoption this practice. Moreover, most of the available research to date refers to the humid Pampa region. In contrast, information on the semi-arid region is very scarce, despite the fact that an increase in cover stubble is particularly useful in water-limited soils. In this paper we report a long-term evaluation (5 to 10 years) of no-tillage practices on: a) chemical (soil organic matter -SOM, total N and NO3-N) and biological (microbial biomass and activity) soil characteristics, and b) quantity and chemical quality of soybean residues in monoculture and soybean-corn rotation. Research was conducted at Manfredi INTA Experimental Station in semi-arid, central Argentina(31°49' S and 63°46' W). Soils under no-tillage system had higher SOM and total N content compared with control (conservation tillage with chisel plow) in soybean monoculture and soybean-corn rotations. The observed difference increased with time (10 and 20% at 5 and 10 years, respectively). Nitrate content, and microbial activity and biomass showed high variability in the measurement periods, depending on climatic condition at the sampling date. Stubble cover was greater in the corn-soybean rotation with corn as preceding crop (2473.9 g m-2) than in soybean monoculture (1035.7 g m-2)). The stubble non-identifiable fraction was very significant in all treatments (ranging between 2-10 t ha-1), which would favor new surface organic soil formation. The soybean-corn rotation with soybean as preceding crop showed the lowest values in all chemical parameters, particularly in soluble compounds (nitrate, ammonium and soluble carbon). Contrarily to what is usually assumed, our results suggest that nutrient release from long-term stubble may become a significant nutrient source for the crops. Therefore, this nutrient source should be considered when evaluating crop fertilization requirements. [ABSTRACT FROM AUTHOR]

La humedad del suelo constituye uno de los principales condicionantes de la respuesta al escurrimiento. Este trabajo plantea como objetivos discutir la incidencia de la humedad antecedente en la estimación del escurrimiento superficial realizada a través del método de la Curva Número (CN) en una cuenca agropecuaria aforada de las Sierras de Tandilia, provincia de Buenos Aires, y estimar la humedad previa empleando un método alternativo a través del ajuste de un balance hídrico calibrado para el área de estudio. El ajuste del balance permitió fijar un límite de diferenciación basado en la reserva de agua en el suelo del día previo a la precipitación entre las condiciones de humedad antecedentes I y II de 87,5 mm. La relación entre los escurrimientos observados y los calculados a través del método del CN con ajuste de la humedad antecedente de acuerdo con la lluvia de los 5 días previos presentó un coeficiente de determinación que explicó solo el 28% de la variabilidad, con sobreestimación de los valores predichos. Cuando el ajuste de la humedad se realizó según el criterio alternativo, la relación observados versus calculados presentó un R2 de 0,48, lográndose una menor sobreestimación de las escorrentías comparado con el caso anterior. El balance hídrico propuesto resultaría de utilidad para la evaluación de la humedad antecedente de la región cercana a la subcuenca bajo estudio, al mejorar la predicción del escurrimiento respecto del método original del Servicio de Conservación de Suelos. Se pone de relieve la conveniencia de intensificar los estudios de predicción de la humedad edáfica inicial, por ser esta una variable muy sensible para la estimación de escurrimientos en concordancia con lo hallado en este trabajo como así también en otros reportes locales e internacionales.Soil moisture is one of the major factors affecting rainfall-runoff response. The objectives of this paper are to discuss the effect of antecedent moisture condition on surface runoff calculated by Curve Number (CN) method on a gauged basin of Tandilia hills, Buenos Aires province, and to estimate this moisture condition by an alternative method employing a soil water balance calibrated for the study area. The limit set between antecedent moisture conditions I and II was 87,5 mm of soil water reserve at the rainfall previous day. This variable was estimated by water balance adjustment. The relationship between observed and estimated runoff by CN method and 5-day antecedent rainfall had a coefficient of determination that only explained 28% of the variability and overestimated predicted values. The same relationship but adjusting antecedent moisture using soil water reserve at the rainfall previous day showed an R2 of 0.48, with less overestimation of runoff depths than the first method. It follows that new runoff estimations were improved compared to those obtained by the original Soil Conservation Service CN method. This shows that the water balance procedure can be useful to evaluate antecedent moisture conditions for the study region. According to the present results and others from local and international sources, initial moisture condition proved to be a highly sensitive variable for runoff estimation. This highlights the need to carry on further studies to improve the prediction of this soil water variable.

El Intervalo Hídrico Óptimo (IHO) es la fracción de agua edáfica fácilmente utilizable por los cultivos, durante la cual el suelo puede ser penetrado por las raíces sin mayor resistencia y la aeración no limita la respiración radical. En este trabajo se discuten los límites superior e inferior del IHO. El primero es èCC -agua retenida en capacidad de campo- si garantiza una aceptable capacidad de aire (èa); de lo contrario, el límite se alcanza cuando èa no restringe la respiración radical. El límite inferior queda determinado por la variable de mayor valor entre èRP (contenido hídrico edáfico por debajo del cual las raíces restringen su crecimiento), y èFU (agua fácilmente utilizable por debajo del cual comienza el estrés hídrico). Se analiza y discute la validez de los límites, y las dificultades metodológicas que implican sus determinaciones. Se comparan valores del IHO obtenidos por otros autores, que utilizaron diferentes límites, con los calculados con los límites críticos aquí propuestos. Cada situación agronómica (combinación de suelos, clima, cultivo) requiere valores particulares de IHO que deberán ser determinados para cada región. Para el norte de la Región Pampeana (Argentina) y sus cultivos habituales proponemos los siguientes valores críticos: èCC = contenido hídrico a -10 kPa; èa = 15%; èRP = 2,5 a 6 MPa (según el porcentaje de arcilla) y èFU = -0,17 MPa.The Optimal Hydric Interval (IHO) is the interval of easily available soil water for the crops, during which soil resistance and aeration do not limit root growth. In this paper, the upper and lower limits of the IHO are discussed. The upper limit is èCC (soil water content at field capacity) when air capacity (èa) is not restrictive for root respiration; otherwise, the limit is èa. The lower limit is determined by the variable of greater value between èRP (soil water content at which soil resistance reduces root elongation) and èFU (soil water easily available by crops below which water stress begins). The validity of the limits is analyzed, and methodological problems for their determination are discussed. Values of the IHO obtained by other authors with different critical limits are compared with those obtained using the values proposed in this study. Each agronomic situation (soil, climate, crops) requires specific values of the IHO that should be calculated for each region. For the northern Pampean Region (Argentina) and the usual crops, the following critical values are proposed: èCC = soil water content at -10 kPa, èa = 15%; èRP = 2,5 to 6 MPa (according to the clay content) and èFU = -0,17 MPa.

Los suelos de la provincia de Entre Ríos se han desarrollado sobre diferentes materiales originarios y en una topografía variada, lo que ha resultado en un rico mosaico de suelos. Los objetivos del trabajo fueron caracterizar y establecer relaciones de indicadores biológicos y bioquímicos de calidad de suelos en áreas de mínimo disturbio en Molisoles, Vertisoles y Alfisoles de la provincia de Entre Ríos y analizar sus similitudes y diferencias. Se tomaron muestras de suelos de áreas con un mínimo disturbio y se determinaron los indicadores biológicos y bioquímicos: C orgánico (Corg), N total (Ntot), C y N de biomasa microbiana (CBM y NBM), N mineralizado en incubaciones anaeróbicas de 7 días (N-IA) y respiración. Se estimó el cociente metabólico (qCO2) y relaciones entre estas variables. Los resultados permitieron observar un amplio rango entre valores extremos de los indicadores biológicos. La diferencia encontrada entre valores extremos fue de: 16% para Corg, 16,5% para Ntot, 33% para CBM, 46% para NBM y 62% para N-IA. Las variables destacadas fueron: N-IA, CBM y CBM/Corg. En relación a las variables evaluadas, los suelos que se pudieron agrupar fueron los pertenecientes al orden Vertisol, en primer término y luego el intergrado con Molisol. Para establecer niveles críticos de indicadores de calidad de suelos será necesario contar con valores de referencia para cada subgrupo de los suelos, agrupando solamente aquellos pertenecientes a los Vertisoles.Entre Ríos soils have been developed on different materials and in a varied topography, which has resulted in a variety of soils. The objectives of this paper were to characterize and establish relationships between biological and biochemical indicators of soil quality in areas of minimum disturbance in Mollisols, Vertisols and Alfisols of Entre Ríos and to analyze their similarities and differences. Soil samples were taken in areas with minimal disturbance and biological and biochemical indicators were measured: organic C (Corg), total N (Ntot), microbial biomass C and N (CBM and NBM), N mineralized in 7 days anaerobic incubations (N-IA) and respiration. Metabolic quotient (qCO2) and relationships between these variables were estimated. Results showed a wide range of extreme values of biological indicators. The differences found between extreme values were: 16% for Corg, 16.5% for Ntot, 33% for CBM, 46% for NBM and 62% for N-IA. The variables that were highlighted were: N-IA, CBM and CBM/Corg. In relation to the evaluated variables, soils belonging to the order Vertisol could be grouped first, followed by vertic Argiudoll. To establish critical levels of soil quality indicators, reference values will be required for each soil subgroup, while subgroups belonging to Vertisols may be grouped.

La eficientización de la fertilización en los sistemas pratenses, son una necesidad para los ganaderos del sur de Chile, por su importancia en la alimentación del ganado. El objetivo fue reformular un modelo matemático de simulación propuesto para describir la concentración de nitrógeno total (NT) en el suelo, a fin de determinar las estrategias de fertilización adecuada en pradera para el cultivo de especies y su utilización en la alimentación del ganado, ajustando los datos experimentales reales a los simulados. Las hipótesis básicas consistieron, primero, que la concentración de NT en el suelo depende de la concentración de sus tres componentes principales: nitrógeno (N) orgánico (N-NO), nitrato (N-NO3-) y amonio (N-NH4+); segundo, que el comportamiento de la concentración de estos componentes depende fuertemente de la estación del año y por tanto, los coeficientes en el modelo deben ser distintos para cada estación y tercero, que la porción de suelo que es significativa para el crecimiento de la pradera está entre los primeros 10 cm de profundidad. El modelo modificado está formado por un sistema de ecuaciones diferenciales parciales (EDP), el cual consta de EDP's para N-NO y N-NO3-, en tanto, N-NH4+ fue interpolado por un polinomio cuyo grado varió con la estación. Los parámetros del modelo se calcularon resolviendo un problema de mínimos cuadrados con funcional suma de residuales, utilizando los datos experimentales. Se utilizaron los métodos de optimización para resolver el problema de mínimos cuadrados. El modelo utilizó datos iniciales y de borde aproximados por polinomios para cada estación del año. Los parámetros resultantes fueron dos: un Quasi-Newton (BFGS) y un Algoritmo Genético (AG). La combinación de estos algoritmos tuvo como propósito evitar en lo posible los mínimos locales y encontrar un mínimo global. El AG se utilizó sis­temáticamente para hallar buenos puntos de referencia, los cuales se le daban a BFGS como solución inicial. Esta combinación funcionó satisfactoriamente pues todos los parámetros encontrados minimizan globalmente la suma de cuadrados residuales. Los resultados mostraron que el modelo propuesto se adaptó de manera significativa a los datos (con 3% de error máximo), por lo tanto, los parámetros obtenidos pueden considerarse los correspondientes al modelo para el tipo de suelo y estación del año correspondiente.The fertilization efficiency program in pasture systems for improving livestock feeding is very important for for farmers in southern Chile. This paper reformulates a mathematical simulation model proposed to describe the concentration of total nitrogen (NT) in soil, in order to fit real experimental data. The objective was to determine the appropriate fertilization strategies in pastures and their direct use by livestock. Critical assumptions consisted, first, in that the concentration of TN in the soil depends on the concentration of its three major components: organic nitrogen (N-NO), nitrate nitrogen (N-NO3-) and ammonium nitrogen (N-NH4+) and second, that the behavior of the concentration of these components depends strongly on the season of the year and, therefore, the coefficients in the model must be different for each season and third, that only the first 10 cm of the soil profile are meaningful for pasture growth. The modified model consists of a system of partial differential equations (PDE), which consists of EDP's for N-NO and N-NO3-, while N-NH4+ was interpolated by a polynomial with the degree varying with the season. The model parameters were calculated solving a functional least squares sum of residuals, using the experimental data. We used optimization methods to solve the problem of least squares. The model used initial data and boundaries approximated by polynomials for each season of the year. The resulting parameters were two: A Quasi-Newton (BFGS) and a Genetic Algorithm (GA). The combination of these algorithms was used to avoid possible local minima and to find a global minimum. The GA was used systematically to find good reference points, which gave BFGS as the initial solution. This combination worked well as all the parameters found globally minimized the residual sum of squares. The results showed that the proposed model was significantly adapted to the data (with a 3% maximum error); therefore, the parameters obtained can be considered for the model for the soil type and season accordingly.

RESUMEN El contenido total de un nutriente en el suelo es importante para conocer la fertilidad potencial para la nutrición vegetal y constituye una información básica en estudios ambientales y edafogenéticos. El objetivo de este trabajo fue determinar el contenido «pseudototal» de Cu, Zn, Fe y Mn en suelos de la llanura chaco-pampeana de Córdoba, Argentina, mediante una extracción multielemental con HNO3 4 M, pudiendo ser utilizado como aproximación del fondo geoquímico y de línea geoquímica de referencia según se analicen los datos de muestras superficiales y subsuperficiales o superficiales respectivamente. Estos datos se relacionaron con atributos edáficos de importancia agronómica: carbono orgánico, acidez, salinidad y carbonatos. Los contenidos promedios obtenidos fueron: 11,3 a 19,2 mg Cu kg-¹; 29,4 a 61,5 mg Zn kg-¹; 285 a 626 mg Mn kg-¹ y 9 a 19,9 g Fe kg-¹ en la profundidad 0-60 cm de los suelos de la llanura chaco-pampeana de Córdoba (Argentina) y están dentro del rango de valores de referencia a escala mundial, con los valores menores en los suelos de textura más gruesa. Para el suelo superficial (0-20 cm), los valores promedio fueron de 15,7 a 17,7 mg Cu kg-¹, 53,5 a 56,5 mg Zn kg-¹, 548 a 564 mg Mn kg-¹ y 15,8 a 16,¹ g Fe kg-¹ en suelos loéssicos y limo-loéssicos y de 11,9 mg Cu kg-¹ (DSt: 2,8); 34,6 mg Zn kg-¹ (DSt: 8); 309 mg Mn kg-¹ (DSt: 98) y 11,9 g Fe kg-¹ (DSt: 3,2) en suelos franco-arenosos. Las diferencias texturales entre las regiones de suelos loéssicos y arenosos se tradujeron en valores de fondo geoquímico diferentes para los cuatro elementos estudiados, con menores contenidos en los suelos de textura más gruesa. El análisis de regresión múltiple incluyó a Fe y Mn como las principales variables explicativas de los cuatro elementos en todas las profundidades, relacionado con la alta afinidad existente entre los metales de transición, con tendencia a coprecipitar como óxidos de baja cristalinidad. El carbono orgánico en superficie como segunda variable en la mayoría de los modelos para los cuatro elementos confirma la importancia de la materia orgánica como fuente de estos microelementos.Data on the total nutrient content of soils is essential for assessing potential fertility and is fundamental to environmental and edaphogenetic studies. The aim of this paper was to measure Cu, Zn, Fe y Mn in soils of the Chaco Pampean Plain in Argentina using the simultaneous acid nitric (HNO3 4 M) extraction procedure (called pseudototal) to infer geochemical background and geochemical baseline data by analysing surface and subsurface samples. The results can be related with other edaphic features such as organic carbon, acidity, salinity and carbonates. Average values of 11.3 to 19.2 mg Cu kg-¹, 29.4 to 61.5 mg Zn kg-¹, 285 to 626 mg Mn kg-¹ g-¹ and 9 to 19.9 g Fe kg-¹ were found at a soil depth of 0-60 cm, falling within the range reported in worldwide literature. The lowest values were found in sandy soils. The values at a soil depth of 0-20 cm were 17 mg Cu kg-1, 55 mg Zn kg-¹, 562 mg Mn kg-¹ and 16 g Fe kg-¹ in loessic and loam loessic soils and 12 Cu kg-¹, 36 mg Zn kg-¹, 347 mg Mn kg-¹ and 11 g Fe kg-¹in loam sandy soils. The textural difference between loessic and sandy soils reflects different background values for the four elements studied, the lowest values corresponding to sandy soils. Multiple regression analysis included Fe and Mn as the main variables to explain the amounts found for each of the four elements at each depth which is related to the high affinity between transition metals and their tendency to co-precipitate as low cristallinity oxides.The second variable in most of the models for the studied elements was organic carbon, confirming the importance of organic matter as a primary source of these micronutrients.

Accelerated soil erosion is, at present, one of the most widespread environmental problems in the world. Geographic Information Systems (GIS) have become an essential tool in soil erosion studies and consequently in the development of appropriate soil conservation strategies. The objective of this paper was to assess the degree of soil erosion associated with land cover dynamics through GIS analysis and to validate the modeling with indicators of soil erosion. Universal Soil Loss Equation (USLE) model, GIS technology and ground-truth dataset (erosion indicators) were employed to elaborate the soil loss maps for four dates at Sorocaba Municipality (SP, Brazil). It was verified that, although the predicted soil loss rate is normally small along the study area, such rate is significantly greater than the soil formation rate. This shows a non-sustainable situation of soil and land cover management. Unplanned urban expansion seems be the main driving force that acts in increasing the erosion risk/occurrence along the study area.A erosão acelerada é um dos maiores problemas ambientais ocorrentes em larga escala na atualidade. Por sua vez, Sistemas de Informação Geográfica (SIG) tornou-se uma ferramenta essencial em estudos de erosão e conseqüentemente no desenvolvimento de estratégias apropriadas para a conservação do solo. O objetivo deste trabalho foi avaliar o grau de erosão do solo associada com a dinâmica da cobertura do solo através de uma análise geoespacial e validar a modelagem com indicadores de erosão. Utilizou-se a Equação Universal de Perda de Solo (EUPS), recursos de SIG e dados de campo (indicadores de erosão) para elaborar os mapas de perda de solo para quatro datas para o município de Sorocaba (SP, Brasil). Verificou-se que, embora a taxa de perda de solo ao longo da área de estudo é normalmente baixa, esta taxa é expressivamente maior que as taxas de formação do solo. Isto mostra uma situação não sustentável de uso da terra. Expansão urbana não planejada parece ser o principal agente que proporciona o crescimento da ocorrência/risco de erosão ao longo da área de estudo.

El fósforo (P) es un nutriente de baja solubilidad y movilidad en los suelos, que se encuentra generalmente en situaciones de deficiencia para el crecimiento vegetal, y sólo puede ser repuesto mediante la fertilización. Debido a la variabilidad en la evaluación de la disponibilidad de P en el suelo, se realizó este trabajo con el objetivo de: a) comparar entre sí dos de los métodos más comunes de evaluación de disponibilidad de P del suelo (Bray I y Olsen), y el método de la tirita de papel de filtro embebida en óxido de hierro (Strip); b) estimar cual de los métodos se relaciona mejor con algunas variables vegetales ante distintas condiciones de manejo y tipos de suelos. Se estudiaron suelos de los órdenes Entisol, Alfisol y Vertisol de la provincia de Corrientes en condición natural o cultivado con Citrus, arroz o pasturas, respectivamente. Se determinaron algunas propiedades físicas y químicas, verificando la similitud textural entre los suelos Testigos y Cultivados. Se realizó un ensayo en invernadero de cada uno de los seis suelos con once niveles de P (entre 0-200 mg P por kg de suelo) y luego se los incubó durante 25 días a 28 °C. Al finalizar la incubación se determinó el P disponible mediante los procedimientos recomendados para los métodos de Bray I, Olsen y Strip. Se sembró "rye grass" (Lolium perenne) que se cosechó a los 45 días de la siembra para cuantificar la materia seca aérea y análisis de P en tejido. Los resultados obtenidos en este trabajo sugieren que todos los métodos de evaluación de la disponibilidad de P del suelo describieron de manera adecuada y significativa las relaciones entre MS (R² entre 0,35 a 0,95, y valores extremos para el Vertisol y el Entisol), %P (con R² entre 0,92 y 0,95) y P absorbido (R² entre 0,93 y 0,96 y con muy pocas diferencias entre los suelos) con el P extractado por los tres métodos. Sin embargo, la bondad de los ajustes fue diferente entre suelos, extractantes y manejos productivos, y sugieren la existencia de una interacción tripartita que arroja diferentes resultados en el valor final del P disponible. Se concluye que, no necesariamente el método más sencillo en la evaluación de P disponible para el vegetal es el que mejor refleja la relación con la materia seca o con la concentración del P en el tejido.Phosphorus is a nutrient with low soil solubility and mobility and may present limited availability for plant growth. One way to increase phosphorus availability in soil is by fertilization. Due to the variability in the evaluation of phosphorus availability in soil, the study was carried out with the following objectives: a) to compare two of the most common soil available P methods (Bray I and Olsen), and the iron oxide impregnated filter paper method (Strip); b) to evaluate which of the methods is better related to some plant variables under different managements and soil conditions. The soils selected from Corrientes Province were: 1) Entisol: natural soil as a control and cultivated with Citrus, 2) Alfisol: control and cultivated with rice, 3) Vertisol: control and cultivated with pastures. Physical and chemical soil properties indicated that soils from the same order differed in the textural composition, despite having similar chemical properties, suggesting that the differences among soils can be ascribed to cultivation. In addition, a greenhouse pot trial was conducted.Six soils were fertilized with eleven levels of P (0-200 mg P kg-1) and then incubated during 25 days at 28 °C. After incubation, soil samples were analyzed for P by the Olsen, Bray I and Strip methods. Rye grass was grown in pots during 45 days and the shoot dry matter was harvested and its P content analyzed. The results obtained in this work suggest that the three studied methods of P availability in soils described adequately and significantly the relationship between extracted P and dry matter yield (R² between 0.35 for the Vertisol and 0.95, for the Entisol), % P (R² between 0.92 and 0.95) and absorbed P (R² between 0.93 and 0.96). Nevertheless, the adjustments were different between soils, extractants and crop managements, suggesting the existence of a three-way interaction that determines different results in the final value of P availability in soil. Finally, we can conclude that the simplest method may not be the one that is most positively related to dry matter production or the concentration of the P in plant tissue.

El objetivo del presente trabajo fue estudiar la aplicabilidad del método de Número de Curva (CN) del USDA para una microcuenca agrícola de 300 ha de Pampa Ondulada, bajo labranza convencional (LC) durante el período 1994-1998 y posteriormente bajo siembra directa (SD) durante el período 1999-2004 a partir del análisis de lluvias y escurrimientos medidos in situ. El uso de la tierra consistió predominantemente en cultivos anuales, siendo la soja el cultivo más frecuente. De las 583 lluvias analizadas, tan solo el 11% provocó escurrimientos registrables. La mayoría de los escurrimientos ocurrió bajo condición antecedente de humedad (AMC) I, situación que fue definida por la lluvia caída los 5 días anteriores al evento considerado, lo cual muestra un aspecto de discusión crítica para el uso de esta metodología. A través del análisis de la serie ordenada de datos, se observó que LC y SD presentaban valores prácticamente coincidentes entre sí tanto para AMC II (CN 82) como para AMC III (CN 96). Sin embargo, al considerar AMC I (correspondiente al 10% inferior de dicha serie), la labranza convencional presentó una tendencia a generar menores escurrimientos que siembra directa (CN 56 y 68, respectivamente) particularmente durante el período otoño invernal, época en que se realizaron las labores primarias de remoción del suelo que dejaron el suelo rugoso y por ende, con alta capacidad de infiltración.The aim of this paper was to study the applicability of the Curve Number method (CN, USDA) for a small arable watershed of 300 ha belonging to the Rolling Pampa under conventional tillage from 1994 to 1998 and subsequently under no tillage until 2004. This analysis was performed by studying rainfall and runoff paired data recorded in situ. Land use consisted mainly of annual crops, particularly soybean. Considering a data pool of 583 rainfall events, only 11% produced appreciable surface runoff. Most of the runoff occurred under antecedent moisture condition I (AMC I). This condition was defined according to the amount of rainfall corresponding to the previous 5 days, thereby opening a critical argumentation for the use of this methodology in the Rolling Pampa. The analysis of the ordered paired data series showed similar CN values under no-tillage and conventional tillage for AMC II (CN 82) and AMC III (CN 96), respectively. However, considering the AMC I condition which corresponds to the lower 10% of the ordered paired data series, the watershed under conventional tillage showed a tendency to produce lower runoff volumes compared to the same catchment area under no-tillage (CN 56 and 68, respectively). This was particularly appreciable for the autumn and winter periods, in which primary tillage operations under conventional tillage produced surface roughness resulting in high infiltration rates.

El avance de la agricultura en áreas con cierto grado de fragilidad hace necesario realizar evaluaciones del estado del sistema suelo mediante indicadores. El objetivo del trabajo fue desarrollar y aplicar un set mínimo de indicadores del estado del recurso suelo para evaluar la calidad del suelo en agroecosistemas con Molisoles de bajo a moderado desarrollo. La metodología se probó en una unidad ambiental homogénea, con Hapludoles típicos, bajo diferentes sistemas de uso y manejo, en una cuenca pedemontana del SO de la provincia de Córdoba. A las propiedades medidas (carbono orgánico, pH, saturación de bases, agregados estables en agua, velocidad de infiltración, densidad aparente y el espesor horizonte A) se le establecieron rangos de calidad a partir de los cuales se normalizaron los indicadores. Los indicadores seleccionados son un número mínimo de variables con alto grado de agregación, fáciles de medir y repetibles, representando las condiciones locales. Estos indicadores de estado del recurso suelo no son universales ya que fueron elegidos en función del tipo de ambiente y suelo de la región en estudio.The expansion of agriculture in areas with a certain degree of fragility, make it necessary to evaluate the state of soil system by means of indicators. The aim of this paper was to develop and apply a minimum set of indicators of the state of the resource to assess soil quality in agroecosystems with low to moderate development Mollisols. The methodology was tested in a homogeneous environmental unit (with Typic Hapludolls) under different uses and management systems in a piedmont basin in SW Córdoba province. Quality ranges were established for the measured properties (organic carbon, pH, base saturation, water stable aggregates, infiltration rate, bulk density, A horizon depth) to normalize the indicators. Selected indicators constitute a minimum number of variables with a high aggregation degree, easy to measure and repeatable, representing the local conditions. These soil resource state indicators are not universal since they were selected in function of the environment and soil type in the studied region.

Cobre, hierro, manganeso y zinc son cuatro metales esenciales para el crecimiento vegetal. A pesar de las pequeñas cantidades requeridas por las plantas, los suelos agrícolas suelen ser deficitarios en uno o más micronutrientes de forma que su concentración en los tejidos de los vegetales cae por debajo de los niveles que permiten un crecimiento óptimo. La naturaleza del suelo juega un papel fundamental en la disponibilidad de micronutrientes y en su comportamiento a nivel suelo-planta. Los objetivos planteados en el presente estudio son: a) establecer la relación entre los parámetros edáficos y la dinámica de los metales dentro del perfil del suelo, y b) determinar la biodisponibilidad y zonas de deficiencia de micronutrientes en suelos agrícolas y suelos con riesgo de salinización. El porcentaje de materia orgánica es el factor determinante en el contenido y distribución de los micronutrientes en el suelo objeto de estudio, siendo el horizonte superficial el de mayor acumulación. Tanto CuDTPA, FeDTPA como MnDTPA tienen cierta movilidad en el perfil, mientras que ZnDTPA permanece adsorbido sin un desplazamiento vertical. El ZnDTPA es el único metal que además, muestra diferencias como consecuencia de la salinidad y granulometría de los suelos. No obstante, las condiciones geoquímicas del suelo implican una baja extractabilidad y una cierta dificultad de absorción de los micronutrientes por parte de las plantas.Copper, iron, manganese and zinc are among the essential elements for plant growth. Despite the small amounts required by plants, agricultural soils are usually deficient in one or more of these micronutrients. Therefore, their concentration in plant tissues falls below the optimum levels. Soil nature plays a fundamental role in the availability of micronutrients and their behavior at a soil-plant level. The aims of this paper were: a) to establish the relationship between soil properties and micronutrient dynamics within the soil profile and b) to determine the plant availability and areas of deficiency in agricultural soils with risk of salinization. The percentage of organic matter was the determining factor in the presence and distribution of the available metals in the soils of the studied area, being the top horizon the one of greatest accumulation. CuDTPA, FeDPTA and MnDPTA were mobile within the profile, whereas ZnDPTA remained adsorbed without vertical displacement. ZnDTPA was the only available metal which also showed differences due to the soil salinity and textural classes. However, soil geochemical conditions imply low extractability and a certain difficulty for micronutrient absorption by plants.

Los suelos con capa freática poco profunda poseen mayor probabilidad de ser afectados por anegamiento. La predicción de la oscilación temporal del nivel freático constituye una importante herramienta para valorar el riesgo de ocurrencia de tal proceso. El objetivo de este trabajo es presentar los fundamentos teóricos, la estructura operativa y la capacidad predictiva del modelo de simulación del balance hídrico Freat.1. El modelo se fundamenta en el cálculo de la transferencia de agua entre la atmósfera, el perfil del suelo, la vegetación y la capa freática. Los procesos de transferencia simulados son: escurrimiento superficial saliente, ascenso del nivel freático por efecto de la lluvia neta y del escurrimiento subterráneo entrante y descenso del nivel freático por efectos del escurrimiento subterráneo saliente, evaporación, ascenso capilar desde la capa freática y transpiración de la vegetación. Se evalúan los resultados de su aplicación en un Haplustol udorténtico y en un Natralbol típico ambos con freática oscilando a menos de tres metros de profundidad. El error de predicción estimado como la raíz del error cuadrático medio entre registros freáticos observados y simulados es menor de 15 cm para ambos suelos. Se concluye que el modelo resulta apropiado para predecir oscilaciones temporales de capa freática y evaluar el riesgo de inundación por anegamiento en suelos con capa freática cercana a la superficie.Soils with shallow water table have greater probability of being affected by waterlogging. The prediction of the water table depth temporal oscillation is an important tool to assess the risk of occurrence of such processes. The goal of this paper is to present the theoretical foundations, operative structure and predictive capacity of the water balance simulation model Freat.1. This model is based on the calculus of water transference between atmosphere, soil profile, vegetation and water table. The simulated processes are: outgoing runoff, water table level rise due to net rainfall values and the incoming underground runoff, water table level descent due to underground outgoing runoff, evaporation, capillary rise from the water table and vegetation transpiration. We present the results of its application on Udortenthic Haplustoll and Typic Natralboll soils with a water table oscillating above three meters depth. The prediction error when indicated as the root of the quadratic error between observed and simulated watertable records reached values minor of 15 cm for both soils. The simulation model turns out to be appropriate to predict temporal oscillations of the water table depth and to evaluate the risk of soil waterlogging.

La siembra directa (SD) es relativamente reciente en Argentina, por lo que existen escasas posibilidades de evaluar cambios a largo plazo. Además, la mayoría de los trabajos han sido realizados en la región húmeda pampeana siendo escasas las referencias para la zona semiárida central, a pesar de que el incremento de la cobertura de rastrojo es particularmente útil en suelos con limitante de agua. En este trabajo se evaluó el efecto de la SD a largo plazo (5 y 10 años) sobre: a) características químicas (MO, N total y NO3-N) y biológicas (actividad y biomasa microbiana) del suelo; y b) cantidad, fracciones identificables y composición química del rastrojo en dos tipos de ensayos: monocultivo de soja y rotación soja-maíz. La investigación fue realizada en la Estación Experimental Agropecuaria INTA Manfredi en la región semi-árida central. Los suelos bajo siembra directa, presentaron mayor contenido de MO y N total que los suelos control (labranza conservacionista). Las diferencias observados se incrementaron con el tiempo (10% y 20% a los 5 y 10 años, respectivamente). El contenido de NO3-N, y la biomasa y actividad microbiana mostraron alta variabilidad en ambas fechas de muestreo en relación a las condiciones climáticas. La cobertura del rastrojo fue mayor en rotación maíz-soja con antecesor maíz (2.473,9 g m-2) que en el monocultivo de soja (1.035,7 g m-2). La fracción del rastrojo no identificable fue muy importante en todos los tratamientos (rangos entre 2-10 t ha-1), lo que favorecería la formación de nuevo suelo superficial. Estos resultados sugieren que la liberación de nutrientes a partir de un abundante rastrojo en descomposición puede constuir una importante fuente de nutrientes, por lo que debería incluirse en los cálculos para requerimientos de fertilización de los cultivos.Evaluation of the effect of crop residues accumulation on soil under no-tillage cultivation is difficult in Argentina because the relative recent adoption of no-tillage practices in the country. Moreover, most of the available research on no-tillage in Argentina refers to the humid Pampas region. In contrast, information on the semi-arid region is very scarce, despite the fact that an increased cover stubble is particularly useful in water-limited soils. In this paper we report a long-term evaluation (5 and 10 years periods) of no-tillage practices on a) chemical (SOM, total N and NO3-N) and biological (microbial biomass and activity) soil characteristics, and b) quantity, identifiable fractions, and chemical quality of stubble material in soybean monoculture and soybean-corn rotation. Research was conducted at Manfredi INTA Experimental Station in semi-arid, central Argentina (31°49' S and 63°46' W). Soils under no-tillage system had higher SOM and total N content compared with control (conservation tillage with chisel plow) in both, soybean monoculture and soybean-corn rotations. The observed difference increased with time (10 and 20% at 5 and 10 years, respectively). Nitrate content, and microbial activity and biomass showed high variability in the measurement periods, depending on climatic condition at the sampling date. Stubble cover was greater in the corn-soybean rotation with corn as preceding crop (2473.9 g m-2) than in soybean monoculture (1035.7 g m-2). The stubble non-identifiable fraction was very significant in all treatments (ranging between 2-10 t ha-1), which would favor new surface soil formation. The soybean-corn rotation with soybean as preceding crop showed the lowest values in all chemical parameters, particularly in soluble compounds (nitrate, ammonium and soluble carbon). Contrarily with what is usually assumed, our results suggest that nutrient release from long-term stubble may become a significant nutrient source for the crops. Therefore, this nutrient source should be considered when evaluating crop fertilization requirements.