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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]

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]

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]