[en] The approach commonly used for crop management at the plot scale is nowadays changing its focus. The implementation of variable N fertilization requires an increase in the resolution and analysis of the processes that affect N availability for the crops. Therefore, the use of fertilizers needs to be adapted to all the processes that are related to the provision of nutrients to plants. In agricultural systems of low inputs, the availability of N and other elements is a function of the rates of waste decomposition, and depends mainly on the rate of mineralization of the nitrogen contained in the soil organic matter. The quantification of the nitrogen mineralization using a mass balance (Nap) at the field scale is a prerequisite to improve the current recommendations of fertilization with N. The aim of this Ph. D. thesis was to evaluate the mineralization of organic nitrogen through different approaches at the field scale under a maize crop for the specific region of the Flat Inland Pampas. The main soils found in this area are Typic Hapludolls in the lowest landscape positions and Entic Hapludols at the relatively highest positions. The first chapter of this thesis contains an introduction, which describes the antecedents found in the literature about management of spatial heterogeneity for site specific or variable nitrogen fertilization at the field scale in agricultural systems of the Argentinean Pampean. In addition, the chapter provides support for the importance of nitrogen mineralization in the studied systems. Chapter 2 analyses the spatial variability of apparent N mineralized in different subareas at the field scale and its relationship with various soil, climate, and crop properties. Predictive models for assessing the quantity of mineralized N based on climatic, soil and spectral radiance characteristics of the crop are proposed. In chapter 3, the importance of spatial autocorrelation is considered when using statistical models of prediction for Nap prediction from site attributes (soil, crop and altitude) measured over a georeferenced grid (equidistance of sampling 25 m). In the chapter 4, the validity of a calibrated subroutine of the CERES-Corn model to estimate apparent N mineralization is analysed, and also this model is used to quantify the temporal variability of the estimated Nap and its relationship with site variables. Final considerations are presented in chapter 5. At the subarea scale defined by the topographic position, the best predictive model for assessing Nap included the variables silt fraction and precipitations accumulated during the period September to November, and resulted in a coefficient of determination of 62%. Also other univariate and bivariate models of prediction were proposed, as they yield good adjustments, using crop reflectance (NDVI), and sand content as predictive variables. Sufficient evidence for the presence of spatial autocorrelation was found for the mixed models (at the sampling scale of 25 m), which were able to predict the relationship between the sand fraction and the potential nitrogen mineralization with a coefficient of determination of 58%. In contrast the models for estimating Nap from topographical variables, such as the height of the sampling point, and from crop variables such as the reflectance assessed in 10 leaves of the corn crop didn't require an "ad-hoc" recalibration of the spatial autocorrelation parameters. Therefore, models of ordinary linear regression were found to be valuable for estimating N mineralization from the measured variables The CERES-N model was able to simulate the N mineralization during the maize crop cycle for the studied area with an average error of 20%. Thus, this model showed sensitivity to the changes of sample location at the field scale, which mainly were related to the quality of the substrate to be mineralized and to the soil water storage. The parameter SLNF with a value equal to 2,5 was selected to perform the calibration of the subroutine CERES-N for the sites evaluated at the field scale. The analysis of the temporal variability of the N mineralization at the field scale taken into account historical climatic series with a length of 33 years allowed estimating the probability of occurrence of N inputs from mineralization. The sampled sites with higher soil quality showed a greater temporal variability of N mineralization along the crop cycle. The sites located at the top positions within the field showed lower levels of N mineralization and also exhibited a lower variability in nitrogen mineralized, which ranged from 47 to 108 kg N ha-1. In the lowest positions of the field, the contribution of N mineralization during the crop cycle was higher, ranging from 105 to 190 kg N ha-1.

[gl] Actualmente existe unha evolución no enfoque da xestión dos cultivos a escala de lote. A execución da fertilización variable de N require un aumento na resolución e análise dos procesos que afectan a dispoñibilidade de N para os cultivos. Neste sentido, o uso de fertilizantes debe adecuarse aos procesos relacionados coa provisión de nutrientes. Nos sistemas agrícolas de baixos insumos a dispoñibilidade de N e outros minerais é función das taxas de descomposición de residuos e principalmente da taxa de mineralización do nitróxeno da materia orgánica. A cuantificación da mineralización do nitróxeno por balance de masas (Nap) a escala de lote é necesaria para mellorar as actuais recomendacións de fertilizantes N. Esta tese aborda a valoración da mineralización de nitróxeno orgánico a través de diferentes aproximacións a escala de lote para o cultivo de millo na rexión da Pampa Interior Plana, Arxentina onde predominan a escala de lote os solos chamados Hapludoles Típicos nas posicións máis baixas do relevo e os Hapludoles Enticos nas posicións máis elevadas. No primeiro capítulo introdutorio preséntanse os antecedentes sobre o manexo da heteroxeneidade espacial da fertilización variable do nitróxeno a escala de parcela en sistemas de produción agrícola da Rexión Pampeana arxentina e fundamentase a importancia de valorar a mineralización do nitróxeno nos devanditos sistemas. No capítulo 2, descríbese a variabilidade espacial do N mineralizado aparente en diferentes subzonas delimitadas escala de lote e a súa relación con distintas propiedades do solo, clima e cultivo. Propóñerse modelos para predicir da cantidade de N mineralizado baseados en clima,solos, e características espectrais do cultivo. No capítulo 3, avaliouse a importancia da autocorrelación espacial nos modelos estatísticos de predición de Nap a partir de atributos de sitio (solo, cultivo e altimétricos) a partir dunha rede de mostraxe xeorreferenciada (equidistancia de mostraxe 25 m). No capítulo 4, validouse e calibrouse a subrutina de N do CERES-Millo para estimar o N mineralizado aparente e cuantificouse a variabilidade temporal do Nap estimado e a súa relación con variables de sitio. As consideracións finais preséntanse no capítulo 5. A escala de subzonas delimitadas por posición topográfica, o mellor modelo de predición do Nap utilizou á fracción limo e as precipitacións acumuladas durante o período de setembro a novembro cun coeficiente de determinación do 62%. Tamén se propón outros modelos de predición con bos axustes que utilizaron variables de reflectancia do cultivo (NDVI), concentración de area en modelos univariados ou bivariados. Atopáronse evidencias suficientes para detectar a presenza de autocorrelación espacial nos modelos mixtos (escala 25 m) que poden predicir o Nap coa fracción area e o nitróxeno potencialmente mineralizable cun coeficiente de determinación do 58%. En cambio, os modelos de estimación de Nap a partir de variables topográficas, tal como a cota e de cultivo tal como a reflectancia capturada a través do índice do desprazamento do bordo vermello capturado en 10 follas expandidas do cultivo de millo non requiriron reestimación de parámetros por autocorrelación espacial. Por tanto, para a estimación con estas variables os modelos de regresión lineal ordinarios foron validos. O modelo CERES-N simulou o N mineralizado durante o ciclo do cultivo de millo para a zona en estudo cun erro media do 20%, mostrando sensibilidade aos cambios de sitios a escala de lote, preferentemente relacionados coa calidade do substrato a mineralizar e a capacidade de almacenamento de auga. O parámetro SLNF igual a 2,5 foi seleccionado na calibración da subrutina CERES-N para os sitios avaliados a escala de lote. A análise da variabilidade temporal do N mineralizado a escala de lote coa inclusión dunha serie histórica climática de 33 anos, permitiu estimar a probabilidade de ocorrencia de niveis de achegues por esta vía. Os sitios con maior calidade de chan mostraron unha maior variabilidade temporal do N mineralizado durante o ciclo do cultivo. Os sitios situados nas posicións de lomba mostran menores contidos de N mineralizado e tamén menor rango de variabilidade, sendo os límites de 47 a 108 kg N ha-1. En cambio, nas posicións máis baixas da parcela, o aporte de N mineralizado durante o ciclo do cultivo foi maior, cun rango de 105 a 190 kg N ha-1.