There have been many papers on this, so I suggest some literature research. You will not get a simple answer to your question.  Try to develop a conceptual framework.

Keep in mind that the amount of N leached depends on (I) the size of the source (the amount of N, mainly nitrate - but this can be replenished from endogenous and exogenous sources and is very dynamic in soil) and (ii) the volume of water moving through the soil, which is a function of both the supply of water and the soil hydraulic properties.

Hi My Dear Evangelos Tziritis; Here are few links will be helpful in your research. Good Luck n regards

https://dl.sciencesocieties.org/publications/sssaj/abstracts/36/3/SS0360030465

http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2389.1993.tb00433.x/abstract

http://www.sciencedirect.com/science/article/pii/S0167880905002896

http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2389.1993.tb02325.x/full

Hola Evangelos

Te adjunto un trabajo que realizamos en la En Alto Valle de Río Negro y evaluamos la distribución de nitratos a diferentes profundidades extrayendo las muestras con barreno. Te adjunto la técnica que usamos y foto del equipo. Los datos son muy confiables.

Saludos Cristina