Nitrogen distribution in vadose zone under some Bulgarian soils

The objective of this study is to estimate and compare the nitrogen distribution in geological materials underlying soils under natural and anthropogenic loading in different agro-climatic regions in Bulgaria. The obtained experimental results show that the applied fertilizer rates in excess of the nitrogen uptake by agricultural crops has led to considerable enrichment with NO₃-N of the entire profile (0–5 m) under the Fluvisol and the Chromic Luvisol. At the same conditions on the Vertisol nitrate nitrogen content is found till the 2 m depth and there is no direct relation between the fertilizer rates and contaminated shallow groundwater. The deep drillings completed in Haplic Chernozems show that independent of land use NO₃-N is detected in all samples from the soil surface to the groundwater table and varies from 0.2 to 33.0 mg.kg ^˗1. The area of the big dairy farm could be classified as a point source of contamination as about 400 kg.ha^˗1 NO₃-N is accumulated in the 2-meter layer.