The Nitrogen-Kjeldahl is part of the Total Nitrogen. This includes the organic nitrogen and ammonia/ammonium. In soil samples, most of the Nitrogen is present as organic Nitrogen and Ammonia. The nitrite and nitrate are just small parts of it, sometimes those are even negligible.
The organic nitrogen is present in the soil organic matter in high concentrations. Therefore, the top soil layer should contain a higher concentration of Nitrogen-Kjeldahl than the deeper parts of the soil layer. This is true because the topsoil contains high amounts of organic matter, such as plants and humus. The humus consists of decayed plant and animal matter, algae, and bacteria.
The samples were taken at four locations. Two samples were taken at each location. One near the surface soil and at a deeper depth near where the groundwater begins (about 1-3 m deep). Each sample was tested twice to account for possible variations in the sample and the experiment.
On average, the soil top layer contained more organic nitrogen and ammonia, except location 3, which is the grassy area, where the lower soil layer showed higher results.
The topsoil forest contained the highest Nitrogen-Kjeldahl concentrations in comparison with the other results due to the higher organic matter.
The grassy areas had lower Nitrogen Kjeldhal concentrations compared to the other sampling sites.