Nitrogen use efficiency in most extensive and intensive crops is low under Chilean conditions, where the main fertilizer used is urea (46%N). Main reasons are: excessive N rates, small number of splits, and inadequate irrigation management or high precipitation levels. The use of nitrification inhibitors might contribute to increase N-Fertilizer Use Efficiency (NFUE) or apparent N recovery efficiency. Maintaining more ammonium (NH₄⁺) available in the soil might also enhance P absorption and therefore increase P-Fertilizer Use Efficiency (PFUE). Two N fertilizer products, Ammonium Sulfate (AS) and Ammonium Sulfate Nitrate (ASN), containing the nitrification inhibitor 3,4-DiMethylPyrazole Phosphate (DMPP) were evaluated in pot and field experiments in comparison to traditional N sources such as urea and nitrate (NO₃^-) forms. Experiments were performed in soils belonging to Andisol and Inceptisol orders, and different crops were used as test plants. In pot experiments, excess irrigation water was applied in order to cause leaching. Evaluations included, among others: yield, N, P, K, and S plant uptake, N and P fertilizer use efficiency, and NO₃^- concentrations on the leacheates. In some experiments, different P rates were applied and the PFUE was compared for treatments fertilized with different N sources. A preliminary model was developed in order to estimate P rates when the N source has a nitrification inhibitor compared to a traditional N source. Other experiences included the evaluation of NP or NPK fertilizer containing DMPP. Several N split forms as well as application ways were evaluated. Under controlled experiments, ASN+DMPP reached a higher NFUE than urea and NO₃^- forms, by maintaining higher levels of NH₄⁺ in the soil and thereby reducing nitrate leaching. Similar results were observed under field conditions were reduced N rates applied as AS+DMPP or ASN+DMPP produced the same yield and quality compared to a full N rate applied as urea or nitrate forms. On the other side, fertigation programs that included fertilizers with DMPP were more efficient that those fertilized with traditional fertilizers. A better relationship NO₃^-/NH₄⁺ in the soil when using DMPP can be one of the factors explaining these effects. In most experiments, P uptake was improved by the use of N sources containing DMPP, which in turn increased PFUE. According to these results it could be possible to reduce the P rate when applying a N-fertilizer containing DMPP. The use of ammonium N sources with the nitrification inhibitor DMPP shows promise to increase N and P FUE under Chilean conditions. Both AS+DMPP and ASN+DMPP together with NP or NPK fertilizer containing DMPP are being adopted by innovative farmers, who choose these N sources because their easiness of application and the possibility of reducing N rates and still get the same or better yields.