Source: https://www.researchgate.net/profile/Horia-Halmajan/publication/265805438_FERTILIZAREA_SUPLIMENTARA_CU_AZOT_SI_SULF_A_PLANTELOR_DE_RAPITA/links/54f9bf2d0cf25371374ff7f9/FERTILIZAREA-SUPLIMENTARA-CU-AZOT-SI-SULF-A-PLANTELOR-DE-RAPITA.pdf