Vertical variability of arsenic, cadmium and lead in stagnosol after long-term mineral nitrogen fertilization

Današnja poljoprivredna proizvodnja iziskuje primjenu velikih količina mineralnih gnojiva, naročito dušičnih. Gnojiva mogu sadržavati značajne količine potencijalno opasnih elemenata u tragovima geološkog ili umjetnog podrijetla. Cilj ovog diplomskog rada bio je utvrditi vertikalnu varijabilnost arsena, kadmija i olova u pseudogleju do 80 cm dubine tla nakon višegodišnje primjene mineralnih dušičnih gnojiva. Istraživanje je uključivalo analizu 12 arhiviranih uzoraka tla koji su 2018. godine prikupljeni sa stacionarnog poljskog pokusa smještenog u središnjem dijelu Hrvatske (lokalitet Potok) nakon 22 godine primijene rastućih doza dušičnih gnojiva (0, 100, 200, 300 kg N/ha) sa tri dubine: 0-30, 30-50 i 50-80 cm. Metodom prijenosne rendgenske florescencije u tri ponavljanja određen je sadržaj As, Cd i Pb, a statistička obrada podataka provedena je analizom varijance. Rezultati ukazuju da su rastuće doze dušične gnojidbe nakon 22 godine uzastopne primjene mineralnih gnojiva značajno utjecale na raspodjelu arsena (Pr>F = 0,0228) i olova (Pr>F = 0,0356) u površinskom sloju tla. Prosječan sadržaj arsena varirao je od 11,7 mg/kg na N300 tretmanu do 15,0 mg/kg na N100 tretmanu, dok je sadržaj olova bio u rasponu od 17,3 mg/kg na N100 tretmanu do 22,0 mg/kg na N200 tretmanu. Utvrđeni sadržaj kadmija varirao je u vrlo uskom rasponu od svega 1 mg/kg (8 mg/kg - 9 mg/kg) s prosječnim koeficijentom varijance na sva četiri tretmana od 1,73 %. Sadržaj arsena značajno je rastao s porastom dubine na N0, N200 i N300 tretmanima, dok se sadržaj olova značajno smanjivao s porastom dubine na N0 i N200 tretmanu, te relativno povećavao na N100 i N300 tretmanu. Rezultati ukazuju na značajno ispiranje arsena u dublje slojeve tla i činjenicu da je u dubljim slojevima tla u odnosu na površinski sloj tla pseudoglej onečišćen ovim elementom na kontrolnom tretmanu (50-80 cm - 18,7 mg/kg), N100 tretmanu (50-80 cm - 16,7 mg/kg), N200 tretmanu (30-50 cm - 19,0 mg/kg; 50-80 cm - 22,3 mg/kg) i N300 tretmanu (50-80 cm - 21,3 mg/kg). Utvrđena je i značajna negativna i vrlo jaka ovisnost arsena i sadržaja humusa (r = -0,7076) i značajna slaba pozitivna ovisnost između olova i sadržaja humusa (r = 0,3945).Today's agricultural production requires the use of large amounts of mineral fertilizers, especially nitrogen fertilizers. Fertilizers can contain significant amounts of potentially dangerous trace elements of geological or artificial origin. The aim of this thesis was to determine the vertical variability of arsenic, cadmium and lead in stagnosol up to 80 cm soil deep after long-term application of mineral nitrogen fertilizers. The research included the analysis of 12 archived soil samples that were collected in 2018 from a stationary field experiment located in the central part of Croatia (locality Potok) after 22 years of applied increasing doses of nitrogen fertilizers (0, 100, 200, 300 kg N/ha) from three depths: 0-30, 30-50 and 50-80 cm. The content of As, Cd and Pb was determined by portable X-ray fluorescence in three repetitions and the statistical data analyses was carried out by the analysis of variance. The results indicate that increasing doses of nitrogen fertilization after 22 years of consecutive application of mineral fertilizers significantly influenced the distribution of arsenic (Pr>F = 0.0228) and lead (Pr>F = 0.0356) in the surface soil layer. The average content of arsenic varied from 11.7 mg/kg in the N300 treatment to 15.0 mg/kg in the N100 treatment, while the lead content ranged from 17.3 mg/kg in the N100 treatment to 22.0 mg/kg on N200 treatment. The determined cadmium content varied in a very narrow range of only 1 mg/kg (8 mg/kg - 9 mg/kg) with an average coefficient of variation for all four treatments of 1.73%. Arsenic content increased significantly with increase of the depth at N0, N200 and N300 treatments, while lead content significantly decreased along with soil depth at N0 and N200 treatments, and relatively increased in N100 and N300 treatments. The results indicate a significant leaching of arsenic into the deeper soil layers and the fact that in the deeper soil layers compared to the surface soil layer, pseudogley was contaminated with this element at the control treatment (50-80 cm - 18.7 mg/kg), at N100 treatment (50- 80 cm - 16.7 mg/kg), at N200 treatment (30-50 cm - 19.0 mg/kg; 50-80 cm - 22.3 mg/kg) and at N300 treatment (50-80 cm - 21.3 mg/kg). A significant negative and very strong dependence of arsenic and organic matter content (r= -0.7076) and a significant positive weak dependence between lead and organic matter content (r= 0.3945) were found