THE IMPACT OF THE AMOUNT OF HUMUS IN THE POTENTIAL MINERALIZATION OF NITROGEN IN THE SOIL

Cilj rada je bio na temelju rezultata agrokemijskih analiza tla i bioloških metoda utvrditi sposobnost tla za mineralizaciju dušika. Proveden je laboratorijski pokus inkubacije uzoraka tla tijekom 4 tjedna gdje je utvrđen potencijal mineralizacije dušika za 30 uzoraka tla različitog sadržaja humusa mjerenjem koncentracije nitratnog dušika u tlu. Uzorci su podijeljeni u 2 skupine na temelju sadržaja humusa: slabo humozna tla i humozna tla. Također je analizirana povezanost sadržaja ukupnog dušika u tlu, sadržaja mineralnog dušika u tlu, te intenziteta disanja tla sa utvrđenom razinom mineralnog dušika u nitratnom obliku nakon 28 dana inkubacije. Ukupna razina mineralnog dušika u nitratnom obliku pokazala je rapidan porast nakon prvih 7 dana inkubacije. Na temelju prosjeka svih 30 uzoraka tla, prosječan dnevni porast koncentracije nitratnog dušika u mineralnom obliku je tijekom prvih 7 dana iznosio 2,81 mg/kg/dan. U relativnom iznosu porast je nakon 7 dana inkubacije iznosio 168,5 % u odnosu na početno stanje. Iako je u apsolutnom iznosu koncentracija nitratnog dušika u mineralnom obliku rasla tijekom četiri tjedna inkubacije, u relativnom iznosu je za svaki slijedeći tjedan utvrđeno postupno opadanje intenziteta mineralizacije dušika. Veći intenzitet mineralizacije je utvrđen za humozna tla. Tijekom prvih 7 dana prosječan dnevni porast koncentracije nitratnog dušika u mineralnom obliku je za humozna tla iznosio 3,25 mg/kg/dan odnosno 168,2 % u odnosu na početno stanje, dok je za slabo humozna tla iznosio 2,36 mg/kg/dan ili 168,9 % u odnosu na početno stanje. Na temelju rezultata svih 30 uzoraka tla provedena je statistička analiza odnosa koncentracije nitratnog dušika u tlu nakon 28 dana inkubacije i vrijednosti sadržaja ukupnog dušika u tlu, sadržaja mineralnog dušika u tlu, te intenziteta disanja tla.Objective of this study was to determine , based on results of agrochemical analisis of the soil and biological methods, ability of soil for the nitrogen mineralization. Laboratorical experiment was conducted with soil examples during 4 weeks. Potential of the nitrogen mineralization is stated for 30 soil samples with different content of humus by measuring concentration of nitrate nitrogen int he soil. Samples are diveded into 2 groups according to content of humus: on poor-humus soils and humus soils. Relation between content of total nitrogen int he soil, content mineralized nitrogen in the soil and intensity of soil-breathing with stated level of mineralized nitrogen in nitrate form after 28 days of incubation is also analized. Total level of mineralized nitrogen in the nitrate form has showed rapid increase after 7 days of incubation. Based on matemathical average of all 30 samples, average daily increase of nitrate nitrogen concetration in mineral form in first 7 days was 2,81 mg/kg/per day. In relative sum increase after 7 days of incubation was 168,5 % in relation to initial state. Althoug int he absolute sum the concetration oft he nitrate nitrogen in mineralized form was increasing during the four weeks of incubation, in relative sum for every other week there has been gradual decrease of intensity of nitrogen mineralization. Bigger decrease was stated for the humus soils. During the first 7 days average daily concentration increase of nitrate nitrogen in mineral form for the humus soils was 3,25 mg/kg/per day or 168,2 % in relation to initial state; for the the poor- humus soils it was 2,36 mg/kg/per day or 168,9 % in relation to its initial state. According to results of all 30 samples there has been statistic analisys between concetration of nitrate nitrogen int he soil after 28 days of incubation anda mount of content of total nitrogen int he soil, content of mineralized nitrogen in the soil and intensity of soil-breathing