Specific transformations of mineral forms of nitrogen in acid soils

Abstract

Investigations were performed on soils of different acidity, ranging in the pH interval 4.65-5.80 (in water). Changes of the mineral nitrogen forms in the examined soils were studied by applying short-term incubation experiments performed under aerobic conditions, with a humidity of 30 % and a temperature of 20°C, both with and without the addition of 100 and 300 ppm NH4-N. The results of the incubation experiments showed that retarded nitrification was present in all the examined soils. Increased and toxic quantities of nitrites (35.7 ppm) were formed during the incubation, which remained in the soil solution for several days, and even weeks, in spite of favorable conditions of moisture, aeration and temperature for the development of the process of chemoautotrophic nitrification. Decelerated chemoautotrophic nitrification was the source of the occurrence of nitrite in the examined less acid soil (soil 1), while in soils of higher acidity (soils 2 and 3) after addition of 100 and 300 ppm NH4-N, nitrite occurred due to chemical denitrification (chemodenitrification). Nitrites formed in the process of chemodenitrification underwent spontaneous chemical oxidation resulting in nitrate formation (chemical nitrification). The content of mineral nitrogen (NH4 + NO3 + NO2-N) decreased during the incubation period, proving gaseous losses from the examined soils. Application of lower doses of nitrogen fertilizers could decrease nitrogen losses by denitrification as well as the occurrence of nitrite in toxic quantities in the investigated pseudogley soil.

Istraživanja su obavljena na zemljištu tipa pseudoglej iz okoline Šapca. Ispitivana zemljišta spadaju u grupu kiselih i jako kiselih zemljišta. Promene mineralnih oblika azota su praćene pomoću kratkotrajnih inkubacionih ogleda (vlažnost 30 % i temperatura 20 °S), sa i bez dodatka 100 i 300 ppm NH4-N. Tokom inkubacije utvrđene su povišene i toksične količine nitrita, koje su se u zemljišnom rastvoru zadržavale više dana i nedelja. Utvrđene količine nitrita su se javljale kao posledica usporene biološke nitrifikacije (kod manje kiselog zemljišta), dok su pri dodatku 100 i 300 ppm NH4-N one nastajale u procesu hemodenitrifikacije. U ispitivanim zemljištima se odvijala i spontana oksidacija nastalih nitrita hemijskim putem (hemijska nitrifikacija). Da bi se smanjili gubici azota procesom denitrifikacije i stvaranje toksičnih količina nitrita na pseudoglejnom zemljištu se može preporučiti primena nižih doza azotnih đubriva u odnosu na doze koje se primenjuju kod neutralnih i alkalnih zemljišta.