Laboratory studies on the behaviour of mineral nitrogen in three Manitoba soil materials

Abstract

A study was undertaken of the behaviour of mineral nitrogen in three Manitoba soil materials under laboratory conditions. The aim was to trace and understand the changes undergone by mineral nitrogen during incubation, especially those changes related to losses of applied fertilizer nitrogen by chemical denitrification involving nitrite. A preliminary evaluation of the extraction-distillation procedure of estimating mineral-N revealed that recoveries of applied ammonium- and nitrate-N were satisfactory on all three soils. Nitrite recoveries were more complete and reproducible using the Griess-Illosvay procedure... Twelve-day incubations with 50 ppm-N revealed losses of mineral-N which could be predominantly ascribed to ammonium fixation. The nitrogen mineralized during incubation was reduced in the presence of fertilizer, especially ammonium sulphate, in Wellwood and Holland. Salt effects are a possible explanation for this. The nitrification rate was increased in the calcareous Lakeland in the presence of phosphate, whilst net mineralized-N was reduced. This could reflect an increase in microbial activity with phosphate, leading to enhanced immobilization. Incubations for fifteen weeks showed large discrepancies in the recovery of N from ammonium sulphate, urea, sodium nitrite, and potassium nitrate. Mineralization and immobilization balances appeared mainly to account for this observation... Investigations using three techniques to demonstrate the interaction of soil and nitrite showed that nitrite is an important avenue of N loss. The losses obtained confirmed the apparent pH relationship noted above in that nitrite-N disappearance increased with decreasing pH... The study revealed that losses of fertilizer-N can occur under conditions of good aeration, concomitant with active nitrification.