The estimation of mineralization, immobilization and nitrification in nitrogen‐15 field experiments using computer simulation

Abstract

A combination of mathematical analysis and computer simulation, using parameters readily measured in a nitrogen‐15 field experiment, is employed to determine rates of mineralization, immobilization and nitrification under a growing crop. The procedure also yields the proportion of crop nitrogen uptake occurring as ammonium and nitrate. When applied to ‐results from grass lysimeters receiving 250 or 900 kg N ha–1 a–1 as ammonium nitrate, the analysis suggested that at 250 kgN ha–1 a–1 64–66% of crop nitrogen uptake was as ammonium; at 900 kg N ha–1 a–1 the figure was 43–49%. Nitrification at 250kgNha–1 was only 13–19kgN ha–1 over 160d while at 900 kg N ha–1 between 191 and 232 kg N ha–1 were nitrified. The results suggested that the apparent inhibition of nitrification in grassland soils may simply reflect poor substrate competition by nitrifying bacteria. Finally, there was a suggestion that mineralization/immobilization was lower at the high fertilizer rate. Copyright © 1987, Wiley Blackwell. All rights reserved