
TY  - JOUR
A1  - Rochester, IJ 
A1  - Constable, GA 
A1  - MacLeod, DA 
T1  - Mineral nitrogen dynamics in a fallow grey clay
JF  - Australian Journal of Experimental Agriculture
JO  - Aust. J. Exp. Agric.
Y1  - 1991
VL  - 31
IS  - 2
SP  - 237
EP  - 244
KW  - 
UR  - https://doi.org/10.1071/EA9910237 
N2  - An annual cyclic pattern of nitrate accumulation and dissipation was identified in a fallow grey clay. The pattern was regular during the 3 years studied, with maximum values of nitrate nitrogen (N) (to 34 mg nitrate-N/kg) occurring in late autumn (May) and minimal values (to 7 mg nitrate-N/kg) in late winter (August). Ammonium levels were low throughout the 3 years, except for a short period following the incorporation of crop residues. The cycle of soil nitrate lagged behind the annual temperature cycle by about 3 months. Multiple regression using temperature and soil water deficit explained 68% of the variation in nitrate-N. The identification of this pattern of soil nitrate may now enable the prediction of September soil nitrate (currently used to estimate N fertiliser requirement for the forthcoming crop) from soil sampled up to 3 months earlier. Laboratory incubation studies confirmed temperature and soil water as highly significant in determining the soil's mineral N status. By applying the temperature and soil water deficits which prevailed during the field observations to the regression equation derived from the laboratory data, a similar fluctuating pattern of soil nitrate emerged. Incubation of intact field cores under low temperatures produced a net N immobilisation and high temperatures produced a net N mineralisation. Immobilisation and remineralisation of N by the soil biomass (rather than leaching or denitrification) were responsible for the oscillations in nitrate-N, and these processes were largely driven by temperature and soil water status. 
ER  -

