
TY  - JOUR
A1  - Smith, C. J. 
A1  - Dunin, F. X. 
A1  - Poss, R. 
A1  - Angus, J. F. 
T1  - Nitrogen budget of wheat growing on a Riverine clay soil
JF  - Australian Journal of Agricultural Research
JO  - Aust. J.  Agric. Res.
Y1  - 2000
VL  - 51
IS  - 7
SP  - 867
EP  - 876
KW  - bromide, denitrification, nitrate leaching, mineralisation.
UR  - https://doi.org/10.1071/AR99138 
N2  - The fate of nitrogen in wheat grown on a Mesotrophic, Red Kandosol near Wagga Wagga was studied in the 1993 growing season, which had above-average rainfall: 417 mm (31 May&#8211;30 November 1993) compared with an average (June&#8211;November) of 289 mm. Nitrogen supply (fertiliser and mineralisation) was partitioned between crop uptake, gaseous and leaching losses, and residual mineral N in the soil profile. The study plots were 2 adjacent 5-ha areas. At stem elongation (Zadock&#8217;s decimal code 31), one area was topdressed with urea at 14 g N/m2 (fertilised crop). The total N supply to the fertilised crop was 29 g N/m2&#8212;8 g N/m2 of mineral N in the soil at sowing, net mineralisation of 5.3 g N/m2, and fertiliser inputs of 1.7 and 14 g N/m2. The corresponding value for the non-fertilised crop was 15 g N/m2. The urea application produced a 50% increase in above-ground biomass (1521 and 1008 g/m2 dry matter at harvest) and a 1.8-fold increase in grain yield (692 and 384 g/m2). The proportion of the total N supply recovered in the crops was similar (55% and 60% for the non-fertilised and fertilised treatments, respectively). Leaching losses were low (0.4 and 0.5 g N/m2), even though &#x2248;100 mm drained beyond the root-zone (equivalent to 24% of the seasonal rainfall). The periods of saturated soil required to generate drainage also caused denitrification losses of 1.7 and 3.4 g N/m2 for the non-fertilised and fertilised treatments, respectively. Increased net mineralisation and reduced crop N uptake that began a month prior to anthesis were responsible for the substantial amounts of mineral N remaining in the soil after harvest (4.7 and 4.3 g N/m2, respectively). The low NO3 leaching loss associated with high drainage was explained by displacement flow mechanics operating in soil that has a high water retention capacity, which is confirmed by Br and 15N tracer analysis. The N balance was closed for the non-fertilised crop, but a discrepancy of 2.8 g N/m2 remains for the fertilised crop. The uncertainty of &#x2248;10% of the fertilised treatment may possibly be due to ammonia volatilisation following topdressing with urea. 
ER  -

