
%0 Journal Article
%A Craswell, ET 
%A Martin, AE 
%T Isotopic studies of the nitrogen balance in a cracking clay. I. Recovery of added nitrogen from soil and wheat in the glasshouse and gas lysimeter
%J Soil Research
%D 1975/06/01
%V 13
%N 1
%P 43-52
%K 
%R https://doi.org/10.1071/SR9750043
%U https://www.publish.csiro.au/paper/SR9750043 
%X The stable isotope 15N was used to study the fate of nitrogen fertilizers applied to a black earth growing wheat. In a glasshouse experiment using soil packed at 56 % moisture (pF 2) into pots, added nitrate was almost completely recovered (mean, 98.8 ± 2.3 %) by soil and plant analysis. This experiment was repeated using 15N-labelled ammonium as well as nitrate; mean recoveries at 15 weeks were 96.8 and 97% respectively (± 2.2% at P < 0.05). A series of pots with soil wetter than pF 2 (at 63% moisture) was also included in an attempt to favour denitrification. Again, virtually complete recovery of added 15N was measured, 97 and 96.8% at 56 and 63% moisture respectively. Fallow and planted systems were then studied in a gas lysimeter. During experiments lasting up to 14 weeks, gaseous losses as 15N-labelled denitrification products were less than the equivalent of 0.2 µg nitrogen/g soil (the lower limit of detection with a mass spectrometer). Although analysis of plant and soil from the lysimeter in two experiments showed virtually quantitative recovery (99.7 and 97.05%), small (0.16%) losses of labelled ammonia into the lysimeter atmosphere were detected. The significance of these results is discussed in relation to the common finding of large deficits in nitrogen balance studies. 
