
%0 Journal Article
%A Anderson, G. C. 
%A Fillery, I. R. P. 
%A Dunin, F. X. 
%A Dolling, P. J. 
%A Asseng, S. 
%T Nitrogen and water flows under pasture&#8211;wheat and lupin&#8211;wheat rotations in deep sands in Western Australia.  2. Drainage and nitrate leaching
%J Australian Journal of Agricultural Research
%D 1997/03/13
%V 49
%N 3
%P 345-362
%K N loss, eciency N use, &#8216;spared&#8217; N, subterranean clover, capeweed, time domain reflectrometry.
%R https://doi.org/10.1071/A97142
%U https://www.publish.csiro.au/paper/A97142 
%X Quantification of nitrate (NO-3) leaching is fundamental to understanding the efficiency with which plants use soil-derived nitrogen (N). A deep sand located in the northern wheatbelt of Western Australia was maintained under a lupin (Lupinus angustifolius)-wheat (Triticum aestivum) and a subterranean clover (Trifolium subterraneum) based annual pasture-wheat rotation from 1994to 1996. Fluxes of water and NO-3 through, and beyond, the root-zone were examined. Drainage was calculated on a daily basis from measurements of rainfall, evapotranspiration, and the change in soil water content to a depth of 1&#183;5 m. Evapotranspiration was estimated from Bowen ratio measurements,and soil water content was determined by time domain reflectrometry. Soil was sampled in layers to1&#183;5 m at the onset of winter rains and analysed for NO-3 . Ceramic suction cups were installed at 0&#183;25, 0&#183;4, 0&#183;6, 0&#183;8, 1&#183;0, 1&#183;2, and 1&#183;4 m to sample soil solution from June to mid August. The NO-3 leached from each layer was computed by multiplying the daily drainage through each layer by the estimated concentration of NO-3 within the layer. The estimated concentration of NO-3 in a layer was calculated by taking into account NO-3 either entering that layer through mineralisation and leachingor leaving the layer through plant uptake. Mineral N was added to the surface 0&#183;2 m in accordance with measured rates of net N mineralisation, and daily N uptake was calculated from the measured above-ground plant N derived from soil N. Root sampling was undertaken to determine root lengthdensity under pastures, lupin, and wheat. Cumulative drainage below 1&#183;5 m was similar under wheat and lupin, and accounted for 214 mmfrom 11 May to 15 August 1995 and 114 mm from 2 July to 15 September 1996. The cumulative evapotranspiration (Ea) over these periods was 169 mm from a wheat crop in 1995, and 178 mm from a lupin crop in 1996. The amount of NO-3 in soil at the start of the growing season was afiected by previous crop, with a lower range following wheat (31-68 kg N/ha) than following legumes (40-106 kgN/ha). These large quantities of NO-3 in the soil at the break of the season contributed substantially to NO-3 leaching. Leaching of NO-3 below 1&#183;5 m in wheat crops accounted for 40-59 kg N/ha where these followed either lupin or pasture. In contrast, less NO-3 was found to leach below 1&#183;5 m in pastures (17-28 kg N/ha). Greater N uptake by capeweed (Arctotheca calendula L.) than by either wheat or lupin was the main reason for the lower amount of NO-3 leached in pastures. 
