
TY  - JOUR
A1  - Russell, C. A. 
A1  - Fillery, I. R. P. 
T1  - Turnover of nitrogen from components of lupin stubble to wheat in sandy soil
JF  - Soil Research
JO  - Soil Res.
Y1  - 1999
VL  - 37
IS  - 3
SP  - 575
EP  - 592
KW  - Lupinus angustifolius, N turnover, mineralisation, 15N, residues, substrate quality.
UR  - https://doi.org/10.1071/S98071 
N2  - The rate of decomposition of 15N-labelled lupin (Lupinus angustifolius) stubble and the use of mineralised 15N by wheat were determined in field experiments on a deep loamy sand previously cropped to lupin. In one experiment, leaf, stem, and pod (pod-valve) components were applied separately to mini-plots that were either left unplanted or subsequently planted to wheat. In the second experiment, leaf and stem components, each of either low or high N concentration, were applied separately to mini-plots which were subsequently planted to wheat. Soil was recovered in layers to a maximum depth of 1 m and subsequently analysed for 15N in NH + 4 , NO-3 , and total N. The net mineralisation of stubble 15N was estimated from the decrease in soil organic 15N (total 15N &#8211; inorganic 15N), and the uptake of 15N by wheat was measured periodically. All treatments were characterised by the high retention of lupin stubble 15N in the soil organic matter. Between 9 and 34% of stem and pod 15N, and 19&#8211;49% of leaf 15N, was mineralised within a 10-month period. From these data the annual net mineralisation of a typical lupin stubble was estimated at 25&#8211;42 kg N/ha, an N benefit similar to that estimated from agronomic trials. Wheat uptake of lupin-stubble 15N ranged from 9 to 27%. Of the stubble components, only the leaf contained sufficient quantities of mineralisable N to be an important source of N for wheat. At wheat maturity in the first experiment, losses of stubble 15N ranged from 13% (leaf) to 7% (stem). In the second experiment, losses of 15N were only observed from the high N treatments (leaf 8%, stem 15&#183;5%). Stubble component chemistry appeared to affect net mineralisation and plant uptake differently. Across both experiments, annual net mineralisation best correlated (R = 0&#183;69) with the N concentration of the stubble components. Wheat N uptake was strongly positively correlated with polysaccharide content (R = 0&#183;89) but negatively correlated with lignin content (R = &#8211; 0&#183;79). Although large quantities (58 and 98 kg N/ha) of soil-derived inorganic N were found in the root-zone (&#8211;1&#183;0 m) of wheat sown after lupins, and attributed to the decomposition of lupin root systems and surface residues prior to the establishment of each experiment, it is concluded that the short-term decomposition of lupin stubble 15N results in a modest release of inorganic N. Consequently, the primary value of lupin stubble in the N economy of lupin : cereal rotations is to replenish the soil organic N reserve. 
ER  -

