
TY  - JOUR
A1  - Thompson, R. B. 
A1  - Fillery, I. R. P. 
T1  - Mineralisation of nitrogen contained in mature subterranean clover, capeweed and annual ryegrass, and subsequent nitrogen use by wheat in dryland farming systems in southern Australia
JF  - Soil Research
JO  - Soil Res.
Y1  - 2002
VL  - 40
IS  - 2
SP  - 299
EP  - 315
KW  - pasture, shoots, roots, 15N, rotation, cereals, burr.
UR  - https://doi.org/10.1071/SR00041 
N2  - Net nitrogen (N) mineralisation in soil and N uptake by wheat from mature shoots and roots of subterranean clover, capeweed, and annual ryegrass, and from clover burrs were assessed with 15N-labelled plant material in 2 field studies, using confined micro-plots. In the first study, shoot residues of the 3 species (150 g DM&sol;m2) were placed on the soil surface, and roots of the 3 species (75 g DM&sol;m2) were mixed into 0&#8211;10 cm soil. The treatments were applied in March 1991. The shoot residues were incorporated into soil in early June 1991. Net 15N mineralisation from the clover, capeweed, and ryegrass shoots during the 8-month experimental period was estimated to be, respectively, 15&percnt;, 12&percnt;, and 12&percnt;, and for the corresponding roots was 10&percnt;, 7&percnt;, and 6&percnt;. Negligible net mineralisation of 15N occurred during the 2.5 months that the shoot residues were on the soil surface. Crop 15N recoveries in wheat, at maturity, in November 1991 were 9&percnt;, 7&percnt;, and 7&percnt;, respectively, of that applied in the clover, capeweed, and ryegrass shoot residues. The respective crop recoveries from the root residues were 6&percnt;, 5&percnt;, and 3&percnt;. Less than 5&percnt; of N taken up by wheat was obtained from shoot or root residues. In a second similar study, 15N-labelled subterranean clover shoots (200 g DM&sol;m2) and burrs (75 g DM&sol;m2) were applied in December 1992; 3&percnt; of 15N in the clover shoots was net mineralised during the 5 months they were on the soil surface. Crop recoveries of 15N in October 1993, at the time of wheat anthesis, from the clover shoots and burrs were, respectively, 14&percnt; and 17&percnt; of applied 15N. The results of these field studies suggest that mature shoot residues and the associated intact roots (recoverable by wet-sieving), and clover burrs, make only a small direct contribution to the N response of cereals immediately following ley pasture in southern Australia. They also indicate that, under Mediterranean climatic conditions, generally very little net N mineralisation occurs from mature shoot residues until the shoots are incorporated into soil. pasture, shoots, roots, 15N, rotation, cereals, burr. 
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