
TY  - JOUR
A1  - Wood, M. 
A1  - Pilbeam, C. J. 
A1  - Harris, H. C. 
A1  - Tuladhar, J. 
T1  - Productivity and nitrogen use of three different wheat-based rotations in North West Syria
JF  - Australian Journal of Agricultural Research
JO  - Aust. J.  Agric. Res.
Y1  - 1997
VL  - 49
IS  - 3
SP  - 451
EP  - 458
KW  - chickpea, fallow, N fixation, soil N, sustainability.
UR  - https://doi.org/10.1071/A97015 
N2  - Productivity of 3 different 2-year crop rotations, namely continuous wheat, wheat-chickpea, and wheat-fallow, was measured over 4 consecutive seasons beginning in 1991-92 at the ICARDA station, Tel Hadya, Syria. Nitrogen (N) fertiliser (30 kg N/ha at sowing) was broadcast every other year in the continuous wheat only. 15N-labelled fertiliser was used to quantify the amount of nitrogen supplied to the crops through current and past applications of fertiliser and by N2 fixation. The remaining N in the crop was assumed to come from the soil. In any single season, wheat yields were unaffected by rotation or N level. However, 2-year biomass production was significantly greater (32%, on average) in the continuously cropped plots than in the wheat-fallow rotation. On average, &#60;10% of the N in the wheat crop came from fertiliser in the season of application, and &#60;1&#183;2 kg N/ha of the residual fertiliser was recovered by a subsequent wheat crop. Chickpea fixed 16-48 kg N/ha, depending on the season, but a negative soil N budget was still likely because the amount of N removed in the grain was usually greater than the amount of atmospheric N2 fixed. Uptake of soil N was similar in the cereal phase of all 3 rotations (38 kg N/ha, on average), but over the whole rotation at least 33% more soil N was removed from continuously cropped plots than from the wheat-fallow rotation, suggesting that the latter is a more sustainable system. A laboratory study showed that although wheat and chickpea residues enhanced the gross rate of N mineralisation by c. 50%, net rates of N mineralisation were usually negative. Given the high C/N ratio of the residue, immobilisation, rather than loss processes, is the likely cause of the decline in the mineral N content of the soil. Consequently, decomposition of crop residues in the field may in the short term reduce rather than increase the availability of N for crop growth. 
ER  -

