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The objective of this study was to investigate the influence of different nitrogen fertiliser application levels in combination with different defoliation intervals on the dry matter (DM) production and water-use efficiency of ryegrass (Lolium multiflorum,) cv. Midmar. In a field trial, four nitrogen levels (0, 150, 300 and 450 kg N ha -1 ) were combined with five defoliation intervals (every 2, 4, 6 and 8 weeks and twice a season). Soil moisture levels were measured with a neutron hydroprobe and were used to schedule irrigation. The dry matter production, nitrogen-use efficiency (NUE), plant DM content and water-use efficiency were influenced (P<0.01) by nitrogen level, defoliation interval, and the interaction between these factors. Total DM production varied from 64 to 20 922 kg DM ha -1 . Dry matter production per unit of applied N decreased with an increase in N level within a defoliation interval. The plant DM content varied from 14.0% to 35.6%. The plant DM content decreased (P<0.05) with increasing N applications, while a lengthening of the defoliation interval resulted in an increase (P<0.05) in the DM content. No difference (P>0.05) was found in total water used when plants received N. Water-use efficiency varied from 1.2 to 25.8 kg DM ha -1 mm -1 water received.

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