Effect of grazing time and intensity on growth and yield of spring wheat(Triticum aestivum L.)

A simulated grazing field experiment was conducted to determine the effect of timing and intensity of grazing on the growth and yield of a mid-late maturing spring wheat（cv. Flanker） under different watering regimes, at Wagga Wagga in southeastern Australia. The experiment was a factorial design of watering regime and pasture "grazing" as factors, with three replications. The two watering regimes were rainfed（R） and supplemental irrigation（I）. There were four simulated grazing treatments: no grazing, "crash" grazing by mowing to 5 cm height on 13 June（Cut1-5）, "crash" grazing by mowing to 5 cm on 15 July（Cut2-5） and "clip" grazing by mowing to 15 cm height on 15 July（Cut2-15）. The lowest dry matter（simulated grazing） was obtained from RCut1-5(0.13 t ha;) and the highest(0.86 t ha;) was from ICut2-5. There was no significant difference（P<0.05） among the grain yields of the grazing treatments in the respective watering regimes. However, there was significant difference（P<0.05） between the grain yields of the rainfed(3.60 t ha;) and irrigated(6.0 t ha;) treatments. Under both watering regimes, the highest grain yield was obtained from the late "clip" grazings: 3.79 t ha;（RCut2-15） for rainfed and 6.47 t ha;（ICut2-15） for irrigated treatments. The lowest grain yield for the rainfed treatment was 3.26 t ha;（RCut1-5） and for the irrigated treatments, the lowest grain yield was 5.50 t ha;（ICut2-5）. Harvest index（HI） was not significantly affected（P>0.05） by either the watering regime or grazing. Seed weight was significantly（P<0.05） affected both by the watering regime and grazing with the lowest value for 1 000-seed weight of 30.05 g（RCut2-5） and the highest value of 38.00 g（ICut2-15）. Water use efficiency was significantly（P<0.05） affected both by the watering regime and grazing with the lowest value of 9.94 kg ha;mm;（ICut2-5） and the highest value 13.43 kg ha;mm;（RCut2-5）. By "crash" grazing late（just before stem elongation stage） to a height of 5 cm, a significantly higher（P<0.05） above ground dry matter can be grazed without significantly affecting the yield both in seasons with low amount of rainfall and high amount of rainfall（irrigated in this study） although in a wet season a slightly lower（15% lower） grain yield is obtained relative to "clip grazing" to 15 cm height. Grazing of mid-late maturing wheat cultivars has the potential to fill the feed gap without significantly affecting grain yield.