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−1) and the highest (0.86 t ha−1) 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−1) and irrigated (6.0 t ha−1) treatments. Under both watering regimes, the highest grain yield was obtained from the late “clip” grazings: 3.79 t ha−1 (RCut2-15) for rainfed and 6.47 t ha−1 (ICut2-15) for irrigated treatments. The lowest grain yield for the rainfed treatment was 3.26 t ha−1 (RCut1-5) and for the irrigated treatments, the lowest grain yield was 5.50 t ha−1 (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 1000-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−1 mm−1 (ICut2-5) and the highest value 13.43 kg ha−1 mm−1 (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.