Ground Cover Supplement : GC Supplement - Pastures
PERENNIAL PASTURES ARE known to increase the sustainability of cropping rotations. They use more water than annual pastures and so reduce leakage to the water table, and they improve ground cover over the summer months. The main perennial species, lucerne, provides more biologically fixed nitrogen than annual legumes. But what happens to crops growing after perennial pastures? In two experiments in the Junee Reefs district of south- ern NSW we investigated the effects of lucerne, phalaris and cocksfoot on following wheat crops. The most recent experiment – in the dry seasons of 2001, 2002 and 2003 – came up with some surprising results. Averaged across the three years when annual rainfall averaged 380 millimetres, yield of wheat growing after a mixed phalaris and cocksfoot pasture was not sig- nificantly less than wheat in a continuous canola-wheat rotation (Figure 1). Yield of wheat after lucerne was low because the soil was consistently drier than after all other pastures and the continuous crop The reason we studied the effects of perennial grasses on yield was to confirm measurements made in a large crop-pasture experiment from 1994 to 1998 when the average annual rainfall was 519mm. Over five years of comparisons in this experiment, wheat growing after a mixed phalaris and cocksfoot pasture was compared with crops growing after annual pasture, lucerne, and a mixed lucerne, phalaris and cocksfoot pasture. There was a total of 15 comparisons. In 11 of these, the highest yields were after the phalaris and cocksfoot pasture. Averaged over the 15 compari- 0 1.5 1.0 0.5 2.0 2.5 3.0 Continuous cropping Phalaris Cocksfoot Lucerne + Phalaris + Cocksfoot Lucerne Phalaris + Cocksfoot Pasture or crop in the previous year Wheat yield (t/ha) l.s.d. sons, crops growing after phalaris and cocksfoot pasture yielded 18 per cent more than wheat after lucerne. Combined, the two experiments show similar results. In both favourable and tough seasons, wheat after perennial grass yielded more than wheat after lucerne. In addition, the mineral nitrogen levels in soil after perennial grasses were often greater than in soil after lucerne. This result is surprising because unlike lucerne, perennial grass pastures do not contribute biologically fixed nitrogen. The reasons for the benefits of perennial pastures in dry years are clear – they leave more water in the soil than lucerne. The benefits of perennial pastures in wet seasons are not so clear. It may be that they control cereal root disease because they are not host to the main pathogens and also crowd out annual grasses better than legumes. It may be that the fine roots of perennial grass- es provide root channels for the following crops. Or it may be that the roots of perennial grasses cycle nitrogen to the surface soil, where it becomes slowly available to the following crops. Overall, it seems there is great potential for the inclusion of perennial grass pastures in cropping rotations in south-eastern Australia. Sarah Ellis is a PhD student at Charles Sturt University and CSIRO Plant Industry; John Angus is an agronomist with CSIRO Plant Industry. GRDC Research Code CSP337 More information: John Angus, 02 6246 5095, firstname.lastname@example.org Perennial pastures produce surprise crop results PROJECT: IMPROVED CROP YIELD AFTER A PERENNIAL GRASS PASTURE. SARAH ELLIS AND JOHN ANGUS PERENNIALS FIGURE 1 YIELD OF WHEAT GROWING IN THE FIRST YEAR AFTER DIFFERENT PASTURES AND CROPS. THE RESULTS ARE THE MEAN OF THREE DRY YEARS AT JUNEE REEFS Perennial pastures lead to increased yield of following wheat crops.
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