Cover crops and a range of incorporation techniques have successfully boosted grain yields and protein levels in a previously underperforming paddock at Mullewa in Western Australia.
Legume cover crops and green manuring (discing), green mulching (slashing) and brown manuring (chemical desiccation) incorporation methods all showed potential as paddock ‘renovators’ during a research trial supported by growers and the Federal Government through the GRDC.
Researchers evaluated the green manure potential of field peas, lathyrus, vetch, oats, oat/vetch mix, mustard and canola during 1998 on a hard-setting clay loam at Mullewa. Grain yields in the 1999 and 2000 wheat crops were compared to those on control plots which had experienced harvest control (field pea) and chemical fallow. Renovation treatments were imposed at flowering in September 1998.
Field pea and. lathyrus - best choice
In 1999, green manure crops of field peas and lathyrus set up significantly higher yields for Carnamah wheat than other treatments and averaged yields 20 per cent higher than the harvest control. This was attributed to a combination of high plant biomass and higher plant nitrogen.
The same benefits were seen over the three years of the crop rotation, with overall profitability (in terms of total income and total income per hectare) being just as high when a green manure crop was used instead of a legume in a legume-wheat-wheat rotation.
The message is clear: some legume species provide more potential than others for yield improvements in subsequent wheat crops.
Additional benefits with green or brown manuring include improved weed control, organic matter content and soil structure, and longer-term productivity gains.
With the cost of seeding and maintenance of a green manure crop greatly influencing the gains or losses growers experienced, tactical implementation is recommended where seasonal factors such as low rainfall, disease and frost suggest low crop yield potential.
Benefits outlast the season
Researchers saw yield and quality benefits continue for the second cropping phase after renovation techniques were used at the Mullewa site.
In the 2000 season, plots that had been fallowed or from which a green manure crop (field peas) had been removed had consistently lower wheat grain yields. This suggested to researchers that the benefits of renovation techniques may be maintained for longer than a single season.
However, the poorer performance in the second cropping phase on sandplain soil at Yuna indicates medium-term productivity gains may be more closely associated with heavier soil types.
Due to the relatively low rainfall experienced at this site during the 2000 growing season, subsequent reductions in grain quality were largely associated with small grain screenings greater than 5 per cent. Grain screenings (whole and cracked < 2 mm) were otherwise below 5 per cent for this trial.
Grain protein for the site was above the 11.5 per cent typically required for Australian Hard, although it was higher for legume crop rotations. Grain protein increases corresponded to nitrogen application, although no interaction with crop species was seen by researchers.
Wetter year, different incorporations show equal potential
No significant differences in grain yield or protein were observed under the different incorporation techniques such as green manuring, brown manuring or mulching in either year at the Mullewa site.
Although a wetter 1999 season could be the reason for this, the results do suggest that brown manuring and mulching techniques have considerable potential under no-tillage farming systems and on lighter soils where the risk of erosion excludes the use of green manuring.
Researchers warned that in a drier year the results could vary considerably between different incorporation methods.
Program 3,5.3 Contact: Ms Frances Hoyle 08 9690 2000 email firstname.lastname@example.org
This is an edited version of a paper first presented at the 2001 Western Australian Crop Updates, supported by growers and the Federal Government through the GRDC.
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