Cover cropping for better weed control
From the November 2008 edition of Agriculture Today.
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Cover cropping has been used on the South American continent for decades to protect bare soil from erosion, to improve water infiltration and suppress weeds.
As part of a Grains Research and Development Corporation funded project on Integrated Weed Management (IWM), researchers from NSW Department of Primary Industries at the Wagga Wagga Agricultural Institute are investigating the benefits of cover cropping for weed control in no-till and organic systems.
"It’s already clear cover cropping in organic systems has enormous potential to control weeds and ameliorate the soil," research scientist, Hanwen Wu, said.
In organic systems, green manure crops have previously been included in IWM strategies for problem weedy paddocks but there is some cost to incorporate; similarly in no-till systems, with either green or brown manure crops, and in some cases use of a non-selective herbicide.
Farmers in the Central West are evaluating crimp rolling of the standing cover crop.
"Crimp rollers are generally between 600 millimetres and one metre in diameter with water or oil for additional ballast and are towed behind a tractor to flatten the standing crop," the Department’s technical officer at the Institute, Eric Koetz, said.
"The roller has a series of 10-12 blades or blunt knives running around the drum approximately 15-16 centimetres apart and 6-8cm tall.
"The action of rolling the knives across the crop combined with the weight of the roller flattens the crop and crimps it every 5-6cm, breaking the stem and killing the cover crop."
Crimp rolling produces a mulched layer several centimetres thick on the soil surface, suppressing weed germination, improving water infiltration into the soil and reducing evaporation.
A number of different crops including cereal rye, wheat, oats, barley, vetch, forage canola and mustard are being evaluated in experiments at Wagga Wagga and Wellington.
Three management strategies were applied to the cover crops - cut and removed (as a control), cut and retained, and crimped and rolled.
Potential allelopathic compounds leached from stubble may also help to suppress summer weeds.
Cover cropping dramatically increased soil moisture.
Compared to the cut-removed control, the treatments of cut-retained and crimped-rolled resulted in 100 per cent and 50pc increases in soil gravimetric moisture content in the 0-10cm layer when assessed in May 2008 prior to sowing.
These significant differences were maintained at the 10-30cm layer but all management strategies resulted in very similar moisture contents at 30-50cm.
Retaining a thick mulch for weed control reduces the need to cultivate instead, reduces diesel use and tractor running costs.
Accumulation of soil moisture under cover cropping might further improve crop establishment and yield.
This experiment is into its second year of a three year phase.
Contact Hanwen Wu, (02) 6938 1602 or Eric Koetz, (02) 6938 1954, Wagga Wagga.
