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Brown Manure Crop Management

June 2013

1.  Seed Procurement

  • Ideally all seed would be purchased from a reliable seller at a price that is mutually acceptable.
  • Develop an ongoing agreement if possible.
  • If producing own seed the following should be considered:

–   Choose a paddock with a low weed burden
–   Choose a paddock geographically isolated from other pea crops or pea stubble.
–   If running CTF tracks, consider blocking the seed runs on wheel tracks to reduce disease spread from crop damage.

2.  Time of Sowing

  • Sowing a brown manure crop should not compromise the timing of cash crop sowing.
  • Sowing into warm soils before weeds have germinated will maximise biomass production, competition with weeds and ultimately Nitrogen fixation.
  • If sowing field peas in March or early April, choose varieties with the highest tolerance to Bacterial Blight, provided they are late maturing varieties that produce large amounts of biomass.
  • When comparing trial results for biomass production, ensure that the biomass production is being measured at sprayout timing, not simply peak biomass for the crop grown through to harvest.

–   Any extra growth past mid-September is wasted, as Wild Oat flowering time generally dictates sprayout timing.

  • In areas with high Field Pea intensity, consider delaying sowing until May to avoid Ascochyta spore showers.

3. Weed Management in Brown Manure Crops

  • Aim to minimise Wild Oat seed set in cereal crops prior to Brown Manure crops
  • Ryegrass populations can be successfully reduced with the combination of a Brown Manure crop followed by a canola crop.
  • In situations where grass weed densities are high enough to reduce the establishment of a Brown Manure crop, pre-emergent herbicides may be beneficial, such as:

–   Trifluralin
–   Metribuzin

  • In many cases, sowing field peas into warm soil allows them to outcompete the majority of weeds without the addition of herbicides.

4.  Disease Management in Brown Manure Crops

  • Bacterial Blight is the most important disease of field pea Brown Manure crops, although Ascochyta black spot should also be considered.
  • Bacterial Blight is most effectively managed by reducing physical damage on pea crops, especially when this coincides with frosty conditions.

–   Avoid driving, riding or walking through crops once established.
–  Where possible, do not allow animals to travel through pea crops (sheep, cattle, kangaroos).

  • Severity of Ascochyta black spot is highly dependent on the amount of spore release prior to emergence.
  • Dry conditions from spray out through to sowing will increase disease risk. If wet conditions are experienced between October and March, the majority of Ascochyta spores will have been depleted prior to sowing.
  • If choosing alternative species, the carryover of other diseases must be considered, most importantly:

–   Sclerotinia Stem Rot of Canola (Lupins, Faba Beans and Clover are alternative hosts)
–   Take-all and Crown Rot of Wheat (carried by Oats, Triticale and many other annual grasses)

  • Consider that if a pea crop is sown in March and dies in August from Bacterial Blight it is likely to have already produced 3-4 t/ha of biomass and fixed more than 60 kg/ha of Nitrogen. From that point it could be treated as a long fallow.
  • While Lupins and Faba Beans may not be susceptible to Bacterial Blight, the carryover of Sclerotinia may have a much larger impact on the following canola crop.
  • Disease risk for following cash crops should be more heavily weighted than disease risk in manure crops.

5.  Spraying Out Brown Manure Crops

  • MUST BE SPRAYED OUT BY MID SEPTEMBER.
  • Flowering time for Wild Oats or Ryegrass will usually dictate the time of spraying.
  • Consider adding an insecticide to reduce insect pressure in the following crop.

Refer to the accompanying document “Brown Manure Crops – Sprayout Decisions” for a decision matrix of product choice and timing.

6.  Brown Manure Stubble Management

  • There are a number of operations that can be used to manage Brown Manure Stubbles.
  • Rolling stubbles

–   Can provide some weed control through smothering of weeds under stubble mulch.
–   Improves soil contact to increase breakdown
–   Can improve the coverage of weeds in a “double knock” situation.

  • Cultivation

–   Can range from knife points through to offset discs
–   Any machinery passing through pea stubbles will cause significant shattering when stubbles are dry. The affect is much less when stubble is wet or dewy.
–   Can provide weed control, especially important if weeds escape the knockdown process (eg. Glyphosate resistant weeds)
–   Timing of cultivation needs to be considered in the context of the spraying and sowing systems.

 7.  Sowing Canola into Brown Manure Stubble

  • When > 150 mm rain falls between September sprayout and April sowing, stubble breakdown is generally sufficient for most sowing equipment to sow through Brown Manure stubbles.

–   Operations such as rolling and cultivation will further increase breakdown.

  • If < 100 mm rain falls September to April, stubble breakdown will be much less.

–   Under these conditions, blockages will occur with a range of tyned sowing equipment.
–   Fitting coulters in front of tynes will improve trash flow, provided:

*  Coulters are directly in line with tynes
*  Stubble is dry, so coulters cut through the stubble
*  There is sufficient distance between coulters and tynes for stubble to flow through.

  • When stubbles have not broken down over Summer, small falls of rain, or even heavy dew is enough to create blockages. This can be managed by:

–   Manipulating stubbles during Summer or early Autumn, as discussed above.
–   Commencing canola sowing earlier, with the understanding that sowing may only be possible during daylight hours.
–   Sowing canola into Brown Manure stubbles in dry conditions (when these are likely to be the only paddocks with moisture for establishment) and switching to canola on cereal stubbles if rain occurs.

  • Refer to the document “Sowing into Brown Manure Stubble” to aid decision making through Summer and Autumn.

 8.  Managing Canola after Brown Manure Crops

  • Early crop growth is driven by soil temperature

– Sow early in April to improve crop vigour
– Extra moisture under Brown Manure stubbles will often present additional canola sowing opportunities.

  • Nitrogen from Brown Manure crops may not mineralise until the following spring, so a small amount of Nitrogen (either Pre-sowing or At-sowing) will promote growth and development until mineralisation occurs.
  • Use the full suite of knockdown, pre-emergent and post-emergent herbicides available to control weeds in the canola crop to ensure that costs are minimised in the following wheat crop.