When do I need to reduce the stubble load

Sowing into stubble
Sowing into stubble. Source: GRDC.

Retaining stubble has many benefits including, reducing erosion risk over summer, maintaining or improving soil structure, soil health and nutrient retention, providing a source of feed for livestock and improving water infiltration and soil moisture retention.

However, there can also be disadvantages to retaining stubble. Consider reducing the stubble load if it will:

  • Affect the timeliness of seeding, cause uneven seeding depth or potentially reduce establishment due to blockages
  • Potentially increase the risk of frost in frost prone areas
  • Increase risk of pests such as mice and snails
  • Reduce herbicide efficacy
  • Increase stubble-borne disease inoculum
  • Tie-up nitrogen at crop establishment

Every grower and their situation is different. All options need to be considered when developing cropping systems as what works in some regions will generally need to be adapted to suit other regions.

Seeding system (tyne or disc)

Stubble management for the next seeding starts at harvest and stubble length is the key factor. There is no single solution to stubble management as it will depend on crop type and residue breakdown, farming systems, livestock grazing, machinery and seeding systems.

Tyne seeders have less ability to handle longer straw than disc seeders. To improve success with a tyne seeder, consider options such as a lower harvest cutting height, chopping and spreading of residues or the use of harvest weed seed capture. Maximise the tyne spacing and clearance.

Disc seeders can handle heavy crop residues without clumping or blockages, and without specific requirements for stubble harvest or post-harvest management. However, stubbles need to be managed to prevent residue hair-pinning by minimising the need to cut residue that is laying down and maximising the capacity to cut residue.

Read more about How do I setup my seeder to handle stubble?

Frost

The soil heat bank captures heat during the day and radiates heat into the canopy overnight to minimise frost damage. Stubble can reduce the amount of heat that is absorbed during the day. Reducing stubble loads can reduce the severity and duration of frost events. Read more about Frost.

Pests

Maintaining stubbles may increase potential pests, especially snails and mice, as the stubble provides shelter and a feed source. Mulching of stubbles to improve seeding provides the perfect habitat for seedling pests such as earwigs and slaters.

Options for dealing with pest problems include:

  • Livestock grazing to consume or reduce residues
  • A late burn prior to sowing
  • Incorporating stubbles by tillage post-harvest

Specific guidelines and information pest management under stubble retention will soon be available as part of the Stubble Initiative.

Read more about How do I manage pests in a stubble-retained system?

Herbicides

Herbicides differ in how well they binding to stubble residues and move through the soil profile with soil water, which affects the uptake of the herbicide by weeds and the crop. Stubble, existing weed cover and crop cover (for post-sowing applications) will intercept some of the herbicide before it reaches the soil. The amount of herbicide intercepted will be proportional to the percentage of ground cover.

If grass weeds are an issue in paddocks with high stubble loads (greater than 50 per cent stubble cover), removal of some stubble may improve herbicide activity and grass weed control. Other management options to increase herbicide activity in paddocks with high stubble loads include:

  • Increasing chemical and water rates
  • Using nozzle types that increase spray coverage
  • Reducing the height of the boom spray or stubble height so herbicides reach the soil surface more easily and cover the soil more evenly

Stubble-borne diseases

Stubble borne diseases such as take-all, crown rot, yellow leaf spot, eyespot and white grain in wheat, and barley scald, barley net and spot form of net blotch, will all have increased inoculum levels in an infected paddock with the retention of stubble. Every disease is different and may require a different management strategy, so know the factors which influence the disease inoculum and disease risk.

Stubble management, removal by grazing, burning or cultivation, and seeding position may help with disease management. Fungicides may give economic control for some diseases, but not others.

Nitrogen tie-up

Retained stubble can tie-up early-season nitrogen (N) when soil microbes use it as a source of fuel to break down stubble. This tie-up restricts the amount available for crop emergence and early growth. It is only a temporary constraint in cropping soils as the immobilised nitrogen will be released through microbial turnover, generally later in the crop season in spring.

Nitrogen tie-up by cereal residue is not just a problem following incorporation. It occurs in surface-retained and standing-stubble systems. A worst-case scenario for nitrogen tie-up is when large amounts of cereal residue are incorporated into the soil close to the time of sowing, as the competition between microbes and the crop for nitrogen is intense, and early nitrogen deficiency can limit crop yield potential in some circumstances.

Additional nitrogen at sowing helps to provide the nutrition required to break down the previous stubble and also makes sure the germinating crop has sufficient nitrogen to establish, which ultimately helps maintain yield potential.

Read more about the impact of stubble retention on nutrition in How do I manage nitrogen in a stubble-retained system? or through the GRDC Update paper: The effect of stubble on nitrogen tie-up and supply.

What mechanical options could I consider?

Mechanical stubble management can be useful when growers need to manage a stubble-related issue (Table 1). By retaining some stubble growers can still retain many of the benefits of stubble-retention compared to burning or cultivation.

Table 1. Mechanical stubble management options for stubble-related issues. Source: UNFS Mechanical stubble management (PDF 1.4Mb).

Issue

Retained stubble solution

Challenge

Mechanical management solution

Weed control

Weed seed destruction (e.g. Seed Destructor)

Weed seed destruction can require high capital investment.

Retained stubble can reduce efficacy of some pre-emergent herbicides.

Collect residue with chaff cart and burn or graze to destroy seeds.

Stubble-borne disease

Sow break crops with reduced disease risk or choose resistant varieties.

A high-risk crop may be required for other reasons, such as weeds, nutrition or gross margins considerations

Harvest lower or double-cut to reduce stubble load.

Nutrition

Retain nutrients through full stubble retention.

High stubble loads can immobilise nutrients, making them unavailable to the crop and increasing fertiliser requirements in the short term.

Cut and spread straw at harvest to retain nutrients.

Smaller straw pieces will break down faster to improve availability of nutrients to the crop.

Seeding capability

Change seeding configuration to one that can handle full stubble loads.

Changing seeding configuration can require high capital investment.

Harvest lower or double-cut to reduce stubble load.

Snail control

Baiting

Baiting alone may not be sufficient when snail pressure is high.

Cable or roll paddocks in summer to kill snails.

More Information

Farming Systems Groups

Calculators

  • Stubble Management Optimiser to calculate the overall financial and nutritional cost of managing stubble both at harvest and during post-harvest treatments

Other resources