How do I want to manage stubble at harvest

Stubble management begins at harvest and will depend on the farming system and the specific issues that need to be managed. How the harvester is setup for harvest will influence what kind of stubble remains during the fallow period and what condition it will be in when planting the next crop.

Stubble management begins at harvest and will depend on the farming system and the specific issues that need to be managed. How the header is setup for harvest will influence what kind of stubble remains during the fallow period and what condition it will be in when planting the next crop.

Assess crops prior to harvest for desired stubble characteristics, and use expected grain yields to estimate stubble loads so that the best management practices can be planned and implemented at harvest.

Estimating stubble load is important. As a rule of thumb, the remaining stubble load will be about 1.5 to 2 times the grain yield for wheat and about 3 times the grain yield for canola (Figure 1). For instance, a 4t/ha wheat crop will leave 6 to 8t/ha stubble, and a 2t/ha canola crop about 6t/ha.

Chart showing stubble loads in wheat, lupin and canola

Figure 1: Estimating stubble loads in wheat, lupin and canola. Source: D Heenan and M Conyers via Developments in stubble retention in cropping systems in southern Australia

What factors will influence my stubble management?

The stubble generated and desired for seeding by each individual farming system varies greatly. It can be influenced by harvest and seeding equipment, crop rotation, soil type and the presence or absence of livestock, weed, pest and disease burdens.

The key stubble management considerations are:

  • What is my preferred tillage system?
  • What is my seeding system (disc or tyne)?
  • What is my row spacing and accuracy of sowing? Can I accurately use inter-row sowing?
  • What is the type of crop residue?
  • How much crop residue will be present, and is it standing or lodged?
  • What is my preferred harvest speed and height?
  • How well does the harvester spread straw?
  • What crop will I sow next season?
  • Will the stubble be grazed?
  • Do I have a weed problem that I need to manage? How – harvest weed seed control, narrow windrows, chaff carts, etc?
  • Am I prepared to process stubble further after harvest - mulch, incorporate, bale or late burn?
  • What is the risk of stubble-borne disease to next year’s crop?
  • What is the risk of pests to next year’s crop (mice, snails, slugs, invertebrates)?
  • Do I have a weed problem in canola that may be best managed by spray topping when windrowing?
  • What is the risk of erosion and how much stubble will I need to protect the soil?

The next crop

The crop type that will be sown into the stubble during the following season can influence stubble management. Small seeded crops such as canola need a clear surface to emerge and compete. A heavy surface stubble load or large clumps of residue increase the risk of uneven emergence and poor crop establishment in all crops, except for large-seeded legumes.

Pests

Retaining stubbles within crop rotations may increase pests, especially snails and mice, as it provides food and shelter.

Herbicide efficacy

The amount of stubble remaining can influence herbicide activity and the resulting weed control. Stubble can reduce herbicide contact and chemical may bind to plant residues.

Weed management

The need to manage grassy weeds and herbicide resistance may influence stubble management.

Nutrients

The management of cereal stubble can affect microbial activity and the cycling and supply of nutrients to growing crops, especially nitrogen and phosphorus. Nitrogen is immobilised during the breakdown of cereal stubble due to the high carbon/nitrogen ratio. This may lead to nitrogen deficiency in crops in retained-stubble systems under cold wet conditions, often at the start of the growing season.

Soil biology

GRDC’s Stubble Initiative research has improved the understanding of microbial activity and nitrogen mineralisation processes. Soil mineralisation processes and rates are improved by stubble loads of up to around 3t/ha, with limited additional benefit from retaining higher stubble loads.

Soil moisture

GRDC’s Water Use Efficiency Initiative found that stubble residues slow the evaporation rate of soil moisture through the creation of a microclimate and by reducing surface wind speed. Retained stubbles also have a positive effect on soil structure that allows for better water infiltration, reducing evaporation, minimising runoff and the impact of raindrops on the surface.

However, it is not always possible to reduce the rate of surface evaporation with stubble ground cover, especially if rainfall is low and evaporation demand high.

Frost

GRDC’s Frost Initiative found retaining more than 2.5t/ha of stubble can increase the risk of frost damage, making the frosts colder and longer, with lower temperatures at head height. The retained stubble reduces the heat radiating from soil at night, resulting in less warming of the crop canopy.

Livestock

If livestock are part of the farming system, stubble type will also be a consideration. Trampled stubble post-grazing can lead to blockages at seeding.

Soil erosion

Stubble retention can reduce the potential for soil erosion through wind, especially in sandy and sandy loam soils.

Break crops

Sowing break crops into standing cereal stubble provides early protection of both small plants and soils from wind damage.

Stubble-borne diseases

Retention of stubble will increase the inoculum levels in paddocks infected with 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. If disease level is an issue, a break from cereal in an infected paddock or stubble removal will reduce the number of airborne spores present in that paddock in the subsequent year.

Seeder type and harvest height

The type of seeder that will be used next season (disc or tyne) and its ability to handle stubble will influence the stubble design and level achieved at harvest. Lines of straw and chaff residues from harvest can result in greater stubble handling problems as up to twice the paddock residue level can be found in the line and they can remain wetter for longer.

The ideal harvest cutting height will vary according to crop type and yield, next season’s crop and capability of seeding equipment. The risk of weather damage and impact on fallow spraying are also important.

More information

Farming systems groups

Other resources