GRDC fallow management output No. 7
How do I manage stubbles during a fallow?
A fallow paddock is a crop rotation management option in which a paddock is left uncultivated for an extended period of time. Following a fallow, there is a reduced risk of low yields in dry years due to more available soil moisture plus the added ability to control weeds and retain soil nitrogen for subsequent crops.
Rainfall during summer fallow makes a significant contribution to winter crop use and grain yield, particularly in regions with limited summer rainfall patterns (Hunt, J 2016). If weeds aren’t controlled during a fallow period, water and nitrogen savings are quickly lost.
Standing stubble during a fallow period will provide more protection from wind and water erosion compared to a bare fallow paddock. At least 40 per cent of standing stubble (figure 1) is required at the end of a fallow period to allow for optimal soil moisture conservation.
Weed control between crops, also known as controlling the green bridge, has become a critical part of both summer fallow and rotational fallow management to help decrease disease pressure. Common green bridge pests and diseases are:
- Rusts: spores can be windblown and affect crops that are km’s away. If high levels of rust are present in a green bridge when crops are sown, even crops selected for their rust resistance are likely to be severely affected.
- Wheat streak mosaic virus (WSMV): transmitted by the wheat curl mite and infected seed. Hosts for WSMV include volunteer wheat, barley grass, annual ryegrass, small burr grass, stink grass and witch grass.
- Barley yellow dwarf virus (BYDV): transmitted by aphids who have been able to feed off a green bridge. Virus will affect all cereals.
- Beet western yellow virus (BWYV): BWYV is an aphid-borne virus that causes yield and quality losses in canola crops and requires a green bridge for the vector (Green Peach Aphid) to survive. BWYV is not seed-borne and survives from one growing season to the next in over-summering canola, broad-leafed weed species, and perennial legume pastures.
- Diamond back moth (DBM): numbers will increase when volunteer broadleaf weeds are present. Note that insecticides can only control the grubs, not adults.
- Mites: mite populations breed among the green bridge, if a susceptible crop like canola is sown, consequences could be devastating.
When managing fallows, both weed control and stubble management are of equal importance as they complement each other. Stubble management techniques can influence the amount of nutrients and moisture retained as the stubble architecture changes depending on how it’s managed.
The careful and continual monitoring of fallow can lead to many benefits in crop emergence, weed and disease suppression and soil structure. Things to consider when monitoring stubble during the fallow period include:
- Over grazing. Producers with sheep may also need to weigh up the value of grazing fallow paddocks against any trade-offssuch as ground cover reduction, weed control and the flow on effects on stored soil water and nutrients.
- If the stubble load is very high, consider the penetration of sprays getting through the ‘mat’ of stubble. Water rates can help this situation.
- Managing stubble begins at harvest where you can determine cut height, windrows and spreading width.
- Knowing how your seeder handles stubble will help in making decisions about stubble management early.
As part of the ‘maintaining profitable farming systems with retained stubble in Victoria and Tasmania’ project, Birchip Cropping Group (BCG), Southern Farming Systems (SFS), Irrigated Cropping Council (ICC) and Victorian No-Till Farmers Association (VNTFA) have investigated stubble nutrition and its influence on stubble retained systems.
Field trials and observations from the grower groups have been conducted as part of this project which has been supplemented by previous research and anecdotal evidence from industry experts and experienced growers across Victoria. This output has been primarily focused on the Wimmera and Mallee regions and the Southern high rainfall region of Victoria.
Disclaimer: Any recommendations, suggestions or opinions contained in this publication do not necessarily represent the policy or views of the Birchip Cropping Group (BCG), Southern Farming Systems (SFS), Irrigated Cropping Council (ICC), Victorian No-till Farmers Association (VNTFA) or the Grains Research and Development Corporation (GRDC). No person should act on the basis of the contents of this publication without first obtaining specific, independent professional advice. BCG and GRDC and contributors to these guidelines may identify products by proprietary or trade names to help readers identify particular types of products. We do not endorse or recommend the products of any manufacturer referred to. Other products may perform as well as or better than those specifically referred to. BCG, SFS, ICC, VNTFA and GRDC will not be liable for any loss, damage, cost or expense incurred or arising by reason of any person using or relying on the information in this publication.