Allelopathy: The suppression of growth of one plant species by another due to the release of toxic substances from their residues.
Burnt stubble: Stubble can be burnt at any time from immediately post-harvest to just before sowing. The burn from immediately post-harvest to early autumn is frequently referred to as a ’hot burn‘ and the burn just before sowing is referred to as a late autumn burn or a ’cool burn‘. The terms ’hot‘ and ’cool‘ burn are avoided in this review as they are ambiguous. In fire fighting a ’hot‘ burn is considered as a grass fire with flame height >1.5 m and a ’cool‘ burn is a fire with flame height.
Coleoptile: The pointed protective sheath covering the emerging shoot in monocotyledons such as cereal crops.
Conservation farming: Conservation farming promotes minimal disturbance of the soil by tillage and maintenance of groundcover by plants or their residues. Conservation farming aims to conserve soil and water by using surface cover (mulch) to minimise run-off and erosion and improve the conditions for plant establishment and growth. It involves planting crops and pastures directly into land which is protected by a mulch using minimum or no-tillage techniques.
Direct drilling: Low soil disturbance sowing system where the crop is sown directly into a paddock without prior cultivation. One pass sowing with a full–cut soil disturbance.
Fungal hyphal networks: Long thread like structures of the growth of fungi.
Grazed stubble: Stubble which is grazed by livestock between harvest and sowing. Grazing intensity can vary from light grazing, where the intent is to utilise available feed in the stubble for the benefit of livestock while maintaining substantial groundcover, to heavy grazing where the intent is substantial removal of stubble. Light grazed stubble can be included as retained stubble, while heavy stubble is considered to be stubble removal or reduction.
Hair pinning: Stubble is bent rather than cut and pushed into the sowing groove with the seed. This can reduce soil-seed contact or contaminate the seed row with herbicides impacting on seedling emergence.
Harrington Seed Destructor: A machine that destroys weed seeds that pass through the header.
Incorporated: Mixing the stubble into the cultivation depth; usually with a disc plough, disc harrow or scarifier.
Incorporated stubble: Incorporated stubble is buried or partially buried by cultivation with a disc ploughing or tined implement (such as a scarifier), where a substantial proportion of stubble is buried. A disc buried an average of 62% of stubble by weight in one pass (Sallaway et al. 1988).
Intact stubble: Intact stubble is undisturbed after harvest and is retained after sowing. This may disregard spraying operations to control weeds during summer. This may be referred to as full stubble retention or standing stubble. In practice ‘standing stubble’ is partially flattened by the harvest operations (including harvester, chaser bins and trucks).
Micro-climate: The climate of a small, specific place within an area as contrasted with the climate of the entire area.
Micro-organism: Any organism, such as a bacterium, protozoan, or virus, of microscopic size.
Mulched: Stubble lying as a layer on the soil surface. This can be achieved by using a flail mulcher, slasher, harrow or roller. This can also mean cultivation with a blade plough with wide sweeps intended to cultivate and leave a maximum amount of stubble on the soil surface.
Mulched stubble: Stubble which has been mechanically treated and forms a layer on the soil surface.
Multiple tillage: Two or more tillage operations before sowing.
Nitrogen tie-up (otherwise known as immobilisation): When nitrogen is bound in the soil micro-organisms as they decompose the stubble, making it unavailable for other plants.
Non-symbiotic nitrogen fixing bacteria: Bacteria in the soil that can fix nitrogen from the air into plant available nitrogen in the soil without the need for a legume host plant.
No-till and zero-till: ‘No-till’ refers to crops sown with between 5 and 20% of soil disturbed and no prior cultivation, and ‘zero till’ refers to sowing crops with < 5% of the soil disturbed (for example, disc seeded). These terms are sometimes used to imply full stubble retention, however, this is not always clear. For example, 20% of farmers regarded as no-till operators burnt stubble (Llewellyn and D’Emden 2009).
No–tillage: Knife or disc sowing with 5–20% disturbance with no prior tillage.
Reduced tillage: One pass prior to sowing.
Retained stubble: Stubble remaining in the field without removal or burning. Stubble may be incorporated, mulched, slashed etc or left standing. Retained stubble present from harvest to sowing whether disturbed or undisturbed. This definition includes ‘intact stubble’ and stubble which have been flail mulched, slashed, harrow, crushed, rolled, incorporated or otherwise mechanically treated. This usually includes stubble which has been lightly grazed. The stubble is present after sowing.
Soil aggregation: The ‘clumping’ of soil particles together by moist clay, organic matter (such as roots), by organic compounds (from bacteria and fungi) and by fungal hyphae.
Standing: Upright stems, with only the disturbance of harvesting machinery.
Straw: Stems only of cereals.
Stubble: Plant residue left in the field after harvest, including stem, leaf and glume of cereals.
Stubble removed: Stubble removed from the paddock other than by burning. This can be achieved by a low cutting height and baling of the residue at harvest, by windrowing at harvest and subsequent removal or by cutting post-harvest and removal (‘windrowed and removed’ see below).
Surface retained stubble: Stubble retained on the soil surface, including intact, mulched and retained stubble, other than incorporated stubble. This term is commonly used to indicate the stubble was substantially on the soil surface even though the soil was cultivated. This can be achieved by using rod weeders or by cultivating with widely spaced tines using wide sweep points. In the research of Sallaway et al. (1988) a blade plough retained an average of 83% of the stubble on the soil surface.
Windrowed and burnt: The residue from the harvester is placed in a narrow windrow (50 to 80 cm wide) at harvest and burnt the following autumn. The aim is to place harvested weed seeds in the windrow and to destroy them with a high temperature burn while leaving stubble across the rest of the paddock. A similar technique has been used to destroy snails which are encouraged to shelter in windrowed harvest residue, particularly during hot weather, and are then destroyed by burning the windrow.
Zero–tillage: Disc sowing with <5% disturbance, with no prior tillage.
This glossary has been compiled from the following sources:
- Developments in stubble retention in cropping systems in southern Australia: Report to the GRDC
- Stubble Management: A guide for Mallee farmers
- Stubble Retention in Cropping Systems in Southern Australia: Benefits and Challenges