Farm Table says:
Grain and Graze3 present six ways in which cereal grain crops can be utilised by livestock:
- Grazing dual-purpose crops during the late vegetative and early reproductive phases with the intention of preserving most – if not all – of the grain yield. These systems are the focus of most attention in the Grain and Graze program.
- Sacrificial grazing during mid-late reproductive phases, where there is little prospect of a commercial grain harvest, such as in a drought.
- Conserving crop biomass prior to harvest, where crops may be cut either for hay (usually early in reproductive growth) or for whole-crop silage (later in reproductive growth). This option can be attractive at times when there is a scarcity of fodder in other regions.
- Grazing standing crops after maturity, where livestock utilise both the grain and the stover. This is often done to carry other fodder over into the summer period when it may be in short supply.
- Grazing dry crop stubbles after harvest, traditionally done in many cropping systems
- Grazing stubble regrowth after harvest. This often occurs with weak perennials such as grain sorghum; if the crop is not killed at harvest re-sprouting of shoots can occur, producing new vegetative biomass that is able to be grazed.
The different nutritional values of cereal biomass at the different stages will influence production.
- During winter and early spring when dual-purpose grazing is practised, the quality of cereal forage is extremely high (DM digestibility 80-90%, crude protein 21-26%). The timing of grazing will generally be determined by the tradeoff between maximizing herbage mass and avoiding grain yield losses. Wheat forage at this time is commonly deficient in sodium and may also be deficient in magnesium; supplementation with these elements is a cheap and effective insurance policy.
- There are few Australian data for the quality of cereal forage during reproductive growth, at the times when sacrificial grazing and conservation will be carried out. Overseas data for wheat show a marked drop in forage digestibility from about 80% part-way through stem elongation to about 60% at anthesis, with a levelling-off from anthesis until grain ripening.
- Post-harvest, the quality of cereal stover will be low (average digestibility in modern cultivars can be expected to be below 40%). Livestock placed on stubbles will be extremely selective, concentrating their grazing effort on spilt grain, on any germinating “green pick” and on the relatively small proportion of leaf in the stubble. A short period of weight maintenance (about 4
weeks) is generally followed by significant weight losses once these higher-quality components of the stubble are exhausted.
Impacts on grain yield are also discussed:
- Provided grazing does not extend beyond the point where animals eat too many of the elongating floral meristems, the crop can regrow and produce grain. Cereal crops can compensate for the removal of some meristems by means of increased tillering.
- Grazing will reduce the leaf area index of the crop, which in turn will slow its growth during the post-grazing period. All else being equal, this will reduce grain yield.
- However, the reduced leaf area after grazing also means that the soil accumulates more water until the crop canopy recovers. This water will then be used later in the growing season (e.g. during grain filling), when the water-use efficiency for grain production is higher. As a result, an early-season grazing can increase yield in years with a dry spring.
- Grazing will also delay the development of grain crops, which can allow them to respond to late rain it falls.
Finally, other costs and benefits are outlined:
- On the benefits side, in paddocks with high weed burdens, sacrificial grazing may provide an ideal opportunity to control weeds late in growth without having to switch to a pasture phase.
- In dual purpose systems, reduction in vegetative material through an early season grazing may reduce stubble burdens following harvest. High stubble burdens can hamper following crop
establishment, and can be difficult to reduce after harvest if livestock numbers are limited or there are restrictions to traditional methods of disposal (tillage, burning).
- Conversely, in lower yielding areas a reduction in stubble biomass may have consequences for stubble carryover, ground cover and hence erosion risk.
- On the costs side, soil compaction is often cited as a negative, particularly for cattle and on clay soils in wet conditions. In tramline farming systems, livestock could be seen as incompatible with cropping practices.