Title: Other Options for Weed Seed Collection at Harvest
Baling systems
Baling crop residue, directly from the header at harvest, minimises weed seed additions to the seed-bank.
Baling the chaff is an alternative to grazing. Because the material is already chopped, chaff bales are more attractive to dairy farmers than the conventional straw bales. As proximity to market and price can be limiting factors, this option appeals to those farmers who have access to a stock-feed market such as a dairy, beef feedlot or stock-feed mill.
Three baling systems are practised. The most efficient involves trailing a baler behind the header and directing all the chaff and straw into the baler.
Alternative systems involve baling the header trails and the chaff dumps from a chaff cart system. Picking up header trails with a baler once the material has been on the ground is problematic because much of the seed is missed. This applies even where a system devised to put straw underneath the chaff is employed, referred to as a ‘Chafftop’.
The chafftop
The chafftop uses a device fitted to the header to collect the chaff and straw. It concentrates the chaff on top of the straw windrow for later baling, which is the reverse of the usual harvesting technique of scattering the chaff behind the header
Baling systems offer a distinct advantage by processing the material into a transportable and therefore saleable state. Markets for straw and chaff include:
Roughage in cattle feedlot rations and dairies
Briquettes
Mulch
Grazing crop residues
Grazing weed contaminated crop residue can be a cost-effective way of controlling weed growth. Animal digestion of weed seeds prevents a large proportion from entering the seed-bank.
It should be noted that the feed value of the crop residue will be variable, and grazing has the potential to spread undigested weed seeds.
Grazing reduces the number of weed seeds added to the soil seed-bank. Depending on the weed species, grazing can greatly reduce the number of viable seeds in the soil seed-bank. Animals eat the seed heads and vegetative growth of the weed, thus decreasing the number of seeds entering the seed-bank.
Grazing can be used to dispose of, and gain value from, weed seed contaminated fodder. Weed seed contaminated fodder includes not only hay, silage and feed grain but also harvest residues that may be weed infested. Harvest residues can be collected using chaff carts to remove residue and weed seeds from the header, leaving chaff dumps in the paddock which can be used as a low-value livestock feed source.
Livestock trampling tends to bury weed seed, which can decrease the efficiency of burning as a means of killing seeds. Depending on the weed species, burial may also increase germination rates. In the process of grazing, stock will knock seed to the ground and bury weed seeds with their hooves. Shallow burial during grazing may result in increased germination, similar an autumn tickle, due to the placement of the seed in a better environment for germination.
Grazing may also cause:
An increased risk of soil, water and wind erosion
Increased soil compaction
Potential toxicity issues
Whole-farm benefits
There are additional benefits to be obtained when using grazing of crop residue as a weed management method:
Weed seeds can provide a significant proportion of the nutritional value when stock graze crop residue.
Post-harvest grazing may reduce crop establishment problems through reduction in stubble burdens.
Seed burial through trampling may enhance weed germination pre-sowing.
Seed of desirable plants (pasture species) may be distributed in faeces.
Contaminated fodder needs to be checked for its feed value and the presence of toxins. It should be fed in a sacrifice area (such as a feedlot) to minimise the spread of seeds.
The impact of grazing on weed numbers in the seed-bank is dependent on the biological features of the weed. Grazing is successful in reducing weed seed numbers in weeds that are palatable and where the seeds can be easily eaten and digested. However, seed palatability varies from weed to weed. The presence of awns, thorns or biochemical traits makes some weeds less attractive to grazing animals, than others.
Seed location
Stock must be able to access seed to ingest it. Seed still in the head, or in chaff dumps or feed troughs, is easier to access than seed lying on the soil surface.
Seed size
Once shed from the seed head, small seeds are more difficult for animals to graze. Small seeds are also more likely to survive ingestion and digestion.
Hard seeds
A high proportion of hard seeds will remain viable after digestion. The digestive process can also break seed dormancy, encouraging the germination of seeds shed in faecal matter.
Silage
Silage is less risky because cutting is carried out when the weed seeds are less mature. More importantly, the silage process kills most weed seeds although some do survive the process.
