Weed seed collection at harvest, grazing chaff dumps instead of burning, and swathing barley crops are key weapons growers Andrew and Marjorie Boultbee have in their arsenal for their war on weeds on their property at York, Western Australia.
The couple’s priority is to implement a farming system where crop rotation choices are uninhibited by planting date, weed density or herbicide resistance pressures.
“To optimise profits, we want to be able to change our rotation quickly – if necessary – in reaction to shifts in commodity prices or seasonal conditions,” Andrew says.
“This is made possible by having a low weed seedbank.”
York, Western Australia, grain grower Andrew Boultbee is using chaff cart weed-seed collection at harvest and swathing to reduce the weed seedbank on his property.
Historically the Boultbees used herbicide, rotation and some narrow windrow burning after harvest to control weeds.
However, Andrew says he found burning windrows was costly (he estimates $4 per hectare), time consuming, hard on machinery, unhealthy – keeping him awake at night worrying about fires up to 70 kilometres away – and not conducive to stubble retention.
In 2002, he decided to use chaff carts as an alternative way to capture weed seeds at harvest, lower the property’s overall weed seedbank and facilitate ongoing continuous cropping.
Instead of burning the chaff heaps, the Boultbees started grazing this resource during summer. The sheep flatten the chaff heaps to a very small pile and help to redistribute some of the nutrients in these heaps back out to the paddock.
It is a win-win for achieving good weed control and filling a sheep feedgap that, in turn, has contributed to boosting lambing percentages.
Andrew says the sheep eat down canola heaps and the minimal amount of residue remaining is sown through with no extra treatment.
“The cereal chaff heaps are well grazed, but there is a small pile left,” he says. “So we run a scarifier through this residue, straight down the row of heaps to knock the tops off, levelling it to a height of about 30 centimetres.
“This effectively joins the heaps together into a continuous strip at 90 degrees to the seeding direction, which the seeder can easily go over.”
Research has shown that only three to six per cent of ryegrass seeds that sheep pick up from chaff heaps survive digestion.
“What we are finding is that the weed seeds that get through the chaff carts and sheep digestion have little protection against the composting effect of the 30cm layer of chaff on the ground during the winter rains and they rot,” Andrew says.
“Even though we don’t burn the chaff dumps, we don’t see many weeds in them at all. Two years after leaving a dump, it is the best part of the paddock – big crop growth and very few weeds.”
Andrew says he now uses two chaff carts and the system is a cost-effective tool that is destroying enough weed seeds to lower the seedbank.
However, he says there are costs involved in clearing paddocks of rocks to drop the front of the harvester to cut stubble as low as eight to 10cm and in reducing harvest speeds to about 8km/hour.
Andrew estimates the cost to run the chaff carts is about $5 to $6/ha – similar to the cost of narrow windrow burning.
“Using such a low cut height at harvest and with an increased volume of straw, we have had to upgrade our header size and run two headers, at considerable expense,” he says.
“That has been the biggest downside to moving to weed seed collection at harvest.
“The benefits are that our time of sowing and crop choice is less inhibited by weed pressures, we don’t have to burn chaff heaps and our stock are doing well on this feed resource.”
Using chaff carts, the Boultbees also retain full stubble cover and are noticing increased stored soil moisture at seeding, less waterlogging after big rain events, less wind erosion, increased soil microbial activity and fewer weeds.
Annual ryegrass is their highest-priority weed and another tool to tackle this is to swathe barley crops.
“The idea is to get as many seeds into the front of the harvester as possible and stop any lodging or shedding of ryegrass and brome grass seeds,” Andrew says.
“The same goes for wild radish, which is usually dry and shedding, or green, and therefore it’s hard to get weed seeds down on the sieve.”
Swathed barley crops are left for up to four weeks, allowing standing crops, which have priority, to be harvested.
Andrew says the system depends on swaths being laid “just right”, requiring crops to be cut low and consistently to enable effective weed seed and barley grain collection.
“If you are going to get into the swathing barley game you have to get it right,” he says.
“We use Buloke barley because it is tall and competitive, so it makes a good windrow.
“It also has a hard seed, so we can thresh it hard to make sure that we get most of the weed seeds into the cart.
“We don’t like using Hindmarsh barley for this purpose because it is too short to make good swaths and the seed is soft, so will crack if we thresh it too hard.”
Andrew says in high weed burden areas, two or three consecutive barley crops are grown and swathed in the rotation using this system.
He says canola follows the second barley crop if conditions are right, or is dropped out if prices or the season appear unfavourable.
Andrew now rarely uses post-emergent herbicides for ryegrass control in cereals. Herbicides are rotated with crops, there are long breaks between using the same herbicide in a paddock twice and minimal glyphosate is used prior to seeding.
To hear Andrew Boultbee discuss his chaff cart and integrated weed management system, watch the GRDC Ground Cover video below.