Manuring legumes for weed control
Mark and Steven Day run Woodlea Ag Enterprises in conjunction with their father Max, with the backing and support of their wives and families in the decision making process. The continuous cropping operation at Lockhart, NSW is based on a zero till, 12 m controlled traffic system on 3 m wheeltracks and using an NDF disc seeder.
Returning to the farm in the 2000s after completing their tertiary studies, Mark and Steven have developed a farming system that uses new technologies and capitalises on well-worn rotational farming concepts.
In 2009 the Days noticed that weed pressure was building and they were concerned that the weed seed bank would soon be unmanageable in their canola-wheat-wheat rotation.
“We took the advice of our agronomist and decided to introduce a legume brown manure phase,” said Mark. “Our first choice was field pea because they are the most competitive legume option and provide a good level of ground cover and biomass. In recent years we have also grown vetch, lupins and faba beans to avoid disease build-up in field peas.”
Over the last 10 years the Days have settled into a stable double break rotation, which has been a key strategy to keep weed numbers low in their cropping operation, and they have also introduced chaff decks for the last three harvests for weed seed management.
Pre-2009 – CTF, continuous cropping canola, wheat, wheat and variable rate technology (for lime and gypsum prescriptions and P replacement)
2009 – legume brown manure introduced in response to increasing weed pressure
2012 – NDF seeder and full stubble retention
2016 – chaff deck for HWSC across whole farm
“We start with the brown manure legume followed by TT canola, then a double cereal phase of wheat and barley,” he said. “This sequence allows for optimal use of herbicides within the stubble retention system and we can rotate a range of herbicides.”
“Herbicide rotation and double knocking to protect glyphosate is keeping a wide range of herbicides effective and we take advantage of the differences in stubble load to use each product in the most effective way,” he said. “For example, we apply Sakura when planting wheat following canola crop and the stubble load is not excessive, allowing the Sakura to work well.”
The legume brown manure followed by canola gives Mark and Steven the opportunity to use a range of herbicide tactics, including rotating propyzamide, atrazine and clethodim, to drive down grass and broadleaf weed numbers. They also occasionally apply grass selective herbicide over the top before brown manuring if required. The manure crop also helps retain soil moisture and maintain a baseline of nitrogen in their system.
Adding stubble retention also contributes to soil moisture and nutrient conservation, but the crop sequence is key to making the NDF disc seeding system work well.
“Our rotation is set up so canola is established in a low residue situation after the brown manure, wheat is established into canola stubble and the brown manure pulses are sown into high crop residue situation after the cereals using a deeper disc setting,” said Mark.
When it comes to managing weeds through the rotation, the legume is brown manured using a traditional glyphosate paraquat double knock following a roller to achieve better spray coverage of weeds low in the canopy. The double knock is also applied prior to seeding.
Tillage is used on about five per cent of the cropped area each year in response to specific situations such as providing a triple knock of the brown manure crop, for restoration of wheeltracks and headlands and to incorporate lime or address nutrient stratification. Strategic cultivation also enables the effective use of trifluralin in the disc seeding system.
In-crop strategies include increasing seeding rates in weedy or high pressure areas using variable rate technology, spraying under the cutter bar when windrowing canola and crop-topping feed barley at the end of the rotation.
Harvest weed seed control – Chaff decks
Even though the system was humming along well, the extreme wet conditions in 2016 led to significant weed escapes, prompting the Days to look into harvest weed seed control. Having seen the benefits of the chaff deck system, Mark and Steven bought one for their own harvester and worked with their contractor, Warwick and Di Holding, to have one fitted to the harvester that operates on their property.
“At first we had to convince ourselves that the weeds really were coming off the sieves and we were amazed just how much is collected and deposited on the wheeltracks when the harvester is set up correctly,” said Mark. “The whole farm is now treated with the chaff deck for harvest weed seed control, every year. The weeds are confined to a manageable and defined area. Other benefits include the reduction in dust over summer and we can easily assess harvest losses.”
There have also been a few downsides to the chaff deck system that need to be worked around, such as stubble lumps on wheeltracks and the potential for nutrient redistribution to the wheeltracks over time.
“We have seen poor establishment in some situations and certainly black oats can evade all harvest weed seed control tactics as the seed has already shed by harvest time,” he said. “Windrowing barley may be a worthwhile method to address this problem.”
The Days expect to move to an impact mill for HWSC in time.