Zonal tillage aids in weed control without increasing erosion risk.
Wayne and Leanne Ziesemer farm 1300 ha of self-mulching black clay soil at Bongeen on Queensland’s Darling Downs.
To protect these deep, fertile soils from erosion, the Ziesemer family began strip cropping practices in the 1970s. The Queensland DPI Soil Conservation Service surveyed the 146 m wide strips at 90 degrees to overland water flow, and farmers alternate crops and fallow in the strips to reduce the area of bare land exposed to heavy rainfall or overland flow.
The Ziesemers use a three-phase crop rotation of a summer crop (mostly corn), a winter crop (usually wheat) and a bare fallow. Each strip rotates through the crop cycle every 18 months. The crop stubble is left standing to maximise water infiltration and to reduce raindrop impact on the soil surface. Even during very heavy rainfall events, the runoff water is remarkably clean. The wheat crop is sown between the old corn rows in winter the following year, and then the strip is generally short-fallowed before planting corn (or another summer crop).
Their main weeds are feathertop Rhodes grass, fleabane and sowthistle, which Wayne and farm manager Clint Kummerow tackle with an optical spot sprayer, residual herbicides, strategic tillage in the fallow and zonal tillage to prepare a weed-free seedbed. Combining these chemical and non-chemical tactics ticks most of the WeedSmart Big 6 boxes for an integrated weed management program.
About nine years ago, Wayne introduced zonal tillage for seedbed preparation. This one-pass operation with an Orthman 1tRIPr zonal cultivator pre-applies the fertiliser (urea and deep-banded phosphorus) and mixes it into the soil. The rolling basket at the rear leaves the seedbed in excellent tilth and free of weeds. The centres of these seedbed zones are 91 cm apart for corn then wheat is sown in two rows between the corn stalks.
“Corn crops are sown with a precision planter, and we can plant our 400 ha crop in about three days into the 30 cm wide seedbed zones,” says Wayne. “There is minimal crop competition early in the corn crop, which compromises weed control, but we have the option for inter-row cultivation to control weeds and apply fertiliser side-dressing in our summer crops if needed.”
“The wheat crop is sown between the standing corn stubble into two 15 cm wide zones on 22 cm row centres to provide better crop competition. The seedbed preparation for the summer and winter crops also mixes the applied fertiliser across the paddock to give us better nutrient utilisation through the rotation.”
Two rows of wheat are planted between the rows of corn stalks.
By the end of the 18 months rotation, each farming strip will have been fully cultivated, but only a portion of the strip is tilled at any one time, and standing stubble is retained. This system effectively protects the soil from erosion while including a non-herbicide weed control tactic in the row area.
The machinery is not fully matched for controlled traffic farming, but Wayne has chosen machinery with multiples of 9 m widths to minimise traffic compaction. Their 9.14 m header is on dual tyres, the broadacre gear is all 18.24 m wide, the boom sprayer is 36 m wide, and the Weed-IT optical sprayer is 18 m wide.
“We end up with three sets of tracks, which might cost us some yield, but we have minimal track damage and don’t need to do track renovation,” says Wayne.
In the fallow phase, Wayne uses full cultivation if the density of difficult-to-control weeds reaches unacceptable levels in any of the farming strips. Full tillage costs about $5/ha for diesel because the soil is easy to work. If the strips have low weed density, about 5 per cent of the area or less, the Weed-IT is an economical and effective way to treat feathertop Rhodes grass, fleabane and sowthistle.
Wayne says the addition of the Weed-IT optical sprayer in the last 4 or 5 years has made an enormous difference to their herbicide use. They have shifted away from relying mainly on glyphosate to manage these hard-to-control weeds and now use more glufosinate and some paraquat, as well as glyphosate, through the Weed-IT.
A blanket spray of glyphosate would cost $12/ha in chemical alone, but they now spend around $1.50 to achieve the same result with the Weed-IT applying the higher permitted rate for optical sprayers to just 5 per cent of the area.
“We are also conscious of the need to use the Weed-IT when the weeds are small. In the past, we have allowed some of these difficult weeds to get too mature before treating them in fallows, and we have paid the price with a large seedbank that takes several years to run down,” says Wayne. “Our Weed-IT has dual spray lines, so we can do a broadacre and spot spray application in one pass, giving us more options to treat multiple weed germinations in fallow.”
The broadacre sprayer also allows Wayne to apply herbicides to the inter-row area early in the corn crop using droppers if necessary.
In recent years Wayne has been working with his agronomist, Jamie Innes (Nutrien, Pittsworth), to incorporate more residual herbicides such as isoxaflutole (Group 27, e.g. Balance) and picloram/2,4-D (Group 4, e.g. Tordon 75-D) into their grass and broadleaf weed control program in the fallow.
“The three-phase system allows us to confidently use residual products, knowing there is enough time for the herbicide to degrade before the next crop is planted,” says Wayne.
Wayne and Clint slash their roadside boundaries to reduce feathertop Rhodes grass incursions from public land.