GroundCover™ Issue: 129 July - August 2017 | Author: Clarisa Collis
A sophisticated drainage system is set to help a Tasmanian couple secure a more reliable and productive grain and graze operation on irrigated country prone to yield losses through waterlogging
Inside Rob and Jo Bradley’s farm office, a note reminding the couple to “focus on irrigated drainage and fencing” affirms the main pillars of a sophisticated strategy to lift the profitability of their 1020-hectare farm business in Tasmania.
In developing this integrated strategy, Rob says the central aim is to build more resilient, productive soils able to overcome waterlogging losses due to high rainfall in winter and saturation from centre pivot irrigation in summer. (The topography and soils are such that large patches within the overall area needing irrigation become waterlogged but cannot be isolated from the operation.) The Bradleys see resolving this as the key to a more robust mixed-farming operation that yields more grain and supports more livestock in a part of the Northern Midlands region which averages 600 to 700 millimetres of rainfall a year. This is the big-picture vision for their two properties, ‘Woollen Park’ and ‘Rosemount’, at Longford and Cressy respectively. A step towards this has been the introduction of a suite of perennial crops – lucerne, ryegrass seed and clover seed – to improve the health and vitality of their topsoil and to better harmonise grain and livestock.
Now, however, the Bradleys have taken their long-term strategy to the next level, with plans for a drainage system targeting the entire soil profile, particularly its hostile subsoils, to hopefully provide an exponential increase in productivity.
The system developed for the couple’s farm business comprises a network of channels and drains that combines to drain excess water from their Cressy shaley loam and Kinburn clay soils. It incorporates three types of drainage. First, 2.8 kilometres of open trench drains, similar to channels, which are one metre deep and about 50 centimetres wide. These trench drains are the main arteries of the system that help draw water across the landscape, lowering the watertable and allowing surplus water to exit paddocks. There are also 16km of underground pipe drains containing 10cm-diameter plastic ag-pipe. These underground pipe drains, installed at a depth of 70cm and backfilled with gravel to a depth of 30cm below the soil surface, function to intercept groundwater flow and lower the watertable over a large area. Third, mole and surface spoon drains across 14.7ha serve to provide at least 40cm of drained soil for crop growth by removing flooding from the soil surface after heavy rain.
Rob estimates the “underground plumbing”, which is based on similar systems he observed during his travel to Europe as part of a 2009 Nuffield Scholarship, will return about $200,000 a year on the couple’s $1 million capital investment in the drainage works, staged over five years. Based on this calculation, they expect to recoup their expenditure on the drainage system installed across 142ha irrigated by centre pivots by 2023.
The cost-benefits are expected to mostly flow from reduced grain yield losses from waterlogging, which in wet seasons can be up to 40 per cent, Rob says. Putting the frequency of these grain losses into perspective, he says waterlogging generally “smashes” crop yields in four out of 10 seasons. In addition to the anticipated lift in average yields, they also hope the free-draining soils will increase the efficiency of their fertiliser applications and reduce weed pressure, especially ryegrass, because the spray rig can access paddocks during winter to control in-crop weeds. Better crop competition is set to further contribute to a reduction in weed pressure, Rob says.
The Bradleys took advantage of the wet 2016 winter conditions to map out a plan for ‘best practice land drainage’ in consultation with Tasmanian Institute of Agriculture soil scientist Dr Bill Cotching. They then waited until summer when the soil was dry enough to support the machinery brought in to install drains in the first 15ha stage. Since installing these drains in December 2016 the soil is already noticeably improved. Wheat sown on the site is showing more uniform growth on the drier, free-draining soil profile. This contrasts with the patchy germination that occurred previously on saturated paddocks.
It is this lift in the overall resilience of their soils that has given rise to the other main area of focus in their integrated strategy – fencing to alllow for livestock intensification. Rob says plans to fence the 142ha in which the first drainage has been installed will allow them to lift the productivity and profitability of their livestock enterprises – 1600 composite ewes and 800 dairy cows. For example, using fencing to divide their highly productive irrigated area into 10ha paddocks, in part guided by the need to protect open trench drains from livestock, would enable the Bradleys to almost triple their stocking rates from 15 to 40 sheep per hectare.
But Rob adds that the fencing will be removeable so they can alternate with high-value crops not suitable for grazing, such as carrot seed, processing peas and onions, depending on their sequencing program.
Crop sequence for grain and graze
Rob Bradley has fine-tuned his balance of grain and graze enterprises since undertaking a Nuffield Scholarship in 2009 in which he looked at options to help improve on-farm sustainability through better integration of cropping and livestock. “Our system has shifted to include a more even mix of crop and livestock enterprises,” Rob says.
“And we’ve integrated more perennial and dual-purpose crops into our sequence to help improve soil health and maintain both productivity and profitability. All our crops, apart from carrot seed and processing peas, are grazed as part of our sequencing program.”
Highlighting the profitability of dual-purpose cropping in their rotation is the Bradleys’ approach to growing ryegrass, which repeatedly produces dry matter for their sheep and dairy cows and returns a seed crop in just one season. For example, when the crop is harvested for ryegrass seed, its straw is baled to provide fodder for their dairy cows throughout the year; the harvested crop is then also grazed by their cows, followed by lambing ewes.
Growing ryegrass in sequence with grain crops also helps control herbicide-resistant ryegrass because commercial ryegrass cultivars are able to out-compete their wild counterparts. A typical rotation on their dryland country comprises three years of ryegrass pasture, followed by wheat, canola and wheat.
A typical rotation on their irrigated country comprises a sequence of mostly higher-value crops, such as carrot seed, followed by processing peas, wheat and then a ryegrass or clover seed crop. The Bradleys’ long-term vision for their mixed-farming operation would see them simplify the diversity of their enterprise mix, while maintaining a balance between cropping and livestock to help spread seasonal and market risk.
For more, see GroundCoverTM Supplement: 'Integration of Livestock and Cropping Systems' (with this issue)
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