BACK on September 20, 2018, Farm Weekly published an article on the value of coastal limesand and better types of lime for fixing up acid subsoils of red sand dunes.
Since then other measurements have been made and the wheat plants in the trial have been harvested, so we can report on the grain yield responses of the various treatments used on Anthill Farm, Dartmoor.
Original soil conditions are shown in the graph above.
The severity of the aluminium problem at this site is considerable (up to 70 parts per million in the calcium chloride extraction test).
The hardpan was often too strong to get a penetrometer into, even when moist.
Some other nutrients at the trial site showed a significant accumulation in the subsoil beneath the pan (up to five times more sulphur and 25 per cent more molybdenum than in the topsoil), offering more possible useful savings for crop nutrition when made accessible.
We used six metre square plots to compare six different lime treatments – each plot was half deep ripped and half unripped before the limes were applied.
Westonia wheat was sown at 60 kilograms per hectare on May 27 with 65kg/ha of Summit’s Mallee fertiliser and urea.
On July 12, 30kg/ha urea was top- dressed.
The crop had 94.4 millimetres of summer rain (Jan-Feb) and 251mm of rain between May and October.
The treatments used are shown in the table below.
Heat stress experienced by the crop was estimated with measurements of canopy (leaf) temperature by a hand-held infra-red gun.
Maximum air temperature reached 32 degrees Celsius on September 21, but high air temperatures were not common at Dartmoor in spring 2018, so there was relatively little heat stress compared to some recent seasons.
Plant establishment averaged 110 plants per square metre.
Heads/m2 ranged from 240 to 328 – with the highest amount on the unripped dolomite plot and least on the ripped or unripped nil additive plots.
Anthesis biomass followed the same pattern.
Treatment differences in nutrient uptake were mainly in nitrate uptake; deep ripping improved nitrate uptake by an average of 63pc compared to the unripped.
Presumably this is a reflection of faster root growth in the ripped soil allowing easier interception of nitrate being leached through the soil profile.
The dolomite treatment also had a noticeable increased manganese and molybdenum uptake.
Two tonnes a hectare of Manna mixture lifted the pH of the hardpan and 5t/ha lifted the pH of the soil to 500mm depth.
Measurements of grain yield and quality showed partial ripping of the hardpan (deeper tynes at 1 metre spacing with wide points and inclusion plates) gave about 200kg/ha more yield for most amendments.
Responses of the limesand treatments to deep ripping were negligible – 5t/ha of Manna Enterprises 50pc gypsum and 50pc calcium hydroxide without ripping was the highest yield in the trial (approximately 4t/ha).
Deep ripping with the better amendments yielded about 3t/ha.
There were no screenings in any of the treatments and protein was relatively low (8.5pc at 12pc moisture content).
Red sand dunes are not uncommon in the Dartmoor, East Binnu and north Yuna districts – they are very different creatures from the yellow ones.
The red colour is from iron-rich clay, probably blown in from the north east over a very long time.
The clay helps to back off non-wetting and hold nutrients and biology – but there are many downsides compared to the yellow dunes they often lay side-by-side to.
The clay helps the red sand compact tighter than yellow sands, especially under the weight of modern cropping gear, but that is all fixable with Controlled Traffic Farming and modern deep ripping with inclusion plates or mini-delvers.
I think the biggest challenge comes from the fineness of the clay, providing many edges of the clay sheets which can be attacked by hydrogen ions (acidity) and release aluminium ions toxic to the growth of many crop and pasture roots.
A mixture of highly soluble calcium hydroxide (CaOH) and soluble gypsum (CaSO4) seems to be one of the solutions to the aluminium toxicity problem – the gypsum reacts with the aluminium to form harmless aluminium sulphate, the hydroxide raises pH to minimise further formation of toxic aluminium.
Partial ripping of a hardpan such as this can provide benefit and may allow slower supply of moisture from the remnant pan later in the season for better grainfill (2018 was not a good season to test this idea due to the timeliness of the rain).
The responses to amendments revealed a range of profitabilities in the first season, most promising being the higher rate of CaSO4 and CaOH mixture, providing about $170/ha margin over no amendment and without deep ripping.
The reasons for this good response are interesting and a high water retention by a hardpan seems part of the explanation.
The improved pH and aluminium level would allow soil exploration through old root channels and ant burrows – dense hardpans can hold more water against gravity-driven drainage that the same depth of deep ripped soil.
We know that it is a good idea to try to combine with benefits of encouraging macro fauna (ants, termites and earthworms) at the same time as improving the physical and chemical conditions of farming soil.
A one off deeper ripping and addition of soil amendments in a fully matched CTF system, to conserve the benefits, is a sensible strategy to do that.
Hopefully these trial results and observations offer some encouragement to others to test the effectiveness of some of these treatments on their farm, especially on poor red dunes on sandplain.
We also acknowledge the essential support of the Northern Agricultural Catchment Council funds and the assistance of Anthill Farm to enable these trials to occur.