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Work less soil for potato yield benefits and cost savings


Producing a soil with good rooting potential and no compaction is the aim when cultivating for a commercial potato crop. Achieving this was more likely if soil was cultivated to a shallower than normal depth, growers attending the Potato Council Winter Forum in Edinburgh heard.

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Dr Blair McKenzie, of the James Hutton Institute, said: “The quality of the soil relates to the function which the farmer needs it to carry out and that function varies with depth.”


For potatoes, the surface must allow water entry, remain stable and not crack. The mid-ridge at 15-20cm (6-8 inches) depth must allow for tuber expansion, water storage and root growth, while the base and subsoil at 20-35cm (8-14in) depth must allow for root proliferation, water storage and drainage. The furrow must be able to support traffic but not become an erosion flow path.


Dr McKenzie said: “You must realise you are asking a lot of one bit of material.”


But while the texture of soil cannot be changed, the structure can. Dr McKenzie explained how soil structure was the arrangement of particles and, hence pores, which allowed the roots to anchor the plant; water to drain through pores and cracks; air to get to the roots for favourable gas exchange and nutrient release to the roots. In order to get optimum yield conditions, the soil needed to allow root proliferation. And one threat to reducing these optimal conditions was compaction.


Work by the Scottish Arable Survey in 2007 showed a third of arable topsoil had a level of compaction which was highly limiting to roots.


The key to good cultivation was to produce a soil with good rooting potential and no compaction.


“If the chance of damaging the soil is lessened then this has the knock on effect of reducing the likelihood of run off and all the environmental issues that brings with it,” added Dr McKenzie.


Dr Mark Stalham of the National Institute of Agricultural Botany-Cambridge University Farms (NIAB CUF) said: “When cultivating for a potato crop, 28 is the magic number. The shallower the cultivation the less likely you are to damage the soil. Cultivating to a depth of only 28cm has been shown to have considerable benefits and still allows planting at the depth the grower wants.”


Yield could be maintained or increased with shallower than normal destoning, with the same percentage marketable yield. Shallower cultivation had been shown to have no effect on the incidence of common scab, greening and cracking.


Further benefits included the savings which could be made on costs. Fuel savings were only in the range of 6p-20p per tonne, however shallower cultivation enabled machines to move faster when the weather allowed, providing more operating days in the planting season.


The depreciation of the machinery could then be taken over a longer period of time because the machine was likely to have a longer working life.


Soil damage assessment tool

A model available at www.terranimo.dk allows the user to input the machine type, wheel load, tyre pressure, clay content and soil water status. A traffic light system of results is then produced, with green indicating no damage will be done and red indicating that the soil will be damaged.


Allows the user to input the machine type, wheel load, tyre pressure, clay content and soil water status. A traffic light system of results is then produced, with green indicating no damage will be done and red indicating the soil will be damaged.


Soil compaction drivers

  • Soil texture: increased clay
  • Soil carbon: less carbon
  • Soil drainage and water content at time of traffic
  • Axle load of traffic (total weight of machine)
  • Ground pressure of traffic
  • Frequency of passes
  • Speed: creating shear

Source: Dr Blair McKenzie, James Hutton Institute


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