THE recent Institution of Agricultural Engineers Nor-
thern Ireland Branch’s tech-
nical meeting featured pre-sentations dealing with both soil science and practical experiences to reduce soil com-paction on a working County Tyrone dairy farm.
The first speaker was Prof Jane Rickson, current I Agr E President and Professor of Soil Erosion and Conservation at Cranfield University’s Soil and Agrifood In-stitute.
She described how a healthy soil is the basis for satisfying the increasing worldwide demand for safe, nutritious and affordable food. But land is also in demand for other applications such as biofuel production, urban development and infrastructure projects.
Crop production can be increased by management of inputs, such as fertiliser application and irrigation, but yield response is limited unless the soil health and structure is good. The choice of aids to control competitive weeds, pests and diseases is being reduced by the review and withdrawal of some commercial products.
Soil degradation and loss by compaction and erosion, aided by extreme and variable weather events, is of concern. A 2006 EU study assessed the true cost of soil damage and loss in England and Wales alone to be around £1.2 billion per year.
By contrast, some of the general public’s lack of appreciation of the huge value of soil to human health and well being is indicated by the casual use of terms such as “dirt”, “soiled” and “mud”.
As well as being the base for crop growth, soil is essential for water storage management, carbon storage and landscape aesthetics. Fortunately, recent public policy documents seem to increasingly recognise this. Land covers 26 per cent of the earth’s surface but only around half of it is suitable for agriculture of which just three per cent is arable.
Prof Rickson used the graphic image of the limited amount of good top soil on the earth as no more than the thin skin covering on an apple.
Soil texture includes a range of particle sizes (in various proportions) ranging from fine particle clays (less than 0.002mm), silts (0.002mm to 0.06mm) to sands (over 2mm).
Typical make-up of a soil includes 45 per cent minerals (clay, silt and sand), 25 per cent water, 25 per cent air and five per cent organic matter. The ideal open soil structure permits excess water to move freely and provides access to air and nutrients to support plant root growth.
Excess water reduces the load-ing capacity and can cause the structure to collapse under com-paction or cultivation. A well structured soil should provide the three Rs of receiving, retaining and releasing water at the appropriate rate. Recently Defra revealed that of 300 farms surveyed, only 40 per cent had good soil structure. Compaction damage caused an estimated loss of yield worth £481m per year in England and Wales.
As a biological medium, soil contains hugh numbers of minute microbes, carbon, a range of nutrients and seed ready for germination. Natural acidity (mea-
sured as pH) can vary with the natural respiration and de-composition processes going on there.
The developing root systems of plants tend to open and support soil structure, especially under established grassland regimes, where there is less regular cultivation compared to arable cropping. There is also natural recycling of nutrients under live-stock grazing.
Good traffic management practices include minimising machine we-ights, reducing axle loadings, minimising the number of wheel tracks and staying off the land for at least 48 hours after heavy rainfall. In intensive livestock systems, the careful location of drinkers. feeders and gates can reduce compaction.
Mechanical surface loosening tech-
niques can assist but it is always preferable to check first (using simple hand spade-dug inspection pits) to check if this is really needed. Ploughing for routine reseeding is effective in dealing with surface compaction on grassland. In sev-erely impeded drainage locations field drain renewal or moling/sub-soiling may be appropriate.
All of these aspects are covered in the well illustrated Agriculture and Horticulture Development Bo-
ard’s “Healthy Grassland Soils Guide”, which can be viewed via www.healthygrasslandsoils.co.uk
The decision to carry out corrective work is site specific and will depend on cost effectiveness and overall land management prior-ities.
Andrew Wright is a young farmer from County Tyrone. He described how he has been working on his family dairy farm to monitor and minimise compaction, within afford-
able systems, to maintain and improve grassland output there.
As the result of visual observation of reduced grass yields and hearing the results of scientific investigation around the subject of soil com-paction elsewhere, he decided to measure, from 2016 onwards, how much wheeling is done during
He has based this on GPS records of tractor/implement travel during both fertiliser and slurry spreading work. Impressively, as an IT enthusiast, he was able to design and custom-build his own GPS satellite guidance and recording system, avoiding the expense of purchasing proprietary items. This included writing his own software, custom-making all of his GPS components (including etching the
printed circuit board and 3D printing).
The assembled information, in-cluding both steering guidance and a field mapping record of tractor movement, is displayed on a 10” touch screen mounted in the tractor cab. He went on to further refine positional accuracy by adding his own home-built RTK base station system for less than £100!
The total area covered by wheelings is derived from electronic addition of the distance travelled times the tyre width from the digital field map information.
The first map analysis showed up to 80 per cent of the field surface covered by wheelings. Subsequent careful use of the system to guide fertiliser spreading reduced this to 37 per cent.
It was decided to separate slurry haulage from slurry spreading by using the larger 2,750g tanker for transport only and off-loading its contents to a top-fill 1,600g single-axle tanker for field spreading. The load is restricted to around 1,200g to minimise the axle load.
At this stage the tractor’s rear radial tyres run with 16psi inflation pressures and the tanker tyres at 18psi. These are within the tyre manufacturers’ recommendations for the axle loads and travel speed in the field.
The original spread plate on the tanker has been replaced with a Moscha oscillating unit: (a) to increase spread bout width to around 18m and (b) to reduce atomisation and drift from its reduced-pressure spread pattern. Its wag-tail action (as originally designed by a German farmer) is powered by the slurry passing through it.
High rainfall conditions during 2017 were challenging for travel on the heavy loam soils. By contrast, the drought conditions of 2018 were much easier with the added bonus of resulting soil shrinkage cracks continuing to assist drainage in subsequent years.
Grass cutting work, for silage making, is done between 1pm and 5pm to maximise grass sugar levels. The swards are based on Italian ryegrass, which has a strong root system helping to maintain soil structure. Harvesting, using the farm’s own machinery, takes up to four cuts each year. Front and offset mower combinations are used to maximise bout width and minimise the tractor wheelings.
Andrew had previously tried some sub-soiling but felt that, in his conditions, it had not improved grass yield. He favours the “try to reduce it before trying to remove it” approach to compaction and believes that his soil structure has improved. At this stage he aims to minimise the wheelings from his existing equipment rather than take on a more expensive option.
Following the presentations an interactive discussion continued around topics including:
n Digging of test pits and use of the information;
n Types of drainage for sports pitches;
n Use and benefits of slurry dribble-bar systems;
n Possible future use of machine gantry type systems for field work;
n Arable cultivation effects, in-cluding the use of stone separation techniques for root crops in specific soil types.
The chairman closed the meeting with thanks to both speakers for their clear and most informative presentations.