FOR THE JOB
Its an expensive operation but, on many soils, an essential
one. Peter Hill outlines the need for subsoiling and looks at
some of the hefty equipment available for getting it done.
FOR growers with yield-mapping combines, the case for subsoiling is often all too clear. Distinct areas of depressed yield along headlands and in areas where land tends to lie wet.
Other factors may be involved – such as rabbit grazing – and should be considered before jumping to conclusions.
But, if soil compaction is suspected as the principal cause, further investigation with a stout spade will help reveal the extent and intensity of the problem.
Its an ironic twist that, as growers move to bigger tractors, implements and harvest machinery to improve productivity and reduce costs, the soil compaction such equipment can cause adds to costs and can have a significant impact on crop performance.
Compaction impact can be minimised by using tyres of generous dimensions, wide-working implements (to reduce the number of passes across fields), and organising work to keep off land when it is most vulnerable.
None of these measures will avoid the problem altogether but may at least keep it to manageable proportions – in terms of extent and intensity.
One of the advantages of identifying compacted field areas through yield mapping is that it may be possible to subsoil selectively; equally, if the depth to which soils are compacted – which is largely a consequence of gross equipment weight as much as generosity of tyre equipment- then remedial treatments can be shallower and, as a consequence, less costly.
The aim of such treatments, of course, is simply to regenerate an open soil structure that has been compressed by field traffic. Compacted soil contains less oxygen, offers fewer easy routes for plant roots to develop, and slows natural drainage of excess moisture.
Undoing the damage means recreating fissures and loosening the soil profile again. That takes a lot of energy, despite the best efforts of implement designers who have over the years tried numerous ways of getting more soil heave and shatter for the least amount of draft by using wings, angled legs and even powered-leg subsoilers.
Whatever the implement used, though, the key criterion is the state of the soil. When it is rock hard, the effort required to bust soil is uneconomic in terms of fuel and implement wear and tear. Subsoiling when the soil is too wet and elastic, and it tends to simply deform around tines with little or none of the fissuring effect that is the very purpose of carrying out the task.
Conditions ideally, then, need to be drying, with sufficient moisture for good surface traction and ready soil movement, but dry enough to get the necessary heave and shatter.
And dont forget that spade; subsoiling where its value is marginal or going deeper than necessary is an expense that growers can ill afford.
Being able to easily alter the implement to different soil tyres and situations is the idea behind Opicos Vari-Flow subsoiler. Behind a leading row of five tines across the 3.25m (10ft 8in) wide implement is a second row of four tines carried on a separate subframe.
The second row of tines are used when an intensive but relatively shallow soil-working effect is required; or easily raised out of work by hydraulic ram when heavier draft deeper working is necessary.
Depth control is by wheels or, preferably, by a full-width open crumbler roll. Settings are determined using a pin and hole arrangement with a big choice of positions. Apart from regulating subsoiling depth, the roller turns the downward pull of the tines into useful work, crushing any clods and leaving a more level surface finish.
A choice of two wedge-shaped points is available, along with a winged version designed to give extra lift.
The basic implement is priced £3148 with 450mm and 620mm (18in and 24in) crumbler rolls £464 and £815, respectively.
Simbas latest offering, the Combiplow, will work to 60cm (24in) deep but is also designed for shallower operation at faster speeds.
The French implement has extra-slim tines – just 20mm wide – to minimise draft and they are set at a slight angle before turning through 90deg at the base to support a chisel point. The idea behind this layout, it seems, is to lift soil without impedance from the tine itself. Not unlike the Paraplow concept but rather different in its execution.
Power requirement is estimated to be as much as 20% less than conventional subsoilers and, at 45cm depth, operating speeds can typically be in the 8-10kph (5-6mph) range, says Simba. A flexible rubber roller completes the implement, leaving a surface ready for subsequent cultivations and controlling tine depth at one of 12 settings.
There are three models – 3m (9ft 10in) with four tines; 4.5m (14ft 9in) with six tines; and 6m (20ft) with eight tines. The two larger models have a folding frame. Tines are arranged in a single row and are protected by trip mechanisms with large coil return-to-work springs.
Trip-leg protection is also available as an alternative to shear bolt protection on Simbas 300-series FlatLiner. Comprising a hefty compression coil spring, the mechanism allows the leg some rearward movement to clear stones and other obstructions, before moving it back into the working position.
The 300-series is designed for working depths down to 30cm (12in) and comes in seven and nine-tine sizes covering four working widths from 3m to 4.2m (9ft 10in to 14ft) for tractors up to 160hp. Prices start at £6335 or £6474 with trip legs.
The larger 500-series FlatLiner, using 150mm x 150mm x 10mm steel for the triangular shaped frame, works to 50cm (20in) and covers the same widths as the 300-series but with three, five or seven legs. Prices start at £5773.
A toothed steel packer is standard in each case, with depth wheels, trailing kit and additional tines among the options.
The Maxi-Lift range from Tim Howard Engineering also caters for big-power tracked and wheeled tractors. Three and five-leg models head the line-up using a simple vee-frame; at the other end of the scale is a nine-leg trailed design.
Box section 200mm x 10mm steel is arranged in vee or A-formations is used for the frames but doubled up on the bigger implement to cope with tractors in the 450hp to 600hp league.
All versions come with a hydraulically adjusted toothed packer roll to level off any surface heave and help with depth control. Prices climb from £3500 for a 2.25m (7ft 4in) three-leg Maxi-Lift 250-series to £16,400 for a nine-leg 6.3m (21ft) trailed 600-series implement.
The subsoiler design that originated the shallow soil-loosening concept is currently available in two guises – as the Flat-Lift from Spaldings and the Stocks-Lift from Richard Stocks.
Both implements use an extended point and broad wing configuration that gives effective pan-busting without leaving a rough, uneven surface.
The Stocks-Lift range has been extended with medium duty and heavy duty models designed for tractors of 140hp to 290hp and 200hp to 400hp, respectively. Both implements can work to between 200mm and 510mm (8in and 20in) deep.
The medium duty models hefty frame carries up to three to five tines, while the heavier version carries up to seven tines. Optional leading discs help their passage through the soil and discourage a lot of surface heave.
Depth wheels can also be added, along with a steel toothed packer or levelling coil.
The newly introduced Marquis five-leg subsoiler from Browns Agricultural is designed for tractors of 140hp and more. The frame design is unusual in having a narrow leading section to carry a tine, then a full-width two-bar section carrying two tines each to form a vee configuration.
The frame is constructed from 200mm x 100mm box section with a turnbuckle-adjusted open cage roller – principally for depth control – completing the implement.
List price is £5800, plus £65/leg for the optional extra-lift wing kits.
No lateral stresses
Mounting subsoiler tines on pivots stops lateral stresses being imposed by steering movement; its a useful feature of mounted subsoilers being used on a tracklayer or articulated wheel tractor.
The Loosen-It subsoiler from Farmrite Fabrications carries pivot-mounted tines on a single beam in swept-back formation. Largest models are five and seven-tine implements for tractors of 200hp-plus and are capable of working at depths from 200mm to 500mm (8in to 20in).
A disc coulter can be added ahead of each tine to reduce soil deformation at the surface, while a reversible bar point and wings give extra heave down below.
Buyers have a choice of open bar crumbler or toothed packer to complete the implement, adding £1295 and £2025 respectively to the £4875 and £6565 list prices of the five and seven-leg models.
Fosters Acre-Master range includes pivot-leg models – as well as rigid tines – on two- and three-leg subsoilers or on a 3.6m (12ft) double-beam frame with up to five tines.
Broad screw-adjusted depth wheels can be added, along with a full-width open cage crumbler. Prices start at £1950 for a twin leg model; depth wheels add £850, wings £60/leg and a crumbler £1350.
The expanded range of V-Form subsoilers from Cousins of Emneth are similar in using swept-back tool bars but feature rigid-mounted tines and trailed models.
A 3.75m (12ft) wide version – in both mounted and trailed format slots into the range, along with a 2.75m (9ft) mounted implement. That increases the number of sizes available to five, from 2.25m to 4.25m (7ft 4in to 14ft), to cater for a wider range of tractor power and soil types.
The biggest model in each case, fitted with seven or nine legs, is priced £9120 and £10,240 with toothed packer, while the trailed variant is £12,280 and £13,400.
Heavy duty models have 200mm x 100mm box section tool bar beams with turnbuckle adjustment of the depth wheels and finishing roller and there is a three-way choice for the latter of open cage crumbler, tooth packer or steel coil. *
Stocks Lift is now produced in standard, medium and heavy models, offering different frame widths and power ratings. The top version pictured will handle tractors up to 400hp, says Richard Stocks Ltd.
The Farmrite Loosen-It carries tines in vee-formation on a toolbar frame to reduce draft. Pivot mounts allow sideways movement (especially from crawlers or articulated tractors) imposing undue stress on tines.