Farmnote 70/96 [Reviewed October 2006]

Crop establishment series

By Glen Riethmuller and Mohammad Amjad, Agricultural Engineers, Merredin Dryland Research Institute

Summary

Reviews the effectiveness of no-tillage disc machinery and tine machinery in placing seed and fertiliser, and considers chemical weed control.

This Farmnote is one of a series on crop establishment practices which minimise soil disturbance and improve stubble retention. In partnership with primary producers, Agriculture Western Australia is focussed on improved and profitable farming which conserves or improves the quality of the State's soil resources.

The recent upsurge in the adoption of no-tillage crop establishment practices has brought renewed attention to the benefits that can be achieved. These include improved soil conservation and soil conditions and maintained or slightly increased productivity.

A major decision for farmers considering adopting no-tillage practices concerns the choice of machinery. Disc machines handle stubble fairly well and are ideally suited to light soils that are prone to wind erosion. However, they are not as versatile as tined machines which can be easily reconfigured for a variety of soil and crop conditions. Chemicals that need to be incorporated also present a difficult challenge with this type of machine.

Tine machines are less able to cope with stubble than disc seeders. Successful use of these seeders in a stubble retention system requires preparation of stubble at harvest, which may cost more in time and wear on the harvester. However, they have the ability to use points of different shape and size to match a range of requirements for soil disturbance and fertiliser placement. Wider row spacings improve the stubble handling ability, particularly for lupins but wheat yields may be reduced.

There is a range of new machinery or conversions for existing machinery available for farmers contemplating the move to no-till sowing. Farmers can choose the most cost effective machine for their particular environment, soil type, cropping area and budget.

This Farmnote reviews the effectiveness of disc and tine machines to successfully place seed and fertiliser. Farmnote no. 61/96 reviews seeding machinery performance for handling stubble.

Disc machines

The first triple discs seeders consisted of a leading coulter set in line with the direction of travel. This opened the soil and a paired or double disc followed which cut a groove in which the seed was placed. These machines were not particularly successful. One of the biggest problems was that in soils with 10 per cent or more clay (that is, loams and clay loams), the slot was left open and seed was either droughted or flooded. Emergence and crop yields were unreliable and often poor.

Later triple disc machines (Figure 1) have a furrow-following press wheel which controls the depth of the double disc and closes the furrow by placing soil over the seed The latest models used in Western Australia have replaced the plain leading coulter with a wavy disc. This is self-sharpening and cuts through stubble residue as well as disturbing some soil in a narrow slot. The limited slot of disturbed soil leads to better seed-to-soil contact and has the potential to control or reduce the incidence of Rhizoctonia bare patch disease (Farmnote No. 68/96 'Crop disease and no-tillage farming').

However, in particularly loose sandy soils or soft wet soil these coulters may be unable to cut stubble and instead push it into the soil in a folded form. Uncut stubble in the seed furrow can prevent adequate seed-to-soil contact and cause poor emergence.

The latest models are more solidly constructed than the original triple disc machines and penetration on firmer soils is improved. However, even though the amount of soil disturbed can be varied by using coulters with deeper waves, the amount of disturbed soil may still be less than adequate. For example, some soils may need more disturbance than others or fertiliser may be better placed below the seed (Farmnote No. 71/96 'Banding fertilisers in no-tillage farming').

One innovation to increase the amount of soil disturbance is an angled coulter. This has been used successfully to place the fertiliser below the seed and thus avoid or minimise adverse fertiliser toxicity effects, particularly in no-tillage seedbeds.

These machines are quite expensive per unit width but offsetting this cost is the advantage they have in handling high stubble levels. In stubble retention systems they provide timely, untroubled seeding, which improves the chances of obtaining higher yields and profits.

Tine machines

The traditional tined seeders were for primary or secondary tillage with seeding being done only after some form of tillage. As direct drilling and then no-tillage crop establishment in retained stubble were adopted, the need for a primary tillage machine was reduced and seeders had to be more robust. The tine tension or tine break out pressure generally increased to ensure the tines penetrated firmer, undisturbed soil. Around 90 kilograms is now generally required for one-pass no-till sowing, particularly if some disturbance below the seed is required.

The next problem faced by tined seeding machines was the need to handle potentially large quantities of stubble. Some of the methods used to cope with stubble are outlined below.

• Reduce the length of stubble during harvest to half of the clearance distance between the nearest tines of your seeder (this distance is less if wide seed boots are attached) and spread all the cut stubble and chaff evenly.
• Increase the clearance between tines by using wider row spacing, wider bar spacing or more bars on the seeder (Figure 2.) and higher underframe clearance tines, such as chisel plough tines.
• Cut or move the stubble away from in front of the tine.
• Use a rotary harrow to level the seed bed.

Figure 2. John Deere 753® combine (now sold as Forward Engineers 853®) modified to sow on four bars instead of three bars, to improve stubble handling without raising the seed box.

The first option is more suited to wheat, because wheat yields are generally reduced with wider row spacing (Table 1.)

Table 1. Average wheat yields (t/ha) from different seeders and stubble conditions on Merredin sandy clay loam

Another method of improving stubble handling is to cut the stubble in front of the tine with a coulter, or sweep the stubble to the side with a pin wheel rake. The coulter option may not be successful if there is not enough weight on the machine to make it penetrate, or the soil is particularly soft (that is, loose or wet soil) which makes the cutting of damp stubble more difficult. The sweeping option is currently under research.

Tine machines have the flexibility of changing from direct drilling, with full soil disturbance, to no-till seeding by simply using narrow points.

More disturbance below the seed (for loosening compacted soil, disease control or fertiliser placement) can also be achieved by using a very narrow deep working point, provided tine tension is adequate, followed by a shallow seed placing boot. The seed placing boot can also serve as a soil closing device, for example, the Ausplow Deep Blade System (DBS).(Figure 3)

Chemical weed control

Chemical weed control has to be taken into account when using no-tillage seeding. Tines tend to move pre-emergent chemicals away from the seeded rows and some form of harrow may be required to move some soil back over the seed. Rotary harrows are very effective at incorporating chemicals, particularly as they can handle large amounts of stubble.

Press wheels leave any pre-emergent chemical where it is thrown by the soil opener, so they may need following by a harrow to even out the chemical. Care should also be taken with press wheels when seeding lupins, as a relatively low press wheel pressure of 2.4 kg/cm width) has been found to reduce emergence and yields (Table 2).

Table 2. Effects of press wheels (PW) and rotary harrows on lupin yield in short and long stubble

Rotary harrows can be left off when seeding in non-wetting soils. This ensures the seed is placed in the base of a furrow to harvest water. These furrows are best formed with rows slightly wider than 200 mm. Narrow furrows tend to be filled in by following tines.

Fertiliser toxicity

As the row spacing widens in crops sown with no-tillage, fertiliser toxicity becomes more of a problem unless the fertiliser is placed away from the seed (Farmnote No. 72/96). Banding fertiliser below the seed is a useful option for lupins (Table 3). To date, wheat has generally shown no consistent response in yield from banding the fertiliser below the seed in Western Australia (Farmnote no.71/96).

Table 3. Effect on lupin yield (t/ha) of varying row spacing using direct drilling (fertiliser mixed with soil and seed) and tined seeders (fertiliser banded below the seed)

Further reading

• Farmnote No. 61/96 'No-till sowing machinery to control wind erosion' (Agdex 571).
• Farmnote No. 68/96 'Crop disease and no-tillage farming' (Agdex 100/630).
• Farmnote No. 71/96 'Banding fertilisers in no-tillage farming' (Agdex 540).
• Farmnote No. 72/96 'Fertiliser toxicity and crop establishment in no-tillage farming'

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