Point Maintenance
Seed placement and furrow profile can be adversely affected using worn points. Attention to point wear is essential, particularly when you are direct-drilling with narrow points that have to carve a channel through undisturbed soil. Expensive steel points can quickly become irretrievably ruined if they are not regularly hard-faced and maintained. An alternative in abrasive soils is the cast points produced by Primary Sales (Australia) Pty Ltd at Dubbo and referred to below under ‘Points for direct-drill pasture establishment’.
Direct-Drill Pasture Sowing
Machines for direct-drilling small pasture seeds must be able to place seed accurately on moisture at a given depth and place a shallow cover of loose soil over the seed. Sowing when the soil is dry is not recommended as germination has to rely on follow-up rain, which may not fall.
The machines available for pasture sowing are many and varied.
Under good conditions, with proper attention to seed placement, most machines can be successfully used to sow pasture. However, when seasonal conditions are not ideal, some machines are far superior.
The ability of individual tines to follow the ground surface places all machines into one of two classes:
Machines with ground-following capability: These include triple discs, single disc seeders (and their conversions) and drills with trailing tines. All these machines can give a more precise sowing depth than the rigid-frame seeders and are preferred for sowing small pasture seeds.
Generally, tined seeders achieve precise placement and coverage better than disc seeders. The single disc seeder, in particular, produces poor results when direct-drilling is used in a moist seedbed soon after spraying. In these conditions, either the slot is left open and exposed or the sod falls back, burying the seed. Single disc seeders can be converted to fit Caldow points quite cheaply; conversion is recommended for these machines.
Rigid-frame machines: This class includes most combines, coil-tine, spring-tine or springrelease tine drills, and chisel seeders. The significance of a rigid frame is that, in selecting a sowing depth, a compromise is necessary to account for localised ground variations, because all tines have a fixed position in relation to the frame. Average sowing depth is set at 25mm, but ground variations can produce furrows varying in depth from 10 to 40mm. It is important that the furrow walls don’t cave in as the seed will be buried too deeply. Heavy rain soon after sowing can be a major problem for this reason.
Points for Direct-Drill Pasture Establishment
Burying pasture seed under large clods or too much soil is a major cause of sowing failure. Burial is particularly common in conventional seedbeds, and is the reason why seed is often simply dropped on the surface and ‘covered’ by light harrows or a roller. However, seed sown into a dry surface soil or, worse still, exposed on the soil surface, is still at risk. The type of sowing point is thus an important element in accurate seed placement. Narrow points with the leading edge only 6–10mm wide are preferred. A high wear rate is a problem with most narrow soil openers.
Triple disc soil openers have relatively low wear rates and accurate sowing depth. Operate the coulter disc 5–10cm below the sowing discs. In heavier wet clay soils the discs cause smearing and compact the soil at the bottom of the furrow or leave the furrow open with the seed exposed.
Single disc soil openers are generally not recommended for direct-drill pasture sowing as it is difficult to get a tilth for seed coverage until the sod has died and the soil is dry.
Chisel points are 50mm wide and fracture the sod along both sides of the point, forming an open furrow and leaving the seed exposed. Long strips of sod are peeled out and thrown in all directions, some going back in the furrows, burying the seed. Trailing chains behind each tine are essential.
Steel lucerne points are less expensive but must be hard-faced. Wear and maintenance are excessive in most soils. These points perform best on light spring tines, where plenty of vibration can produce a good tilth.
Baker boots (inverted ‘T’ soil openers). These points were designed to permit sowing in slightly less than ideal sowing conditions. The Baker boot produces a flat-bottomed, inverted ‘T’ (?) furrow, protecting the seedling from moisture stress if dry conditions occur after sowing. In many low-clay Australian soils, the side walls fall back, burying the seed, and the large blade becomes quickly worn.
Caldow ‘T’ boots are a development of the Baker boot but are designed to reduce the amount of wearing surface, to produce a ‘V’ shape at the bottom of the furrow and to throw more soil out of the furrow. The ‘V’ bottom is achieved by pitching the point forward so the leading tungsten-protected tip is 6–8mm lower than the rear of the wings. The wings then produce tilth scraped from the sides of the furrow.
The Caldow ‘T’ boot is a great improvement, but wear rates are still a problem in abrasive soils. Extra tungsten can be applied to the wings but cost escalates. Regular hard-facing maintenance is still required to preserve the unprotected parts of the blades.
Cast points. These hard-wearing alloy points are available in Baker boot and Caldow ‘T’ boot designs. NSW Agriculture found that the cast points cost 50% less and were 65% more hard-wearing than triple-tungsten-protected steel Caldow points, and required no maintenance (hard-facing). More than 250ha of abrasive granite soils have been sown with cast Caldows.
Super seeder points are made of the same cast alloy as the cast Caldow point. They were originally developed for direct-drilling crops. Their cross-section is similar in shape to an inverted ‘T’. As well as having good wear rates, these points can be bolted directly to most tines, thus doing away with the need for the expensive adaptor needed for ‘T’ boots.
Band-seeders are strongly recommended in ploughed seedbeds.
