Two long-term trials on loamy soils in Western Australia have shown that no-till sowing minimises water erosion on cropland and promotes earthworm activity.
Research supported by the Land and Water Resources Research and Development Corporation (LWRRDC) in the Chapman Valley near Geraldton and at West Dale, south-east of Perth, provided the data.
The nine-year trials on contour bays at the two sites showed that surface runoff roughly doubled at Chapman following the first tillage in eight years.
No-till sowing using narrow seeder points (<50 mm wide) reduced water erosion on the contour bays by a factor of 35 compared with multiple tillage (from 3.5 t/ha down to 0.1 t/ha).
Agriculture WA researchers say the reason for this reduction is twofold. Studies are showing up to 96 per cent of rainfall infiltrates sandy-loam soil after three years under no-till sowing and only 86 per cent under direct drilling using full cut-out tine points.
In contrast, less than 80 per cent of the rainfall infiltrates under multiple till. Also, direct drilling and multiple tillage loosen the thin layer of topsoil in many agricultural areas, making it susceptible to water erosion.
The highest infiltration levels occurred with minimal soil disturbance in sandy loam soil sown using a triple-disc drill.
The research team also linked multiple tillage at Chapman, on a 5 per cent land slope, to plant nutrient losses.
"Major plant nutrient losses increased by a factor of 10 with multiple tillage, equivalent to 12 kg/ha of urea and 15 kg/ha of superphosphate," said research engineer Kevin Bligh.
The West Dale results showed less extreme soil loss on a 3 per cent land slope. The results ranged up to 0.2t/ha/ year soil loss, with increased tillage having a measurable effect only in extremely heavy rains.
"We ascribe the difference between the two sites to the fact that runoff seldom occurred at West Dale until the more permeable sandy loam upper soil became saturated, usually in late winter," said Mr Bligh.
"The results show that no-till sowing is potentially capable of reducing soil loss from water erosion on cropland. We found that after soils became saturated tillage had little effect on runoff; however, tilled, saturated soils are likely to be more erodable," said Mr Bligh.
Earthworms as indicators
The study also looked at earthworm numbers under tillage and no-till conditions.
"Earthworm numbers and mass increased under direct drilling and particularly no-till sowing and pasture. The total mass of earthworms ranged up to 700 kg/ha in spring under no-till sowing and pasture but only 50 kg/ha under multiple tillage," said Mr Bligh.
He said that after five years the number of earthworms estimated in the no-tillage treatment was 1.4 million/ha, twice the number under pasture and three-times the number under direct drilling with full-cutout points. The number under multiple tillage dropped significantly to 0.15 million/ha.
Mr Bligh said the earthworms, besides aerating the soil, may be an indicator of satisfactory conditions for beneficial soil organisms.
Growers, through the GRDC, are currently supporting research on no-till sowing systems in Western Australia and effects on soil structure, as well as a survey of no-till machinery.
Mr Bligh said WA statistics suggest that about 10 per cent of the State's farmers are sowing without tillage, with 35 per cent having adopted the system on South Coastal sandy soils.
According to the Australian Bureau of Statistics, the national cultivation figures for 1993-94, in thousands of hectares are:
* Conventional tillage is defined as using only disc, tine or ploughs for fallow weed control or seedbed preparation.
# Defined as limited cultivation, with some use of herbicides for fallow weed control.
^ Defined as fallow weed control by herbicide and direct drill or no tillage seeding.
Contact: Mr Kevin Bligh 09 368 3893
WA researchers (see report, left) give the following machinery advice on no-tillage sowing.
Tined air seeders can be adapted to sow without tillage by fitting narrow points, provided that the tines have a high enough break-out force to penetrate untilled soils. Combine seed drills can also be adapted to sow without tillage by removing, raising, or tieing-back cultivated tines.
Commercially available 50 mm-wide 'inverted-T'-shaped points, 30 mm-wide 'spear' or 12 mm-wide 'knife' points are commonly used for no-till sowing. Alternatively, narrow points may be made up in a workshop.
Tungsten carbide strips, silver-soldered on the leading edge, generally last longer than wolfram-nickel rod, braised on using an oxy-torch. The wolfram-nickel rod finish can be replaced when worn.
Disced no-till seeders are also available in single-, double-, and triple-disc forms for improved stubble handling. Wavy front disc coulters, 25 mm-wide, can provide soil disturbance below the seed zone.
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