Spreading the good news about clay
Growers in the Western Australian No Tillage Farmers Association (WANTFA) are meeting the challenge of non-wetting soils by spreading clay-rich subsoil across their farms. Trials starting in 1999 have shown higher yield responses as higher rates of clay are applied.
The trials were set up in response to lively debate about how much clay growers need to apply. Rates were tested at 0, 50, 100, 200, 300 t/ha at two incorporation intensities (10 cm deep with one working, and 15 cm deep with the clay worked in several times).
According to Bill Crabtree, Scientific Officer for WANTFA, pioneering experiences in South Australia have suggested that 200-250 t/ha are needed on deep sands. Local WANTFA grower Matthew Jones of 'Broadview' near Esperance has tried rates of up to 300 t/ha.
"We probably didn't need to go that high," says Mr Jones, "but we wanted to do the job properly after seeing almost no effect of applying lower rates in previous years. We've now managed to reduce non-wetting by 95 per cent."
In areas where he has applied high rates of clay, Mr Jones now sees the soil profile stay moist throughout the growing season. He has also seen a big improvement in germination rates, increasing from 40 plants/m2 to more than 200 plants/m2 after sowing 90 kg/ha of wheat. The other two crops in Mr Jones' rotation — lupins and barley — have been just as successful, and he is now looking forward to starting canola.
The impact of higher germination rates and much improved soils can be seen in the results of the WANTFA trials in the first year after claying (see graph for preliminary results), which show a yield increase of as much as 0.5 t/ha of barley from the highest rates of clay application.
"With only this modest yield response, at a price of $150/t for barley, the cost of excavating and spreading the clay is probably recoverable in two years, even at the higher rates," says Mr Crabtree.
Mr Crabtree adds that higher yields are expected in the second year after claying, as the soil takes a while to 'settle down' and for nutrients to become readily available to plants.
The WANTFA trials have shown that a deeper incorporation with more workings is more effective. However, the difference is slight and Mr Jones has been experimenting with the depth of incorporation in attempts to improve first-year yields, and the associated profits.
"Some of my poorer yield responses might have been due to deep incorporation to begin with. I'm thinking of trying a shallower depth of only 10 cm in the first year, then reworking in later years to the full 15 cm depth," says Mr Jones.
Mr Jones is also thinking of applying more than the usual amount of fertiliser in the first year, to address problems of nutrient deficiency he has found as the clay ties up extra nutrients. In that way he hopes to help claying pay for itself a bit sooner.
"An important way to keep costs down is to make sure the clay pits are within 500 metres if you can, or the costs go up because of the extra distances you need to travel," says Mr Jones. "Our pits can be as much as 1.5 km apart, and that's economic only because we are doing it ourselves and we have a large-capacity scraper. It still took seven days to spread 300 t/ha of clay over 120 hectares."
Mr Jones and other WANTFA growers can see a return to no-till farming within a couple of years, once the clay has been completely worked in.
"The trials have put a number on the yield responses we were seeing in the paddock, so we can start to work out how much clay we need to spread, how we should incorporate it, and still recover costs and our soils, in a reasonable time."
Relatively low rates of clay application — around 100 t/ha — have proven profitable with appropriate application, according to GRDC-supported research under the banner 'claying for profit' on water-repellent soils. A comprehensive set of claying techniques for farmers stemming from this work by AGWEST and the University of Western Australia can be reviewed on a new website, www.agweb.wa.gov.au/progserv/natural/soilman/waterep
Contact: Mr Rob Hetherington 08 9892 8444
Region North, South, West