Subsoil manure incorporation aids growth

In the first year of the SARDI-run, GRDC-funded two-year trial, cattle, sheep, chicken and pig manures were incorporated into the soil when deep ripping, using a Phillips New Horizon Subsoil Extruder.

The Extruder mixes manure with water to form a slurry in its hopper. The slurry then travels through a pipe at the back of the machine and, as the machine moves along, is pushed down to the base of two deep-ripping tynes, which are about one metre apart, to a depth of 40 centimetres.

SARDI researcher Brian Dzoma said in normal farming practices, the majority of nutrition was spread on top of soils or incorporated in the top of the profile, but the benefits of providing nutrition at a depth could be significant.

"In typical Mallee environments, we place organic matter at shallow depths, but that area is dry during most of the growing season, so the roots are growing down and away from nutrition, which can affect uptake and use of less mobile nutrients like phosphorus," he said.

"The whole idea of using manures and deep placement of nutrition is not new, but we're looking at subsoil placement of locally available organic matter to improve crop performance, soil nutrition and health."

The trial consists of nine treatments, replicated three times, including the subsoil injection of each of the four manures - at a concentration balanced to 150 kilograms per hectare of nitrogen - the spreading on top of the soil with cattle, pig and chicken manures, and two controls.

Treatments were applied in April, and sown with Spartacus barley in May.

While there is still analysis to be done, Mr Dzoma said there were encouraging preliminary results.

"The subsoil treatments are doing better than when the manure has been spread on top, and we're also definitely noticing a ripping effect," he said.

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He said the economics of manure injection still had to be carried out.

"At the moment, it's a proof of concept, to see if it works, and then after that we'll do a gross margin analysis to determine if the practice is economically viable," he said.

"For example, achieving a 2 tonne/ha in grain yield does not tell the whole story, if the associated costs of subsoil manuring are ignored."

Project consultant Chris McDonough, Insight Extension for Agriculture, said manure injection while deep ripping could potentially be "quite doable and practical", particularly seeing as soil cover was largely kept while using the Extruder, preventing erosion.

"If through these trials we can prove that it works, and improve the design of the machine to make it more practical to implement, it could really be a winner," he said.

For Paul Rudiger, the decision to try deep ripping this year has been a successful one.

Mr Rudiger crops wheat, barley, chickpeas, vetch, lentils and lupins on 2600 hectares at Loxton, and deep ripped a few sandhills where crops hadn't performed previously.

The paddocks were straight deep ripped (without a manure injection) in February before being sowed with barley in May.

"(On the sandhills) where we haven't ripped at all, the crop is hardly worth harvesting, but where we've ripped, it's made almost twice the growth and bigger heads. It's really significant," he said.

Mr Rudiger deep ripped at a depth of 50 centimetres to 60cm, to get through hardpans at 30cm and at 45cm, and harvested up to 1.5 tonnes a hectare on those areas, as opposed to 0.35t/ha on barley crops which had not been ripped.