Sunday, 04 October 2015

Stubborn soils resist composting and biochar treatments

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The researchers did not find any increase in Mycorrhizas numbers, even in highly micorrhizal plants such as sorghum (pictured). The researchers did not find any increase in Mycorrhizas numbers, even in highly micorrhizal plants such as sorghum (pictured). Image: Cyndy Sims Parr
  • Esperance soil trials falter on long-term soil fertility influence
  • Research to test results from previous research into boosting root length (mycorrhiza activity)
  • Vietnam crops thrived on nutrient-rich biochar

SOILS on WA’s south-east coast, notorious for their non-wetting properties and low nutrient levels, continue to stump agricultural scientists despite being involved in a biochar and composting trial designed to improve their productivity.

With millions of hectares of this stubborn soil type dominating the south coastal farming regions, solutions to soil infertility could be valuable to local farmers by significantly improving the economic value of WA’s commercial crops.

Biochar (charcoal produced from plant matter) and compost were added to the soils over four years to determine if these organic additions could alter the productivity of the soils.

However, despite short-term crop yield gains, the organic amendments did not appear to have a long-term influence on soil fertility, and the solution remains a puzzle to scientists.

Department of Agriculture and Food WA (DAFWA) scientist David Hall, who ran the trials near Esperance, says the research was initiated to test previous studies showing organic amendments could increase mycorrhiza activity.

Mycorrhizas are symbiotic organisms essential in increasing a plant’s root length, allowing them to scavenge more nutrients and water, a function particularly important for crops in sandplain soils.

Mr Hall says similar trials were also being run on sandplain soils in south-central Vietnam as part of an Australian Centre of International Research project, but the results from both trials had been remarkably different.

Department of Agriculture and Food Senior Research Scientist David Hall, Dr Hoang Tam, Dr Brad Keenan and Professor Richard Bell at one of the biochar trial sites in Vietnam.


“When colleagues started looking at the benefits of biochar in Vietnam, one of the biggest issues was that the soils there were highly potassium, sulphur and micronutrient deficient, and so there were big responses to the nutrient-rich biochar,” he says.

“In Australia we have a better fertiliser history, and while the soils in our local trials had low potassium levels, they were not as deficient as in Vietnam.”

Mr Hall says while yield gains averaging 13 per cent were achieved in the first two years after the additions of biochar and compost, any yield gains after that date could not be attributed to the soil amendments.

“Nutrients flow through sandplain soils very quickly, particularly nitrogen, and we wanted to see if these organic amendments had benefits in terms of retaining nutrients in the longer term with the aim of increasing crop yields,” he says.

“We found that any yield increases could only be attributed to the direct nutrient additions from the organic amendments and we couldn’t find any increase in Mycorrhizas numbers, even in highly micorrhizal plants such as sorghum.”

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