Compost raises orange yield

SOUTH AUSTRALIAN RESEARCH AND DEVELOPMENT INSTITUTE

A South Australian Research and Development Institute study has demonstrated yield increases in navel and Valencia orange orchards of 17 to 63 per cent after the application of soil amendments including grape marc, animal manure and compost. SARDI senior entomologist Dr Peter Crisp said fruit measured in the trial increased in diameter by 5 mm to 7 mm on average. “This could provide growers an extra $100 per tonne, with the benefits of the compost lasting well beyond the first year after application,” Dr Crisp said. The SARDI study also evaluated a range of tree and soil health factors including levels of soil moisture, nitrogen and soil carbon. The SARDI research team found that compost application during periods of drought improved tree health compared to trees that did not receive compost.  “Where composted green organics had been applied, trees had dense foliage, good leaf colour and the highest flower production,” Dr Crisp said. “Improved tree health where compost was applied may be attributed to increased soil moisture levels in the root zone. “Moisture sensors 10 cm to 15 cm deep in the soil showed that moisture levels were consistently higher under trees treated with the highest rate of compost compared to control trees.” A cost benefits analysis from this study found all compost applications trialled showed a positive return on the initial investment.  The highest benefit was recorded when an application of 40 m²/ha of compost was used, giving a cost benefit of 5.4 over five years.  The benefits recorded giving a return of between $1.90 to $5.40 for every dollar invested in compost over a five year period. “These are conservative estimates as the potential water savings and improvements in fruit quality were not included in the analysis,” Dr Crisp said. Data from this trial site at Loxton will be collected for a further three years with support from Horticulture Australia Limited and a voluntary contribution from the Australian compost industry.