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Woodchip mulch can boost blueberry yields
by up to 81 per cent, but can reduce soil
PH if used too frequently.
Image: iStockphoto

Research has revealed that mulching with woodchip fines can help blueberry growers in northern NSW to increase their crop.

In comparison with woven black plastic weedmat, woodchip mulch led to an 81 per cent higher berry yield on a grey silty loam and 66 per cent higher yield on a red clay loam.

There was no difference, however, on two other trial sites, red loam or red silty loam.

Soil scientist at the Centre for Tropical Horticulture in Alstonville, Justine Cox, discovered that the woodchip mulch improved the more compacted soils, with a reduction in compaction, increased plant size and soil moisture.

“The range of soil types acted differently, where soils that were loose and friable grew the largest plants with the highest berry yield and showed no differences between the mulches,” Ms Cox said.

“The poorer, more compacted soils responded well to woodchip addition, and over time the physical properties improved.”

A strong relationship was discovered between plant size and berry yield.

The larger the plants were, the more berries they produced.

Yields of 6.5 to 9.6 tonnes per hectare were calculated from the experimental plants in the 2008 harvest.

During the final harvest round, berries were larger and heavier in the woodchip plots for two of the three soil types.

One of the invisible benefits of the woodchip was an increase in the amount of blueberry roots.

“A thick mat of roots was always found growing at the mulch-soil interface in the moist, decomposing woodchip environment.” Justine Cox said.

“This has enabled the blueberry plant to explore more space for water and nutrients.”

The woodchip influenced the root distribution all the way to the base of the mound where the roots were situated.

The effects of the woodchip were seen to 40 centimetres depth in one soil type.

A warning with the use of woodchip was recommended, however, as the soil pH (calcium chloride) dropped substantially to a range between 3.85 and 4.3 after one year – this is too acidic for optimum blueberry growth.

Intervention was required with liming to increase the pH.