Comparison of Plastic Weedmat and Woodchip Mulch on Low Chill Blueberry Soil in New South Wales, Australia

Plastic woven weedmat was compared to woodchip fines mulch in blueberry production in northern New South Wales, since plastic disposal is considered both economically and environmentally unsustainable. Twenty-plant plots Vaccinium corymbosum hybrid (cv. 'Star') were established on three different soil types on one farm in Corindi in December 2005 and monitored for two years. The plant canopy width was no different on two of the three sites and 1.4 times larger in the woodchip than the weedmat treatment on the third site. The woodchip mulch more than halved the daily soil temperature fluctuations compared to the weedmat and reduced the seasonal extremes. The maximum daily range was 13.4 degrees C under the weedmat and 5.6 degrees C under woodchip mulch. The summer maximum was 37 degrees C and winter minimum 5.5 degrees C in the weedmat compared to 8.4 degrees C and 30.7 degrees C in the woodchip treatment. Total carbon was not significantly different between the mulches in two of the three sites. One site however showed significantly higher carbon under the woodchip (4.1%) compared to weedmat (2.55%) after two years. Soil pH values initially ranged from 4.35 to 4.8. After one year, in two of the three sites, the pH (CaCl2) under the woodchip mulch was significantly lower than under the weedmat, reaching levels of 3.85 and 3.95. Lime was applied to all treatments, and pH increased slightly the subsequent year, with no difference between mulch treatments. Overall, the soil types behaved differently in their response to the mulch treatments, highlighting the need for soil characterisation. Monitoring the changes in the soil with this new practice has shown some potential benefits (increased carbon) and some potential risks (reduced pH) of the woodchip mulch.