Mulch application in hops, grapes and olives

To assess the effect of a range of organic mulch materials in perennial crops, trials were established in ‘Super Pride’ hop fields (both organic and conventional), a new planting of ‘Gewurztraminer’ wine grapes (organically grown), and a one year old olive grove.

Hops: compost produced from hop waste was applied as a surface mulch to 4 vine plots at the rate of 70 t/ha in a newly established organic field and a wellestablished field at a conventional site. Mulched plots were compared with control plots in a randomised complete block design with 5 replicates per treatment. Mulch treatments had no effect on vine height. There were no significant differences between the mulched and control plots in hop percentage dry matter, percentage alpha acid, beta acid, or coltumulene, or ratio of acids. Soil bulk density was lower in the mulched plots in both systems. Mulch treatments showed higher available potassium, organic carbon and microbial biomass C.

Grapes: three grades of mulch were compared with an untreated control. Mulch materials were a mature compost (AS4454) mulch composed of eucalypt bark, chicken manure, paper pulp and grape marc; a composted mulch of eucalypt bark mixed with chicken manure; and a non-composted mulch consisting of eucalypt bark. Mulches were applied to a depth of 20 cm along the vine row. Trial design was a randomised complete block with 9 vines per treatment. The increase in trunk diameter was highest in the mature compost mulch plots, as was the pruning weight after 12 months. Non-composted mulch plots showed the highest levels of organic carbon, while the composted mulch plots had the greatest number of earthworms. Both mature and composted mulch plots showed higher levels of available phosphorous and potassium than non-composted mulch or control plots.

Olives: composted bark mulch was compared with an untreated control in a new olive grove planted directly into pasture. Mulch was applied to a depth of 10 cm around the base of each tree, covering a radius of 20 cm from the trunk, with 7 single tree plots per treatment. Tree growth was 35% higher in the mulched plots. There was no effect on soil bulk density, moisture, pH or EC. Soil temperature was higher in the mulched plots.