PHOTO
The flooding headache of pine slash could end up being recycled as researchers look at its promise for chipping it into a mix for improving silt-covered soils in Canterbury and Gisborne.
Both regions were hit by flooding with Mid Canterbury farms smeared with silt after river stopbanks burst in 2021 and pine plantations providing the bulk of beach debris in the Gisborne area after Cyclone Hale this year.
A joint research project between the University of Canterbury and the Institute of Environmental Science and Research (ESR) is investigating pine waste being mixed with urea fertiliser on silt-buried soils.
University master’s student Mingyuan Liu has found this combination the most effective for growing plants, compared with just urea or using compost or other organic matter on soils.
Ms Liu said the study indicated there was an opportunity to use a challenging waste material to fix the soil problem.
Flooding was becoming increasingly common, and pine slash from commercial forestry dislodged by moving water was causing issues, she said.
"We’ve looked at blending pine waste into finer sawdust particles and mixing them with the soil and some fertiliser to make the soil more porous — better for water drainage and for plants to grow," she said.
The results in a campus greenhouse show a large increase in soil fertility with field testing the next step.
In the study, oats were planted in soil treated with pine sawdust and fertiliser.
Ms Liu said oat crops were helpful for stabilising soil structure and increasing organic matter.
"We could immediately see the difference in the crops grown in pine sawdust mixed into the soil."
Her supervisor, Prof Brett Robinson, said preliminary results were exciting.
"Pine slash is a current issue facing New Zealand and the rest of the world. To date, we know of no other reports detailing the rehabilitation of flood-deposited sediment using pine waste. We hope to take it to the next stage — field testing — soon."
This work would be carried our with Dr Maria Jesus Gutierrez-Gines, a science leader at the ESR who co-supervised Ms Liu’s research.
The ESR has provided technical analysis and organised the delivery of sediment from flood-affected Gisborne.
Prof Robinson said pine contained substances known to inhibit plant growth, but when applied in trials to raise the structure of sediment or silt, it helped retain nutrients.
"Essentially, it acts like a sponge and breaks down to humus, which is beneficial to the soil."
Ms Liu is now considering completing a doctorate in environmental science.
