Maintaining peat performance
Bala Tikkisetty
Proper management of peat soils in the Waikato region is a crucial issue for both the profitability of farming and
environmental protection, particularly as we head into summer.
A highly productive resource peat soils are, however, a literally shrinking resource as they lose moisture. But the good
news is that there are strategies farmers can use to protect them and mitigate the impacts of their use on the
environment.
Waikato region has about half New Zealand’s peatlands, some 94,000 hectares containing 2.7 billion cubic metres of peat.
Peat soils need drainage and cultivation to establish productive pastures and crops. This leads to irreversible
shrinkage, estimated to occur at about two centimetres per year.
As peat is drained, its carbon content becomes exposed to air helping form carbon dioxide (CO2), an important greenhouse
gas.
Besides causing excessive shrinkage generally, too much drainage can also cause shrinkage or loss of wetlands and affect
peat lakes, both at-risk natural ecosystems.
From a farm production perspective, the depth of fertile topsoil decreases as peat shrinks, meaning further drainage,
cultivation and pasture renewal are needed to maintain productivity, increasing the cost to farmers.
In some areas, the underlying soils that landowners will be left with may have poor fertility, requiring high inputs to
maintain productivity. Flood risk and pumping costs in low lying areas may increase substantially.
Ultimately, if we don’t manage our peat carefully, it will continue to shrink until eventually there will be no peat
left – a unique and valuable resource will be lost forever.
To help manage the risks and farm successfully on peat soils long-term, farmers must find a balance between keeping the
water table low enough for production but high enough to minimise peat loss.
The following are key ways of maintaining a good water table in peat areas to maximise pasture growth and soil
condition:
• keeping farm drains shallow generally to avoid over drainage
• using weirs and stop gates in drains to help keep the water table high in drier periods
• working with neighbours on combined summer water table management.
It’s also worth noting that controlling weeds and fencing drains to exclude stock reduces maintenance costs associated
with machine cleaning drains, and reduces the related risks of water quality impacts and drains being deepened.
As cultivation causes peat to shrink twice as fast as it does under pasture, the less cultivation you do, the longer
your peat soil will last.
If you do cultivate, use equipment that creates minimal disturbance. Try to avoid chopping the peat too finely. This
destroys the fibrous structure of the soil. Further, avoid using rotary hoes on peat soils and try using disc ploughs.
Use no-till methods to renew pasture where possible – such as direct drilling.
I recommend all peat farmers get the most up to date information on the best pasture species for their areas.
Maintaining a dense pasture sward is one of the best ways to protect the peat soil. Overgrazing should be avoided – any
bare patches of peat will shrink faster, resulting in an uneven surface. Also minimise pugging during the wet winter
months.
A recently formed Waikato Peat Farmers’ Group has initiated, in conjunction with AgResearch and other stake holders, a
research project on sustainable nutrient management for Waikato peat soils. One of its aims is to set out the technical
aspects that should be considered when using peat soils for dairy farming.
The group has a Facebook page at https://www.facebook.com/groups/598258437008558/ or you can find it by searching for Waikato Focus on Peat Group on Facebook.