Dark ages
OPINION: Before we all let The Green Party have at it with their 'bold' emissions reduction plan, the Hound thought it wise to run the numbers through the old Casio.
A highly productive resource, peat soils are however literally a shrinking resource as they lose moisture. But the good news is 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 94,000ha 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 20mm 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 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; this 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 the maintenance costs of 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 among 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, with AgResearch and others, has begun research 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 facebook.com/groups/598258437008558
