Peat productivity

Monday 12 March 2012, 11:43AM
By Waikato Regional Council


By Bala Tikkisetty

Getting peak productivity from the region's prolific peat soils is crucial for farming profitability.

This requires careful management, taking into account the particular characteristics of the peat soils. There are different peat types that require differential management.

About 80 per cent of the peat soils in our region have been developed, mostly for farming.

Peat soils are both highly productive and fragile.

They require different management than mineral soils to maximise their productivity. In particular, farming peat land adjacent to lakes and wetlands requires very careful management to avoid damaging them.

The remains of wetland plants in areas with high water tables contribute to the formation of peat. The high water table in these areas stops the rapid breakdown of the dead plant material. Consequently, peat soils have more than 20 per cent organic carbon in the topsoil.

While drainage and cultivation of peat is essential to establish productive pasture, it leads to irreversible shrinkage of the peat and results in a continued subsidence of the land surface.

Subsidence is the result of consolidation and chemical breakdown of soil carbon, which is estimated at about 200 millimetres per year after the initial cultivation, reducing to around 20 mm per year as the peat becomes more consolidated.

Development and drainage of peat also damages the nearby wetlands and peat lakes. The Waikato peat lakes are the largest remaining collection of such unique habitats in the country and have attracted international attention. Their unique ecosystems are highly dependent on the careful balancing of water levels.

When it comes to the successful farming of peat soils, the effective use of fertilisers is necessary, with care needed over the amount, application timing and type of fertiliser used.

This is because Waikato peat soils have a low nutrient status. Applying the correct amounts of the right type of fertiliser will maintain good pasture for longer periods, reducing the need for frequent cultivation and pasture renewal. Lime is also required to increase the soil pH to an appropriate level for pasture and crop species. Soil and herbage tests determine what fertiliser peat soils on individual properties need.

Timing of fertiliser application should be so that plant uptake is maximised and potential effects on the environment minimised. Fertiliser should be uniformly and evenly applied with none outside the target area. The precision placement of fertiliser depends on a number of factors. It requires careful integration of operator skills, sound equipment and appropriate formulation of fertiliser.

I recommend that farmers follow the code of practice for the placement of fertiliser in New Zealand. The Spreadmark Code of Practice is a fertiliser placement quality assurance programme, which is governed by the Fertiliser Quality Council.

Peat soils typically have a low anion storage capacity. This means the leaching of nutrients to ground water will be significant in peat soils. Increased leaching of nutrients can occur when water tables are near the ground surface.

The following strategies can minimise nutrient leaching:

* Do regular soil and herbage tests that match nutrient inputs to soil requirements. * Undertake nutrient budgeting to ensure nutrient inputs match production and environmental goals. * Apply fertilisers in split applications (not more than 30 kilograms of nitrogen per hectare in any one application). * Leave a good buffer or margin between the fertilised area and water bodies. * Use granulated fertilisers that can be spread more evenly and accurately.

Riparian strips act as a filter to reduce the amount of contaminants that enter the water. Much of the loss of phosphorus to waterways occurs in association with sediment or dung.

Using the right nutrient management programme can reduce both cultivation and renewal costs, and at the same time prolong the life of peat soils.

* Bala Tikkisetty is a sustainable agriculture coordinator at Waikato Regional Council. Contact him on 0800 800 401 or