Protecting peat performance

Protecting peat performance

By Bala Tikkisetty

Protecting the productivity of low nutrient peat soils is essential if they are to be farmed successfully.

In Waikato, there are around 90,000 hectares of these soils around the region, particularly near Gordonton, south of Hamilton and on the Hauraki Plains. In their natural state, they have high organic matter content, low natural nutrient levels and water table fluctuations, so they behave differently from mineral soils in terms of nutrient transformations and cycling.

That means, putting the right type of fertiliser on, at the right time and in the right amounts, is critical.

To help achieve this goal, farmers should know the capacity of their peat soils to assimilate nutrients, including from farm dairy effluent.

It is also important to understand the risks associated with the application of nitrogen fertilisers and effluent to peat soils, while optimising nutrient use efficiency for plant production.

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.

Besides soil and herbage tests to match nutrient inputs to soil needs, a number of other strategies help minimise nutrient leaching from peat soils used for farming.

· Nutrient budgeting helps ensure nutrient inputs match production and environmental goals.

· Applying nitrogenous fertilisers in split applications (not more than 30 kilogrammes of nitrogen per hectare in any one application) helps reduce environmental risks.

· Avoid application if heavy rain is likely or when there are puddles on pasture.

· Allow a good buffer or margin between the fertilised area and waterways.

· Also, because peat soils have a high water table, care should be taken when applying dairy effluent to pasture.

Applying fertiliser correctly to peat soils 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 optimum level for pasture and crop species. Soil and herbage tests will determine what nutrients peat soils need.

Time fertiliser application to ensure plant uptake is maximised and any potential effects on the environment minimised.

Fertiliser should be uniformly and evenly applied with none outside the target area. The precise placement of fertiliser depends on a number of factors. It requires careful integration of operator skills, sound equipment and appropriate formulation of fertiliser.

It is recommended farmers follow the Spreadmark Code of Practice for fertiliser application, a programme governed by the Fertiliser Quality Council.

Another factor to bear in mind is that, while drainage and cultivation of peat are necessary to establish productive pasture, they lead to irreversible shrinkage of the peat and results in continued subsidence of the land surface.

Shrinkage is a result of consolidation following water removal and particle breakdown during cultivation, and also as a result of exposure to air. Shrinkage is estimated at about 200 millimetres per year after the initial cultivation, reducing to around 20mm per year as the peat becomes more consolidated.

These factors mean that farming of peat soils can lead to damage to nearby wetlands and peat lakes and extra care is needed. The Waikato peat lakes, with unique ecosystems, are the largest remaining collection of such unique habitats in the country and have attracted international attention.

In summary, by having the right nutrient management programme, farmers can reduce both cultivation and renewal costs, prolong the life of peat soils and help protect water quality.

· Bala Tikkisetty is a sustainable agriculture coordinator at Waikato Regional Council, phone 0800 800

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