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Column: Post-winter cultivation is critical

by Bala Tikkisetty

The future of farming, on which our region’s economic and social wellbeing relies heavily, could be at risk if the quality and extent of our soils are not maintained.

Sediment and nutrients from farming operations, along with pathogenic microbes, are some of the most important causes of reduced water quality during the post-winter period, when farmers are cultivating their paddocks.

Top-soil erosion, especially in hill country, of bare or cultivated land, leads to the loss of valuable nutrients. It also disrupts infrastructure and increases the costs of maintenance activity, such as cleaning culverts and drains.

Landowners and cultivation contractors can help mitigate the environmental risks associated with cultivation, and at the same time protect their soil resources.

The greatest risk can be at times like now when the protective plant cover is lost through cultivation of soils for pasture renewal and crop establishment.

Soils should be cultivated when the moisture content is neither too high nor too low. To assess if soils are suitable for primary cultivation, take a piece of soil (half the volume of an index finger) and press firmly to form a pencil.

Roll the soil into a “worm” on the palm of one hand with the fingers of the other until it is about 50 mm long and 4 mm thick. Exert sufficient pressure with your fingers to reduce the diameter of the worm to 4 mm in 15 to 20 complete forward and back movements of the fingers. Conditions are suitable for cultivation if the soil cracks before the worm is made. The soil is too wet to cultivate if you can make the worm.

Contour cultivation, sowing at right angles to the prevailing wind, sediment retention, reducing run off are recommended for minimising soil loss.

Other conservation cultivation techniques include minimum or no tillage. If soil has been continuously cultivated for many years, the structure is likely to be poor due to reduced soil organic matter levels. No-tillage will not repair the damage overnight but, with residue retention, it will eventually. Chemical spraying followed by direct drilling is an option on light erodible soils.

Sediment and some nutrients, particularly phosphorus, are carried to streams primarily in the overland flow of water.

An effective filter strip needs to be established and maintained where overland water enters water bodies. Healthy riparian vegetation in these areas will improve bank stability, increase water quality, reduce stock losses, filter surface run-off and to provide habitat for wild life.

Good riparian vegetation slows run off down so that sediment, phosphorous (which binds to soil particles) and faecal matter can settle out before the run off reaches waterways. Studies show that up to 90 per cent of sediment can be caught in an effectively constructed filter strip. Any faecal bacteria that are trapped in long grass strips will die off.

In the filter strips, generally, grasses should be kept to a height of at least 10-15 cm with a high density of stems and leaves at ground level for maximum trapping effect.

The spread of pests, particularly weeds and pathogens, by vehicles, cultivation machinery and equipment has significant consequences and is an ongoing problem. Machinery hygiene must be practiced any time a machine is moved between properties.

I would like to remind you again that the Waikato Regional Council has a rule in the Regional Plan, which says farmers must not cultivate paddocks within two metres of a river, stream or lake bed.

  • Bala Tikkisetty is a sustainable agriculture advisor at Waikato Regional Council. Contact him on 0800 800 401 or email bala.tikkisetty@waikatoregion.govt.nz

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