Cultivate With Care After Big Wet
By Bala Tikkisetty
Following the wettest winter on record, farmers are currently cultivating their paddocks for pasture or crop rotation.
As they do so, it’s important to be aware of and manage the associated environmental risks.
Sediment and nutrients from farming operations, along with erosion generally, are some of the most important causes of
reduced water quality and cultivation increases the potential for problems.
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.
The time of 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.
However, there are a range of measures farmers can take to help mitigate the environmental risks associated with
cultivation, and with erosion generally, while at the same time protecting soil resources.
Contour cultivation, sowing at right angles to the prevailing wind, sediment retention, diverting overland flow, and
reducing runoff are recommended for minimising soil loss.
Satisfactory results are achieved when cultivation is carried out at a suitable soil moisture content and at a suitable
depth.
If good precautions are observed, a two-pass cultivation is often all that is needed to prepare a seedbed.
Other soil conservation cultivation techniques include the suite of practices known as minimum tillage or no tillage.
When soil has been continuously cultivated for many years, the structure is likely to be poor because cultivation
reduces 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.
Dissolved nutrients such as nitrogen and other materials (including dissolved organic carbon) can also move through the
soil in underground flows and contaminate watercourses.
The area beside waterways that forms the interface between water and land is called the riparian margin. This area is a
crucial buffer between land use activities and the natural waterway.
To help prevent the transfer of sediment and nutrients to waterways, an effective filter strip needs to be established
and maintained where overland water enters these water bodies.
Healthy riparian vegetation in these areas, as well as grass margins, should be maintained to improve bank stability,
increase water quality, reduce stock losses, filter surface run-off and provide habitat for wild life.
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 filter strips will die off in sunlight.
In the filter strips, grasses should generally be kept to a height of at least 10-15 centimetres with a high density of
stems and leaves at ground level for maximum trapping effect.
Riparian vegetation also has an important additional benefit in providing shade to the stream, thereby reducing water
temperatures and the growth of nuisance plants and algae.
Waikato Regional Council’s Proposed Plan Change 1 for the Waikato and Waipa rivers catchment has a suggested rule which
says farmers must maintain appropriate buffers (a minimum of five metres) between cultivated areas and water bodies.
Finally, as a general comment I’d say that the future of farming, on which our country’s economic and social wellbeing
relies heavily, could be at risk if the quality and extent of our soils are not maintained.
So following good cultivation practices aids both environmental and financial well-being.
Bala Tikkisetty is a sustainable agriculture co-ordinator at Waikato Regional Council
ENDS