Cultivating the right approach
October 13, 2014
Mechanical cultivation of paddocks for producing summer forage or fodder crop is a common sight on farms at this time of
year. This is also a time when high intensity local storms are common, adding substantial risk to an important farming
practice.
To help maximise production, the protection of soil properties and the environment, there are a number of factors to
bear in mind when planning for cultivation.
The physical, chemical and biological soil environment will be impacted due to cultivation and this effect, particularly
on potential erosion, differs greatly depending on the soil type, slope, moisture levels, and cultivation methods.
Topsoil erosion of bare or cultivated land leads to the loss of the very basis of the farm production system. Erosion
can also disrupt infrastructure and increase the costs of maintenance, such as cleaning culverts and drains and repair
of tracks and races. The resulting sediment and nutrients getting into waterways can smother and disrupt the ecosystem,
resulting in reduced biodiversity and lower fish stocks.
There are a number of techniques farmers can use to help reduce the environmental risks associated with cultivation, and
with erosion generally, and at the same time protect their soil resources.
Contour cultivation, sowing at right angles to the slope, helps prevent sediment and nutrient running off paddocks to
places they’re not wanted. Avoid large, unbroken areas of bare soil at any one time. If a large sloping paddock is to be
cultivated, leave strips of undisturbed land at intervals across the slope where possible.
Soils should be cultivated when 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 millimetres long
and four mm thick. Exert sufficient pressure with fingers to reduce the diameter of the worm to four 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 the worm can be made.
If good precautions are observed a two-pass cultivation is often all that is needed to prepare a seedbed.
Other conservation cultivation techniques include a suite of practices known as minimum tillage or no tillage. These
include spraying chemical to remove vegetation and direct drilling of seed into soil.
If soil has been continuously cultivated for many years, the structure is likely to be poor because cultivation reduces
soil organic matter levels. Minimum or no-tillage will not repair the damage overnight but, with residue retention, it
will eventually. Where the soil structure has been damaged by repeated cultivation, consider maintaining pasture on the
damaged area for a year or two to enable the soil to restore itself.
Because of certain textural differences, in some soils the natural rate of water infiltration is low. But the
infiltration rate can also be low due to soil structure damage caused by frequent tillage or other management-related
issues like compaction. Run-off from these areas increases the risk of erosion, so more care is needed in such cases.
To assess the current condition of your soils, consider engaging a soil consultant, or use the Visual Soil Assessment
tool which is designed for use by non-scientists. You will find information on this tool on our “For Farmers” pages (http://www.waikatoregion.govt.nz/Community/Your-community/For-Farmers/Soil-management/). Our catchment management officers are also able to provide advice on soil condition.
As an additional protection measure an effective filter strip needs to be established and maintained between any
cultivation and water bodies. Healthy riparian vegetation in these areas including dense ground cover or rank grass
should be maintained to improve bank stability, increase water quality, filter surface run-off and to 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, generally, grasses should 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.
Remember too that 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. This is designed to prevent contamination of waterways.
And finally, be cautious when moving cultivation equipment between farms so as not to spread pest plants and other soil
borne diseases. Decontaminate the equipment by thoroughly washing it before taking to another farm.
*************
Bala Tikkisetty is a sustainable agriculture co-ordinator at Waikato Regional Council.