A national water strategy and water storage facilities top the wish list of the country’s 3500 irrigators.
To help maximise production, and protect the soil properties and 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.
Other conservation cultivation techniques include 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, the natural rate of water infiltration in some soils 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.
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 wildlife.
Studies show that up to 90% of sediment can be caught in an effectively constructed filter strip. Any pathogenic organisms trapped in long grass filter strips will die off in sunlight. So, the wider the buffer strip the greater the benefit.
In the filter strips, generally, grasses should be kept to a height of at least 10-15cm with a high density of stems and leaves at ground level for maximum trapping effect.
Remember that Waikato Regional Council has a rule in the regional plan which says farmers must not cultivate paddocks within 2m of a river, stream or lake bed. This is designed to prevent contamination of waterways.
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 advisor (technical) at Waikato Regional Council.