Good habits to be cultivated
Using good cultivation practices helps farmers protect both the financial and environmental bottom lines of their properties.
Post-winter is the time when farmers are cultivating their paddocks to ensure they can best provide fresh pasture or the next crop.
Also, so-called ‘‘sacrifice paddocks’’ are normally cultivated about now and sown with a summer crop to restore damaged soil.
As farmers go about this work, there are a number of factors to bear in mind to maximise farm efficiency and minimise their environmental footprint.
Sediment and nutrients from farming operations, along with erosion generally, are some of the important causes of reduced water quality in our region.
Although much of the Waikato’s 2.5 million hectares is relatively stable, the national land resources inventory has identified more than 1 million ha affected to some degree by erosion, with erosion on almost 36,000ha ranked as severe to extreme. A further 400,000ha is classified as having severe erosion potential.
Top soil erosion, especially in hill country, of bare or cultivated land, leads to the loss of valuable nutrients.
It can also disrupt infrastructure and increases the costs of maintenance activity, such as cleaning culverts and drains.
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.
Even with well-established shelterbelts protecting paddocks, wind erosion can still occur because of inappropriate cultivation techniques.
Farmers with lighter soils should consider ‘‘conservation cultivation’’ measures.
These are cultivation practices aimed at maintaining maximum vegetative cover on the soil surface and which encourage moisture retention in soils. The aim is to produce an uneven soil surface in as ‘‘rough’’ a condition as practicable and to restrict the cultivation period to the minimum time.
The use of the chisel plough or grubbers is recommended as these give a fine deep seedbed while still retaining a cloddy surface. Topworking implements, discing and rolling can create a fine seedbed prone to erosion even in wellsheltered situations.
Contour cultivation, sowing at right angles to the prevailing wind, sediment retention, and reducing runoff are recommended for minimising soil loss.
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.
Clods that are too dry will not break down with cultivation to give a good seedbed.
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’’ (ie two passes of cultivation equipment) is needed to prepare a seedbed.
Other conservation cultivation techniques include the suite of practices known as minimum tillage or no tillage – the least cultivation possible, or none at all, to reduce soil disturbance.
If 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 erodable soils.
A range of material from adjacent land can contaminate watercourses.
This can include sediment, nutrients such as nitrogen and phosphorous, other chemicals and microbes.
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.
An effective filter strip should be established and maintained where overland water can enter water bodies. Healthy riparian vegetation in these areas should be maintained to improve bank stability, reduce erosion, increase water quality, reduce stock losses, filter surface run-off and to provide habitat for wild life.
Suitable riparian species filter sediment, bacteria and nutrients from surface runoff. 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 at least 10 to 15 centimetres high with a good 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 growth of nuisance plants and algae as well as providing bank stability.
The Waikato Regional Council has a rule that farmers must not cultivate paddocks within two metres of a river, stream or lake bed.
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.