Agriculture Reference
In-Depth Information
5 million ha naturally predisposed to the problem (Summers 1987; Crabtree and
Henderson 1999; Cann 2000).
This problem is debilitating to farming. King (1981) discusses crops and weeds
germinating over a 3-month period and how water repellence makes weed con-
trol very difficult. Nutrients are tied up in the dry topsoil, and microbial activity is
restricted. Insects can become established on the first flush of emerging weeds that
typically grow in the hollows, making later-emerging weeds, in colder conditions,
more exposed to insect attack.
Several solutions have been adopted to overcome the problem. The most common
and successful technique is to apply clay to the topsoil and physically mix the sand
into the clay such that the top 15 cm of soil now contains an average of 3% to 5% clay
(Cann 2000). The hydrophilic nature of the clay overcomes the hydrophobic nature
of the waxed sand. The technique is called “claying,” and it is considered a likely
permanent solution. After claying, farmers typically revert back to no-tillage.
In some environments, no-till can reduce the impact of water repellence. The
technique requires disc seeders, continuous no-till, full stubble retention, no sheep
in the farming system, and no pulse crops in the rotation (Margaret Roper, personal
communication). The less tillage, the better, and indeed work by Roper at Munglinup
(Western Australia) has shown that such a system creates biopores that assist in soil
wetting. It is not clear if this option has broad applicability, though.
Compaction:
Soil compaction is a real constraint, although subtle and often
unseen. The driving of vehicles across paddocks causes compaction at up to 50-cm
depth (Ellington 1986). This compaction restricts root growth. Farming with live-
stock can also cause surface compaction. Some soils, with shrink-and-swell clay
characteristics, can self-heal, while others, like loamy sands, do not and may require
deep tillage to ameliorate them (Jarvis 2000). Improved microbial activity, as a result
of no-tillage and stubble retention, also helps to soften soils.
A combination of controlled traffic and no-till has been shown to give strong yield
improvements and enables soils to soften (Tullberg et al. 1998). The technique has
been readily enabled by GPS guided farming machinery with matching implement
widths and is becoming increasingly adopted.
Waterlogging and sodicity:
These two degradation issues are restricted to small
areas of the Australian cropping landscape. No-till enables more diverse crop rota-
tions, which help manage waterlogging. Permanent raised beds (PRBs) are also used
with good effect (Bakker et al. 2005). Sodicity is improved with no-till and further
improved with the addition of gypsum.
Australia is a harsh and unforgiving countryside, due to some poor soils and
erratic weather where drought and floods are common. Australian farmers have to
make radical adaptations to their agricultural practices to minimize the extent of
soil degradation. The standout and single most successful soil management strategy,
which has had almost complete adoption in Western Australia, is no-till. No-till
adoption was largely and proudly farmer led, with minimal government support or
investment. The Australian farmer groups, the universities, and the Australian and
state governments each play a necessary part in monitoring and providing insight into
the best practices to help overcome soil degradation and to even improve Australian
soils over their natural state.
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