Chemistry Reference
In-Depth Information
4.6 to 5.1 MPa in untilled soil layers, as compared with 3.6 MPa for tilled
topsoils
83
due to roots exploiting a network of continuous biopores in the tilled
soil. Such pore networks enable roots to penetrate to depth in very hard
Australian sub-soils, where wheat-root growth is confined almost entirely to
biopores.
84
Plenty of scope therefore exists to develop better soil quality
indicators that describe limitations to crop productivity.
Root penetration rates have been used in the field
85
and laboratory
86
to
identify soil and plant limitations to rooting depth. These show promise in
matching genotype to farm management, thereby offering considerable
potential to increase productivity.
87
Crop cultivars perform differently under
a range of tillage practices
88
due to the rate and formation of root
establishment and tolerance to soil physical stress. Phosphorus-use efficiency
in soils with different physical constraints can also vary significantly between
different genotypes.
89
Cultivar performance in relation to soil biopores is also
being investigated using a new screening approach.
90
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4 Soil Physical Restoration and Food Security
Crop yields can be enhanced by improving soil physical conditions and
selecting crop traits that are more resilient to soil physical constraints.
1
Despite
impressive improvements in the yield of key crops globally over the past
several decades, achieving even greater yield presents a great challenge.
91
The
focus in plant science research has been above ground, in the leaves, stems and
crop. A switch is occurring to consider plant roots in greater detail, because it
is recognised that this is where the untapped potential lies. Chapter 1 describes
this research in greater detail. By selecting root traits that are resilient to the
physical
constraints
imposed
by
soil,
greater
yield
should
be
possible,
particularly in drought-stricken regions.
84
Livestock production is another facet of food security that will benefit from
improved soil physical conditions.
92
Earlier, the effects of overgrazing on soil
physical conditions, particularly erosion, were reviewed. Compacted or
'poached' fields produce less vegetation and hence less feed for livestock.
There is potential both for improved management and for improved pasture
crop varieties so that production systems become more sustainable.
There are some impressive global examples where improvements to the
management of soil physical conditions have underpinned local food security
and successful farming enterprises. Arable farming would be much less viable
in the Cerrado region of Brazil
93
and many regions of Australia
94
if reduced
tillage farming had not been adopted locally. Food is now produced on what
used to be severely degraded soils in the Loess Plateau and Red Soil region of
China.
A range of practices exist to manage or improve the physical condition of
soil. The massive shift in soil cultivation systems towards reduced tillage has
been the greatest change globally. Compacted soils can also be subsoiled and
tilled intensively to break up plough pans, but the longer-term effectiveness is
