Chemistry Reference
In-Depth Information
cultivation remains poorly understood. Without detailed knowledge of
soil physical conditions and how they interact with crops, optimising
crop yields is not possible.
There are serious implications to food security. Soil erosion and capping
can render large areas unproductive for agriculture. Modern crops have
been bred for ideal soil conditions that do not exist on many farms.
Selecting root traits that can penetrate compacted layers, access
biopores and form an extensive network to access water and nutrients
requires collaboration between plant and soil scientists. There is
considerable untapped potential beneath our feet that needs to be
tapped into to secure the global supply of food into the future.
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1 Introduction
Crop yield and hence food security are limited considerably by physical
constraints from soil.
1
Farmers recognise the huge yield gap they face due to
physically constrained soils, so over the past several decades major changes
have occurred in soil management practices.
2-4
Since Roman times, the plough
dominated agricultural production systems. Combined with secondary tillage
operations, ploughing was used to break up compacted layers and form an
aggregated seedbed that was ideal for plant establishment and subsequent
growth.
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For many regions of the globe, particularly in higher yielding
temperate regions, the use of the plough continues. It is viewed as an essential
intervention to maximise yield and hence farm-gate profitability. Whether this
is based on fact or habit will be discussed in this chapter.
Intensive farming and ploughing, however, have had a negative impact on
many farming regions internationally.
6,7
At the extreme end are environmental
disasters, including the Great Dust Bowl in the US Midwest in the 1930s, and
current dust bowls that plague the Loess Plateau region in China. Ploughing,
intensive grazing and changes in vegetation stripped the soils in these areas of
organic matter and fibrous root systems that held the soil together. Large-scale
erosion and dust storms resulted, producing crop failures locally and dust
storms that have been tracked from China to the west coast of the USA.
Farming practices can also compact soil from machinery traffic or animal
grazing.
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Compaction decreases the amount and connectivity of soil porosity,
so the transport of water and gases through soil and available spaces for root
growth and microbial colonisation becomes impaired.
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As compacted soils
dry, the strength that develops can impede root growth and hence the capacity
of plants to access water and nutrients from deeper soil layers.
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Yield penalties
of up to 30% are not uncommon in compacted soils.
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Another major soil physical constraint to crop production is soil structural
instability. Crusting of surface soils from rainfall can produce barriers to
seedling emergence.
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Unstable seedbeds also slump over time, resulting in the
coalescence of previously aggregated structures into a denser mass.
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