Chemistry Reference
In-Depth Information
capless mutant that shed neither mucilage nor border cells had zones of greater
density in front of the root tip.
The degree of particle displacement around roots is important not only for
determining soil physical properties but also the degree of root-soil contact and
hence the accessibility of nutrients and water. In water-saturated and heavily
compacted soils, problems with gas exchange can occur, while incomplete root-
soil contact due to soil structure or root shrinkage can reduce the uptake of
water and nutrients such as nitrate.
56
Root-soil contact has been known for a
long time to affect the growth rates of crops, with the production of a good
tilth being a prime requirement of seedbed formation. New techniques, such as
X-ray computed tomography, are increasingly being used as a non-invasive
methodology to visualise and quantify these interactions.
57
d
n
1
r
2
n
g
|
1
3 Contributions to Recent Increases in Crop Production
As discussed in section 1, while food production alone cannot guarantee food
security, it is an essential component of food systems. During the last 60 years,
the world's human population has increased from about 2.2 billion in 1950 to
about 7 billion in 2011 and this has been sustained by substantial increases in
crop and animal production.
58
Only about 3 billion of the world's 13.4 billion
hectare land surface is suitable for crop production and about one half of this
is already cultivated (1.4 billion ha in 2008).
59
It is widely recognised that,
globally, only a small proportion of future increases in crop production will
come from the cultivation of new land (about 20%), with the majority coming
from intensification via increased yield (67%) and higher cropping intensity
(12%; Table 1).
60,61
This means that per capita arable land area will continue to
decrease (it decreased from 0.415 ha in 1961 to 0.214 ha in 2007) while average
cereal yield will need to increase by about 25% from 3.23 t ha
21
in 2005-07 to
4.34 t ha
21
d
n
6
h
3
in 2030.
59,61
Yield
results
from
the
interaction
of
three
factors:
genotype
(G) 6
environment (E) 6 management (M).
62
Evans highlights how the synergistic
effects
of
these
interactions,
linked
to
innovative
technologies,
have
Table 1
Projected contributions (%) to increased crop production between
1997-99 and 2030. (Source: adapted from Bruinsma).
61
Land area
expansion
Increase in
cropping intensity
Yield
increase
All developing countries
21
12
67
Sub-Saharan Africa
27
12
61
Near East/North Africa
13
19
68
Latin America and Caribbean
33
21
46
South Asia
6
13
81
East Asia
5
14
81
