Chemistry Reference
In-Depth Information
greenhouse gas emissions would increase to 3 Gt yr
21
and N use to 250 Mt
yr
21
. However, if intensification were concentrated on existing cropland, and
transfer and adoption of high-yielding technologies were successful, then only
0.2 billion ha would be cleared, GHG emissions would be reduced to one-third
(1 Gt yr
21
) and global N use would be 225 Mt yr
21
. Although this analysis
omits any effects of future climate change, it indicates what might be possible
with investment in innovative technologies, education and infrastructure.
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4.1 Improved Efficiency of Resource Use
One aphorism that summarises the current thinking about future intensifica-
tion of production is that we shall need to produce ''more with less'' and, in the
case of irrigation, ''more crop per drop''. A major requirement is to produce
higher yields with inputs that do not lead to environmental problems either on-
or off-site.
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4.1.1 Nutrients
Nutrient additions that are inadequate relative to crop offtake degrade land
through nutrient mining, while additions that are excessive degrade land, water
and air through leaching, eutrophication and gaseous emissions.
75
Ideally
nutrient additions (whether as mineral fertilisers or manures) and soil biota
should be managed to deliver nutrients to crops synchronously with demand,
87
but this has proved difficult to achieve in practice because applications must
normally be made before the demand exists and large crop canopies do not
permit application of solid sources to soils.
In developed countries, fertilisers are often applied in response to soil test
results of available nutrients such as P and K, and with regard to the likely
level of offtake for nutrients such as N.
29
Increasingly, models of crop and soil-
nutrient dynamics are being employed in decision support systems to adjust
applications to local conditions.
29
Furthermore, the rapid evolution of
''precision agriculture'' techniques in the last decade has allowed the
application of chemical inputs at the sub-field scale.
88,89
Harvesters with
weighing facilities and global positioning systems have allowed the production
of yield maps on an almost routine basis and these, together with grid and
transect sampling of soils to produce maps of nutrients, are allowing farmers to
contemplate site-specific nutrient management.
90
Such management is knowl-
edge-intensive and requires multiple forms of knowledge to be integrated in a
way that can be practically managed. This is all a far cry from the situation in
many developing countries where fertilisers are scarce and, when present, are
often applied to poor effect.
In several regions, broader integrated approaches to the maintenance of soil
fertility have proved capable of sustaining production for prolonged periods.
29
Such approaches involve inputs of organic materials in the form of crop
residues, targeted use of legumes in the crop rotation, agro-forestry systems,
