Agriculture Reference
In-Depth Information
referred to as pollutants, as they originate to a great extent from anthropogenic
activities but also from volcanic activities. It has, however, been shown that some of
these gases have an ambivalent mode of action on plants, as they are not only toxic
if too high in concentration but can also serve as nutrients (De Kok et al.
2002
,
2007
). This can either happen by wet deposition,
i.e.
a deposition to the soil by rain,
or by dry deposition via the stomata of plants. This additional nutrition from the
atmosphere and predictions for changes in the concentration of these gases should
be included in future calculations of NUE and fertilisation regimes.
The third variable that complicates efforts to define one general concept for NUE
is the nutrient itself, as nutrients differ not only in their physiochemical properties
but also in their uptake by and function in the plant. For each of them, the relevance
of the underlying physiological processes for NUE differs and so do the necessary
strategies for the improvement of NUE. For one nutrient the capacity of storage
might be crucial, while for another the uptake or the allocation to the sink organ
limits production. For this reason, studies on NUE in which different nutrients are
used are often difficult to compare. More specific definitions and components have
to be developed to accommodate this diversity. A recent study suggested three
components for NitUE: N uptake efficiency, grain-specific N efficiency and grain N
concentration (Weih et al.
2011
). S for example is involved in plant defence and
thereby using less S while maintaining the same defence status should increase S
use efficiency. Some micronutrients are co-factors of particular enzymes so conse-
quently a higher efficiency and decreased amount of these enzymes could increase
the NUE of these micronutrients. Furthermore, some nutrients are of nutritional
value, which again increases the relevance of translocation to the yield organ,
e.g.
the grain, while other nutrients are not desired to be part of the yield but play a role
in its production. Conclusively the NUE of a given nutrient depends on its impor-
tance for yield production and its value for human nutrition,
i.e.
its concentration in
the yield. Each case needs a different set of strategies for an improvement of NUE.
Improvement of NUE
Although controlled by man, agriculture remains a semi-artificial environment,
which is still subject to oscillations, particularly from outside the agroecosystem.
These oscillations may be entirely different from those in the ancient, natural
habitat of the plant species and thus transferring it to an agricultural system may
lead to sub-optimal growth and yield. Since the beginning of agricultural practice
(ca. 11,000-13,000 years ago; Allard
1999
) farmers have tried to solve these
problems with two different approaches:
(i) By reducing the amplitude of environmental oscillations either by growing
plants only in a certain season to avoid extremes in weather (
e.g.
cold winter, dry
summers or rainy seasons) or by creating more stable conditions in the field (
e.g.
by
using hedges as wind protection and digging moats to avoid flooding or, in modern
times, building partially closed and controlled environments such as greenhouses).
