Agriculture Reference
In-Depth Information
physiological processes that are involved in NUE may be modified by environmen-
tal conditions. For instance, drought has numerous implications for the mineral
nutrition of plants. As the uptake of many nutrients is depending on the mass flow of
water there is a direct relationship between water availability and the uptake of
mobile nutrients such as nitrate (Smika et al.
1965
; Buljovcic and Engels
2001
). In
turn, an optimal N supply was shown to alleviate detrimental effects of drought in
Zea mays
(Zhang et al.
2007
). However, not only the uptake but also the translo-
cation to the shoot via the xylem is impaired during drought stress, which may
affect all nutrients but which has been shown for P (Rasnick
1970
). Even moderate
drought stress might cause P deficiency in crops, which is an explanation for the
often-observed positive effect of increased P fertilisation under dry conditions
(Turner
1985
; Garg et al.
2004
).
It is known that growth rate and the uptake of certain nutrients (
e.g.
P but not N)
may show a strong decline under low light compared to high light conditions, if the
nutrient supply is adequate (Bloom
1985
; Chapin
1991
). The same is true for both
low and high temperatures (Tindall et al.
1990
). This dependency of growth and
nutrient uptake on temperature and light leads to a different relevance of these
processes for NUE in different patches of a field, during different seasons and in
different climatic regions of the world.
The mineralization and cycles of essential nutrients such as N are mainly driven
by the properties of the soil. Litter decomposition plays a crucial role in overall
nutrient cycling in an ecosystem as well as in an agroecosystem. Globally the extent
of litter decomposition depends mainly on temperature, while on a regional scale
the chemical composition of the litter becomes most important (Aerts and Chapin
1999
). In this way the soil not only plays a crucial role in the NUE of a field or a
whole agroecosystem but also at plant level where NUE is partly governed by soil
specific factors. Nutrient uptake is the process, which is affected most obviously. In
natural ecosystems nutrient uptake is ultimately dependent on the nutrient supply
rate by the parental rock material. Its mineral composition, age and weathering rate
determine the nutritional status of a soil (Lambers et al.
2008
). In an agricultural
system the nutrient composition of the soil is mainly controlled by fertilisation.
However, there are other factors with an impact on nutrient uptake, which are
usually under much less control. One is the pH of the rhizosphere, which has a
tremendous impact on the ability of the plant root to acquire different nutrients. In
addition the soil is much more than just part of the plant
s
abiotic
environment. It
hosts a still widely unknown diversity of microbial life. Interactions with arbuscular
mycorrhiza and rhizobacteria that increase the uptake surface of plant roots and
provide nutrients to it may alter the NUE of crops, increase yield significantly and
improve fertiliser management on a field scale (Smith et al.
1992
; Adesemoye
et al.
2008
; Adesemoye and Kloepper
2009
).
While the below ground part of the plant is surrounded by soil, the above-ground
part is exposed to the atmosphere and although almost 100 % of its volume is equal
in composition around the globe, there are traces of gases which fluctuate in their
local concentrations (Kraus
2006
). Some of these gases can have a significant
impact on plant metabolism. Most of these N- and S-containing gases are usually
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