Agriculture Reference
In-Depth Information
(Barbottin et al. 2005 ). While N translocation to grain determines its quality, on
improving NUE of P could be achieved by decreasing its translocation to the grain
(Rose et al. 2010 ). Additionally it should be noticed that the efficient translocation
of nutrients (as well as C) to yield organs is not only determined by the efficiency of
the exploitation of the sink organs but also by the sink strength ( e.g. for wheat:
Reynolds et al. 2005 ; for rice: Ntanos and Koutroubas 2002 ).
The loss of nutrients to the outside may be the most obvious constraint to NUE.
There are several paths by which nutrients can be lost by plants to their environ-
ment. Leaves lose nutrients by leaching, in some cases as gases or other volatile
compounds (Eichert and Fern´ndez 2012 ) and finally by litter fall, i.e. senescence.
These processes of nutrient loss can either be a way for the plant to balance its
nutritional status or may be unavoidable, for example due to wash-off by rain or
evaporation due to a trade-off with stomatal conductance. In the latter case, a
reduction of nutrient loss from the plant to its environment before harvest may be
a target for the improvement of NUE, particularly in crop systems where litter and
its nutritional status play a minor role. Further research is required to more fully
understand the physiological significance of these losses in order to distinguish
between avoidable leaks and metabolic valves, which assure internal nutrient
balance and thereby optimal plant functioning.
Factors Affecting NUE
The complex physiological basis of NUE becomes even more complex in reality, as
the contribution of these processes is modified by numerous factors, which can be
categorized into plant, environment and nutrient (Fig. 1.3 ). Numerous studies and
reviews have pointed out that concrete definitions of NUE depend to a great extent
on plant species and growth type. Again it should be stated that NUE is an artificial
term based on a hypothetical input-output concept. The diversity of NUE in nature,
however, reflects the diversity of plant strategies to survive and produce successful
offspring in their very different niches. How they perform if we apply the agricul-
tural standard of NUE does not reflect their ecological and evolutionary fitness.
Despite breeding the strong influence of the respective phylogenetic background of
a cultivated plant on its performance and peculiarities in the field adds another
degree of difficulty when defining one general concept for NUE. Fundamental
differences between crops can be metabolic in nature, e.g. between C 3 and C 4
plants (Brown 1978 ) or arise from different growth forms such as trees which are
harvested after decades, and herbaceous crop species which produce their yield
within months. Processes such as nutrient storage and reallocation function very
differently and have different significance for NUE in annual and perennial species
(Aerts and Chapin 1999 ), as well as in deciduous and evergreens (Chapin and
Kedrowski 1983 ; Aerts 1990 ; Franklin et al. 2009 ). This variability in plant growth
strategy makes it hard to derive one concept and set of definitions for NUE and its
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