Agriculture Reference
In-Depth Information
respective habitat in order to reach a lifespan of hours, days, weeks, months, years
or decades and finally produce successful offspring. This is especially true of plants
which being sessile, have evolved strategies to synchronize their internal processes
with the external oscillations of their environment to their best advantage. This
synchronization includes life cycle, developmental program, morphology, diurnal
physiological rhythms (Somers et al.
1998
; McClung
2006
) and also uptake and
assimilation of nutrients (Zhang et al.
1991
; Bot and Kirkby
1992
; Delhon
et al.
1995
; Haydon et al.
2011
) on different timescales. A well-adjusted synchro-
nization with the environment will increase the performance of a plant and increase
competiveness. From this ecological and evolutionary point of view plants can be
called “nutrient efficient”, if they use the temporal and spatial availability of
nutrients for an optimal and balanced vegetative and reproductive growth, which
is most suitable to survive and compete in their respective habitat and niche.
In an agricultural context, however, the quality of the
intended outcome
shifts.
Instead of offspring the plant produces a desired yield product, which can be
utilized for food production and other economically relevant purposes. With agri-
cultural practice and plant breeding to increase the production of this agronomic
intended outcome
the plant is detached from its ecological and evolutionary con-
text. No longer exposed to the natural selection pressure but the artificial selection
by man, plants are reshaped for agriculture: development, morphology and fluxes of
resources are rerouted towards increased production of whatever yield is desired.
Even after thousands of years of breeding, plants still bear their ecological heritage,
which may conflict with agricultural interests and may limit the potential for
traditional plant breeding to improve NUE. Bringing these two contexts together
is one of the main tasks for plant scientists to understand the functioning of a plant
in the semi-natural system of agriculture. In this way, ecophysiological potentials of
plants might be further exploited for agricultural production and the limits for
improving plants with traditional breeding might be identified and overcome. A
profound understanding of the physiological background of NUE is the basis for
modern plant breeding using molecular techniques.
In an ecological context, NUE can be examined at the level of individuals,
populations, species, communities or entire ecosystems (Nardoto et al.
2006
). NUE
in agronomy can also be discussed on several levels (Fig.
1.1
). On each level, input
and output differ in kind, and different components have to be considered to
adequately calculate the NUE of the respective system. In scientific discussions it
is important to consider the same level to avoid confusion and misunderstanding.
During the past few decades, scientists have become increasingly aware that
agricultural systems can be regarded as ecosystems in which the role of soil
composition and fertility, the influences of biotic interactions as well as abiotic
environmental factors should not be underestimated. This is brought together in the
concept of agroecology (Gliessman
1990
; Schnug and Haneklaus
1998
; Francis
et al.
2003
). In this holistic approach, not only the
intended outcome
but also the
input of costs
becomes very complex, as negative impacts of fertilisation, pesticides
etc. have to be considered. In modern approaches many different benefits that an
intact ecosystem delivers to society are assessed. These “ecosystem services”
