Agriculture Reference
In-Depth Information
deployment of dwarfing genes. This in turn was only possible with better weed
control through the development of herbicides so that the smaller cereals were not
overgrown by wild weeds. This innovative trinity of the Green Revolution made it
possible to neglect the input-output ratio and exclusively focus on maximum output
(Evans
1998
). As a result, yield per hectare increased tremendously during the last
century and enabled an explosion of human population counting billions instead of
millions. However, it has become more and more apparent that this practice cannot
continue in the future. Parallel to a linear increase of global yields since the 1960s,
the NUE of agricultural system (measured as unit yield per unit fertiliser applied)
continuously declined. This “law of diminishing returns” implies that further
increases in fertiliser application will not lead to higher yields in the same propor-
tion as in the past (Tilman et al.
2002
). High levels of nutrient input have resulted in
pollution of the environment on the one hand and anticipated shortages of
non-renewable resources such as inorganic P on the other. Furthermore, the benefits
of these high outputs are very unevenly distributed over the world and with some
production wasted in Europe and North America, spikes in food prices and hunger
crises are expected to occur more frequently in developing countries. The aware-
ness of this alarming trend led policymakers to put “food security” on the top of
political agendas and consequently also into scientific focus (Rosegrant and Cline
2003
; Vitousek et al.
2009
; Godfray et al.
2010
; Hawkesford et al.
2013
).
To some extent the agriculture of the future has to come back to the old paradigm
of requiring a more optimal input-output ratio. However, maintenance of the
ongoing trend of increasing output in form of yield is an imperative due to the
still-growing world population and no concept, which reduces the output, can be
realistically considered (Evans
1998
). Consequently, modifications of the input-
output ratio have to concentrate on the input side of the equation. At field level
(Fig.
1.1
) the approaches to improve the input-output ratio may be categorized in
two dimensions: time and space. This is again based on the general conception of
plant and environment as two non-stationary, heterogeneous and oscillating sys-
tems. The supply with nutrients (fertiliser) can be adapted to the need of the plant
for growth over time to lose fewer nutrients from the system in times of a low crop
demand and to avoid concentrations being too low if the demand is high. In
addition, nutrient supply and its demand in the field are not homogenously distrib-
uted in space but instead graduated or patchy. A homogenous application of
nutrients thereby leads to excess supply in some parts of the field, resulting in
nutrient loss, and to a sub-optimal supply in other parts, resulting in a non-optimal
growth and yield. For both dimensions technological innovations have been devel-
oped, commonly summarized with the term “precision agriculture” (Pierce and
Nowak
1999
; Stafford
2000
; Zhang et al.
2002
). However, in addition there might
be ways to breed or genetically manipulate the plant in a way that it uses nutrients
more efficient and consequently produces the desired yield with less nutrient input.
While transgenic and genetic techniques offer the possibility for accelerated
improvement through genetic modifications and marker assisted breeding, whole
plant physiology provides the knowledge to use these tools in an effective way. To
practically improve the NUE of a plant in a particular agricultural system, the
