Agriculture Reference
In-Depth Information
From the less holistic perspective of agronomy, the field is usually the level of
choice for calculations of NUE. For farmers, the field represents an economic
entity, where the inputs are the costs for labour and materials while the output is
the harvest, usually measured by criteria such as “harvest index” (Donald and
Hamblin
1976
). In addition to NUE the term “fertiliser efficiency” is often used
to describe how efficiently the applied fertiliser is used by the agronomic system:
how much yield is produced, the quantity of nutrients which remains in the soil and
how much is lost from the system by leaching and emission (Saurbeck and Helal
1990
; Oenema et al.
2009
). However, NUE can also be discussed at the plant level
where a single plant instead of a whole field is regarded as an input-output system
and in the present chapter we will deal with the individual plant and its NUE to
discuss all the other dimensions and factors in relation to it. Improvement of NUE at
the plant level also has the potential to improve NUE at higher levels and therefore
has strong agronomic and environmental implications.
A common conceptual framework ensures a consistent use of terminology and
definitions. As was noted above, NUE can be discussed in an ecological as well as
an agronomical context. One context again can be divided into a sub-set of different
levels of organization. By coming down to the level of an individual plant in an
agronomical context, much of the universality of the term has been reduced. As
already mentioned, the term
efficiency
implies the achievement of an intended
outcome with a lowest possible input of costs. Therefore a very simplified definition
for the efficiency of a given system can be expressed in the equation:
Efficiency
¼
Output
Input
=
If values for input and output are competitive, the maximum value of efficiency
is 1, in an ideal case where input equals output. Either decreasing the input or
increasing the output might achieve higher efficiency. Every economical concept,
which has to generate profit, in principle follows this simplified equation and
agronomy is no exception. In all sectors of an industrialized economy it is desirable
to make working processes less costly while maintaining or increasing the output.
Technical innovation leads to more sophisticated techniques and methods, which
also revolutionized the efficiency of agricultural practice at the field level. There is,
however, an essential difference in improving an inanimate machine or process,
which has been planned and constructed by man and improving a living organism
such as a plant whose functioning is still far from being fully understood.
From a whole plant perspective NUE consists of several components and by
regarding a plant as an input-output system, physiologists have established equa-
tions that put these components into context in relation to NUE. In the most
universal approach, NUE at a plant level can be divided into two main components:
the efficiency of nutrient acquisition (NAcE) and the efficiency with which the
nutrient is utilized to produce the desired yield (nutrient utilization efficiency,
NUtE):
