Agriculture Reference
In-Depth Information
Another important factor is the nutrient content of the soil, which was controlled by
deploying manure before the revolutionary discovery of Liebig
s law of the min-
'
imum and the advent of modern fertilisers.
(ii) By reducing all kinds of
unfavourable dynamics and traits in the plant
s phenotype, which are relics of
adaptation to its ancient habitat and/or part of its developmental program but no
longer needed in cultivation. This is done by breeding, which makes use of the same
mechanisms as evolution (variation and selection). Plants are selected for traits of
agricultural interest with a main focus on bigger sink organs and higher concentra-
tions of the compounds of interest at the expense of traits and adaptations that are no
longer necessary.
In theory a combination of (i) and (ii) could result in a stable farming system in
which environment and plant are under full control and no unfavourable oscilla-
tions and dynamics should occur anymore. Nutrient loss from the system would be
at a minimum resulting in an optimal input-output ratio. The result would be to
equal out all the variables that make NUE such a complicated trait: plant, environ-
ment and nutrient specific factors (see above). In reality, however, this is an ideal
scenario and is presently far from being achievable. First, the technological effort to
control all environmental factors and their respective oscillations is uneconomical
and second the complex ways in which plant functioning is still largely unknown.
Consequently the compromise that has developed over thousands of years of plant
domestication is the attempt to synchronize the oscillations of environment and
plant as well as possible. This is especially true for fertilisation because the
discrepancy between demand of the plant and availability of nutrients in the soil
is an important factor that can hinder optimal growth. Nutrient storage can buffer
this discrepancy only to some extent and matching nutrient supply by fertiliser
application to plant demand is regarded as one of the most promising ways to reach
higher fertiliser use efficiency (Cassman et al.
1993
; Frink et al.
1999
; Tilman
et al.
2002
).
Without a deeper understanding of the biochemical and physiological processes
involved, traditional breeding managed for more than 10,000 years of agriculture to
develop plants with massive yield organs containing high protein, starch or oil
content, compared to their ancestors (Mazoyer and Roudart
2006
). At the same time
major steps towards increasing output-input-ratios have been made by the progress
of agricultural practice, technology and science (Russell
1966
; Thompson
2011
).
With Liebig
'
s postulation of the “law of the minimum” (see review Browne
1942
) and its resolution in terms of N supply by industrial production of relatively
cheap nitrogenous fertilisers (mainly by the Haber-Bosch process in which N and
hydrogen are directly converted to ammonia, see
e.g.
Tour
1920
), the modern age of
agriculture began and led to a historical change of paradigms, also named the
“Green Revolution” (Borlaug
1972
). Instead of trying to have an optimal input-
output ratio, as it is necessary if fertiliser is a rare commodity, the highest possible
output became the primary aim and remains so in present agricultural practice. The
increased growth of cereals due to super-optimal N supply led to another factor
becoming a major constraint for yield, namely the damage caused by lodging. The
solution was the breeding of “dwarf cultivars” of wheat and rice in the 1960s by
'
