Agriculture Reference
In-Depth Information
price of fertilisers, although fluctuating, have been burgeoning and it is highly
improbable that this trend will change in the next few years (
http://faostat3.fao.org/
Only a fraction of the nutrient provided to the soil as fertiliser is taken up from
the crops. This fraction, expressed as a percentage, is defined as the crop
Apparent
Recovery
(
AR
; Craswell and Godwin
1984
):
AR
¼
100 N
F
ð
N
nF
Þ=
F
where N
F
and N
nF
are the total amount of the nutrient absorbed by the crop, if
fertilised or not, respectively, and
F
is the amount of the nutrient added to the soil
with the fertiliser. For the main crops quite low average values of
AR
are reported:
about 35 % for N (Raun and Johnson
1999
), 10-30 % for P (Malhi et al.
2002
) and
seldom higher than 50 % for K (Rengel and Damon
2008
). The low capacity of
crops in removing the nutritional elements added to the soil has significant envi-
ronmental implications and reflects limits in the management of the fertilisation
practices, the existence of constraints due to both chemical-physical and microbi-
ological soil properties and plant intrinsic biological limits.
AR
does not consider
yield traits. On the contrary, the
Agronomic Efficiency
(
AE
) of the fertiliser, defined
by the ratio d
Y/
d
F
, where d
Y
is the infinitesimal yield (
Y
) and d
F
is the infinitesimal
increase in the amount of the nutrient in the soil (
F
) due to the fertiliser application,
considers such traits.
AE
can in turn be expressed considering two components: the
crop
Removal Efficiency
(
RE
), defined as the ratio d
N
F
/
dF
, where d
N
F
is the
infinitesimal incremental amount of the nutrient taken up by plant after the
fertilisation, and the
Physiologic Efficiency
(
PE
), defined as the ratio d
Y
/d
N
F
:
AE
¼
RE
PE
¼
d
N
F
=
d
F
d
Y
=
d
N
F
¼
d
Y
=
d
F
In the field, both
RE
and
PE,
and then
AE,
depend on the interaction between
genetic and environmental factors. In other chapters of this topic the molecular and
genetic aspects determining
AE
for some essential elements are extensively
reviewed. Here, in a perspective of precision farming (Pierce and Nowak
1999
),
some strategies to improve
AE
by optimising
dN
F
throughout the use of plant-based
sensor systems are presented and discussed.
Fertiliser Best Management Practices
Definitions
In order to limit the intrinsic risks of diffuse pollution due to intensive agriculture,
both local and supranational authorities are committed to the fine tuning of methods
or techniques found to be the most effective and practical means in achieving yield
objective optimisation and preventing contaminations of soils, water resources and
air. As a whole, these recommended measures are defined as agronomic Best